WO2002037726A2 - Bulk optical (de)multiplexer apparatus and method of packaging - Google Patents

Bulk optical (de)multiplexer apparatus and method of packaging Download PDF

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Publication number
WO2002037726A2
WO2002037726A2 PCT/US2001/045276 US0145276W WO0237726A2 WO 2002037726 A2 WO2002037726 A2 WO 2002037726A2 US 0145276 W US0145276 W US 0145276W WO 0237726 A2 WO0237726 A2 WO 0237726A2
Authority
WO
WIPO (PCT)
Prior art keywords
frame
multiplexer
optical
waveguide array
axis
Prior art date
Application number
PCT/US2001/045276
Other languages
French (fr)
Other versions
WO2002037726A3 (en
Inventor
Robert Harr
Pei Huang
George G. Krotchko
Original Assignee
Zolo Technologies, Inc.
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Priority claimed from US09/702,550 external-priority patent/US6421479B1/en
Application filed by Zolo Technologies, Inc. filed Critical Zolo Technologies, Inc.
Priority to AU2002227101A priority Critical patent/AU2002227101A1/en
Publication of WO2002037726A2 publication Critical patent/WO2002037726A2/en
Publication of WO2002037726A3 publication Critical patent/WO2002037726A3/en

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Classifications

    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
    • G02B6/24—Coupling light guides
    • G02B6/26—Optical coupling means
    • G02B6/28—Optical coupling means having data bus means, i.e. plural waveguides interconnected and providing an inherently bidirectional system by mixing and splitting signals
    • G02B6/293—Optical coupling means having data bus means, i.e. plural waveguides interconnected and providing an inherently bidirectional system by mixing and splitting signals with wavelength selective means
    • G02B6/29304—Optical coupling means having data bus means, i.e. plural waveguides interconnected and providing an inherently bidirectional system by mixing and splitting signals with wavelength selective means operating by diffraction, e.g. grating
    • G02B6/29305—Optical coupling means having data bus means, i.e. plural waveguides interconnected and providing an inherently bidirectional system by mixing and splitting signals with wavelength selective means operating by diffraction, e.g. grating as bulk element, i.e. free space arrangement external to a light guide
    • G02B6/2931—Diffractive element operating in reflection
    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
    • G02B6/24—Coupling light guides
    • G02B6/26—Optical coupling means
    • G02B6/28—Optical coupling means having data bus means, i.e. plural waveguides interconnected and providing an inherently bidirectional system by mixing and splitting signals
    • G02B6/293—Optical coupling means having data bus means, i.e. plural waveguides interconnected and providing an inherently bidirectional system by mixing and splitting signals with wavelength selective means
    • G02B6/29304—Optical coupling means having data bus means, i.e. plural waveguides interconnected and providing an inherently bidirectional system by mixing and splitting signals with wavelength selective means operating by diffraction, e.g. grating
    • G02B6/29305—Optical coupling means having data bus means, i.e. plural waveguides interconnected and providing an inherently bidirectional system by mixing and splitting signals with wavelength selective means operating by diffraction, e.g. grating as bulk element, i.e. free space arrangement external to a light guide
    • G02B6/29313—Optical coupling means having data bus means, i.e. plural waveguides interconnected and providing an inherently bidirectional system by mixing and splitting signals with wavelength selective means operating by diffraction, e.g. grating as bulk element, i.e. free space arrangement external to a light guide characterised by means for controlling the position or direction of light incident to or leaving the diffractive element, e.g. for varying the wavelength response
    • G02B6/29314—Optical coupling means having data bus means, i.e. plural waveguides interconnected and providing an inherently bidirectional system by mixing and splitting signals with wavelength selective means operating by diffraction, e.g. grating as bulk element, i.e. free space arrangement external to a light guide characterised by means for controlling the position or direction of light incident to or leaving the diffractive element, e.g. for varying the wavelength response by moving or modifying the diffractive element, e.g. deforming
    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
    • G02B6/24—Coupling light guides
    • G02B6/26—Optical coupling means
    • G02B6/28—Optical coupling means having data bus means, i.e. plural waveguides interconnected and providing an inherently bidirectional system by mixing and splitting signals
    • G02B6/293—Optical coupling means having data bus means, i.e. plural waveguides interconnected and providing an inherently bidirectional system by mixing and splitting signals with wavelength selective means
    • G02B6/29379—Optical coupling means having data bus means, i.e. plural waveguides interconnected and providing an inherently bidirectional system by mixing and splitting signals with wavelength selective means characterised by the function or use of the complete device
    • G02B6/2938—Optical coupling means having data bus means, i.e. plural waveguides interconnected and providing an inherently bidirectional system by mixing and splitting signals with wavelength selective means characterised by the function or use of the complete device for multiplexing or demultiplexing, i.e. combining or separating wavelengths, e.g. 1xN, NxM
    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
    • G02B6/24—Coupling light guides
    • G02B6/26—Optical coupling means
    • G02B6/28—Optical coupling means having data bus means, i.e. plural waveguides interconnected and providing an inherently bidirectional system by mixing and splitting signals
    • G02B6/293—Optical coupling means having data bus means, i.e. plural waveguides interconnected and providing an inherently bidirectional system by mixing and splitting signals with wavelength selective means
    • G02B6/29379—Optical coupling means having data bus means, i.e. plural waveguides interconnected and providing an inherently bidirectional system by mixing and splitting signals with wavelength selective means characterised by the function or use of the complete device
    • G02B6/29398—Temperature insensitivity
    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
    • G02B6/24—Coupling light guides
    • G02B6/36—Mechanical coupling means
    • G02B6/3628—Mechanical coupling means for mounting fibres to supporting carriers
    • G02B6/3632—Mechanical coupling means for mounting fibres to supporting carriers characterised by the cross-sectional shape of the mechanical coupling means
    • G02B6/3636—Mechanical coupling means for mounting fibres to supporting carriers characterised by the cross-sectional shape of the mechanical coupling means the mechanical coupling means being grooves
    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
    • G02B6/24—Coupling light guides
    • G02B6/36—Mechanical coupling means
    • G02B6/3628—Mechanical coupling means for mounting fibres to supporting carriers
    • G02B6/3648—Supporting carriers of a microbench type, i.e. with micromachined additional mechanical structures
    • G02B6/3652—Supporting carriers of a microbench type, i.e. with micromachined additional mechanical structures the additional structures being prepositioning mounting areas, allowing only movement in one dimension, e.g. grooves, trenches or vias in the microbench surface, i.e. self aligning supporting carriers
    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
    • G02B6/24—Coupling light guides
    • G02B6/36—Mechanical coupling means
    • G02B6/3628—Mechanical coupling means for mounting fibres to supporting carriers
    • G02B6/3684—Mechanical coupling means for mounting fibres to supporting carriers characterised by the manufacturing process of surface profiling of the supporting carrier
    • G02B6/3692—Mechanical coupling means for mounting fibres to supporting carriers characterised by the manufacturing process of surface profiling of the supporting carrier with surface micromachining involving etching, e.g. wet or dry etching steps

Definitions

  • the present invention is directed toward optical communications, and more particularly toward an apparatus and method of packaging for aligning a bulk optical multiplexer/demultiplexer.
  • DWDM Dense wavelength division multiplexing
  • the wavelength of each channel is selected so that channels do not interfere with each other and the transmission losses to the fiber are minimized. While typical DWDM allows up to 40 channels to be simultaneously transmitted by a fiber, there is an ongoing effort to further increase the number of channels transmitted for a given wavelength band by an optical fiber.
  • DWDM requires two conceptually symmetric devices: a multiplexer and a demultiplexer.
  • a multiplexer takes multiple beams or channels of light, each at a discreet wavelength and from a discreet source and combines the channels into a single multi-channel or multiplexed beam.
  • the input is typically a linear array of waveguides such as a linear array of optical fibers.
  • the output is typically a single waveguide such as an optical fiber.
  • a (de)multiplexer spatially separates a multiplexed beam into separate channels according to wavelength.
  • Input is typically a single input waveguide or fiber and the output is typically a linear array of waveguides such as optical fibers.
  • DWDM devices There are a number of different DWDM devices known in the art, including array waveguides (see Li, U.S. Patent No. 5,706,377), devices using a network of filters and/or fiber Bragg gratings for channel separation (see Pan, U.S. Patent No. 5,748,350), and a variety of bulk optical DWDM devices.
  • Bulk optical multiplexers and (de)multiplexers consist of discreet optically aligned optical elements mounted to a frame.
  • a wavelength dispersive element such as a reflective diffraction grating, a focusing optic such as a lens, and a waveguide array which may consist of a multi-channel or multiplex waveguide such as a single mode optical fiber and a linear array of single channel waveguides, typically also single mode optical fibers.
  • the multi-channel or multiplexed optical signal is emitted -from the multi-channel waveguide, directed through and collimated by the focusing optic, and reflected off the diffraction grating.
  • the diffraction grating divides the multichannel beam into single channel beam components which are reflected through the focusing optic and focused by the focusing optic to optical focal points coupling with the single channel optical waveguides.
  • the multiplexer simply works in reverse, with single channel signals being emitted from the single channel optical fibers, combined into a multiplex signal and coupled to the multiplex optical fiber. Because a single device can perform as a multiplexer or a (de)multiplexer, it is referred to as a (de)multiplexer herein. Critical to the proper operation of a bulk optic (de)multiplexer is obtaining and maintaining proper optical alignment of the waveguide array, focusing optic, and diffraction grating to provide efficient coupling of the optical signals to the respective waveguides with minimal or no crosstalk.
  • Ignatuc U.S. Patent No. 5,195,707, is directed to an optic positioning device for holding an optical element which has a center and for adjusting the optical element relative to the center.
  • the positioning device includes a supporting base having a concave spherical surface and a holding body having a convex spherical surface which is slidably mated with the concave spherical surface. Both the concave and convex spherical surfaces have radial centers at the center of the optical element. Ignatuc allows for gimbaled movement of the optical element about its optical center.
  • the mating concave and convex spherical surfaces provide a large surface contact area which can make it difficult to make small, precise movements of the optical element due to "sticktion" between the surfaces.
  • Ignatuc also requires that both spherical surfaces be made to precise tolerances in order to insure the center of the optical element remains at a fixed location. This increases manufacturing costs.
  • Important to maintaining optical alignment is to minimize the effect of shock and vibration which can degrade the integrity of optical alignment of optical components or allow micro variations in alignment, which lead to loss of light, but no discernable displacement of physical components. Total (de)multiplexer failure may result if rigid connections between components and the frame become loosened.
  • Rodino U.S. Patent No. 5,074,630 is directed to an integrated optic device having an integrated optic chip attached to a substrate which in turn is connected by a visco-elastic polymer adhesive to a support package structure.
  • the visco-elastic polymer adhesive is intended to minimize transmitted stress to the substrate during shock, vibration and thermal expansion applied to the substrate.
  • the adhesive of Rodino is suitable for vibration damping for a bulk optic device. It is intended for absorbing high G shock loads applied to a very low mass integrated optical component, and the teaching of Rodino would not be applicable to high mass bulk optical elements.
  • Dueck U.S. Patent No. 6,011,884, teaches a structure which purportedly yields a (de)multiplexer which is thermally stable.
  • Dueck is directed to an integrated bi-directional axially gradient refractive index diffraction grating (demultiplexer.
  • the (demultiplexer of Dueck consists of a waveguide array and a diffraction grating with a focusing optic disposed therebetween and the elements optically coupled and aligned along an optical axis.
  • Dueck provides a first homogenous boot lens disposed between the waveguide array and the lens and a second homogenous boot lens disposed between the focusing lens and the diffraction grating.
  • Dueck teaches that not only do the homogenous index boot lenses allow for integration of the optical components into a single integrated device, the single integrated device increases thermal stability and avoids the introduction of air spaces which cause increased alignment sensitivity.
  • the use of index boot lens as taught by Dueck is incompatible with the notion of a bulk optic (de)multiplexer.
  • the homogenous index boot lenses add additional product components, complicating the (de)multiplexer.
  • Laude U.S. Patent No. 5,991,482 teaches the use of thermally stable optical components in association with a grating of a (de)multiplexer to thermally stabilize his (de)multiplexer. This solution has limited application to the (de)multiplexer structure taught in Laude. It is not useful for bulk optic (de)multiplexers generally.
  • Hamblin U.S. Patent No. 5,745,289, is of interest because of its teachings of athermalized diffractive optical components that have an effective focal length that does not shift substantially with temperature.
  • Keyworth teaches the use of a compensator associated with a waveguide array to laterally shift the waveguide array to compensate for lateral shifts in the location of light beams induced by changes of temperature.
  • the compensator taught by Keyworth is made of a thermally expansive material which is cantilevered laterally from the frame and which is associated with a resistive heating element to heat the compensator to induce lateral shift. While Keyworth may be useful in compensating for lateral shifts in beams, Keyworth does not address the problem of changes in focal length that may result from temperature induced changes of refractive index or the shape of optical elements. Keyworth further requires the use of a resistive heating element and presumably associated temperature monitors and controls to appropriately actuate the heating element as needed. Not only does this increase (de)multiplexer complexity and cost, it provides another system for potential failure in operation. Moreover, it requires ongoing energy input, not unlike thermally stabilizing the operating environment.
  • the present invention is intended to overcome one or more of the problems discussed above.
  • a first aspect of the invention is a bulk optic (de)multip lexer for fiber optic communications systems including a diffraction grating having a diffraction surface, a waveguide array including a plurality of waveguides having an input/output end for emitting and receiving optical signals, and a focusing optic in optical communication between the diffraction grating and the waveguide array along an optical axis.
  • the focusing optic focuses beams from the diffraction surface of the grating for optical coupling with the input/output ends of the waveguides.
  • the (de)multiplexer further includes a frame. A fixed mount is provided between the focusing optic and the frame.
  • a first adjustable mount is provided between the waveguide array and the frame and a second adjustable mount is provided between the diffraction grating and the frame.
  • the first adjustable mount is configured to provide for linear movement of the waveguide array along the Z axis corresponding to the optical axis and independent movement of the input/output axis within a plane parallel to the X, Y axes.
  • the second adjustable mount is preferably configured to provide only for gimbaled movement of the grating about a point on the diffraction surface of the grating intersecting the optical axis.
  • a fixed mount can replace the second adjustable mount the first adjustable mount can provide for linear movement along an XY plane and an XZ plane and rotational movement about the Y and Z axes.
  • a second aspect of the present invention is an attachment assembly for attaching a diffraction grating having a diffraction surface of an optical (de)multiplexer to a frame of the (de)multiplexer, the (de)multiplexer having optical elements in addition to the grating, the optical elements being attached to the frame and aligned along an optical axis.
  • the attachment assembly includes a grating mount having a leading surface to which the grating is attached with a diffraction surface in a select orientation relative to the grating mount and a spherical surface having a radial center at a point on the diffraction surface of the grating.
  • a receptacle on the frame has a surface which is conical about a central axis receiving the spherical surface of the grating mount with the optical axis intersecting the point on the refractive surface of the grating.
  • a clamp or stay is operatively associated with the grating mount and the frame for fixing the grating mount relative to the frame with the diffraction surface in a select orientation relative to the optical axis.
  • the bulk optic (de)multip lexer of the present invention provides a combination of fixed and adjustable mounts which eases alignment of the (demultiplexer optical elements.
  • the fixed mount of the focusing lens allows the optical axis of the focusing lens to define a reference about which the other optical elements can be aligned.
  • the adjustable mount between the grating and the frame not only provides for gimbaled movement of the grating about a point on the grating surface intersected by the optical axis to aid in proper alignment of the grating, it also provides a structure which prevents a change of orientation of the grating relative to the optical axis while providing movement of the grating only along the optical axis due to temperature changes or clamping of the adjustable mount.
  • the adjustable mount associated with the waveguide array allows for independent movement of the waveguide array along the optical axis and for independent movement of the waveguide array in a plane normal to the optical axis. This independence of movement further facilitates efficient alignment.
  • the embodiment providing a fixed grating and a 6 way adjustable mount for the waveguide array may further simplify alignment.
  • the apparatus further facilitates the claimed method of aligning the (de)multiplexer which simplifies and expedites alignment of the optical elements.
  • a third aspect of the present invention is a (de)multiplexer for fiber optic communications systems including a wavelength dispersive element, a waveguide array including a plurality of waveguides having an input/output end for emitting and receiving optical signals, and a focusing optic in optical communication between the wavelength dispersive element and the input/output ends of the waveguides.
  • the focusing optic focuses beams from the wavelength dispersive element to select focal points for optical coupling with the input/output ends of the waveguides.
  • a location of the select focal points varies as a function of changes in (de)multiplexer temperature.
  • the wavelength dispersive element, the waveguide array, and the focusing optic are attached to a thermally expansive frame.
  • the frame supports the waveguide array and the focusing optic for movement relative to one another as a function of changes in (de)multip lexer temperature to maintain optical coupling between the input/output ends and the focused beam.
  • a fourth aspect of the present invention is a (de)multiplexer for fiber optic communications systems including a wavelength dispersive element, a waveguide array including a plurality of waveguides located in a substrate having an input/output end emitting and receiving optical signals, and a focusing optic in optical communication between the wavelength dispersive element and the input/output ends of the waveguides.
  • the focusing optic focuses beams from the wavelength dispersive element to select focal points for optical coupling with the input/output ends.
  • the wavelength dispersive element, the waveguides of the waveguide array, and the focusing optic are aligned along an optical axis and are attached to a frame.
  • the location of the focal points moves along a transverse axis relative to the optical axis as a function of changes in (de)multiplexer temperature.
  • a thermally expansive member extends transverse the optical axis.
  • the waveguide array is attached to the transverse member to move as a function of temperature to maintain optical coupling.
  • the substrate of the waveguide is also preferably thermally expansive to match the spread between alignment beams to maintain optical coupling between fibers and beams as temperatures vary.
  • a fifth aspect of the present invention is a method of thermally stabilizing a (de)multiplexer having a wavelength dispersive element, a waveguide array, and a focusing optic in optical communication between the wavelength dispersive element and the input/output ends of the waveguides.
  • the focusing optic focuses beams from the wavelength dispersive element to select focal points for optical coupling with the input/output ends.
  • the method includes varying the location of the select focal points as a function of changes in (de)multiplexer temperature and moving the wavelength array relative to the focusing optic as a function of (de)multiplexer temperature to maintain optical coupling between the input/output ends and the focused beams.
  • the method may further include attaching the wavelength dispersive element, the focusing optic and a waveguide array to a thermally expansive frame along an optical axis and varying the location of the focal points by changing the focal length along the optical axis between the focusing optic and the focal points as a function of (de)multiplexer temperature.
  • the method may also include varying the location of the focal points along a transverse axis relative to the optical axis and moving the waveguide array along the transverse axis in a direction along the transverse axis corresponding to a direction of movement of the focal points by thermally expanding a thermally expansive connector between the waveguide array and the frame.
  • the thermally stable multiplexer/demultiplexer of the present invention provides optical elements which vary the location of the focal points of a focusing lens in a known manner as a function of changes in (de)multiplexer temperature, over a range of -5°C to 65°C.
  • the use of a thermally expansive frame connecting the focusing optic and the waveguide array provides for movement of the input/output ends of the waveguide array as a function of changes in (de)multiplexer temperature in a manner maintaining efficient optical coupling between the input/output ends of the waveguides and the focal points.
  • the invention does not require any additional energy input to maintain this efficient coupling; rather, the coupling is maintained automatically by matching the dimensions and coefficient of thermal expansion of the frame elements to the effects of temperature on the optical elements.
  • the system also does not require special "athermal" optics which could otherwise induce design tradeoffs.
  • the thermally expansive frame can be made of aluminum alloy or other readily available materials, which helps minimize (de)multiplexer cost.
  • a sixth aspect of the invention is an optical (de)multiplexer including a plurality of discrete optically aligned bulk optical elements.
  • the bulk optical elements are rigidly attached to a rigid frame in optical alignment relative to each other.
  • the rigid frame is attached to a platform or housing by a vibration damping support to isolate the rigid frame from vibrations applied to the platform.
  • a vibration damping support may comprise a pair of spaced rigid plates, each plate having a fastener for attachment to one of the rigid frame and the platform.
  • a vibration damping elastomer is between and fixably attached to the plates.
  • the rigid frame and the rigid housing may be elongate along an optical axis with the plurality of the vibration supports being located between the ends of the rigid frame.
  • the optical (de)multiplexer further includes a plurality of elastomeric bumpers at an extreme end of the frame between the frame and the housing configured to alleviate impact generated shock.
  • Yet another aspect of the present invention is a method of isolating a (de)multiplexer from external vibrations.
  • the (de)multiplexer includes a plurality of discrete optically aligned bulk optical elements.
  • the method includes rigidly affixing the optically aligned bulk optical elements to a rigid frame, providing a platform and connecting the rigid frame to the platform with a vibration damping support.
  • the platform preferably comprises a housing sized to receive the rigid frame and the method further includes placing the rigid frame within the housing.
  • the vibration damping of the present invention provides a bulk optic (de)multiplexer where the bulk optic elements are isolated from vibration and shock within a protective housing.
  • the structure facilitates a (de)multiplexer which can be deployed in the field without the need for an additional vibration damping foundation underlying the (de)multiplexer. This considerably expands the options for deployment of the (de)multip lexer.
  • the vibration damping structure is easily manufactured and assembled, providing the highly desirable vibration damping at a minimal cost.
  • FIG. 1 is a plan view of a first embodiment of a (de)multip lexer in accordance with the present invention with the top of the (de)multiplexer housing removed;
  • Fig. 2 is a perspective view of a (de)multiplexer frame of Fig. 1 in accordance with the present invention
  • Fig. 3 is a cross-section of the (de)multiplexer frame of Fig. 2 taken along line 3-3 of Fig. 2;
  • Fig. 4 is a schematic perspective view of an optical fiber waveguide array used in the present invention.
  • Fig. 5 is an enlarged cross-section of a slidable connection between fixed and moving X, Y stages;
  • Fig. 6 is a front elevation view of a moving X, Y stage in accordance with the present invention
  • Fig. 7 is a cross-section view of the moving X, Y stage of Fig. 6 taken along line 7-7 of Fig. 6;
  • Fig. 8 is a front elevation view of a waveguide array attached to the cantilevered platform of the movable X, Y stage in accordance with the present invention
  • Fig. 9 is a perspective view of a grating holder depicted in Fig. 3
  • Fig. 10 is a sectional view illustrating pivoting of the grating holder about the optical axis
  • Fig. 11 is a schematic representation of a properly aligned (de)multiplexer
  • Fig. 12 illustrates movement of the focal points of single channel beams as a function of an increase in temperature along with the movement of the waveguide array as a function of increase in temperature to maintain coupling with the single channel beams;
  • Fig. 13 is a plan view of an alternate embodiment of a vibration damping support for a (de)multip lexer in accordance with the present invention with the top of the multiplexer housing removed;
  • Fig. 14 is a perspective view of a vibration damping support in accordance with the present invention;
  • Fig. 15 is a cross-section view taken along lines 15-15 of Fig. 13;
  • Fig. 16 is a cross-section of an alternate embodiment of a vibration damping support in accordance with the present invention
  • Fig. 17 is a perspective view of a second embodiment of the (de)multiplexer in accordance with the present invention.
  • Fig 18 is an exploded view of the (de)multiplexer of Fig. 17;
  • Fig. 19 is an enlarged cut away of the first adjustable mount of the (de)multiplexer of Fig. 18;
  • Fig. 20 is an exploded view of the adjustable mount of Fig. 19;
  • Fig. 21 is an exploded view of the waveguide array carrier of Fig. 20;
  • Fig. 22 is a cross-section of assembled XYZ stage, waveguide array carrier and fiber pigtail array taken along line 22A-22A of Fig. 19;
  • Fig. 23 is an exploded view of a third embodiment of the (de)multiplexer of the present invention.
  • Fig. 24 is a partial enlargement of Fig. 23.
  • Fig. 1 is a plan view of a first embodiment (de)multiplexer in accordance with the present invention.
  • a (de)multiplexer frame 12 resides within a housing 14.
  • the housing 14 consists of a top and a bottom portion that fit together in a sealing relationship as will be described in greater detail below. In Fig. 1 the top portion has been removed to reveal the (de)multiplexer frame.
  • the (de)multiplexer frame 12 is shown in perspective removed from the housing 14 in Fig. 2.
  • the (de)multiplexer frame maintains the optical elements of the (de)multiplexer in optical alignment.
  • Fig. 2 also includes a depiction of orthogonal X, Y, Z axis which will be used as reference axis throughout this description.
  • the Z axis is collinear with the optical axis 22.
  • the optical elements of the (de)multiplexer include a wavelength dispersive element 16, a focusing optic 18, and a waveguide array 20.
  • the wavelength dispersive element, the focusing optic, and the waveguide array are maintained by connection to the frame in optical communication with one another along an optical axis 22.
  • the elements are in what is commonly known as littrow alignment.
  • the wavelength dispersive element 16 is preferably a reflective diffraction grating formed using conventional techniques from a glass substrate having a negligible coefficient of thermal expansion.
  • a glass substrate having a negligible coefficient of thermal expansion.
  • One preferred substrate material is ZERODUR, manufactured by the Schott Company.
  • a diffraction surface 24 of the grating has a large number of grooves which are formed parallel to an Y axis normal to the cross-sectional plane of Fig. 3.
  • the grooved surface has a highly reflective coating, such as gold.
  • Representative gratings include echellette and preferably echelle gratings, as are disclosed in commonly assigned, copending U. S. Patent Application Serial No. 09/628,774, entitled "Echelle Grating Dense Wavelength Division Multiplexer/Demultiplexer", the contents of which are incorporated in their entirety herein.
  • the focusing optic 18 is preferably a spherical symmetric doublet lens, although other lens structures could be suitable as well.
  • the spherical symmetric doublet lens has a select focal length within a relatively narrow range of tolerance along an optical axis.
  • the lens also has a refractive index that varies a known amount as a function of temperature. Furthermore, the lens surfaces deform in a predictable manner with changes in temperature.
  • the waveguide array 20 is shown in greater detail in Fig. 4.
  • the waveguide array 20 consists of a number of single channel waveguides 26 having an input/output end 28 with the input/output ends 28 aligned along an input/output end axis 30 and a multiplex or multichannel waveguide 32 vertically below and at the center of the single channel waveguides 26.
  • Other embodiments known in the art such as having the multiplex waveguide coincident with the input/output end axis or above it, may also be suitable.
  • stacked multiplex waveguides and single channel arrays (as described in U.S. Patent Application Serial No. 09/628,774) may be used with the invention described herein.
  • single cham el waveguides here, 20, have been shown as comprising the waveguide array.
  • the preferred embodiment will have many more single channel waveguides, such as 48 or more.
  • the single channel waveguides 26 and the multiplex waveguide 32 are all single mode optical fibers.
  • the fibers are held in place between two pieces of a silicon substrate or wafer 34 having N-shaped grooves 36 which are precisely etched in the substrate pieces to maintain the single channel fibers at a precise desired spacing from one another.
  • the silicon is preferably high purity prime grade.
  • the multiplex optical fiber 32 is held in a precise location relative to the single channel optical fibers by a third piece of silicon substrate with an appropriate N groove.
  • the input/output ends of the single channel fibers terminate along an input/output end axis 30, and this axis is in the same plane as the input/output end of the multiplex waveguide 32.
  • the spacing of the waveguides increases slightly from left to right so as to couple with the corresponding single channel beams, which increase in separation in a like manner.
  • the dimensions of the assembled substrate are 15 mm along the X axis, 1.5 mm high and 12 mm deep.
  • a microlens array 37 may be incorporated into the substrate.
  • the microlens array also increases band pass.
  • the microlens array consists of a focusing lens 38 along an optical axis of each waveguide, with the lenses coupled by a frame 39 attached to the substrate 34 made of a material having a CTE matching that of the substrate 34 to thermally expand with the substrate to promote optical coupling along the waveguide optical axis.
  • the (de)multiplexer frame 12 of the first preferred embodiment includes a telescope portion 40, a cone housing portion 42 attached to one end of the telescope portion by conventional fasteners such as screws, and a flexure portion 44 similarly attached to the other end of the telescope portion 40.
  • the frame could be a single integral piece, two pieces or more than three pieces.
  • the multiplexer frame 12 further includes a first adjustable mount 46 associated with the flexure portion 44, a second adjustable mount 48 associated with the cone housing portion 42 and a fixed mount 50 within the telescope portion 40.
  • the first adjustable mount 46 consists of a flexure 52, which is movable axially within a limited range ( ⁇ 1 mm) only along a Z axis as indicated by the arrow 54.
  • the flexure is integrally formed of the flexure portion of the frame, but it could also be a separate structural element affixed to the frame by suitable connectors.
  • the preferred embodiment includes identical top and bottom flexure elements 52A and 52B to prevent tipping of the waveguide array as the flexure is moved along the Z axis.
  • a single flexure element suitably arranged could perform the same function as well and is within the scope of the invention.
  • Other structures for providing movement only along the Z axis may be suitable as well.
  • a noninfluencing lock piece assembly 56 preferably connects the flexure 52 to the flexure portion of the frame so that the flexure 54 can be secured in a select position along the Z axis. Referring to Fig.
  • the preferred embodiment uses two noninfluencing lock piece assemblies 56A and 56B, one on the top and one on the bottom of the flexure with each assembly secured on opposite sides of the frame.
  • Other stay structures or clamps may be used instead of the noninfluencing lock piece, but substitutes would preferably also not influence the Z axis position as they are secured.
  • the first adjustable mount 46 further consists of a fixed X, Y stage 58 which is fixedly attached to the Z axis flexure 52 by screws or the like (not shown) so that the first X, Y stage moves with the Z axis flexure 52.
  • the fixed X, Y stage 58 has a planar surface 60 substantially normal to the optical axis 22.
  • a moving X, Y stage 62 has a planar surface 64 which abuts the planar surface 60 of the fixed X, Y stage 62.
  • the planar surfaces can be moved relative to one another parallel to the X, Y axis by virtue of sliding connectors 66, and the planar surfaces are preferably anodized aluminum to facilitate sliding.
  • a sliding connector 66 is shown in greater detail in Fig. 5.
  • the sliding connector 66 consists of a bolt 68 having a shaft body 70 and a threaded tip 72.
  • the threaded tip 72 is threadably engaged in a threaded hole 74 in the moving X, Y stage 62.
  • the shaft body 70 resides in a hole 74 in the fixed X, Y stage 58 having an inner diameter greater than the outer diameter of the shaft body 70 to allow a desired degree of freedom of movement of the moving X, Y stage relative to the fixed X, Y stage in an X, Y plane. In the preferred embodiment this is about + .5 mm of movement.
  • a washer 76 resides between the head of the bolt 68 and a planar surface of the fixed X, Y stage 58 opposite the planar surface 60.
  • the washer 76 has an annular trough abutting the fixed X, Y stage which is filled with tiny glass beads having a diameter slightly greater than the depth of the annular trough encased in suitable grease.
  • the sliding connector 66 allows limited movement between the moving X, Y stage and the fixed X, Y stage within an X, Y plane with minimal friction induced sticktion between the planar surfaces of the stationary and moving stages.
  • the moving X, Y stage is secured in place by noninterfering lock pieces 77 on opposing sides of the moving X, Y stage, or other suitable stays or clamps.
  • the non-influencing lock piece assemblies 56 and 77 collectively form a stay for the first adjustable mount 46.
  • the moving X, Y stage and the associated waveguide array 20 may be moved axially of the Z axis, rotated about the Z axis, and moved linearly within an X, Y plane normal to the Z axis.
  • the waveguide array 20 can be moved independently along the Z axis.
  • the first adjustable mount might be limited to the Z axis flexure (or some other structure providing movement along the Z axis) without the moving X, Y stage, or vice versa.
  • Fig. 6 is a front elevation view of the moving X, Y stage and Fig. 7 is a sectional view taken along line 7-7 of Fig. 6.
  • a cantilevered connector 80 extends from the moving X, Y stage from a side opposite and in a direction normal to the planar surface 64.
  • the cantilevered connector 80 consists of a platform 82, which extends in a cantilevered manner from a post 84.
  • the top surface of the platform has a recess 86.
  • Fig. 8 illustrates how the waveguide array 20 is attached to the platform 82 by a flexible connector 88 which allows the waveguide array to expand when heated relative to the platform 82.
  • the flexible comiector 88 consists of a rigid connection 90 between a bottom of the substrate 34 near the post 84 and an elastic connection 92 near the distal end of the cantilevered platform 82.
  • the rigid connection 90 is made by a suitable rigid curing epoxy and the flexible connection 92 is made by a suitable elastic curing epoxy.
  • the waveguide array 20 is epoxied in place bringing the waveguide array into registration with appropriate guides and spacers (not shown) associated with the platform 82. Both the rigid and elastic curing epoxies have virtually identical thermal coefficiencies of expansion to preventing tipping of the waveguide array 20 about a Z axis by changes in temperature.
  • the second adjustable mount 48 includes the rear wall of the cone housing portion 42 of the frame 12 having a concave and preferably a conical recess or receptacle 98 formed therein.
  • the conical recess 98 is symmetric about a central axis which is preferably collinear or very close to collinear with the optical axis 22.
  • a circular hole 100 having a central axis along the optical axis 22 extends from the conical wall of the conical recess 98 through the rear wall.
  • the surface of the rear wall opposite the conical recess 102 is spherical and has a radial center which preferably is at about a point 104 where the optical axis 22 intersects the diffraction surface 24 of the grating 16.
  • the second adjustable mount 48 further includes a grating mount 106 having a leading planar surface 108 and a trailing spherical surface 110.
  • the spherical surface 110 may include a low friction coating 111 such as PTFE or carbide.
  • the spherical surface 110 has a radial center at the point 104 where the optical axis intersects the diffraction surface 24 of the grating with the trailing spherical surface 110 nested in the conical recess 98.
  • a clamp assembly or stay 112 secures the grating mount 106 with its spherical surface engaging the conical recess 98 as illustrated in Fig. 3.
  • the clamp preferably consists of a threaded tail 114, which extends along a central axis of the spherical surface through the hole 100 in the rear wall of the cone housing.
  • a washer 116 having a spherical recess 118 including an annular contact rib 120 resides between the spherical wall 102 and a locking nut 122 with the contact rib 120 contacting the spherical wall 102.
  • the contact rib 120 has a low friction coating 121 such as PTFE or carbide.
  • a spring washer 124 is preferably provided between the locking nut and the spherical washer 116.
  • the spring washer 124 allows the locking nut to be loosened somewhat while the clamp assembly 112 is still held in position so that the grating mount 106 can be repositioned.
  • the cooperation between the spherical surface of the grating mount and the conical recess 98 allows for true gimbaled movement of the diffraction surface of the grating about the point 104.
  • the grating can be rotated about the point 104 along orthogonal three axes within a limited range of motion. This is illustrated in Fig. 10.
  • a notch 125 at the distal end of the threaded tail 114 defines a first planar surface 126 in an Z, Y plane and a second planar surface 127 in an X, Y plane as depicted in Fig. 3, parallel to the grooves of the grating 16, to facilitate course alignment of the grating 16.
  • the grating mount 106 is shown in a perspective view in Fig. 9. Extending on either side of the leading planar surface 108 are standing ribs 128. The standing ribs 128 are included to ensure that as the grating holder is subjected to changes in temperature, it expands and contracts along the optical axis 22 with the diffraction surface of the grating maintaining its orientation relative to the optical axis 22, as illustrated schematically in Fig. 12.
  • the grating mount is preferably made of titanium or 416 stainless steel to ensure rigidity and strength, although other low CTE materials such as INVAR, KOVAR or ZERODUR may be used as well.
  • the grating is attached to the leading planar surface 108 by a suitable epoxy and is positioned on the leading surface in a select orientation by registration with an inner wall of the standing ribs 128 and suitable spacers.
  • Fig. 10 illustrates gimbaled movement of the diffraction surface about the point 104.
  • the point 104 is still intersected by the optical axis 22.
  • the washer 100 is self-aligning relative to the spherical surface 102 to maintain complete contact of the annular contacting rib 120 with the spherical surface. This structure also keeps a ring of contact of the washer opposite that of the spherical surface 110 of the holder to minimize distortion of the cone housing. While in the preferred embodiment the spherical surface 100 and conical recess 98 have central axes along the optical axis 22, their central axes could be non-colinear with the optical axis and still allow for the desired gimbaled movement.
  • the fixed mount 50 simply consists of an enlarged inner diameter portion 130 of the telescope portion 40 of the frame 12.
  • the focusing optic 18 is axially inserted in this enlarged diameter of portion 130 and secured in place by an appropriate adhesive or held in place by an appropriate mechanical clamp suitable for maintaining the optical alignment over a wide temperature range, e.g., -5°C-65°C.
  • the optical elements of the (demultiplexer 10 are aligned as follows. First, the lens 18 is brought into registration with the wall at the end of the larger diameter portion of the fixed mount 130 and the optical axis of the lens defines the optical axis 22 of the (de)multiplexer. The lens is then cemented or clamped in place. The grating is coarsely aligned by having the first surface 126 parallel to the Z, Y reference plane and the second surface 127 parallel to the X, Y reference plane. The moving X, Y stage is coarsely aligned simply by connection of the X, Y moving stage to the X, Y fixed stage with waveguide array attached to the X, Y moving stage as discussed above.
  • an actuator for moving the Z flexure along the Z axis is operatively associated with the Z flexure
  • an actuator for moving the X, Y moving plate along the X axis is associated with the X, Y moving plate
  • an actuator for moving the X, Y moving plate along the Y axis is associated with the X, Y moving plate.
  • an actuator for each rotational degree of movement of the second adjustable mount is operatively associated with the grating mount 106.
  • a multiplex beam of the operative wave band of light is propagated to the multiplexer through the multiplex optical fiber 32.
  • Photo detectors are associated with the end single mode fibers to monitor light output at these points.
  • the actuators could combine one or more degree of movement.
  • An automatic alignment device utilizing a six axis feed back loop controlled algorithm controls actuation of each actuator to move the grating and waveguide array relative to the optical axis to optimize optical signal strength at the extreme ends of the single channel array. First the beam strength is optimized at one end of the signal channel array and then the other by coordinated movements of the six actuators by the automatic alignment device until signal strength in these single channel optical fibers is maximized. Then the first and second adjustable mounts 46, 48 are clamped into place as described above.
  • the multiplexer 10 is also configured so that "optical coupling" or the coupling integrity, that is efficiency and the level of crosstalk, remain within acceptable specified levels within a relatively wide range of temperatures, more particularly from about -5°C to 65 °C. For example, for efficiency, loss should not increase greater than 0.5 db and cross-talk should not increase more than 5 db.
  • "optical coupling" or the coupling integrity that is efficiency and the level of crosstalk
  • the multi-channel or multiplex waveguide 32 is projected as a multi-channel beam to the focusing optic 18 which collimates the multi-channel beam and directs it off the diffraction surface 24 of the grating 16.
  • the diffraction grating divides the multi-channel beam by wavelength into a number of single channel beams which are diffracted off the diffraction surface 24 to the focusing optic 18 which directs the focused singled channel beams to select focal points for optical coupling with the input/output ends of the single channel waveguides 26.
  • Fig. 12 illustrates the effect of an increase in temperature on the beams 140.
  • the refractive index of the lens 18 decreases and the surfaces of lens are slightly deformed so as to cause the focal length of the lens 18 to increase.
  • the select focal points extend beyond the plane of the input/output ends of the optical fibers 26, 32.
  • there is a change in the refractive index of the air occupying the space between the diffraction grating 16 and the lens 18 and the air between the lens 18 and the waveguide array 20. This change in the refractive index of the air causes a lateral shift of the select focal points of the single channel beams 140 along the X axis as is also illustrated Fig. 12.
  • temperature changes result in both axial and radial movement of the focal points as a function of temperature.
  • some form of athermalization could eliminate either the radial or axial movement, hi such alternate embodiments, it would be necessary only to provide for a corresponding movement of the input/output ends of the waveguides.
  • the position of the grating may move along the optical axis as a result of temperature changes expanding or contracting the frame between the lens and the grating and thermal expansion or. contraction of the grating holder itself, the light in this region is collimated so these movements have no optical effect.
  • the grating substrate is athermal (negligible CTE) and the grating holder is configured to maintain the orientation of the diffractive surface of the grating as the grating holder is subjected to temperature changes.
  • the grating itself is believed to be insensitive to temperature changes for alignment purposes.
  • the frame 12 of the (de)multiplexer includes a number of novel features.
  • the frame is made of a thermally expansive material, for example, an aluminum alloy such as 6061 T6 having a coefficient of thermal expansion (CTE) that allows the frame to vary in length as a function of temperature.
  • CTE coefficient of thermal expansion
  • thermally expansive and “thermal expansion” and the like are used to mean both expansion or contraction, with the ⁇ L being positive or expansive as temperature increases and ⁇ L being negative or there being a contraction as the temperature decreases, unless the context clearly indicates it is intended to be limited to an expansion, such as where the term is associated with an increase in (de)multiplexer temperature.
  • the frame 12 is symmetric about the optical axis 22 to provide equal lengths L of material along the optical axis 22, and therefore uniform expansion along the optical axis with changes in (de)multiplexer temperature.
  • the telescope portion of the frame 40, the cone portion 42 of the frame and flexure portion 44 of the frame are all symmetric about the optical axis.
  • these portions of the frame change length only along the optical axis 22, simplifying maintaining alignment during temperature induced length changes.
  • the length of frame material connecting the lens 18 and the waveguide array 20 along with the material(s) from which this portion of the frame is made are selected to provide a length L and CTE such that the length along the optical axis of the portion of the frame between the waveguide array and the lens changes with temperature about the same amount that the focal length of the single channel focusing beams changes as a function of temperature to maintain optical coupling of the focusing points and the input/output ends of the single channel fibers.
  • the structure is similar in principle.
  • the substrate 34 of the waveguide array 20 is a thermally expansive material so that increases in temperature will cause it to expand and decreases in temperature will cause it to contract along the X axis.
  • the flexible connector 88 includes the first end of the substrate 34 having a rigid connection 90 to the cantilevered connector 80 near the post 84 and an elastic connection 92 near the distal end of the cantilevered connector 80.
  • the substrate 34 grows along its X axis as a function of increases in temperature, the substrate will expand toward the elastic connection 92, causing distortion of the elastic connection 92 as illustrated in phantom lines in Fig.
  • the cantilevered connector 80 is also made of a thermally expansive material such as an aluminum alloy.
  • the distance L c as well as the coefficient of thermal expansion of the material from which the cantilevered connector 80 is made can be adjusted to provide sufficient movement along the X axis to insure the maintenance of optical coupling between the single channel beams 140 and the input/output ends of the single channel fibers 126.
  • the preferred embodiment compensates for lateral shift along the X axis by combining the thermal expansion of the waveguide substrate and the cantilevered connector
  • either one may provide the necessary lateral shift to maintain suitable optical coupling, and the other could be "athermalized.”
  • the flexible connector between the substrate and the cantilevered connector could have two elastic connections (and no rigid connection) so that only thermal expansion of the cantilevered connector 80 moves the input/output ends a significant amount to maintain optical coupling.
  • the cantilevered connector 80 could be modified to not be cantilevered or it could be made of an athermal material so optical coupling is maintained solely by thermal expansion of the waveguide substrate.
  • Fig. 12 also illustrates schematically the effect of temperature on the grating mount 106.
  • the standing ribs 128 insure that the grating mount 106 will move the diffraction grating 16 along the optical axis 22 while maintaining the diffraction surface 24 in the same select orientation relative to the optical axis 22.
  • vibration damping supports 150 support the (de)multiplexer frame 12 within the housing 14.
  • the vibration damping supports 150 include vertical supports 152 and horizontal supports 154. Both the vertical and horizontal supports 152, 154 are positioned to suspend the frame within the housing.
  • the vertical and horizontal supports 152, 154 are made of an elastomeric material of a select formulation chosen to dissipate vibrations most likely to be encountered by the (de)multiplexer 10.
  • Representative vibrations of concern would be low frequency vibrations such as might be incurred in an earthquake, middle frequency vibrations such as might be incurred during transport of the assembled (de)multiplexers and high frequency vibrations which might be generated by cooling fans and the like deployed in the vicinity of the multiplexer in operation.
  • Representative materials for the vibration damping supports include natural and synthetic rubber, urethane and other polymeric elastomers, with urethanes being preferred. Choice of a particular material would be a function of many factors, including anticipated frequencies, anticipated temperatures, mass of the (de)multiplexer and the like.
  • a top housing piece mates with the bottom housing piece illustrated in Fig. 1 and 13.
  • a seal 156 is deployed between the housing segments so that the interior of the housing can be pressurized with nitrogen or another suitable gas to minimize the risk of corrosion of sensitive optical and mechanical parts as well as to provide for a uniform gaseous medium through which the beams are transmitted within the (de)m u h--P- e ⁇ er -
  • FIG. 13-15 Another embodiment of the vibration damping support structure is illustrated in Figs. 13-15.
  • four vibration damping supports 160 attach the telescope portion 40 of the frame to the bottom of the housing 14.
  • a vibration damping support 160 is shown in a perspective view in Fig. 14 and it can be viewed in cross-section in Fig. 15.
  • the vibration damping support 160 consists of a round top plate 162 and a round bottom plate 164.
  • An axial post 166, 168 extends outwardly from the round top plate and round bottom plate, respectively.
  • Each post is externally threaded in order that it can be fastened between the frame 12 and the housing 14 as illustrated in Fig. 15.
  • Between the top and bottom plates 162, 164 is an elastomeric vibration damping spacer 170.
  • the plates 162, 164 and the axially posts 166, 168 are preferably integrally formed from a suitable rigid material such as steel.
  • the vibration damping supports 160 are preferably formed by pouring the elastomer 170 in a liquid state in a mold between the plates. Where the elastomer is , for example, a urethane, the urethane will bond directly to the plates eliminating the need for an adhesive.
  • the bonding interface area is specially treated to create a chemical bond between the rigid plate and the elastomer that equals or exceeds the inherent split/tear strength of the elastomer itself. It is treated by creating a surface texture on the plates by sand blasting or the like, thoroughly cleaning the textured surface and applying a surface bonding agent suitable for enhancing the bond between the material of the plate and the elastomer. Where a different elastomer is used that cannot form a sufficiently robust bond with the metal plates, a suitable adhesive such as an epoxy may join the elastomer and the plates.
  • the telescope portion of the frame 40 includes flange extensions 172 that define mounting brackets for the frame 12.
  • Each flange extension 172 has a countersunk bore 174 with the lesser diameter portion being sized to axially receive the post 166.
  • Corresponding attachment bosses 176 extend from a bottom surface of the housing 14 as illustrated in Fig. 15. Each boss has an internally threaded bore 178.
  • the frame 12 lies within the housing and juxtaposed with the bottom of the housing 12.
  • each vibration damping support 160 is threadably engaged in an internally threaded bore 178.
  • Each countersunk bore 174 of the frame in turn receives a post 166 of a vibration damping support 160.
  • Nuts 180 threadably engage the threaded post 166 to secure the frame to the housing 14. As viewed in Figs. 13 and 15, with the frame secured within the housing in this manner, the frame is otherwise spaced from and does not contact the housing.
  • mushroom bumpers 182 are spaced about the distal end of 184 of the flexure portion 44 of the frame 12.
  • mushroom bumpers 182 prevent direct contact between the frame and the housing in the event the (de)multiplexer is subjected to severe vibrations or shock, as may be encountered if the (de)multiplexer is dropped.
  • the mushroom bumpers control the deceleration of the frame.
  • the function of the bumper is to absorb the energy without transferring an impact frequency into the frame itself. Material choice influences the rate of deceleration and the performance over time when exposed to continuous vibration (60Hz, office environment).
  • continuous vibration damping supports 150 discussed with reference to Fig.
  • the elastomeric material 170 is made of a select formulation chosen to attenuate shocks and vibrations likely to be encountered during handling and operation of the (de)multiplexer lO.
  • the formulation of the elastomer, preferably urethane is controlled very specifically and is tuned to absorb specific frequency ranges.
  • These urethanes can be chosen from different families of urethanes, most specifically ether based or ester based, depending on environmental compatibilities of the specific application. For instance, an ester-based urethane is more applicable in an environment that may contain high moisture or petroleum based solvents. Ethers are more applicable in an environment that requires elevated physical properties (rebound, split/tear strength, % elongation, hysteresis, etc.).
  • the preferred embodiment will incorporate formulations from the ether family. Very strict stoichiometric ratio control is necessary to ensure complete chain reaction and free radical termination. This is pertinent with regard to the issue of off gassing. Careful control of the chemical ratios eliminates the possibility of unreacted chemicals leeching out of the material over time.
  • FIG 16 is an alternate embodiment of a vibration damping support 200.
  • the vibration damping support 200 has a top attachment member 202 and a bottom attachment member 204 which are identical in structure.
  • the attachment members 202 and 204 have an enlarged diameter base 206, a smaller diameter intermediate portion 208 and an externally threaded post 210.
  • the attachment members 202, 204 are aligned coaxially with the threaded posts extending in opposite directions. As illustrated in Fig. 16, with the elastomer 170 molded to the top and bottom attachment members 202, 204, the enlarged base 206 is embedded within the elastomer.
  • FIG. 17 is an alternate embodiment of a (de)multiplexer 300 in accordance with the present invention.
  • the (de)multiplexer 300 includes the same optical elements as the (de)multip lexer 10 illustrated in Figs. 1-16 and generally the same features to provide passive thermal compensation. Like elements will be identified with the same reference number for ease of reference.
  • the (de)multiplexer 300 includes a housing 14 and input/output fiber optic cable assembly 302.
  • Fig. 18, which is an exploded view of the (de)multiplexer 300 of Fig. 17, the housing 14 has a bottom 304 and a top 306. Both the top and the bottom 304, 306 have a corresponding peripheral groove 308 containing a seal 156 as discussed above with respect to the first embodiment of the (de)multiplexer 10.
  • the housing bottom 304 also includes an orifice 310, which retains a silicon plug 312.
  • the input/output cable assembly 302 is received between complimentary semicircular cuts 314, 316 in the housing bottom and top.
  • An o-ring 318 in an annular groove 320 of the input/output cable 302 seals with the semicircular cuts 314, 316.
  • Alternative seal structures could also be used, such as gaskets, semi-liquid sealant or laser welding of the top and bottom of the housing.
  • the (de)multiplexer frame 12 of the second embodiment 300 is similar in configuration to that of the first embodiment of the (de)multiplexer 10. As shown in Fig. 10, it may include a second adjustable mount 48 having the same components as those set forth in Fig. 3.
  • a fixed grating mount 320 maybe employed.
  • the diffraction grating 16 is rigidly mounted to the fixed grating mount 320.
  • the fixed grating mount 320 is attached to the frame 12 by aligning dowels 322 on the frame 12 with receiving holes 324 (one shown in Fig. 18) on the fixed grating mount.
  • the fixed grating mount is then secured in position by bolts 326 threadably engaging the frame 12 through the holes 328.
  • the greatest difference between the second embodiment 300 and the first embodiment illustrated in Figs. 1-16 is the first adjustable mount 340 for attaching the waveguide array 20 to the frame 12.
  • Fig. 19 is a cut away of the frame 12 depicted in Fig. 18 showing the first adjustable mount 340 in a larger scale.
  • the first adjustable mount 340 is shown in an exploded view in Fig. 20.
  • the first adjustable mount 340 consists of an X, Y, Z stage 342, a waveguide array carrier 344, a spring retention plate 346, an upper aluminum clamp plate 348 and a lower aluminum clamp plate 350.
  • the first adjustable mount 340 also includes a trailing portion 352 of the (de)multiplexer frame 12.
  • the trailing portion 352 of the (de)multiplexer 12 includes corner posts 354 having inner threaded bores 356.
  • a pair of magnets 358 is embedded in a trailing planar surface 360 of a trailing portion 352 of the frame 12.
  • Four screw holes 361 are also provided in the trailing planar surface 360.
  • the X, Y, Z stage 342 has a planar leading surface 362 and a pair of steel implants 364 embedded in the leading planar surface 362 to register with the magnets 358 in the planar trailing surface of the frame 12. Both the magnets 358 and the steel implants 364 are either flush or slightly indented within the planar surfaces so that the planar surfaces may be flush to one another when assembled.
  • the X, Y, Z stage 342 further includes a bottom platform 366 having a recess 368. Corner voids 372 in the leading surface 362 are configured to receive the corner posts 354 of the frame 12 when assembled as illustrated in Fig. 19.
  • a leading flange of the stage includes four square holes 374, two of which are shown in Fig. 20, which align with the threaded holes 361 in the trailing planar surface 360 of the frame 12.
  • the waveguide array carrier 344 has a pair of leading wings 378 and trailing wings 380.
  • a waveguide array or fiber pigtail assembly 376 is attached to the underside of the waveguide array carrier 344, as is more clearly illustrated in Fig. 21.
  • the leading wings 378 each include an elongate slot 382, which extends along the Z axis, which has a sufficient width to provide a limited range of motion along the X axis with a screw 390 received therein.
  • the spring retention plate 346 has a pair of downward extending flap springs 384 and three holes 386 substantially evenly spaced along the Z axis on opposite sides of the spring retention plate 346.
  • the spring retention plate is preferably made of a resilient metal such as stainless steel, aluminum, or copper beryllium.
  • the first adjustable mount 340 is assembled by mating the waveguide array carrier 344 with the X, Y, Z stage 342. The mating is accomplished by receiving the fiber pigtail harness 376 in the recess 368 with the trailing wings 380 rearward of the posts 370, 371 and the leading wings 378 forward of the posts 370, 371.
  • the spring retention plate 346 is then attached to the X, Y, Z stage 342 by the corner screws 388, which are tightened in place.
  • the middle screws 390 are received in corresponding holes in the X, Y, Z stage 342 and left untightened.
  • the downward flap springs 384 apply a downward pressure to the waveguide array carrier 344 to prevent it from moving without application of a significant outside force.
  • the screws 390 are tightened and thus act as non-influencing locks.
  • planar leading surface 362 of the X, Y, Z stage 342 is made flush with the planar trailing surface 360 of the frame 12 with the corner posts 354 received in the corner voids 372 as best seen in Fig. 19.
  • the X, Y, Z stage 342 will be held in place relative to the surface of the frame by attraction of the magnets 358 and the steel implants 364.
  • the upper and lower aluminum clamp plates 348, 350 are next brought into position and the corner screws 392 are tightened into the inner threaded bores 356.
  • the middle screws 394 are received in the bore holes 374 of the X, Y, Z stage 342 and loosely screwed into the holes 361.
  • the tolerances of the first adjustable mount 340 are such that when assembled as described, there is a slight clearance between the leading wings 378 of the waveguide array carrier 344 and the spring retention plate 346. As a result of this clearance and the elongate slots 382 in the leading wings 378, the waveguide array carrier 344 can move in the X, Z plane and may rotate slightly around the Y axis as illustrated by the coordinates 396. When the waveguide array carrier is in the desired alignment, it is held in place by the springs 384. Similarly, there is a slight clearance between the X, Y, Z stage 342 and the upper and lower aluminum clamp plates 346, 348 that allows for movement between the X, Y, Z stage 342 and the trailing surface 360 of the frame 12.
  • the X, Y, Z stage 342 is able to move within the X, Y plane and to rotate above the Z axis as illustrated by the coordinates 398.
  • the X, Y, Z stage 342 is held in place relative to the frame 12 by magnetic attraction between the magnets 358 and the steel implants 364. Thereafter the inner screws 394 can be tightened down to form a non-influencing lock between the X, Y, Z stage 342 and the frame 12.
  • the first adjustable mount 340 provides for 6 degrees of movement of the fiber pigtail harness 376 relative to the frame 12.
  • the X, Y, Z stage 342 can move within the X, Y plane and they rotate around the Z axis.
  • the waveguide array carrier 344 is moveable within the X, Z plane and rotatable about the Y axis.
  • a rigid curing epoxy is applied to one side of the fiber pigtail array wafer and an elastic curing epoxy is applied to the other in a manner described above with respect to Fig. 8.
  • This embodiment eliminates the cantilever platform 82 and relies solely on thermal expansion of the silicon wafer retaining the optical fibers and the mass balance of the waveguide carrier to maintain optical alignment of the fiber inputs and the single channel and multichannel beams as the (de)multip lexer is subjected to temperature variations.
  • the dimensions and the silicon material of the pigtail array wafer as well as the dimensions and material of the waveguide array carrier must be carefully chosen to maintain the "athermalization" of the device.
  • Fig. 22 is a schematic cross-section of the assembled XYZ stage 342, waveguide array carrier 344 and fiber pigtail array 376 taken along line 22A-22A of Fig. 19 with details such as the spring retention plate 346 removed for clarity.
  • Fig. 22 illustrates how application of epoxy between the fiber pigtail array 376 and the waveguide array carrier 344 can be used to maintain optical alignment between the fiber inputs and the single channel and multi-channel beams as the (de)multiplexer is subjected to temperature variations.
  • the centerline (C ) of the assembly is shown for reference purposes. As the XYZ stage 342 and the waveguide array carrier 344 are subjected to increases in temperature, they will expand relative to the center line.
  • Phantom line OA sip represents the optical axis of the (de)multiplexer at standard temperature and pressure.
  • dashed line OA ⁇ t in Fig. 22 At the fiber input this results in a shift ⁇ Xi.
  • ⁇ Xi To accommodate this ⁇ Xi shift so as to maintain optical alignment, in the embodiment illustrated in Fig.
  • the epoxy connection 402 is positioned relative to the centerline (C L ) to move the fiber pigtail array 376 to the left a distance substantially equal to ⁇ i as the waveguide array carrier 344 and the XYZ stage 342 expand about the centerline (C L ).
  • the distance the epoxy bond 402 is spaced from the centerline (C L ) is a function of the amount of shift ⁇ X necessary to accommodate movement of the optical axis as a function of temperature.
  • the epoxy bond 402 could be made by a number of spots of epoxy along a line perpendicular to the plane of the page of Fig. 22 or could be a line of epoxy along a line perpendicular to the page of Fig. 22.
  • the epoxy could be a rigid or flexible epoxy. If a rigid epoxy is used at 402, a flexible epoxy could be deployed laterally of the spot 402 to provide additional support for the fiber pigtail array 376.
  • the fiber pigtail array 376 will also be subject to expansion with temperature. This expansion will result in the distance between adjacent fiber inputs being increased slightly.
  • the dimensions and coefficient of thermal expansion of the fiber pigtail array substrate should be chosen to compensate for changes in "spread” or "breadth" of channel spacing that results in an increase in temperature.
  • the housing hermetically seals the (de)multiplexer components within. Air is evacuated from the multiplexer housing by inserting a needle through the silicone plug 312. Thereafter an inert gas such as nitrogen is inserted into the interior of the housing.
  • the nitrogen jacket surrounding the frame 12 forms an insulator for the optical components and frame 12 and protect them from temperature extremes to which the housing itself is exposed. This further enhances the "athermalization” or “passive thermal compensation” of the (de)multiplexer. Moreover, by fixing the number of gas molecules within the hermetically sealed housing, effects of temperature on the refractive index of the gas inside the housing is minimized or eliminated, thus minimizing displacement of light beams as a function of temperature. This property is found in all the embodiments discussed herein.
  • vibration isolation in the second embodiment 300 is provided by vertical vibration damping supports 152 and horizontal damping supports 154, which engage the housing bottom 304 and housing top 306.
  • Four horizontal bumpers are provided on the top of the frame 12 and four (not shown) are provided on the bottom of the frame.
  • Four vertical vibration damping supports 152 are provided, with one on each of the angled faces of the frame as illustrated in Fig. 18 (with only two showing).
  • the vibration supports are in the form of mushroom tops and the material is chosen in accordance with the discussion above.
  • Fig. 23 is a third embodiment of the (de)multiplexer 410 which differs from the second embodiment of the (de)multiplexer 300 only by the vibration damping structure as described below.
  • the angled faces of the housing bottom and top 304, 306 shown in Fig. 18 are eliminated.
  • a total of four donut shaped vibration dampers 414 are attached to receptacles 416 on horizontal surfaces of the frame 12.
  • the housing bottom 304 has a pair of square posts 418 extending therefrom and spaced to register with the circular hole of the donut shaped vibration dampers 414.
  • square posts 420 extend from the inside of the housing top 306 and register with the corresponding donut shaped vibration dampers 414.
  • two horizontal damping supports 154 are provided on the top of the frame 12 and two more horizontal damping supports (not shown) are provided on the bottom of the frame 12. These supports register with corresponding receptacles 424 on the inside of the housing bottom and top 304, 306.
  • Vertical damping supports 152 are provided on each vertical wall of the end of the frame adjacent the grating (one shown in Fig. 23).
  • the square posts 418, 420 register with the round holes of the donut shaped vibration dampers 414 to provide a snug fit.
  • the posts mate securely with the donut shaped vibration dampers to secure the frame 12 relative to the top 306 and bottom 304 of the housing.
  • the horizontal and vertical dampers 154, 152 at the second end of the frame 422 are sized and spaced to snuggly engage the top, bottom and sidewalls of the housing with the top 306 and bottom 304 mated.
  • the vibration damping structure of the third embodiment further minimizes the potential movement of the frame 12 relative to the platform or housing 14.
  • the second embodiment of the (de)multiplexer 300 described with reference to Figs. 17-21, as well as the third embodiment illustrated in Figs. 23 and 24 simplify the embodiment discussed in Figs. 1-16 by eliminating the flexures of the first adjustable mount and providing the option of eliminating the second adjustable mount 48 in favor of a fixed grating mount.
  • the first adjustable mount of the second embodiment allows for 6 degrees of movement and greatly reduces the complexity the adjustable mount structure, thus providing a simple, elegant and inexpensive alignment structure.
  • the spring retention plate 346 helps hold the waveguide array carrier 344 in a select position during alignment which can be secured using the non- influencing lock of the screws 390.
  • the magnetic attraction between the frame 12 and the X, Y, Z plate 342 allows the X, Y, Z plate to be moved to a suitable alignment an then secured in place by the non-influencing lock provided by the bolts 394.
  • the available 6 degrees of movement of the fiber pigtail array allows the use of a fixed grating mount for the grating which greatly enhances the ease of alignment and further simplifies both the structure and the assembly process. It further greatly reduces costs by eliminating a large number of high precision machined components.
  • the second and third embodiments provide an insulating nitrogen layer to protect the optical components and their critical optical alignment from temperature extremes applied to the housing.
  • the second and third embodiments also include a convenient way for evacuating air from and providing the nitrogen gas to the interior of the housing.

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Abstract

A bulk optic (de)multiplexer (10) consists of a fiber pigtail array (20), a focusing optic (18) and a wavelength dispersive element or grating (16) in optical alignment along an optical axis (22). The focusing optic is rigidly affixed to the frame and the fiber pigtail array (20) and wavelength dispersive element (16) are attached by adjustable connectors (112, 56, 340) to facilitate al ignment. The frame (12) has thermally expansive elements to compensate for shifts in light beams processed by the (de)multiplexer as a function of temperature. Vibration dampers (150, 152, 154, 160, 200) isolate the frame and optical elements form vibrations applied to the (de)multiplexer.

Description

APPARATUS AND METHOD OF PACKAGING OF A BULK OPTICAL (DE)MULTIPLEXERTECHNICAL FIELD
The present invention is directed toward optical communications, and more particularly toward an apparatus and method of packaging for aligning a bulk optical multiplexer/demultiplexer.
BACKGROUND ART
At the inception of fiber optic communications, typically a fiber was used to carry a single channel of data at a single wavelength. Dense wavelength division multiplexing (DWDM) enables multiple channels at distinct wavelengths within a given wavelength band to be sent over a single mode fiber, thus greatly expanding the volume of data that can be transmitted per optical fiber. The wavelength of each channel is selected so that channels do not interfere with each other and the transmission losses to the fiber are minimized. While typical DWDM allows up to 40 channels to be simultaneously transmitted by a fiber, there is an ongoing effort to further increase the number of channels transmitted for a given wavelength band by an optical fiber.
DWDM requires two conceptually symmetric devices: a multiplexer and a demultiplexer. A multiplexer takes multiple beams or channels of light, each at a discreet wavelength and from a discreet source and combines the channels into a single multi-channel or multiplexed beam. The input is typically a linear array of waveguides such as a linear array of optical fibers. The output is typically a single waveguide such as an optical fiber. A (de)multiplexer spatially separates a multiplexed beam into separate channels according to wavelength. Input is typically a single input waveguide or fiber and the output is typically a linear array of waveguides such as optical fibers.
There are a number of different DWDM devices known in the art, including array waveguides (see Li, U.S. Patent No. 5,706,377), devices using a network of filters and/or fiber Bragg gratings for channel separation (see Pan, U.S. Patent No. 5,748,350), and a variety of bulk optical DWDM devices. Bulk optical multiplexers and (de)multiplexers consist of discreet optically aligned optical elements mounted to a frame. For example, a wavelength dispersive element such as a reflective diffraction grating, a focusing optic such as a lens, and a waveguide array which may consist of a multi-channel or multiplex waveguide such as a single mode optical fiber and a linear array of single channel waveguides, typically also single mode optical fibers. In a demultiplexing operation, the multi-channel or multiplexed optical signal is emitted -from the multi-channel waveguide, directed through and collimated by the focusing optic, and reflected off the diffraction grating. The diffraction grating divides the multichannel beam into single channel beam components which are reflected through the focusing optic and focused by the focusing optic to optical focal points coupling with the single channel optical waveguides. The multiplexer simply works in reverse, with single channel signals being emitted from the single channel optical fibers, combined into a multiplex signal and coupled to the multiplex optical fiber. Because a single device can perform as a multiplexer or a (de)multiplexer, it is referred to as a (de)multiplexer herein. Critical to the proper operation of a bulk optic (de)multiplexer is obtaining and maintaining proper optical alignment of the waveguide array, focusing optic, and diffraction grating to provide efficient coupling of the optical signals to the respective waveguides with minimal or no crosstalk.
To date, providing a structure for facilitating proper alignment of the optical elements and for maintaining the optical elements in the desired optical alignment has proven illusive. Schultheiss, U.S. Patent No. 4,718,056, is directed to a bulk optical (de)multiplexer including a diffraction grating, a lens and an optical fiber harness, i Schultheiss, the diffraction grating, lens, and fiber harness are all mounted to a frame by adjustable mounts. While having each of the optical elements on its own adjustable mount clearly makes it possible to optimize the optical alignment of the (de)multiplexer optical elements, it actually over complicates alignment because none of the optical elements are fixed relative to the frame to provide a reference point, thus necessitating adjustment of each element during optical alignment.
Ignatuc, U.S. Patent No. 5,195,707, is directed to an optic positioning device for holding an optical element which has a center and for adjusting the optical element relative to the center. The positioning device includes a supporting base having a concave spherical surface and a holding body having a convex spherical surface which is slidably mated with the concave spherical surface. Both the concave and convex spherical surfaces have radial centers at the center of the optical element. Ignatuc allows for gimbaled movement of the optical element about its optical center. However, the mating concave and convex spherical surfaces provide a large surface contact area which can make it difficult to make small, precise movements of the optical element due to "sticktion" between the surfaces. Ignatuc also requires that both spherical surfaces be made to precise tolerances in order to insure the center of the optical element remains at a fixed location. This increases manufacturing costs. Important to maintaining optical alignment is to minimize the effect of shock and vibration which can degrade the integrity of optical alignment of optical components or allow micro variations in alignment, which lead to loss of light, but no discernable displacement of physical components. Total (de)multiplexer failure may result if rigid connections between components and the frame become loosened.
Known (demultiplexers have not provided for internal vibration damping. Instead, they rely upon vibration damping tables or the like to underlie the multiplexers to attenuate environmental vibrations. This can severely limit where these (de)multiplexers can be deployed. Such a structure also does not accommodate differences in thermal expansion between the (de)multiplexer and the tables to which they are attached.
Some optical devices do include some form of vibration damping. Rodino, U.S. Patent No. 5,074,630 is directed to an integrated optic device having an integrated optic chip attached to a substrate which in turn is connected by a visco-elastic polymer adhesive to a support package structure. The visco-elastic polymer adhesive is intended to minimize transmitted stress to the substrate during shock, vibration and thermal expansion applied to the substrate. There is no teaching that the adhesive of Rodino is suitable for vibration damping for a bulk optic device. It is intended for absorbing high G shock loads applied to a very low mass integrated optical component, and the teaching of Rodino would not be applicable to high mass bulk optical elements. Because of the sensitivity of (de)multiplexers to temperature changes, a standard practice has been to deploy (de)multiplexers only in temperature controlled environments where the ambient temperatures stay within a narrow range to eliminate the effect of changing temperatures on the optical elements. However, controlling the ambient temperature increases the costs of deploying the (demultiplexers, creates ongoing energy costs, and may lead to space requirements and constraints which are rather significant. Thus, a superior solution is needed to produce (demultiplexers which are athermal or thermally stable.
Dueck, U.S. Patent No. 6,011,884, teaches a structure which purportedly yields a (de)multiplexer which is thermally stable. Dueck is directed to an integrated bi-directional axially gradient refractive index diffraction grating (demultiplexer. The (demultiplexer of Dueck consists of a waveguide array and a diffraction grating with a focusing optic disposed therebetween and the elements optically coupled and aligned along an optical axis. Dueck provides a first homogenous boot lens disposed between the waveguide array and the lens and a second homogenous boot lens disposed between the focusing lens and the diffraction grating. Dueck teaches that not only do the homogenous index boot lenses allow for integration of the optical components into a single integrated device, the single integrated device increases thermal stability and avoids the introduction of air spaces which cause increased alignment sensitivity. As an initial matter, the use of index boot lens as taught by Dueck is incompatible with the notion of a bulk optic (de)multiplexer. In addition, the homogenous index boot lenses add additional product components, complicating the (de)multiplexer. Also, it is not clear over what temperature range utilization of the homogenous index boot lenses will provide thermal stability. Also known in the prior art is providing athermal optical components to athermalize a
(de)multiplexer. Laude, U.S. Patent No. 5,991,482, teaches the use of thermally stable optical components in association with a grating of a (de)multiplexer to thermally stabilize his (de)multiplexer. This solution has limited application to the (de)multiplexer structure taught in Laude. It is not useful for bulk optic (de)multiplexers generally. Hamblin, U.S. Patent No. 5,745,289, is of interest because of its teachings of athermalized diffractive optical components that have an effective focal length that does not shift substantially with temperature. Attempting to athermalize a (de)multip lexer by providing athermal optical elements of the type taught by Hamblin and Laude can significantly increase (de)multiplexer cost and introduce performance limitations associated with these specialized optical components. Keyworth, U.S. Patent No. 6,134,359, teaches a (de)multiplexer having bulk optical components mounted to a frame having a low coefficient of thermal expansion to help minimize misalignment due to variations in ambient temperatures. While use of such a frame can curtail or eliminate misalignments due to thermal expansion of the frame, it cannot compensate for temperature induced changes in refractive index of the components and transmission media. Keyworth recognizes that temperature changes can cause a lateral shift in the focal points of light beams. Keyworth teaches the use of a compensator associated with a waveguide array to laterally shift the waveguide array to compensate for lateral shifts in the location of light beams induced by changes of temperature. The compensator taught by Keyworth is made of a thermally expansive material which is cantilevered laterally from the frame and which is associated with a resistive heating element to heat the compensator to induce lateral shift. While Keyworth may be useful in compensating for lateral shifts in beams, Keyworth does not address the problem of changes in focal length that may result from temperature induced changes of refractive index or the shape of optical elements. Keyworth further requires the use of a resistive heating element and presumably associated temperature monitors and controls to appropriately actuate the heating element as needed. Not only does this increase (de)multiplexer complexity and cost, it provides another system for potential failure in operation. Moreover, it requires ongoing energy input, not unlike thermally stabilizing the operating environment.
The present invention is intended to overcome one or more of the problems discussed above.
SUMMARY OF THE INVENTION
A first aspect of the invention is a bulk optic (de)multip lexer for fiber optic communications systems including a diffraction grating having a diffraction surface, a waveguide array including a plurality of waveguides having an input/output end for emitting and receiving optical signals, and a focusing optic in optical communication between the diffraction grating and the waveguide array along an optical axis. The focusing optic focuses beams from the diffraction surface of the grating for optical coupling with the input/output ends of the waveguides. The (de)multiplexer further includes a frame. A fixed mount is provided between the focusing optic and the frame. A first adjustable mount is provided between the waveguide array and the frame and a second adjustable mount is provided between the diffraction grating and the frame. The first adjustable mount is configured to provide for linear movement of the waveguide array along the Z axis corresponding to the optical axis and independent movement of the input/output axis within a plane parallel to the X, Y axes. The second adjustable mount is preferably configured to provide only for gimbaled movement of the grating about a point on the diffraction surface of the grating intersecting the optical axis. Alternatively, a fixed mount can replace the second adjustable mount the first adjustable mount can provide for linear movement along an XY plane and an XZ plane and rotational movement about the Y and Z axes.
A second aspect of the present invention is an attachment assembly for attaching a diffraction grating having a diffraction surface of an optical (de)multiplexer to a frame of the (de)multiplexer, the (de)multiplexer having optical elements in addition to the grating, the optical elements being attached to the frame and aligned along an optical axis. The attachment assembly includes a grating mount having a leading surface to which the grating is attached with a diffraction surface in a select orientation relative to the grating mount and a spherical surface having a radial center at a point on the diffraction surface of the grating. A receptacle on the frame has a surface which is conical about a central axis receiving the spherical surface of the grating mount with the optical axis intersecting the point on the refractive surface of the grating. A clamp or stay is operatively associated with the grating mount and the frame for fixing the grating mount relative to the frame with the diffraction surface in a select orientation relative to the optical axis.
The bulk optic (de)multip lexer of the present invention provides a combination of fixed and adjustable mounts which eases alignment of the (demultiplexer optical elements. The fixed mount of the focusing lens allows the optical axis of the focusing lens to define a reference about which the other optical elements can be aligned. The adjustable mount between the grating and the frame not only provides for gimbaled movement of the grating about a point on the grating surface intersected by the optical axis to aid in proper alignment of the grating, it also provides a structure which prevents a change of orientation of the grating relative to the optical axis while providing movement of the grating only along the optical axis due to temperature changes or clamping of the adjustable mount. The adjustable mount associated with the waveguide array allows for independent movement of the waveguide array along the optical axis and for independent movement of the waveguide array in a plane normal to the optical axis. This independence of movement further facilitates efficient alignment. The embodiment providing a fixed grating and a 6 way adjustable mount for the waveguide array may further simplify alignment. The apparatus further facilitates the claimed method of aligning the (de)multiplexer which simplifies and expedites alignment of the optical elements.
A third aspect of the present invention is a (de)multiplexer for fiber optic communications systems including a wavelength dispersive element, a waveguide array including a plurality of waveguides having an input/output end for emitting and receiving optical signals, and a focusing optic in optical communication between the wavelength dispersive element and the input/output ends of the waveguides. The focusing optic focuses beams from the wavelength dispersive element to select focal points for optical coupling with the input/output ends of the waveguides. A location of the select focal points varies as a function of changes in (de)multiplexer temperature. The wavelength dispersive element, the waveguide array, and the focusing optic are attached to a thermally expansive frame. The frame supports the waveguide array and the focusing optic for movement relative to one another as a function of changes in (de)multip lexer temperature to maintain optical coupling between the input/output ends and the focused beam.
A fourth aspect of the present invention is a (de)multiplexer for fiber optic communications systems including a wavelength dispersive element, a waveguide array including a plurality of waveguides located in a substrate having an input/output end emitting and receiving optical signals, and a focusing optic in optical communication between the wavelength dispersive element and the input/output ends of the waveguides. The focusing optic focuses beams from the wavelength dispersive element to select focal points for optical coupling with the input/output ends. At a select temperature, the wavelength dispersive element, the waveguides of the waveguide array, and the focusing optic are aligned along an optical axis and are attached to a frame. The location of the focal points moves along a transverse axis relative to the optical axis as a function of changes in (de)multiplexer temperature. A thermally expansive member extends transverse the optical axis. The waveguide array is attached to the transverse member to move as a function of temperature to maintain optical coupling. The substrate of the waveguide is also preferably thermally expansive to match the spread between alignment beams to maintain optical coupling between fibers and beams as temperatures vary.
A fifth aspect of the present invention is a method of thermally stabilizing a (de)multiplexer having a wavelength dispersive element, a waveguide array, and a focusing optic in optical communication between the wavelength dispersive element and the input/output ends of the waveguides. The focusing optic focuses beams from the wavelength dispersive element to select focal points for optical coupling with the input/output ends. The method includes varying the location of the select focal points as a function of changes in (de)multiplexer temperature and moving the wavelength array relative to the focusing optic as a function of (de)multiplexer temperature to maintain optical coupling between the input/output ends and the focused beams. The method may further include attaching the wavelength dispersive element, the focusing optic and a waveguide array to a thermally expansive frame along an optical axis and varying the location of the focal points by changing the focal length along the optical axis between the focusing optic and the focal points as a function of (de)multiplexer temperature. The method may also include varying the location of the focal points along a transverse axis relative to the optical axis and moving the waveguide array along the transverse axis in a direction along the transverse axis corresponding to a direction of movement of the focal points by thermally expanding a thermally expansive connector between the waveguide array and the frame.
The thermally stable multiplexer/demultiplexer of the present invention provides optical elements which vary the location of the focal points of a focusing lens in a known manner as a function of changes in (de)multiplexer temperature, over a range of -5°C to 65°C. The use of a thermally expansive frame connecting the focusing optic and the waveguide array provides for movement of the input/output ends of the waveguide array as a function of changes in (de)multiplexer temperature in a manner maintaining efficient optical coupling between the input/output ends of the waveguides and the focal points. The invention does not require any additional energy input to maintain this efficient coupling; rather, the coupling is maintained automatically by matching the dimensions and coefficient of thermal expansion of the frame elements to the effects of temperature on the optical elements. The system also does not require special "athermal" optics which could otherwise induce design tradeoffs. In addition, the thermally expansive frame can be made of aluminum alloy or other readily available materials, which helps minimize (de)multiplexer cost.
A sixth aspect of the invention is an optical (de)multiplexer including a plurality of discrete optically aligned bulk optical elements. The bulk optical elements are rigidly attached to a rigid frame in optical alignment relative to each other. The rigid frame is attached to a platform or housing by a vibration damping support to isolate the rigid frame from vibrations applied to the platform. Preferably a plurality of vibration damping supports are used. Each vibration damping support may comprise a pair of spaced rigid plates, each plate having a fastener for attachment to one of the rigid frame and the platform. A vibration damping elastomer is between and fixably attached to the plates. The rigid frame and the rigid housing may be elongate along an optical axis with the plurality of the vibration supports being located between the ends of the rigid frame. In this configuration the optical (de)multiplexer further includes a plurality of elastomeric bumpers at an extreme end of the frame between the frame and the housing configured to alleviate impact generated shock.
Yet another aspect of the present invention is a method of isolating a (de)multiplexer from external vibrations. The (de)multiplexer includes a plurality of discrete optically aligned bulk optical elements. The method includes rigidly affixing the optically aligned bulk optical elements to a rigid frame, providing a platform and connecting the rigid frame to the platform with a vibration damping support. The platform preferably comprises a housing sized to receive the rigid frame and the method further includes placing the rigid frame within the housing.
The vibration damping of the present invention provides a bulk optic (de)multiplexer where the bulk optic elements are isolated from vibration and shock within a protective housing. The structure facilitates a (de)multiplexer which can be deployed in the field without the need for an additional vibration damping foundation underlying the (de)multiplexer. This considerably expands the options for deployment of the (de)multip lexer. Furthermore, the vibration damping structure is easily manufactured and assembled, providing the highly desirable vibration damping at a minimal cost.
BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a plan view of a first embodiment of a (de)multip lexer in accordance with the present invention with the top of the (de)multiplexer housing removed;
Fig. 2 is a perspective view of a (de)multiplexer frame of Fig. 1 in accordance with the present invention;
Fig. 3 is a cross-section of the (de)multiplexer frame of Fig. 2 taken along line 3-3 of Fig. 2;
Fig. 4 is a schematic perspective view of an optical fiber waveguide array used in the present invention;
Fig. 5 is an enlarged cross-section of a slidable connection between fixed and moving X, Y stages; Fig. 6 is a front elevation view of a moving X, Y stage in accordance with the present invention;
Fig. 7 is a cross-section view of the moving X, Y stage of Fig. 6 taken along line 7-7 of Fig. 6;
Fig. 8 is a front elevation view of a waveguide array attached to the cantilevered platform of the movable X, Y stage in accordance with the present invention; Fig. 9 is a perspective view of a grating holder depicted in Fig. 3; Fig. 10 is a sectional view illustrating pivoting of the grating holder about the optical axis;
Fig. 11 is a schematic representation of a properly aligned (de)multiplexer; Fig. 12 illustrates movement of the focal points of single channel beams as a function of an increase in temperature along with the movement of the waveguide array as a function of increase in temperature to maintain coupling with the single channel beams;
Fig. 13 is a plan view of an alternate embodiment of a vibration damping support for a (de)multip lexer in accordance with the present invention with the top of the multiplexer housing removed; Fig. 14 is a perspective view of a vibration damping support in accordance with the present invention;
Fig. 15 is a cross-section view taken along lines 15-15 of Fig. 13;
Fig. 16 is a cross-section of an alternate embodiment of a vibration damping support in accordance with the present invention; Fig. 17 is a perspective view of a second embodiment of the (de)multiplexer in accordance with the present invention;
Fig 18 is an exploded view of the (de)multiplexer of Fig. 17;
Fig. 19 is an enlarged cut away of the first adjustable mount of the (de)multiplexer of Fig. 18; Fig. 20 is an exploded view of the adjustable mount of Fig. 19;
Fig. 21 is an exploded view of the waveguide array carrier of Fig. 20;
Fig. 22 is a cross-section of assembled XYZ stage, waveguide array carrier and fiber pigtail array taken along line 22A-22A of Fig. 19;
Fig. 23 is an exploded view of a third embodiment of the (de)multiplexer of the present invention; and
Fig. 24 is a partial enlargement of Fig. 23.
DETAILED DESCRIPTION OF THE INVENTION
Fig. 1 is a plan view of a first embodiment (de)multiplexer in accordance with the present invention. A (de)multiplexer frame 12 resides within a housing 14. The housing 14 consists of a top and a bottom portion that fit together in a sealing relationship as will be described in greater detail below. In Fig. 1 the top portion has been removed to reveal the (de)multiplexer frame.
The (de)multiplexer frame 12 is shown in perspective removed from the housing 14 in Fig. 2. The (de)multiplexer frame maintains the optical elements of the (de)multiplexer in optical alignment. Fig. 2 also includes a depiction of orthogonal X, Y, Z axis which will be used as reference axis throughout this description. The Z axis is collinear with the optical axis 22.
Referring to Fig. 3, the optical elements of the (de)multiplexer include a wavelength dispersive element 16, a focusing optic 18, and a waveguide array 20. The wavelength dispersive element, the focusing optic, and the waveguide array are maintained by connection to the frame in optical communication with one another along an optical axis 22. Thus, the elements are in what is commonly known as littrow alignment.
The wavelength dispersive element 16 is preferably a reflective diffraction grating formed using conventional techniques from a glass substrate having a negligible coefficient of thermal expansion. One preferred substrate material is ZERODUR, manufactured by the Schott Company. A diffraction surface 24 of the grating has a large number of grooves which are formed parallel to an Y axis normal to the cross-sectional plane of Fig. 3. The grooved surface has a highly reflective coating, such as gold. Representative gratings include echellette and preferably echelle gratings, as are disclosed in commonly assigned, copending U. S. Patent Application Serial No. 09/628,774, entitled "Echelle Grating Dense Wavelength Division Multiplexer/Demultiplexer", the contents of which are incorporated in their entirety herein.
The focusing optic 18 is preferably a spherical symmetric doublet lens, although other lens structures could be suitable as well. The spherical symmetric doublet lens has a select focal length within a relatively narrow range of tolerance along an optical axis. The lens also has a refractive index that varies a known amount as a function of temperature. Furthermore, the lens surfaces deform in a predictable manner with changes in temperature.
The waveguide array 20 is shown in greater detail in Fig. 4. The waveguide array 20 consists of a number of single channel waveguides 26 having an input/output end 28 with the input/output ends 28 aligned along an input/output end axis 30 and a multiplex or multichannel waveguide 32 vertically below and at the center of the single channel waveguides 26. Other embodiments known in the art, such as having the multiplex waveguide coincident with the input/output end axis or above it, may also be suitable. Also, stacked multiplex waveguides and single channel arrays (as described in U.S. Patent Application Serial No. 09/628,774) may be used with the invention described herein. For the sake of simplicity, a limited number of single cham el waveguides, here, 20, have been shown as comprising the waveguide array. The preferred embodiment will have many more single channel waveguides, such as 48 or more. In the preferred embodiment the single channel waveguides 26 and the multiplex waveguide 32 are all single mode optical fibers. The fibers are held in place between two pieces of a silicon substrate or wafer 34 having N-shaped grooves 36 which are precisely etched in the substrate pieces to maintain the single channel fibers at a precise desired spacing from one another. The silicon is preferably high purity prime grade. Likewise, the multiplex optical fiber 32 is held in a precise location relative to the single channel optical fibers by a third piece of silicon substrate with an appropriate N groove. As stated above, the input/output ends of the single channel fibers terminate along an input/output end axis 30, and this axis is in the same plane as the input/output end of the multiplex waveguide 32. As shown in Fig. 4, the spacing of the waveguides increases slightly from left to right so as to couple with the corresponding single channel beams, which increase in separation in a like manner. In the preferred embodiment the dimensions of the assembled substrate are 15 mm along the X axis, 1.5 mm high and 12 mm deep.
In order to simplify alignment and increase alignment tolerances, a microlens array 37 may be incorporated into the substrate. The microlens array also increases band pass. The microlens array consists of a focusing lens 38 along an optical axis of each waveguide, with the lenses coupled by a frame 39 attached to the substrate 34 made of a material having a CTE matching that of the substrate 34 to thermally expand with the substrate to promote optical coupling along the waveguide optical axis.
The (de)multiplexer frame 12 of the first preferred embodiment includes a telescope portion 40, a cone housing portion 42 attached to one end of the telescope portion by conventional fasteners such as screws, and a flexure portion 44 similarly attached to the other end of the telescope portion 40. Alternatively, the frame could be a single integral piece, two pieces or more than three pieces. The multiplexer frame 12 further includes a first adjustable mount 46 associated with the flexure portion 44, a second adjustable mount 48 associated with the cone housing portion 42 and a fixed mount 50 within the telescope portion 40. The first adjustable mount 46 consists of a flexure 52, which is movable axially within a limited range (± 1 mm) only along a Z axis as indicated by the arrow 54. In the preferred embodiment the flexure is integrally formed of the flexure portion of the frame, but it could also be a separate structural element affixed to the frame by suitable connectors. As seen in Fig. 2, the preferred embodiment includes identical top and bottom flexure elements 52A and 52B to prevent tipping of the waveguide array as the flexure is moved along the Z axis. A single flexure element suitably arranged could perform the same function as well and is within the scope of the invention. Other structures for providing movement only along the Z axis may be suitable as well. A noninfluencing lock piece assembly 56 preferably connects the flexure 52 to the flexure portion of the frame so that the flexure 54 can be secured in a select position along the Z axis. Referring to Fig. 2, the preferred embodiment uses two noninfluencing lock piece assemblies 56A and 56B, one on the top and one on the bottom of the flexure with each assembly secured on opposite sides of the frame. Other stay structures or clamps may be used instead of the noninfluencing lock piece, but substitutes would preferably also not influence the Z axis position as they are secured.
The first adjustable mount 46 further consists of a fixed X, Y stage 58 which is fixedly attached to the Z axis flexure 52 by screws or the like (not shown) so that the first X, Y stage moves with the Z axis flexure 52. The fixed X, Y stage 58 has a planar surface 60 substantially normal to the optical axis 22. A moving X, Y stage 62 has a planar surface 64 which abuts the planar surface 60 of the fixed X, Y stage 62. The planar surfaces can be moved relative to one another parallel to the X, Y axis by virtue of sliding connectors 66, and the planar surfaces are preferably anodized aluminum to facilitate sliding. A sliding connector 66 is shown in greater detail in Fig. 5. The sliding connector 66 consists of a bolt 68 having a shaft body 70 and a threaded tip 72. The threaded tip 72 is threadably engaged in a threaded hole 74 in the moving X, Y stage 62. The shaft body 70 resides in a hole 74 in the fixed X, Y stage 58 having an inner diameter greater than the outer diameter of the shaft body 70 to allow a desired degree of freedom of movement of the moving X, Y stage relative to the fixed X, Y stage in an X, Y plane. In the preferred embodiment this is about + .5 mm of movement. A washer 76 resides between the head of the bolt 68 and a planar surface of the fixed X, Y stage 58 opposite the planar surface 60. To facilitate movement of the moving X, Y stage 62 relative to the fixed X, Y stage 58, the washer 76 has an annular trough abutting the fixed X, Y stage which is filled with tiny glass beads having a diameter slightly greater than the depth of the annular trough encased in suitable grease. Thus, the sliding connector 66 allows limited movement between the moving X, Y stage and the fixed X, Y stage within an X, Y plane with minimal friction induced sticktion between the planar surfaces of the stationary and moving stages. The moving X, Y stage is secured in place by noninterfering lock pieces 77 on opposing sides of the moving X, Y stage, or other suitable stays or clamps. The non-influencing lock piece assemblies 56 and 77 collectively form a stay for the first adjustable mount 46. By the combination of the Z axis flexure 52 and the sliding connector 66 between the fixed X, Y stage and the moving X, Y stage, the moving X, Y stage and the associated waveguide array 20 may be moved axially of the Z axis, rotated about the Z axis, and moved linearly within an X, Y plane normal to the Z axis. In addition, the waveguide array 20 can be moved independently along the Z axis. In other embodiments, the first adjustable mount might be limited to the Z axis flexure (or some other structure providing movement along the Z axis) without the moving X, Y stage, or vice versa.
The moving stage is shown in greater detail in Fig. 6 and Fig. 7. Fig. 6 is a front elevation view of the moving X, Y stage and Fig. 7 is a sectional view taken along line 7-7 of Fig. 6. A cantilevered connector 80 extends from the moving X, Y stage from a side opposite and in a direction normal to the planar surface 64. The cantilevered connector 80 consists of a platform 82, which extends in a cantilevered manner from a post 84. The top surface of the platform has a recess 86.
Fig. 8 illustrates how the waveguide array 20 is attached to the platform 82 by a flexible connector 88 which allows the waveguide array to expand when heated relative to the platform 82. In the preferred embodiment the flexible comiector 88 consists of a rigid connection 90 between a bottom of the substrate 34 near the post 84 and an elastic connection 92 near the distal end of the cantilevered platform 82. The rigid connection 90 is made by a suitable rigid curing epoxy and the flexible connection 92 is made by a suitable elastic curing epoxy. The waveguide array 20 is epoxied in place bringing the waveguide array into registration with appropriate guides and spacers (not shown) associated with the platform 82. Both the rigid and elastic curing epoxies have virtually identical thermal coefficiencies of expansion to preventing tipping of the waveguide array 20 about a Z axis by changes in temperature.
The second adjustable mount 48 includes the rear wall of the cone housing portion 42 of the frame 12 having a concave and preferably a conical recess or receptacle 98 formed therein. The conical recess 98 is symmetric about a central axis which is preferably collinear or very close to collinear with the optical axis 22. A circular hole 100 having a central axis along the optical axis 22 extends from the conical wall of the conical recess 98 through the rear wall.
The surface of the rear wall opposite the conical recess 102 is spherical and has a radial center which preferably is at about a point 104 where the optical axis 22 intersects the diffraction surface 24 of the grating 16. The second adjustable mount 48 further includes a grating mount 106 having a leading planar surface 108 and a trailing spherical surface 110. The spherical surface 110 may include a low friction coating 111 such as PTFE or carbide. The spherical surface 110 has a radial center at the point 104 where the optical axis intersects the diffraction surface 24 of the grating with the trailing spherical surface 110 nested in the conical recess 98. A clamp assembly or stay 112 secures the grating mount 106 with its spherical surface engaging the conical recess 98 as illustrated in Fig. 3. The clamp preferably consists of a threaded tail 114, which extends along a central axis of the spherical surface through the hole 100 in the rear wall of the cone housing. A washer 116 having a spherical recess 118 including an annular contact rib 120 resides between the spherical wall 102 and a locking nut 122 with the contact rib 120 contacting the spherical wall 102. The contact rib 120 has a low friction coating 121 such as PTFE or carbide. A spring washer 124 is preferably provided between the locking nut and the spherical washer 116. The spring washer 124 allows the locking nut to be loosened somewhat while the clamp assembly 112 is still held in position so that the grating mount 106 can be repositioned. As should be clear from Fig. 3, the cooperation between the spherical surface of the grating mount and the conical recess 98 allows for true gimbaled movement of the diffraction surface of the grating about the point 104. In other words, the grating can be rotated about the point 104 along orthogonal three axes within a limited range of motion. This is illustrated in Fig. 10. A notch 125 at the distal end of the threaded tail 114 defines a first planar surface 126 in an Z, Y plane and a second planar surface 127 in an X, Y plane as depicted in Fig. 3, parallel to the grooves of the grating 16, to facilitate course alignment of the grating 16.
The grating mount 106 is shown in a perspective view in Fig. 9. Extending on either side of the leading planar surface 108 are standing ribs 128. The standing ribs 128 are included to ensure that as the grating holder is subjected to changes in temperature, it expands and contracts along the optical axis 22 with the diffraction surface of the grating maintaining its orientation relative to the optical axis 22, as illustrated schematically in Fig. 12. The grating mount is preferably made of titanium or 416 stainless steel to ensure rigidity and strength, although other low CTE materials such as INVAR, KOVAR or ZERODUR may be used as well.
The grating is attached to the leading planar surface 108 by a suitable epoxy and is positioned on the leading surface in a select orientation by registration with an inner wall of the standing ribs 128 and suitable spacers. Fig. 10 illustrates gimbaled movement of the diffraction surface about the point 104.
With the grating mount 106 tilted relative to the optical axis 22 as shown in Fig. 10, the point 104 is still intersected by the optical axis 22. Also, the washer 100 is self-aligning relative to the spherical surface 102 to maintain complete contact of the annular contacting rib 120 with the spherical surface. This structure also keeps a ring of contact of the washer opposite that of the spherical surface 110 of the holder to minimize distortion of the cone housing. While in the preferred embodiment the spherical surface 100 and conical recess 98 have central axes along the optical axis 22, their central axes could be non-colinear with the optical axis and still allow for the desired gimbaled movement.
The fixed mount 50 simply consists of an enlarged inner diameter portion 130 of the telescope portion 40 of the frame 12. The focusing optic 18 is axially inserted in this enlarged diameter of portion 130 and secured in place by an appropriate adhesive or held in place by an appropriate mechanical clamp suitable for maintaining the optical alignment over a wide temperature range, e.g., -5°C-65°C.
The optical elements of the (demultiplexer 10 are aligned as follows. First, the lens 18 is brought into registration with the wall at the end of the larger diameter portion of the fixed mount 130 and the optical axis of the lens defines the optical axis 22 of the (de)multiplexer. The lens is then cemented or clamped in place. The grating is coarsely aligned by having the first surface 126 parallel to the Z, Y reference plane and the second surface 127 parallel to the X, Y reference plane. The moving X, Y stage is coarsely aligned simply by connection of the X, Y moving stage to the X, Y fixed stage with waveguide array attached to the X, Y moving stage as discussed above. Following coarse alignment, the optical elements are close to littrow alignment, hi the preferred embodiment, an actuator for moving the Z flexure along the Z axis is operatively associated with the Z flexure, an actuator for moving the X, Y moving plate along the X axis is associated with the X, Y moving plate, and an actuator for moving the X, Y moving plate along the Y axis is associated with the X, Y moving plate. Likewise, an actuator for each rotational degree of movement of the second adjustable mount is operatively associated with the grating mount 106. A multiplex beam of the operative wave band of light is propagated to the multiplexer through the multiplex optical fiber 32. Photo detectors are associated with the end single mode fibers to monitor light output at these points. Alternatively, the actuators could combine one or more degree of movement. An automatic alignment device utilizing a six axis feed back loop controlled algorithm controls actuation of each actuator to move the grating and waveguide array relative to the optical axis to optimize optical signal strength at the extreme ends of the single channel array. First the beam strength is optimized at one end of the signal channel array and then the other by coordinated movements of the six actuators by the automatic alignment device until signal strength in these single channel optical fibers is maximized. Then the first and second adjustable mounts 46, 48 are clamped into place as described above.
The multiplexer 10 is also configured so that "optical coupling" or the coupling integrity, that is efficiency and the level of crosstalk, remain within acceptable specified levels within a relatively wide range of temperatures, more particularly from about -5°C to 65 °C. For example, for efficiency, loss should not increase greater than 0.5 db and cross-talk should not increase more than 5 db. The problem addressed by the unique "athermalized" frame of the present invention is illustrated schematically in Fig. 11 and Fig. 12. Referring to Fig. 11, with the multiplexer properly aligned and with the (de)multiplexer temperature at room temperature, that is about 20°C, light from the multi-channel or multiplex waveguide 32 is projected as a multi-channel beam to the focusing optic 18 which collimates the multi-channel beam and directs it off the diffraction surface 24 of the grating 16. The diffraction grating divides the multi-channel beam by wavelength into a number of single channel beams which are diffracted off the diffraction surface 24 to the focusing optic 18 which directs the focused singled channel beams to select focal points for optical coupling with the input/output ends of the single channel waveguides 26.
Fig. 12 illustrates the effect of an increase in temperature on the beams 140. As temperatures increase the refractive index of the lens 18 decreases and the surfaces of lens are slightly deformed so as to cause the focal length of the lens 18 to increase. Thus, the select focal points extend beyond the plane of the input/output ends of the optical fibers 26, 32. At the same time, there is a change in the refractive index of the air occupying the space between the diffraction grating 16 and the lens 18 and the air between the lens 18 and the waveguide array 20. This change in the refractive index of the air causes a lateral shift of the select focal points of the single channel beams 140 along the X axis as is also illustrated Fig. 12. If the temperature change is great enough, the location of the focal points of the single channel beams can move far enough out of alignment with the input/output ends of the single channel fibers 26 to significantly degrade the efficiency of optical coupling, leading to an unacceptable loss of efficiency and to crosstalk. h the preferred embodiment, temperature changes result in both axial and radial movement of the focal points as a function of temperature. In alternate embodiments, some form of athermalization could eliminate either the radial or axial movement, hi such alternate embodiments, it would be necessary only to provide for a corresponding movement of the input/output ends of the waveguides.
Although the position of the grating may move along the optical axis as a result of temperature changes expanding or contracting the frame between the lens and the grating and thermal expansion or. contraction of the grating holder itself, the light in this region is collimated so these movements have no optical effect. Also, as discussed above, the grating substrate is athermal (negligible CTE) and the grating holder is configured to maintain the orientation of the diffractive surface of the grating as the grating holder is subjected to temperature changes. Thus, the grating itself is believed to be insensitive to temperature changes for alignment purposes.
To address the problem of migration of the focal points as a function of changes in (de)multiplexer temperature, the frame 12 of the (de)multiplexer includes a number of novel features. First, the frame is made of a thermally expansive material, for example, an aluminum alloy such as 6061 T6 having a coefficient of thermal expansion (CTE) that allows the frame to vary in length as a function of temperature. Briefly, the change in length as a function of temperature is determined by the well known equation ΔL = L α ΔT, where ΔL is the change of length, L is the length of the thermally expansive material, α is the coefficient of thermal expansion of the thermally expansive material, and ΔT is the change in temperature. Herein the terms "thermally expansive" and "thermal expansion" and the like are used to mean both expansion or contraction, with the ΔL being positive or expansive as temperature increases and ΔL being negative or there being a contraction as the temperature decreases, unless the context clearly indicates it is intended to be limited to an expansion, such as where the term is associated with an increase in (de)multiplexer temperature. The frame 12 is symmetric about the optical axis 22 to provide equal lengths L of material along the optical axis 22, and therefore uniform expansion along the optical axis with changes in (de)multiplexer temperature. Thus, in the preferred embodiment the telescope portion of the frame 40, the cone portion 42 of the frame and flexure portion 44 of the frame are all symmetric about the optical axis. As a result, these portions of the frame change length only along the optical axis 22, simplifying maintaining alignment during temperature induced length changes. Most importantly, the length of frame material connecting the lens 18 and the waveguide array 20 along with the material(s) from which this portion of the frame is made are selected to provide a length L and CTE such that the length along the optical axis of the portion of the frame between the waveguide array and the lens changes with temperature about the same amount that the focal length of the single channel focusing beams changes as a function of temperature to maintain optical coupling of the focusing points and the input/output ends of the single channel fibers. To compensate for the lateral shift along the X axis of the single channel beams 140 caused by a change in temperature of the air, the structure is similar in principle. Referring first to Fig. 8, the substrate 34 of the waveguide array 20 is a thermally expansive material so that increases in temperature will cause it to expand and decreases in temperature will cause it to contract along the X axis. To move the input/output ends of the single channel waveguides the same direction as the lateral shift of the beams with temperature, the flexible connector 88 includes the first end of the substrate 34 having a rigid connection 90 to the cantilevered connector 80 near the post 84 and an elastic connection 92 near the distal end of the cantilevered connector 80. As a result, as the substrate 34 grows along its X axis as a function of increases in temperature, the substrate will expand toward the elastic connection 92, causing distortion of the elastic connection 92 as illustrated in phantom lines in Fig. 8. This will provide some of the lateral shift in a direction along the X axis necessary to move the input/output ends of the single channel fibers into the desired degree of optical coupling with the focal points of the single channel signals 140. To further move the input/output ends along the X axis, in the preferred embodiment the cantilevered connector 80 is also made of a thermally expansive material such as an aluminum alloy. Referring to Fig. 8, the distance between the midpoint of the post 84 and the rigid connection 90 (Lc) will provide further lateral displacement of the waveguide array along the X axis with changes in temperature. The amount of change, ΔL will be determined as follows: ΔL = Lc α ΔT. Thus, the distance Lc as well as the coefficient of thermal expansion of the material from which the cantilevered connector 80 is made can be adjusted to provide sufficient movement along the X axis to insure the maintenance of optical coupling between the single channel beams 140 and the input/output ends of the single channel fibers 126.
While the preferred embodiment compensates for lateral shift along the X axis by combining the thermal expansion of the waveguide substrate and the cantilevered connector, in other embodiments either one may provide the necessary lateral shift to maintain suitable optical coupling, and the other could be "athermalized." For example, the flexible connector between the substrate and the cantilevered connector could have two elastic connections (and no rigid connection) so that only thermal expansion of the cantilevered connector 80 moves the input/output ends a significant amount to maintain optical coupling. Or, the cantilevered connector 80 could be modified to not be cantilevered or it could be made of an athermal material so optical coupling is maintained solely by thermal expansion of the waveguide substrate.
Fig. 12 also illustrates schematically the effect of temperature on the grating mount 106. As discussed above and as illustrated in Fig. 12, the standing ribs 128 insure that the grating mount 106 will move the diffraction grating 16 along the optical axis 22 while maintaining the diffraction surface 24 in the same select orientation relative to the optical axis 22. Referring back to Fig. 1, vibration damping supports 150 support the (de)multiplexer frame 12 within the housing 14. The vibration damping supports 150 include vertical supports 152 and horizontal supports 154. Both the vertical and horizontal supports 152, 154 are positioned to suspend the frame within the housing. The vertical and horizontal supports 152, 154 are made of an elastomeric material of a select formulation chosen to dissipate vibrations most likely to be encountered by the (de)multiplexer 10. Representative vibrations of concern would be low frequency vibrations such as might be incurred in an earthquake, middle frequency vibrations such as might be incurred during transport of the assembled (de)multiplexers and high frequency vibrations which might be generated by cooling fans and the like deployed in the vicinity of the multiplexer in operation. Representative materials for the vibration damping supports include natural and synthetic rubber, urethane and other polymeric elastomers, with urethanes being preferred. Choice of a particular material would be a function of many factors, including anticipated frequencies, anticipated temperatures, mass of the (de)multiplexer and the like.
Although not shown, a top housing piece mates with the bottom housing piece illustrated in Fig. 1 and 13. A seal 156 is deployed between the housing segments so that the interior of the housing can be pressurized with nitrogen or another suitable gas to minimize the risk of corrosion of sensitive optical and mechanical parts as well as to provide for a uniform gaseous medium through which the beams are transmitted within the (de)muh--P-eχer-
Another embodiment of the vibration damping support structure is illustrated in Figs. 13-15. Referring to Fig. 13, four vibration damping supports 160 attach the telescope portion 40 of the frame to the bottom of the housing 14. It should be appreciated the different configurations of the frame and housing could utilize one or more vibration damping supports with four being preferred in the embodiment of Fig. 13. A vibration damping support 160 is shown in a perspective view in Fig. 14 and it can be viewed in cross-section in Fig. 15. The vibration damping support 160 consists of a round top plate 162 and a round bottom plate 164. An axial post 166, 168 extends outwardly from the round top plate and round bottom plate, respectively. Each post is externally threaded in order that it can be fastened between the frame 12 and the housing 14 as illustrated in Fig. 15. Between the top and bottom plates 162, 164 is an elastomeric vibration damping spacer 170. The plates 162, 164 and the axially posts 166, 168 are preferably integrally formed from a suitable rigid material such as steel. The vibration damping supports 160 are preferably formed by pouring the elastomer 170 in a liquid state in a mold between the plates. Where the elastomer is , for example, a urethane, the urethane will bond directly to the plates eliminating the need for an adhesive. The bonding interface area is specially treated to create a chemical bond between the rigid plate and the elastomer that equals or exceeds the inherent split/tear strength of the elastomer itself. It is treated by creating a surface texture on the plates by sand blasting or the like, thoroughly cleaning the textured surface and applying a surface bonding agent suitable for enhancing the bond between the material of the plate and the elastomer. Where a different elastomer is used that cannot form a sufficiently robust bond with the metal plates, a suitable adhesive such as an epoxy may join the elastomer and the plates.
Referring back to Figures 13 and 15, the use of the vibration damping supports 160 to join the rigid housing 14 to the rigid frame 12 is illustrated. The invention could have application to platforms other than the rigid housing 14 as well. In the embodiment illustrated in Fig. 13, the telescope portion of the frame 40 includes flange extensions 172 that define mounting brackets for the frame 12. Each flange extension 172 has a countersunk bore 174 with the lesser diameter portion being sized to axially receive the post 166. Corresponding attachment bosses 176 extend from a bottom surface of the housing 14 as illustrated in Fig. 15. Each boss has an internally threaded bore 178. The frame 12 lies within the housing and juxtaposed with the bottom of the housing 12. The post 168 of each vibration damping support 160 is threadably engaged in an internally threaded bore 178. Each countersunk bore 174 of the frame in turn receives a post 166 of a vibration damping support 160. Nuts 180 threadably engage the threaded post 166 to secure the frame to the housing 14. As viewed in Figs. 13 and 15, with the frame secured within the housing in this manner, the frame is otherwise spaced from and does not contact the housing. To further prevent contact between the frame and the housing, mushroom bumpers 182 are spaced about the distal end of 184 of the flexure portion 44 of the frame 12. These mushroom bumpers 182 prevent direct contact between the frame and the housing in the event the (de)multiplexer is subjected to severe vibrations or shock, as may be encountered if the (de)multiplexer is dropped. The mushroom bumpers control the deceleration of the frame. The function of the bumper is to absorb the energy without transferring an impact frequency into the frame itself. Material choice influences the rate of deceleration and the performance over time when exposed to continuous vibration (60Hz, office environment). As with the embodiment of the vibration damping supports 150 discussed with reference to Fig. 1, the elastomeric material 170 is made of a select formulation chosen to attenuate shocks and vibrations likely to be encountered during handling and operation of the (de)multiplexer lO.The formulation of the elastomer, preferably urethane, is controlled very specifically and is tuned to absorb specific frequency ranges. These urethanes can be chosen from different families of urethanes, most specifically ether based or ester based, depending on environmental compatibilities of the specific application. For instance, an ester-based urethane is more applicable in an environment that may contain high moisture or petroleum based solvents. Ethers are more applicable in an environment that requires elevated physical properties (rebound, split/tear strength, % elongation, hysteresis, etc.). The preferred embodiment will incorporate formulations from the ether family. Very strict stoichiometric ratio control is necessary to ensure complete chain reaction and free radical termination. This is pertinent with regard to the issue of off gassing. Careful control of the chemical ratios eliminates the possibility of unreacted chemicals leeching out of the material over time.
Figure 16 is an alternate embodiment of a vibration damping support 200. The vibration damping support 200 has a top attachment member 202 and a bottom attachment member 204 which are identical in structure. The attachment members 202 and 204 have an enlarged diameter base 206, a smaller diameter intermediate portion 208 and an externally threaded post 210. The attachment members 202, 204 are aligned coaxially with the threaded posts extending in opposite directions. As illustrated in Fig. 16, with the elastomer 170 molded to the top and bottom attachment members 202, 204, the enlarged base 206 is embedded within the elastomer. This provides an increased surface area for bonding to the elastomer and further physically anchors the attachment member within the elastomer to provide a heartier connection of the attachment members to the elastomer 170. Fig. 17 is an alternate embodiment of a (de)multiplexer 300 in accordance with the present invention. The (de)multiplexer 300 includes the same optical elements as the (de)multip lexer 10 illustrated in Figs. 1-16 and generally the same features to provide passive thermal compensation. Like elements will be identified with the same reference number for ease of reference.
The (de)multiplexer 300 includes a housing 14 and input/output fiber optic cable assembly 302. Referring to Fig. 18, which is an exploded view of the (de)multiplexer 300 of Fig. 17, the housing 14 has a bottom 304 and a top 306. Both the top and the bottom 304, 306 have a corresponding peripheral groove 308 containing a seal 156 as discussed above with respect to the first embodiment of the (de)multiplexer 10. The housing bottom 304 also includes an orifice 310, which retains a silicon plug 312. The input/output cable assembly 302 is received between complimentary semicircular cuts 314, 316 in the housing bottom and top. An o-ring 318 in an annular groove 320 of the input/output cable 302 seals with the semicircular cuts 314, 316. Alternative seal structures could also be used, such as gaskets, semi-liquid sealant or laser welding of the top and bottom of the housing. As a result of the various seals, when the (de)multiplexer housing is assembled as illustrated in Fig. 17, the interior of the housing is hermetically sealed from the outside environment.
The (de)multiplexer frame 12 of the second embodiment 300 is similar in configuration to that of the first embodiment of the (de)multiplexer 10. As shown in Fig. 10, it may include a second adjustable mount 48 having the same components as those set forth in Fig. 3.
Alternatively, a fixed grating mount 320 maybe employed. In this embodiment the diffraction grating 16 is rigidly mounted to the fixed grating mount 320. The fixed grating mount 320 is attached to the frame 12 by aligning dowels 322 on the frame 12 with receiving holes 324 (one shown in Fig. 18) on the fixed grating mount. The fixed grating mount is then secured in position by bolts 326 threadably engaging the frame 12 through the holes 328.
The greatest difference between the second embodiment 300 and the first embodiment illustrated in Figs. 1-16 is the first adjustable mount 340 for attaching the waveguide array 20 to the frame 12. Fig. 19 is a cut away of the frame 12 depicted in Fig. 18 showing the first adjustable mount 340 in a larger scale. The first adjustable mount 340 is shown in an exploded view in Fig. 20.
The first adjustable mount 340 consists of an X, Y, Z stage 342, a waveguide array carrier 344, a spring retention plate 346, an upper aluminum clamp plate 348 and a lower aluminum clamp plate 350. The first adjustable mount 340 also includes a trailing portion 352 of the (de)multiplexer frame 12. The trailing portion 352 of the (de)multiplexer 12 includes corner posts 354 having inner threaded bores 356. In addition, a pair of magnets 358 is embedded in a trailing planar surface 360 of a trailing portion 352 of the frame 12. Four screw holes 361 are also provided in the trailing planar surface 360.
The X, Y, Z stage 342 has a planar leading surface 362 and a pair of steel implants 364 embedded in the leading planar surface 362 to register with the magnets 358 in the planar trailing surface of the frame 12. Both the magnets 358 and the steel implants 364 are either flush or slightly indented within the planar surfaces so that the planar surfaces may be flush to one another when assembled. The X, Y, Z stage 342 further includes a bottom platform 366 having a recess 368. Corner voids 372 in the leading surface 362 are configured to receive the corner posts 354 of the frame 12 when assembled as illustrated in Fig. 19. Finally, a leading flange of the stage includes four square holes 374, two of which are shown in Fig. 20, which align with the threaded holes 361 in the trailing planar surface 360 of the frame 12. The waveguide array carrier 344 has a pair of leading wings 378 and trailing wings 380.
A waveguide array or fiber pigtail assembly 376 is attached to the underside of the waveguide array carrier 344, as is more clearly illustrated in Fig. 21. The leading wings 378 each include an elongate slot 382, which extends along the Z axis, which has a sufficient width to provide a limited range of motion along the X axis with a screw 390 received therein. The spring retention plate 346 has a pair of downward extending flap springs 384 and three holes 386 substantially evenly spaced along the Z axis on opposite sides of the spring retention plate 346. The spring retention plate is preferably made of a resilient metal such as stainless steel, aluminum, or copper beryllium.
The first adjustable mount 340 is assembled by mating the waveguide array carrier 344 with the X, Y, Z stage 342. The mating is accomplished by receiving the fiber pigtail harness 376 in the recess 368 with the trailing wings 380 rearward of the posts 370, 371 and the leading wings 378 forward of the posts 370, 371. The spring retention plate 346 is then attached to the X, Y, Z stage 342 by the corner screws 388, which are tightened in place. The middle screws 390 are received in corresponding holes in the X, Y, Z stage 342 and left untightened. When attached as described, the downward flap springs 384 apply a downward pressure to the waveguide array carrier 344 to prevent it from moving without application of a significant outside force. When, as discussed later, the waveguide array carrier 344 is in a desired position, the screws 390 are tightened and thus act as non-influencing locks.
Next, the planar leading surface 362 of the X, Y, Z stage 342 is made flush with the planar trailing surface 360 of the frame 12 with the corner posts 354 received in the corner voids 372 as best seen in Fig. 19. The X, Y, Z stage 342 will be held in place relative to the surface of the frame by attraction of the magnets 358 and the steel implants 364. The upper and lower aluminum clamp plates 348, 350 are next brought into position and the corner screws 392 are tightened into the inner threaded bores 356. The middle screws 394 are received in the bore holes 374 of the X, Y, Z stage 342 and loosely screwed into the holes 361.
The tolerances of the first adjustable mount 340 are such that when assembled as described, there is a slight clearance between the leading wings 378 of the waveguide array carrier 344 and the spring retention plate 346. As a result of this clearance and the elongate slots 382 in the leading wings 378, the waveguide array carrier 344 can move in the X, Z plane and may rotate slightly around the Y axis as illustrated by the coordinates 396. When the waveguide array carrier is in the desired alignment, it is held in place by the springs 384. Similarly, there is a slight clearance between the X, Y, Z stage 342 and the upper and lower aluminum clamp plates 346, 348 that allows for movement between the X, Y, Z stage 342 and the trailing surface 360 of the frame 12. This movement is accommodated by the square holes 374. The X, Y, Z stage 342 is able to move within the X, Y plane and to rotate above the Z axis as illustrated by the coordinates 398. When the X, Y, Z stage 342 is in the desired alignment, it is held in place relative to the frame 12 by magnetic attraction between the magnets 358 and the steel implants 364. Thereafter the inner screws 394 can be tightened down to form a non-influencing lock between the X, Y, Z stage 342 and the frame 12.
The first adjustable mount 340 provides for 6 degrees of movement of the fiber pigtail harness 376 relative to the frame 12. Specifically, the X, Y, Z stage 342 can move within the X, Y plane and they rotate around the Z axis. The waveguide array carrier 344 is moveable within the X, Z plane and rotatable about the Y axis. These 6 degrees of movement of the fiber pigtail array allows for use of the fixed grating 320, significantly decreasing parts count over the adjustable grating mount option and vastly simplifying alignment of the fiber pigtail harness with the other optical elements carried by the frame 12. Fig. 21 illustrates how the fiber pigtail array 376 attaches to the waveguide array carrier
344. A rigid curing epoxy is applied to one side of the fiber pigtail array wafer and an elastic curing epoxy is applied to the other in a manner described above with respect to Fig. 8. This embodiment eliminates the cantilever platform 82 and relies solely on thermal expansion of the silicon wafer retaining the optical fibers and the mass balance of the waveguide carrier to maintain optical alignment of the fiber inputs and the single channel and multichannel beams as the (de)multip lexer is subjected to temperature variations. Thus, the dimensions and the silicon material of the pigtail array wafer as well as the dimensions and material of the waveguide array carrier must be carefully chosen to maintain the "athermalization" of the device.
Fig. 22 is a schematic cross-section of the assembled XYZ stage 342, waveguide array carrier 344 and fiber pigtail array 376 taken along line 22A-22A of Fig. 19 with details such as the spring retention plate 346 removed for clarity. Fig. 22 illustrates how application of epoxy between the fiber pigtail array 376 and the waveguide array carrier 344 can be used to maintain optical alignment between the fiber inputs and the single channel and multi-channel beams as the (de)multiplexer is subjected to temperature variations. The centerline (C ) of the assembly is shown for reference purposes. As the XYZ stage 342 and the waveguide array carrier 344 are subjected to increases in temperature, they will expand relative to the center line. If the fiber pigtail array 376 were attached to the waveguide array carrier 344 at the centerline, expansion of the waveguide array carrier 344 with temperature would not cause any movement of the fiber pigtail array 376 relative to the waveguide array carrier 344. Phantom line OAsip represents the optical axis of the (de)multiplexer at standard temperature and pressure. In this example, with an increase in temperature, the optical axis shifts somewhat to the left as illustrated by dashed line OAΛt in Fig. 22. At the fiber input this results in a shift ΔXi. To accommodate this ΔXi shift so as to maintain optical alignment, in the embodiment illustrated in Fig. 22 the epoxy connection 402 is positioned relative to the centerline (CL) to move the fiber pigtail array 376 to the left a distance substantially equal to Δi as the waveguide array carrier 344 and the XYZ stage 342 expand about the centerline (CL). The distance the epoxy bond 402 is spaced from the centerline (CL) is a function of the amount of shift ΔX necessary to accommodate movement of the optical axis as a function of temperature. The epoxy bond 402 could be made by a number of spots of epoxy along a line perpendicular to the plane of the page of Fig. 22 or could be a line of epoxy along a line perpendicular to the page of Fig. 22. The epoxy could be a rigid or flexible epoxy. If a rigid epoxy is used at 402, a flexible epoxy could be deployed laterally of the spot 402 to provide additional support for the fiber pigtail array 376.
As illustrated by the phantom lines 404, the fiber pigtail array 376 will also be subject to expansion with temperature. This expansion will result in the distance between adjacent fiber inputs being increased slightly. The dimensions and coefficient of thermal expansion of the fiber pigtail array substrate should be chosen to compensate for changes in "spread" or "breadth" of channel spacing that results in an increase in temperature. As described above, the housing hermetically seals the (de)multiplexer components within. Air is evacuated from the multiplexer housing by inserting a needle through the silicone plug 312. Thereafter an inert gas such as nitrogen is inserted into the interior of the housing. An epoxy is applied to the plug to maintain the integrity of the seal, hi addition to eliminating corrosion and providing a stable media for the transmission light through the multiplexer, the nitrogen jacket surrounding the frame 12 forms an insulator for the optical components and frame 12 and protect them from temperature extremes to which the housing itself is exposed. This further enhances the "athermalization" or "passive thermal compensation" of the (de)multiplexer. Moreover, by fixing the number of gas molecules within the hermetically sealed housing, effects of temperature on the refractive index of the gas inside the housing is minimized or eliminated, thus minimizing displacement of light beams as a function of temperature. This property is found in all the embodiments discussed herein.
Referring to Fig. 18, vibration isolation in the second embodiment 300 is provided by vertical vibration damping supports 152 and horizontal damping supports 154, which engage the housing bottom 304 and housing top 306. Four horizontal bumpers are provided on the top of the frame 12 and four (not shown) are provided on the bottom of the frame. Four vertical vibration damping supports 152 are provided, with one on each of the angled faces of the frame as illustrated in Fig. 18 (with only two showing). The vibration supports are in the form of mushroom tops and the material is chosen in accordance with the discussion above.
Fig. 23 is a third embodiment of the (de)multiplexer 410 which differs from the second embodiment of the (de)multiplexer 300 only by the vibration damping structure as described below. In the third embodiment 410 of Fig. 23, the angled faces of the housing bottom and top 304, 306 shown in Fig. 18 are eliminated. At the portion of the frame 12 adjacent to the fiber pigtail array (the "first end" 412) a total of four donut shaped vibration dampers 414 are attached to receptacles 416 on horizontal surfaces of the frame 12. Referring to Fig. 24, which shows the donut shaped vibration dampers 414 and the first end of the frame 412 in larger scale, the housing bottom 304 has a pair of square posts 418 extending therefrom and spaced to register with the circular hole of the donut shaped vibration dampers 414. Likewise, square posts 420 extend from the inside of the housing top 306 and register with the corresponding donut shaped vibration dampers 414.
Referring back to Fig. 23, at the end of the frame 12 adjacent to the grating (the "second end") 422, two horizontal damping supports 154 are provided on the top of the frame 12 and two more horizontal damping supports (not shown) are provided on the bottom of the frame 12. These supports register with corresponding receptacles 424 on the inside of the housing bottom and top 304, 306. Vertical damping supports 152 are provided on each vertical wall of the end of the frame adjacent the grating (one shown in Fig. 23).
The square posts 418, 420 register with the round holes of the donut shaped vibration dampers 414 to provide a snug fit. The combination of tightly and loosely compressed elastomer of the donut shaped vibration dampers 414, with the tightly compressed elastomer being near the corners of the square posts, enhances the vibration damping ability. In addition, the posts mate securely with the donut shaped vibration dampers to secure the frame 12 relative to the top 306 and bottom 304 of the housing. The horizontal and vertical dampers 154, 152 at the second end of the frame 422 are sized and spaced to snuggly engage the top, bottom and sidewalls of the housing with the top 306 and bottom 304 mated. Thus, the vibration damping structure of the third embodiment further minimizes the potential movement of the frame 12 relative to the platform or housing 14.
The second embodiment of the (de)multiplexer 300 described with reference to Figs. 17-21, as well as the third embodiment illustrated in Figs. 23 and 24 simplify the embodiment discussed in Figs. 1-16 by eliminating the flexures of the first adjustable mount and providing the option of eliminating the second adjustable mount 48 in favor of a fixed grating mount. The first adjustable mount of the second embodiment allows for 6 degrees of movement and greatly reduces the complexity the adjustable mount structure, thus providing a simple, elegant and inexpensive alignment structure. The spring retention plate 346 helps hold the waveguide array carrier 344 in a select position during alignment which can be secured using the non- influencing lock of the screws 390. Likewise, the magnetic attraction between the frame 12 and the X, Y, Z plate 342 allows the X, Y, Z plate to be moved to a suitable alignment an then secured in place by the non-influencing lock provided by the bolts 394. The available 6 degrees of movement of the fiber pigtail array allows the use of a fixed grating mount for the grating which greatly enhances the ease of alignment and further simplifies both the structure and the assembly process. It further greatly reduces costs by eliminating a large number of high precision machined components.
Like the first embodiment, the second and third embodiments provide an insulating nitrogen layer to protect the optical components and their critical optical alignment from temperature extremes applied to the housing. The second and third embodiments also include a convenient way for evacuating air from and providing the nitrogen gas to the interior of the housing.

Claims

1. A (de)multiplexer for fiber optic communications systems comprising: a diffraction grating having a diffraction surface; a waveguide array including a plurality of waveguides having an input/output end for emitting and receiving optical signals; a focusing optic in optical communication between the diffraction grating and the waveguide array along an optical axis, the focusing optic focusing beams from the diffraction surface of the grating for optical coupling with the input/output ends of the waveguides; a frame; a fixed mount between the focusing optic and the frame; a first adjustable mount between the waveguide array and the frame; and a second adjustable mount between the diffraction grating and the frame.
2. The (de)multiplexer of claim 1 wherein the optical axis corresponds to a Z axis of orthogonal X, Y, Z axes and the waveguides of the waveguide array are aligned with the input/output ends along an input/output axis, the first adjustable mount being configured to provide for linear movement of the waveguide array along the Z axis.
3. The (de)multiplexer of claim 2, the first adjustable mount being configured to provide for movement of the input/output axis within a plane parallel to the X, Y axes.
4. The (de)multiplexer of claim 1, the second adjustable mount being configured to provide only for gimbaled movement of the grating about a point on the diffraction surface of the grating intersecting the optical axis.
5. The (de)multiplexer of claim 2, the second adjustable mount being configured to provide only gimbaled movement of the grating about a point on the diffraction surface of the grating intersecting the optical axis.
6. The (de)multiplexer of claim 1 further comprising a first stay between the first adjustable mount and the frame selectively securing the first adjustable mount with the input/output ends in a select orientation relative to the focusing lens and a second stay between the second adjustable mount and the frame selectively securing the second adjustable mount with the diffraction surface of the grating in a select orientation relative to the lens.
7. The (de)multiplexer of claim 1 wherein the optical axis corresponds to a Z axis of orthogonal X,Y,Z axes and the waveguides of the waveguide array are aligned with the input/output ends along an input/output axis parallel to the Z axis, the fist adjustable mount being configured to provide for linear movement of the waveguide array within an XZ plane parallel to the XZ axes and an XY plane parallel to the XY axes and rotational movement about the Z axis and the Y axes.
8. The (de)multip lexer of claim 7 further comprising first means for maintaining the waveguide array in a fixed orientation relative to the optical axis linearly within the XY plane and rotationally about the Z axis in the absence of a moving force of less than a first select amount.
9. The (de)multiplexer of claim 19 further comprising second means for maintaining the waveguide array in a fixed orientation relative to the optical axis linearly within the XZ plane and rotationally about the Y axis in the absence of a moving force of less than a select amount.
10. The (de)multiplexer of claim 1 wherein the second adjustable mount comprises: a grating mount having a leading surface to which the grating is attached with the diffraction surface in a select orientation relative to the grating mount and a spherical surface having a select radius about a point on the diffraction surface of the grating; and a concave surface on the frame receiving the spherical surface of the grating mount with the optical axis intersecting the point on the diffraction surface of the grating.
11. An attachment assembly for attaching a diffraction grating having a diffraction surface of an optical (de)multiplexer to a frame of the (de)multip lexer, the (de)multiplexer having optical elements in addition to the grating, the optical elements being attached to the frame and optically aligned along an optical axis, the attachment assembly comprising: a grating mount having a leading surface to which the grating is attached with the diffraction surface in a select orientation relative to the grating mount and a spherical surface having a select radius about a point on the diffraction surface of the grating; a receptacle on the frame having a surface which is conical about a central axis, the receptacle receiving the spherical surface of the grating mount with the optical axis intersecting the point on the diffraction surface of the grating; and a clamp operatively associated with the grating mount and the frame for fixing the grating mount relative to the frame with the diffraction surface in a select orientation relative to the optical axis.
12. The attachment assembly of claim 11 wherein the grating mount further includes a central axis of the spherical surface, the spherical surface being situated on the grating mount with the central axis generally aligned with the optical axis of the (de)multiplexer.
13. The attachment assembly of claim 12 further comprising the grating mount having a threaded tail extending along the optical axis and the receptacle being formed in a wall of the frame normal to the optical axis with the central axis of the conical surface generally aligned with the optical axis of the (de)multiplexer, the threaded tail being received in a hole about the central axis of the conical surface, the hole extending through the wall, the clamp comprising a nut threadably engaging the threaded tail, whereby the grating mount is fixed relative to the frame by tightening the nut.
14. The attachment assembly of claim 11 wherein the clamp further comprises a convex outer surface formed in the wall of the housing on a side opposite the conical surface and a washer having a concave washer surface mating with the convex outer surface, the washer being received on the treaded tail between the convex outer surface and the nut.
15. The attachment assembly of claim 11 further comprising a low friction coating on the spherical surface.
16. The attachment assembly of claim 14 further comprising a low friction surface coating on the concave washer surface.
17. The attachment assembly of claim 11 further comprising the grating mount having a spherical surface central axis and the receptacle being formed in a wall of the frame normal to the optical axis with the conical surface central axis and the spherical surface central axis aligned with the optical axis of the (de)multiplexer, the grating mount being made of a thermally expansive material and dimensioned to expand and contract along the optical axis when subjected to changes in temperature while maintaining the diffractive surface in a select orientation relative to the optical axis.
18. The attachment assembly of claim 13 further comprising indicia on the stem having a select orientation relative to the grating surface for coarsely aligning the grating.
19. A method of optically aligning a (de)multiplexer for fiber optic communications systems, the (de)multiplexer including a diffraction grating having a diffraction surface for dividing a multi-channel incident beam into a single channel beams, a waveguide array including a plurality of waveguides having an input/output end for receiving the single channel beams, a focusing optic in optical communication between the diffraction grating and the waveguide array along an optical axis, the focusing optic focusing the single channel beams from the diffraction surface of the grating for optical coupling with the input/output ends of the waveguides, and a frame, the method comprising: affixing the focusing optic to the frame with an optical axis of the focusing optic defining the optical axis; moving the waveguide array relative to the focusing optic only linearly along the optical axis; and moving the grating only by rotating the grating about three orthogonal axes at a point on the grating surface intersected by the optical axis.
20. The method of claim 19 further comprising moving the input/output ends of the waveguide array within a plane normal to the optical axis.
21. A (de)multiplexer for fiber optic communications systems comprising: a diffraction grating having a diffraction surface; a waveguide array including a plurality of waveguides having an input/output end for emitting and receiving optical signals; a focusing optic in optical communication between the diffraction grating and and the waveguide array along an optical axis, the focusing optic focusing beams from the diffraction surface of the grating for optical coupling with the input/output ends of the waveguides; a frame; a fixed mount between the focusing optic and the frame; a fixed mount between the diffraction grating and the frame; and an adjustable mount between the waveguide array and the frame, the optical axis corresponding to a Z axis of orthogonal XYZ coordinates, and the adjustable mount providing for linear movement within an XY plane and an XZ plane and rotational movement about the Z axis and the Y axis.
22. The (de)multiplexer of claim 21 further comprising first means for maintaining the waveguide array in a fixed orientation relative to the optical axis linearly within the XY plane and rotationally about the Z axis in the absence of a moving force of less than a first select amount.
23. The (de)multiplexer of claim 22 further comprising second means for maintaining the waveguide array in a fixed orientation relative to the optical axis linearly within the XZ plane and rotationally about the Y axis in the absence of a moving force of less than a select amount.
24. The (de)multip lexer of claim 21 further comprising third means for releasably securing the waveguide array in a fixed orientation relative to the optical axis linearly within the XY plane and rotationally about the Z axis.
25. The (de)multip lexer of claim 24 further comprising fourth means for releasably securing the waveguide array in a fixed orientation relative to the optical axis linearly within the XZ plane and rotationally about the Y axis.
26. The (de)multiplexer of claim 22 wherein the first means comprises a stage supporting the waveguide array and a magnetic force between the frame and stage.
27. The (de)multip lexer of claim 23 wherein the second means comprises a stage supporting the waveguide array and a spring force between the waveguide array and the stage.
28. The (de)multip lexer of claim 25 wherein the third and fourth means are non- influencing locks.
29. A (de)multiplexer for fiber optic communications systems comprising: a wavelength dispersive element; a waveguide array including a plurality of waveguides having an input/output end for emitting and receiving optical signals; a focusing optic in optical communication between the wavelength dispersive element and the input/output ends of the waveguides, the focusing optic focusing beams from the wavelength dispersive element to select focal points for optical coupling with the input/output ends, a location of the select focal points varying as a function of changes in (de)multiplexer temperature; and a thermally expansive frame to which the waveguide array and the focusing optic are attached, the frame supporting the waveguide array and the focusing optic for movement relative to one another as function of changes in (de)multiplexer temperature to maintain optical coupling between the input/output ends and the focused beams.
30. The (de)multiplexer of claim 29 wherein at a select temperature the wavelength dispersive element, the waveguides of the waveguide array and the focusing optic are optically coupled along an optical axis and a focal length between the focusing optic and the focal points along the optical axis corresponds to a distance between the focusing optic and the input/output ends of the waveguides to provide the optical coupling, the focal length varying as function of a change in temperature, the frame comprising a length of frame material connecting the waveguide array and the focusing lens along the optical axis, the length of frame material having a frame material coefficient of thermal expansion moving the distance between the focusing optic and the input/output ends an amount corresponding to the change in focal length for the change in temperature.
31. The (de)multiplexer of claim 29 wherein at a select temperature the wavelength dispersive element, the waveguides of the waveguide array and the focusing optic are optically aligned along an optical axis, the focal points moving along a transverse axis relative to the optical axis as a function of changes in (de)multiplexer temperature, the frame comprising a cantilevered connector to the waveguide array extending from the frame parallel to the transverse axis, the cantilevered connector being made of a thermally expansive material which moves the waveguide array in a direction along the transverse axis corresponding to a direction of movement of the focal points caused by a change of (demultiplexer temperature.
32. The (de)multiplexer of claim 31 wherein the cantilevered connector further comprises a select length of the thermally expansive material between the frame and a rigid connection to the waveguide array, the thermally expansive material having a coefficient of thermal expansion and select length providing a select amount of movement of the waveguide array as a function of a change in (de)multiplexer temperature.
33. The (de)multiplexer of claim 29 wherein at a select temperature the wavelength dispersive element, the waveguides of the waveguide array and the focusing optic are optically aligned along an optical axis, the focal points moving along a transverse axis relative to the optical axis as a function of changes in (de)multip lexer temperature, and the waveguides of the waveguide array comprise optical fibers, the waveguide array further comprising a thermally expansive substrate securing the optical fibers with the input/output ends spaced along the transverse axis, the (de)multiplexer further comprising a flexible connector between the thermally expansive substrate and the frame providing for thermal expansion of the substrate relative to the frame with changes in (de)multiplexer temperature.
34. The (de)multiplexer of claim 33 wherein the flexible connector comprises a rigid connection at an end of the substrate and an elastic connection spaced from the rigid connection to provide movement of the substrate in a direction along the transverse axis corresponding to a direction of movement of the focal points caused by a change of (de)multiρlexer temperature.
35. The (de)multiplexer of claim 32 wherein the waveguides of the waveguide array comprise optical fibers, the waveguide array further comprising a thermally expansive substrate securing the optical fibers with the input/output ends spaced along the transverse axis, the (de)multiplexer further comprising a flexible connector between the thermally expansive substrate and the cantilevered connector, the flexible connector including the rigid connection near an attached end of the cantilevered connector and an elastic connection near the free end of the cantilevered connector, the thermally expansive substrate having a coefficient of thermal expansion and length between input/output ends providing a select amount of movement of the waveguide as a function of a change in (de)multiplexer temperature, whereby the select amount of movement from the cantilevered connector and the select amount of movement from the thermally expansive connector is an amount to maintain optical coupling with the focal points along the transverse axis as a function of change in temperature.
36. The (de)multiplexer of claim 30 wherein the select focal points move along a transverse axis relative to the optical axis as a function of changes in (de)multiplexer temperature, the frame comprising a cantilevered connector to the waveguide extending from the frame parallel to the transverse axis, the cantilevered connector extending from the frame and being made of a thermally expansive material which moves the waveguide array in a direction along the transverse axis corresponding to a direction of movement of the focal points caused by a change of (de)multiplexer temperature.
37. The (de)multiplexer of claim 1 wherein at a select temperature the wavelength dispersive element, the waveguides of the waveguide array and the focusing optic are optically aligned along an optical axis, the focal points moving a distance along a transverse axis relative to the optical axis as a function of changes in (de)multiplexer temperature, the frame comprising a transverse member along the transverse axis made of a thermally expansive material supporting the waveguide array, the waveguide array being attached at a point along the transverse member such that as the transverse member expands as a function of temperature, the waveguide array moves a distance along the transverse axis substantially equal to the distance moved by the focal points.
38. The (de)multiplexer of claim 37 wherein a distance between adjacent beams varies as a function of temperature along the transverse axis and the waveguides of the waveguide array comprise optical fibers, the waveguide array further comprising a thermally expansive substrate securing the optical fibers with the input/output ends spaced along the transverse axis, the thermally expansive substrate varying the distance between adjacent input/output ends as a function of temperature to maintain optical coupling with corresponding adjacent beams.
39. A (de)multiplexer for fiber optic communications systems comprising: a wavelength dispersive element; a waveguide array including a plurality of waveguides located in a substrate having an input/output end for emitting and receiving optical signals; a focusing optic in optical communication between the wavelength dispersive element and the input/output ends of the waveguides, the focusing optic focusing beams from the wavelength dispersive element to select focal points for optical coupling with the input/output ends, wherein at a select temperature the wavelength dispersive element, the waveguides of the waveguide array and the focusing optic are optically aligned along an optical axis and attached to a frame, a location of the focal points moving along a transverse axis relative to the optical axis as a function of changes in (de)multip lexer temperature; the substrate of the waveguide being thermally expansive and securing the input/output ends spaced along the transverse axis; and a flexible connector between the thermally expansive substrate and the frame providing for thermal expansion of the substrate relative to the frame with changes in (de)multiplexer temperature to maintain optical coupling between the input/output ends of the waveguides and the focused beams.
40. A method of thermally stabilizing a (de)multiplexer having a wavelength dispersive element, a waveguide array and a focusing optic in optical communication between the wavelength dispersive element and the input/output ends of the waveguides, the focusing optic focusing beams from the wavelength dispersive element to select focal points for optical coupling with the input/output ends, the method comprising: varying the location of the select focal points as a function of changes in (demultiplexer temperature; and moving the waveguide array relative to focusing optic as a function of (de)multiplexer temperature to maintain optical coupling between the input/output ends and the focused beam.
41. The method of claim 40 further comprising: attaching the wavelength dispersive element, the focusing optic and the waveguide array to a thermally expansive frame along an optical axis; varying the location of the focal points by changing a focal length along the optical axis between the focusing optic and the focal points; and moving the waveguide array along the optical axis relative to the focusing optic by thermally expanding the frame along the optical axis an amount sufficient to maintain optical coupling between the input/output ends and the focused beam.
42. The method of claim 41 wherein the moving of the waveguide array is performed by providing a portion of frame between the focusing optic and the waveguide array having a coefficient of thermal expansion and an optical axial length such that a distance along the optical axis between the focusing optic and the input/output ends of the waveguides varies as a function of change in (de)multiplexer temperature an amount corresponding to the change in focal length.
43. The method of claim 40 further comprising: attaching the wavelength dispersive element, the focusing optic and the waveguide array to a frame along an optical axis, the waveguide array being attached to the frame by a thermally expansive connector extending transverse the optical axis; varying the location of the focal points along a transverse axis relative to the optical axis; and moving the waveguide array along the transverse axis in a direction along the transverse axis corresponding to a direction of movement of the focal points by thermally expanding the thermally expansive connector.
44. The method of claim 41 further comprising: attaching the waveguide array to the frame by a thermally expansive connector extending transverse the optical axis; further varying the location of the focal points along a transverse axis relative to the optical axis; and moving the waveguide array along the transverse axis in a direction along the transverse axis corresponding to a direction of movement of the focal points along the transverse axis by thermally expanding the thermally expansive connector.
45. The method of claim 14 wherein the waveguides of the waveguide array comprise optical fibers, the waveguide array further comprising a thennally expansive substrate securing the optical fibers with the input/output ends spaced along the transverse axis, the method further comprising: moving the input/output ends in a direction along the transverse axis corresponding to a direction of movement of the focal points along the transverse axis by thermally expanding the substrate.
46. The method of claim 43 wherein the waveguides of the waveguide array comprise optical fibers, the waveguide array further comprising a thermally expansive substrate securing the optical fibers with the input/output ends spaced along the transverse axis, the method further comprising: moving the input/output ends in a direction along the transverse axis corresponding to a direction of movement of the focal points along the transverse axis by thermally expanding the substrate.
47. The method of claim 40 wherein the waveguides of the waveguide array comprise optical fibers, the waveguide array further comprising a thermally expansive substrate securing the optical fibers with the input/output ends spaced along an input/output axis, the method further comprising: attaching the wavelength dispersive element, the focusing optic and the thermally expansive substrate to a frame along an optical axis, the thermally expansive substrate being attached with the input/output axis along a transverse axis transverse the optical axis; varying the location of the focal points along the transverse axis; and moving the input/output ends in a direction along the transverse axis corresponding to a direction of movement of the focal points along the transverse axis by thermally expanding the substrate as a function of changes in (de)multiplexer temperature.
48. An optical (de)multiplexer comprising: a plurality of discrete optically aligned bulk optical elements; a rigid frame to which the discrete optical elements are rigidly attached in optical alignment relative to each other; a platform; and a vibration damping support joining the platform and the rigid frame to isolate the rigid frame from vibrations applied to the platform.
49. The optical (de)multiplexer of claim 48 further comprising a plurality of vibration damping supports joining the platform and the rigid frame.
50. The optical (demulti lexer of claim 49 wherein the each vibration damping support comprises a pair of spaced rigid plates, a fastener on each plate for attachment to one of the rigid frame and the platform and a vibration damping elastomer between and fixedly attached to the plates.
51. The optical (de)multiplexer of claim 50 wherein the platform comprises a rigid housing sized to contain the rigid frame.
52. The optical (de)multiplexer of claim 50 wherein the rigid housing comprises a bottom portion and the rigid frame is horizontally juxtaposed with the housing bottom, the vibration damping supports extending vertically between the rigid frame and the housing bottom.
53. The optical (de)multiplexer of claim 50 wherein the vibration damping elastomer comprises at least one of a urethane, natural rubber, and synthetic rubber.
54. The optical (de)multiplexer of claim 51 wherein the rigid frame and the rigid housing are elongate along an optical axis, the plurality of vibration damping supports being located between the ends of the rigid frame, the optical (de)multiplexer further comprising a plurality of elastomeric bumpers at an end of the frame between the frame and the housing configured to attenuate collisions between the housing and the frame.
55. The demultiplexer of claim 50 wherein each vibration damping support comprises: first and second attachment members, each attachment member having an enlarged diameter base and a lesser diameter post extending from the enlarged diameter base, the first and second attachment members being axially aligned with the lesser diameter posts extending in opposite directions and a space between the enlarged diameter portions and a vibration damping elastomer filling the space between the enlarged diameter bases and enveloping the large diameter bases with the lesser diameter posts extending out of the vibration damping elastomer, one of the lesser diameter posts being connected to the frame and the other being connected to the platform.9. A method of isolating a (de)multiplexer from external vibrations, the (de)multiplexer comprising a plurality of discrete optically aligned bulk optical elements, the method comprising: a) rigidly affixing the optically aligned bulk optical elements to a rigid frame; b) providing a platform; and c) connecting the rigid frame to the platform with a vibration damping support.
56. The optical (de)multiplexer of claim 48 wherein the platform defines a cavity within which the rigid frame nests, with the vibration damping support comprising a plurality of bumpers in contact between the platform defining the cavity and the rigid frame.
57. The optical (de)multiplexer of claim 56 further comprising: a number of posts extending from the platform within the cavity; and a corresponding number of holed bumpers, each of the number of holed bumpers defining a hole sized to snuggly receive a post and each of the number of holed bumpers being attached to the rigid frame so that with the rigid frame nested in the cavity each of the posts is received in a hole of a corresponding one of the number of holed bumpers.
58. The optical (de)multiplexer of claim 57 wherein the holed bumper holes are circular and the posts have a non-circular cross section.
59. The optical (de)n ltiplexer of claim 57 wherein the rigid frame is elongate and the number of posts and the number of holed bumpers are located near one end of the frame and near the other end of the frame the remaining of the plurality of bumpers reside in contact between the platform defining the cavity and the rigid frame.
60. The optical (de)multiplexer of claim 57 wherein the platform comprises a cavity top and a cavity bottom, with some of the number of posts extending from the cavity bottom and others of the number of posts extending from the cavity top.
61. A method of isolating a (de)multiplexer from external vibrations, the (de)ιmιltipleχer comprising a plurality of discrete optically aligned bulk optical elements, the method comprising: a) rigidly affixing the optically aligned bulk optical elements to a rigid frame; b) providing a platform; and c) connecting the rigid frame to the platform with a vibration damping support.
62. The method of claim 55 wherein the platform comprises a housing sized to receive the rigid frame and step c) further comprises placing the rigid frame within the housing.
63. A vibration damping support for attaching a frame to which discrete optical elements are attached to a platform while isolating the frame from vibration applied to the platform, the vibration damping support comprising: first and second attachment members, each attachment member having an enlarged diameter base and a lesser diameter post extending from the enlarged diameter base, the first and second attachment members being axially aligned with the lesser diameter posts extending in opposite directions and a space between the enlarged diameter portions; and a vibration damping elastomer filling the space between the enlarged diameter bases and enveloping the large diameter bases with the lesser diameter posts extending out of the vibration damping elastomer.
64. The vibration damping support of claim 63 where the lesser diameter posts are externally threaded.
PCT/US2001/045276 2000-10-31 2001-10-31 Bulk optical (de)multiplexer apparatus and method of packaging WO2002037726A2 (en)

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US70254800A 2000-10-31 2000-10-31
US09/702,548 2000-10-31
US09/702,550 US6421479B1 (en) 2000-10-31 2000-10-31 Apparatus and method facilitating optical alignment of a bulk optical multiplexer/demultiplexer
US09/702,550 2000-10-31
US74729800A 2000-12-21 2000-12-21
US09/747,298 2000-12-21
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EP0123237A1 (en) * 1983-04-23 1984-10-31 Licentia Patent-Verwaltungs-GmbH Optical multiplexer/demultiplexer
US4719614A (en) * 1983-05-20 1988-01-12 Thomson-Csf Optical recording-reading head using an adjustable mount for pivoting mirror
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Publication number Priority date Publication date Assignee Title
EP2071377A1 (en) * 2007-12-12 2009-06-17 JDS Uniphase Corporation Packaging a reconfigurable optical add-drop module
US8121483B2 (en) 2007-12-12 2012-02-21 Nenad Duricic Packaging a reconfigurable optical add-drop module

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