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
• • 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
  • G02B6/29316—Light guides comprising a diffractive element, e.g. grating in or on the light guide such that diffracted light is confined in the light guide
  • G02B6/29317—Light guides of the optical fibre type
  • G02B6/29319—With a cascade of diffractive elements or of diffraction operations
  • G02B6/2932—With a cascade of diffractive elements or of diffraction operations comprising a directional router, e.g. directional coupler, circulator
• • 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
  • G02B6/02—Optical fibres with cladding with or without a coating
  • G02B6/02057—Optical fibres with cladding with or without a coating comprising gratings
  • G02B6/02076—Refractive index modulation gratings, e.g. Bragg gratings
  • G02B6/02195—Refractive index modulation gratings, e.g. Bragg gratings characterised by means for tuning the grating
  • G02B6/022—Refractive index modulation gratings, e.g. Bragg gratings characterised by means for tuning the grating using mechanical stress, e.g. tuning by compression or elongation, special geometrical shapes such as "dog-bone" or taper
• • 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
  • G02B6/29316—Light guides comprising a diffractive element, e.g. grating in or on the light guide such that diffracted light is confined in the light guide
  • G02B6/29317—Light guides of the optical fibre type
  • G02B6/29322—Diffractive elements of the tunable type
• • 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
  • G02B6/29382—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 including at least adding or dropping a signal, i.e. passing the majority of signals
  • G02B6/29383—Adding and dropping
• • 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
  • G02B6/29395—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 configurable, e.g. tunable or reconfigurable
• • 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
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04J—MULTIPLEX COMMUNICATION
  • H04J14/00—Optical multiplex systems
  • H04J14/02—Wavelength-division multiplex systems
  • H04J14/0201—Add-and-drop multiplexing
  • H04J14/0202—Arrangements therefor
  • H04J14/021—Reconfigurable arrangements, e.g. reconfigurable optical add/drop multiplexers [ROADM] or tunable optical add/drop multiplexers [TOADM]

Definitions

• the present invention relates to optical add/drop multiplexer devices, and more particularly, an optical add drop multiplexer (OADM) using a Jarge diameter waveguide for dynamically adding and dropping optical signals from a WDM optical, signal, s
• OADM optical add drop multiplexer
• the need to provide services "just in time” by allocation of wavelengths, and further migration of the optical layer from the high-capacity backbone portion to the local loop, is driving the transformation of the network toward an all optical network in which basic network requirements will be performed in the optical layer
• the optical network is a natural evolution of point-to-point dense wavelength division multiplexing (DWDM) transport to a more dynamic, flexible, and intelligent networking architecture to improve service delivery time.
• the main element of the optical network is the wavelength (channel), which will be provisioned, configured, routed, and managed in the optical domain.
• Intelligent optical networking will be first deployed as an "opaque” network in which periodic optical-electrical conversion will be required to monitor and isolate signal impairments, Longer range, the optical network will evolve to a "transparent" optical network in which a signal is transported from its source to a destination totally within the optical domain.
• a key element of the emerging optical network is an optical add/drop multiplexer (OADM), An OADM will drop or add specific wavelength channels without affecting the throug channels.
• OADMs can simplify the network and readily allow cost-effective DWDM migration from simple point-to-point topologies to fixed multi-point configurations.
• True dynamic OADM in which reconfiguration is done in the optical domain without optical-electrical conversion, would allow dynamically reconfigurable, multi-point DWDM optical networks.
• This dynamically reconfigurable multi-point architecture is slated to be the next major phase in network evolution, with true OADM an enabling network element for this architecture.
• One known commercially is a fixed all-optical OADM that couples fixed optical channel filters, usually fiber Bragg gratings, to passive optical routing and branching components such as couplers and circulators.
• the fiber Bragg gratings are not tuned to filter different wavelengths.
• a tunable grating/circulator approach for dynamically reconfigurable OADM has also been pursued in the prior art by thermal or strain tuning the grating.
• These dynamic or programmable all-optical OADM designs are based on tunable gratings.
• Ball in United States Patent No, 6,020,986, shows an add/drop module haying a circulator 16, an array of tunable fiber Bragg gratings, a piezoelectric device and a controller, which is incorporated herein by reference. Strain is applied by coupling the piezoelectric device to each fiber Bragg grating, and adjusting the current applied to each piezoelectric device from the controller. The wavelength of the grating may be adjusted ("tuned") in the nanometer range for gratings having a wavelength of about 1540 nanometers.
• Ball does not disclose how the piezoelectric device is physically coupled to the fiber Bragg gratings to apply strain. See also United States Patent No, 5,579,143, issued to Huber, and United States Patent No.
• an optical drop filter includes a compression-tuned optical device
• the compression tuned optical device includes an optical waveguide, which has an inner core disposed within an outer cladding and a grating disposed within the inner core.
• the grating reflectd a first reflection wavelength of light back along the inner core and propagates the ⁇ remaining wayelengtlis of light through the grating.
• the optical waveguide includes a pair of opposing surfaces.
• the optical waveguide also includes a compressing device that compresses the optical waveguide for compressing the opposing surfaces towards each other to time the grating and change the reflection wavelength of light reflected back along the inner core.
• the drop filter also includes an optical directing device for 0 providing an input optical signal to the compression-tuned optical device,
• the input optical signal has a plurality of optical channels centered at spaced wavelengths.
• the compression-tuned optical device removes an optical channel from the input optical signal.
• an optical 5 add filter includes a compression-tuned optical device, which has an optical waveguide,
• the optical waveguide includes an inner core disposed within an outer cladding and a grating disposed within the inner core.
• the grating reflects a first reflection wavelength of light back along the inner core and propagates the remaining wavelengths of light through the grating
• the optical waveguide includes a pair of o opposing surfaces.
• a compressing device compresses the opposing surfaces of the optical waveguide to tune the grating and change the reflection wavelength of light reflected back along the inner core,
• An optical directing device is optically connected to the compression-tuned optical device for combining an input optical signal and an added optical channel.
• the input optical signal has a plurality of optical channels 5 centered at spaced wavelengths,
• the compression-tuned optical device provides the optical channel to be combined with the input optical signal to provide a combined output signal,
• an optical add/drop multiplexer includes a compression-tuned optical device that has an optical waveguide.
• the optical waveguide includes an inner core disposed within an outer cladding and a grating disposed within the inner core.
• the grating reflects a first reflection wavelength of light bade along the inner core and propagates the remaining wavelengths of light through, the grating.
• the optical waveguide includes a pair of opposing surfaces, A compressing device compresses the optical waveguide to compress the opposing surfaces towards each other to tune the grating and to change the reflection wavelength of light reflected back along the inner core,
• An optical directing device is optically connected to the compression-tuned optical device for combining an input optical signal and an added optical channel.
• the input optical signal has a plurality of optical channels centered at spaced wavelengths.
• the compression-tuned optical device provides the optical channel to be combined with the input optical signal to provide a combined output signal.
• a compression-tuned optical add/drop module includes a compression device for providing a compression force applied along an axis of compression.
• a grating compression unit having a grating along the axis of compression is responsive to the optical input signal, and further responsive to the compression force, for providing a grating compression unit optical signal having the selected wavelength of the channel to be added to or dropped from the input signal.
• FIG. 1 is a side view of a tunable grating unit of a tunable optical filter and a block diagram of a positional/force feedback control circuit in accordance with the present invention
• FIG. 2 is a side view of a grating element of a tunable optical filter in accordance with the present invention
• FIG. 3 is a block diagram of a tunable drop filter in accordance with the present invention
• FIG. 4 is a block diagram of another embodiment of a tunable drop filter in accordance with the present invention.
• 5 is a block diagram of a tunable add filter in accordance with the present invention.
• FIG. 6 is a block diagram of another embodiment of a tunable add filter in accordance with the present invention.
• FIG, 7 is a block diagram of another embodiment of a tunable add filter in o accordance with the present invention.
• FIG. 8 is a block diagram of another embodiment of a tunable add filter in accordance with the present invention.
• FIG. 9 is a block diagram of a reconfigurable optical add/drop multiplexer (ROADM) in accordance with the present invention.
• FIG. 10 is a block diagram of another embodiment of a reconfigurable optical add/drop multiplexer (ROADM) in accordance with the present invention.
• FIG. 11 is a block diagram of another embodiment of a reconfigurable optical add/drop multiplexer (ROADM) in accordance with the present invention.
• ROADM reconfigurable optical add/drop multiplexer
• FIG. 12 is a block diagram of another embodiment of a reconfigurable optical o add/drop multiplexer (ROADM) in accordance with the present invention.
• ROADM reconfigurable optical o add/drop multiplexer
• FIG, 13 is a block diagram of another embodiment of a reconfigurable optical add/drop multiplexer (ROADM) in accordance with the present invention.
• ROADM reconfigurable optical add/drop multiplexer
• FIGs. 3 and 4 show respective embodiments of tunable drop filters 80, 90 that filter or drop at least one wavelength band or optical channel of light, which is centered at a respective channel wavelength, from a WDM optical input signal 11
• FIGs , 5 - 8 show respective embodiments of tunable add filters 100,110,120,130 that add or combine at least one optical channel to a WDM optical input signal 11
• the tunable drop and add filters 80,90,100,110,120,130 may be combined in a number ways to provide a reconfigurable optical add/drop multiplexer (ROADM) 140,150,160,170,180.
• ROADM reconfigurable optical add/drop multiplexer
• each of the tunable drop filters, add filter and ROADMs shown in Figs. 3 - 13 include at least one tunable Bragg grating unit 10, optically coupled to a port of an optical directing device 12,13 (see Figs, 3 - 6), such as a 3 or 4-port circulator, or optical coupler 1 .
• the grating unit 10 tunes a grating element 14, which is a bulk or large diameter optical waveguide, having an outer cladding 18 and an inner core 16 disposed therein, having a single mode.
• the grating element 14 has an outer diameter of at least .3 mm ' and comprises silica glass (Si0 2 ) having the appropriate dopants, as is known, to allow light 11 to propagate along the inner core 16,
• the grating element (large diameter optical waveguide) may be formed by using fiber drawing techniques now l ⁇ iow or later developed that provide the resultant desired dimensions for the core and the outer dimensions discussed hereinbefore, similar to that disclosed in co-pending US Patent Application, Serial
• the grating element may then be etched, grounded or machined to form a "dogbone” shape, as will be described in greater detail hereiafter.
• a pair of fibers or “pigtails” 17 may be attached to the ends of the grating element 14 by known techniques, such as epoxy or glass fusion)
• the optical grating element 14 maybe formed by heating, collapsing and fusing a glass capillary tube to a fiber (not shown) by a laser, filament, flame, etc, as is described in copending US Patent Application, Serial No. 09/455,865, entitled “Tube-Encased Fiber Grating", which is incorporated herein by reference.
• Other techniques may be used for collapsing and fusing the tubes to the fiber, such as is discussed in US Patent No. 5,745,626, entitled “Method For And Encapsulation. Of An Optical Fiber", to Duck et al context and/or US Patent No.
• the grating element 14 includes a reflective element 20, such as a Bragg grating, is written (embedded or imprinted) into the inner core 16 of the grating element 14.
• T e Bragg grating 20 reflects back a portion the input light 11 as indicated by a line 22 having a predetermined wavelength band of light centered at a o reflection wavelength ⁇ t ,, and passes the remaining wavelengths of the incident light
• the grating 20 is a periodic or aperiodic variation in the effective refractive index and/or effective optical absorption coefficient of an optical waveguide, such as that described in US Patent No. 4,725,110 and 4,807,950, entitled “Method for Impressing s Gratings Within Fiber Optics", to Glenn et al; and US Patent No. 5,388,173, entitled
• any wavelength-tunable grating or reflective element 20 embedded, o written, etched, imprinted, or otherwise formed in the inner core 16 may be used if desired, as used herein, the term “grating” means any of such reflective elements. Further, the reflective element (or grating) 20 may be used in reflection and/or transmission of light.
• the optical grating element 14 may be made of any glass, e.g., silica, phosphate glass, or other glasses, or made of glass and plastic, or solely plastic.
• the grating element 14 is axially compressed by a compression device or housing 30, similar to that described in US Patent Application, Serial No. 09/707,084, entitled ''Compression-Tuned Bragg Grating Based Laser” (CiDRA Docket No. CC- 0129D), One end of the grating element 14 is pressed against a seat 32 in one end 34 of the housing 30.
• the housing also has a pair of arms (or sides) 36, which guide a movable block 3,
• the block 38 has a seat 40 that presses against the other end of the grating element 14,
• the axial end faces of the grating element 14 and/or the seats on s mating surfaces 32,40 may be plated with a material that reduces stresses or enhances the mating of the grating element 14 with the seat on the mating surfaces,
• the ends of the housing 30 and the block 38 have a bore 42 drilled through them to allow the fiber 41 to pass therethrough.
• the end 34 of the housing 30 and the block 38 may provide a planar surface for engaging flush with the o respective ends of the grating element 14.
• the housing 30 may be assembled such that a pre-strain or no pre-stain exists on the grating element 14 prior to applying any outside forces.
• An actuator 44 such as a piezoelectric actuator, engages the moveable block 38, which causes the block to move as indicated by arrows 46, Accordingly, the PZT s actuator 44 provides a predetermined amount of force to the moving block 38 to compress the grating element 14, and thereby tune the grating 20 to desired a reflection wavelength
• the PZT actuator 44 is energized to provide the appropriate compression force necessary to tune the grating element to the o desired Bragg reflection wavelength of the grating 20,
• the control circuit 50 adjusts the expansion and retraction of the actuator 44 in response to an input command 54 and a displacement sensor 56 that provides feedback representative of the strain or compression of the grating element 14 to form non-optical closed-loop control configuration. In other words, light 1 1 propagating through the network or device is 5 not used to provide feedback for the tuning of the grating 20.
• the displacement sensor 56 includes a pair of capacitive elements 58 and a displacement sensor circuit 59, similar to that disclosed in co- pending US Patent Application, Serial No, 09/51 ,802 entitled, "Tunable Optical Structure Featuring Feedback Control", filed March 6, 2000, which is incorporated by reference in its entirety,
• each capacitive element 58 is generally tubular having an annular capacitive end surface 60
• the capacitive elements 58 are mounted to respective ends of the grating element 14 at 62 such that the capacitive surfaces 60 are spaced a predetermined distance apart, for example, approximately 1 - 2 microns, Other spacings may be used if desired.
• the capacitive elements 58 may be bonded or secured using an epoxy or other adhesive compound, or fused to grating element 14 using a C0 2 laser or other heating element.
• the capacitive surfaces 60 are coated with a metallic coating, such as gold, to form a pair of annular capacitive plates 64. The change in capacitance depends on the change in the spacing between the capacitive plates.
• Electrodes 66 ate attached to the capacitive plates 64 to connect the capacitor to the displacement sensor circuit 59.
• the sensor circuit 59 measures the .capacitance between the capacitive plates 64; and provides a sensed signal 67, indicative of the measured capacitance, to the displacement controller 50, As the grating element 14 is strained, the gap between the parallel capacitive plates 64 will vary, thereby causing the capacitance to change correspondingly.
• the gap between the capacitive plates 64 is reduced, resulting in an increase in capacitance
• the change in capacitance is inversely proportional to the change in the reflection wavelength ⁇ b of the grating 20, Since the capacitive elements 58 are directly connected to the grating element 14, the capacitive elements are passive and will not slip.
• the sensor electronics circuit 59 to measure the change in capacitance between the two capacitive plates 64.
• the controller 50 receives the wavelength input signal 54, which represents the desired reflection wavelengtli to tune the grating unit.
• the controller 50 provides a control signal 52 to the actuator 44 to increase or decrease the compression force applied to the grating element 14 to set the desired reflection wavelength of the grating 20.
• the change in applied force to the grating element 14 changes the spacing between the ends of the grating 20, and therefore, the spacmg between the capacitive plates 64, As described above, the change in spacing of the capacitive plates 64 changes the capacitance therebetween provided to the sensor circuit 59, which provides displacement feedback to the controller 50.
• CM controller
• DPT-C-M for a cylindrical actuator
• the invention has been described with respect to using a capacitor 56 to measure the gap distance, it should be understood by those skilled in the art tliat other gap sensing techniques may be used, such as inductive, optical, magnetic, microwave, tirae-of-flight based gap sensors. Moreover, the scope of the invention is also intended to include measuring or sensing a force applied on or about the compressive element, and feeding it back to control the compression tuning of the optical structure. While the embodiment of the present invention described hereinbefore includes means to provide feedback of the displacement of a grating element 20, one should recognize that the grating units may be accurately and repeatably compressed and thus may operate in an open loop mode.
• the grating element 14 may be compressed by another actuator, such as a solenoid, pneumatic force actuator, or any other device that is capable of directly or indirectly applying an axial compressive force on the grating element 14.
• a stepper motor or other type of motor whose rotation or position can be controlled may be used to compress the grating element,
• a mechanical linkage connects the motor, e,gively a screw drive, linear actuator, gears, and/or a cam, to the movable block 38 (or piston), which cause the block to move as indicated by arrows 46, similar to that described in pending U.S.
• the stepper motor may be a high resolution stepper motor driven in a microstepping mode, such as that described in the aforementioned US Patent No, 5,469,520,
• Compression Tuned Fiber Grating to Morey et al, (e.g., a Melles Griot NANOMOVER), incorporated herein by reference.
• the grating element 14 may have a "dogbone" shape having a narrow central section 70 and larger outer sections 72.
• the dogbone shape provides increased sensitivity in converting force applied by the actuator 44 to assure accurate tuning of the grating 20.
• the narrow section 70 may have an outer diameter d2 of about 0.8-1 mm, and a length L2 of about 5-20 mm,
• the large sections 72 each have a diameter d3 of about 2-3 mm and a length L3 of about 2 - 5 mm,
• the overall length LI is about 10-30 mm and tine multi-component grating has a length Lg of about 5-20 mm, Other lengths and diameters of the sections 70,72 may be used, Other dimensions and lengths for the grating element 14 and the multi- component grating may be used,
• An inner transition region 74 of the large sections 72 maybe a sharp vertical or angled edge or may be curved.
• a curved geometry has less stress risers than a sharp edge and thus may reduce the likelihood of breakage.
• the large sections 72 may have the outer fluted sections 76 at the ends.
• the grating element 14 may have tapered (or beveled or angled) outer comers or edges 76 to provide a seat for the grating element 14 to mate with housing 30 and 5 moving block 38 and/or to adjust the force angles on the grating element, or for other reasons.
• the angle of the beveled corners 76 is set to achieve the desired function.
• one or both of the axial ends of the grating element 14 where the fiber 41 attaches may have an outer tapered (or fluted, conical, or nipple) axial section 78,
• the Bragg i o grating may be written in the fiber before or after the capillary tube is encased around and fused to the fiber, such as is discussed in copending US Patent Application, Serial, No. 09/455,865, entitled “Tube-Encased Fiber Grating", filed December 6, 1999 (CiDRA Docket No. CC-0078B), which is incorporated herein by reference, If the grating 20 is written in the fiber after the tube is encased around the grating, the is grating may be written through the tube into the fiber by any desired technique, such as is described in copending US Patent Application, Serial No. 09/205,845, entitled “Method and Apparatus For Forming A Tube-Encased Bragg Grating", filed December 4, 1998, (CiDRA Docket No, CC-0130) which is incorporated herein by reference,
• tunable grating units 10 axe actively tuned to provide a reconfigurable optical add/drop multiplexer (ROADM)
• ROADM reconfigurable optical add/drop multiplexer
• the athermal grating unit is similar to that disclosed in US Patent Application Serial No. 09/699,940 entitled “Temperature Compensated Optical Device” filed October 30, 2000 (CC-0234A), which is incorporated herein by reference.
• the invention also contemplates that some or all the grating units may be substituted for the athermal grating units. Referring to FIG.
• the tunable drop filter 80 includes a plurality of tunable Bragg grating units 10, optically coupled in series to a port of an optical directing device 12, such as a 3-port circulator, At least one grating unit 10 is actuated to compress a respective grating element 14, and therefore, tune a respective grating 20 to reflect the desired optical channel(s) to be dropped from the optical input signal 11 , while the other grating units 10 are tuned or parked to pass the remaining channels of the input signal 11.
• an optical directing device 12 such as a 3-port circulator
• a first port 81 of the circulator 12 receives the input signal 11, having optical channels centered at wavelengths ⁇ i , , , , XN, that is transmitted fluough optical fiber 82.
• the input signal 11 may originate from a light source or tapped off an optical network (not shown).
• the circulator 12 directs the input signal 11 in a clockwise direction to a second port 83 of the circulator,
• the input signal 11 exits the second port 83 and propagates tlirough optical fiber 85 to grating elements 14 of the grating units 10,
• a select number of grating elements 10 are tuned to reflect corresponding optical channels of the input signal 11, effectively dropping the corresponding optical channel from the input signal 11.
• the remaining optical grating units 10 are tuned or parked to pass the remaining optical channels of the input signal 11, to provide an optical signal 86 that does not include the dropped optical channels.
• a pair of grating units 10 are respectively tuned to reflect an optical signal having optical channels centered at wavelengths " , , while the remaining gating units 10 are parked or tuned to pass the remaining channels centered a wavelengths ⁇ , , , , , ⁇ «-
• the grating units 10 may be parked by tuning the grating units such that the filter function of the grating 20 is parked between optical channels, parked outside of the range of optical channels of the input signal 11 , or parked at the same wavelength of the grating of another grating unit, which is tuned lo reflect an optical signal.
• the reflected optical channels propagate back to the second port 83 of the circulator 12, which then directs the reflected channels to a third port 87 of the circulator and through optical fiber 88 to provide a drop optical signal 89,
• Fig. 4 illustrates another embodiment of a tunable drop filter 90
• the tunable 5 drop filter 90 includes a plurality of tunable Bragg grating units 10, optically coupled in series to a port of an optical directing device 12, such as a 3-port circulator. At least one grating unit 10 is actuated to compress a respective grating element 14, and therefore, time a respective grating 14 to pass the desired optical channel(s) to be dropped from the optical input signal 11, while the other grating units are tuned to i o refl ect the remaining optical channels of the input signal , hi the operation of the drop filter 90, a first port 91 of the circulator 12 receives the input signal 11, having optical channels centered at wavelengths ⁇ ,X 2 , ...
• the input signal 11 may originate from a light source or tapped off an optical network (not shown).
• the circulator 12 15 directs the input signal 11 in a counter-clockwise direction to a second port 93 of the circulator, The input signal 11 exits the second port 93 and propagates through optical fiber 94 to grating elements 14 of the grating units 10.
• Each of the grating elements 14 are tuned or parked to pass corresponding optical channels of the input signal 11, effectively dropping the corresponding optical 2 o channels from the input signal,
• a select number of optical grating units are tuned to reflect the remaining optical channels of the input signal 11 to provide an optical signal 98, which does not include the dropped optical channels.
• each of the grating units 10 are respectively tuned or parked to pass an optical signal 95 having a optical channels centered at wavelengths ⁇ 2 , ⁇ 3 , while a 2 s select number of grating units are tuned to reflect the remaining channels centered at wavelengths ⁇ , ⁇ j, ... ⁇ .
• the tunable add filter 100 includes a plurality of tunable Bragg grating units 10 optically coupled in series to a port of an optical directing device 13, such as a 3-port circulator. At least one grating unit 10 is actuated to compress a respective grating element 14, and therefore, tune a respective grating 20 5 to reflect the desired optical channel(s) to be added to the optical input signal 11, while the other grating units are tuned to pass the optical channels of the input signal.
• a first port 101 of the circulator 13 receives the optical signal 102 to be added to the input signal 11.
• the added signal 102 has, for example, a single optical channel centered at wavelength that is o transmitted through optical fiber 103.
• the circulator 13 directs the added optical signal 102 in a clockwise direction to a second port 104 of the circulator,
• the added optical signal 102 exits the second port 104 and propagates through optical fiber 105 to grating elements 14 of the grating units 10, At least one grating element 14 is tuned to reflect the added signal 102 to be combined with the input signal 11.
• the grating elements 14 are tuned or parked to pass the optical channels of the input signal 11 and combine with the added optical signal 102 to provide an optical signal 109 having optical channels centered at wavelengths X ⁇ , ⁇ 2 , ... ⁇ > ? , u
• the combined optical light propagates back to the second port 104 of the circulator 13, which then directs the combined optical light to a third port 107 of the circulator 1,3 and through optical fiber 108 to provide the output signal 109, having optical channels centered at wavelengths ⁇ , ⁇ 2 , , . , X> ⁇ -
• Fig, 6 illustrates another embodiment of a tunable add filter 110.
• the tunable add filter 110 includes a plurality of tunable Bragg grating units 10, optically coupled in series to a port of an optical directing device 13, such as a 3-port circulator,
• the grating units 10 are actuated to compress respective grating elements 14, and s therefore, tune or park gratings 20 to pass the desired optical channel(s) to be added to the optical input signal 11, while the other grating units 10 are tuned to reflect and combine the channels of the input signal 11,
• a first port 111 of the circulator 13 receives the input signal 11 , having optical channels centered at wavelengths ⁇ ⁇ , ⁇ 3 , ... lo X N , that is transmitted through optical fiber 112.
• the input signal 11 may originate from a light source or tapped off an optical network (not shown).
• the circulator 13 directs the input signal 11 in a counter-clockwise direction to a second port 113 of the circulator.
• the input signal 11 exits the second port 113 and propagates through optical fiber 114 to the grating elements 14 of the grating units 10.
• a select number is of grating elements 14 are tuned to reflect the optical channels of the input signal 11 centered at wavelengths ⁇ i. ⁇ a, . , .
• the added signal 115 having an optical channel centered at wavelength ⁇ 2, are transmitted to the grating elements 14 of the grating units 10 through optical fiber 116, Each grating unit 10 is tuned or parked to pass the optical
• the combined optical signal propagates back to the second port 113 of the circulator 13, which then directs the combined optical light to a third port 117 of the 2S circulator 13 and through optical fiber 118 to provide the output signal 119, ha ⁇ ing optical channels centered at wavelengths ⁇ i ⁇ ., ... ⁇ ,
• the tunable add filter 120 is similar to the tunable add filter of FIG. 5, and therefore, like components have the same reference number,
• the tunable add filter 120 includes a plurality of tunable Bragg grating units 10 optically coupled in series to a port of an optical directing device 13, such as a 3-port circulator. At least one grating unit 10 is actuated to compress a respective grating element 14, and therefore, tune a respective grating 20 to reflect the desired optical channel(s) to be added to the optical input signal 11, while the other grating units 10 are tuned or parked to pass the remaining optical channels of the input signal 11,
• a first port 101 of the circulator 13 receives die added optical signal 102 to be added to the input signal 11 ,
• the added signal 102 may, for example, include a plurality of optical channels centered at wavelengths ⁇ , ⁇ 2 , ... ⁇ , any of which that may be added to the input signal 11.
• the added signal 102 is transmitted through optical fiber 103 to the circulator 13, which then directs the added optical signal 102 in a clockwise direction to a second port 104 of the circulator.
• the added optical signal 102 exits the second port 104 and propagates through optical fiber 105 to grating elements 14 of the grating units 10, At least one grating element 14 is tuned to reflect at least one optical channel of the added signal 102.
• one grating unit 10 may be tuned to reflect an optical channel centered at wavelength ⁇ 2 to provide a filtered added signal 109.
• the other grating elements are tuned or parked to pass the remaining optical channels of the added optical signal 102.
• the filtered added signal propagates back to the second port 104 of the circulator 13, which then directs the combined optical light to a third port 107 of the circulator 13 and through optical fiber 108 to provide the filtered added signal 109,
• the output signal 109 is then transmitted to an input port of an optical coupler 121.
• the input signal II having optical channels centered at wavelengths ⁇ , ⁇ 3 , ... ⁇ , are transmitted to a second input port of the optical coupler 121.
• the optical coupler 121 combines the filtered added signal 109 and the input signal 11 and provides a combined optical signal 122 at an output port of the coupler, wherein the combined output signal 122 includes a plurality of channels centered at wavelengths ⁇ , ⁇ 2 , ...
• add filter 120 of FIG. 7 adds a single channel to the input light 11, one skilled in the art will appreciate and recognize that more than one optical signal may be added provided the add filter has a corresponding number of grating units 10, or a single grating unit that has sufficient bandwidth to reflect adjacent optical 5 channels to be added.
• the tunable add filter 130 is similar to the tunable add filter 110 of FIG. 6, and therefore, like components have the same reference number.
• the tunable add filter 130 includes a plurality of tunable Bragg grating units 10 optically coupled in series to a port of an optical directing device 131, such as an optical lo coupler, Each of the grating units 10 are actuated to compress respective grating elements 14, and therefore, tune or park gratings 20 to pass the desired optical channel(s) to be added to the optical input signal 11.
• the added signal 115 may, for example, include a plurality of optical channels centered at wavelengths ⁇ , ⁇ 2 , . , > ⁇ s, any of s which that may be added to the input signal 11.
• the added signal 115 is transmitted to the grating elements 14 of the grating units 10 through optical fiber 116.
• Each grating unit 10 is tuned or parked to pass a selected optical channel(s) of the added signal 115 to be added to the input signal 11.
• each grating unit 10 may be tuned to pass an optical channel at wavelength ⁇ j to provide a filtered added signal
• the filtered added signal 132 is then transmitted to an input port of an optical coupler 131 through optical fiber 114.
• the optical coupler 131 combines the filtered added signal 132 and the input signal 11 and provides a combined optical signal 133 at an output port of the optical coupler 131, wherein the combined output signal 133 includes a plurality of channels centered at wavelengths ⁇ , ⁇ 2 , ... X .
• add filter 130 of FIG. 8 adds a single channel to the input light 11, one skilled in the art will appreciate and recognize that more than one optical signal may be added.
• FIG, 9 illustrates a reconfigurable optical add/drop multiplexer (ROADM) 1 0 that effectively combines the tunable drop filter 80 of FIG. 3 and the tunable add filter 100 of FIG, 5, wherein a single series of grating units 10 are used to both drop a selected optical channel and add a selected optical channel, as discussed hereinbefore , Components similar to the drop filter 80 of FIG. 3, the add filter 100 of FIG. 5 and the ROADM 140 of FIG. 9 have the same reference number, As shown in FIG, 9, a pair of grating units 10 are tuned to reflect optical channels centered at wavelengths , > while the other gratings units are tuned to pass the remaining channels centered at wavelengths ⁇ i A .
• ROADM reconfigurable optical add/drop multiplexer
• the output signal 109 includes optical channels centered at ⁇ , ⁇ 2 , ⁇ 4, ... ⁇ jj.
• FIG. 10 illustrates a reconfigurable optical add/drop multiplexer (ROADM) 150 that effectively combines the tunable drop filter 80 of FIG. 3 and the tunable add filter 110 of FIG, 6, wherein the add filter 110 is optically connected in series with the drop filter 80,
• ROADM reconfigurable optical add/drop multiplexer
• a pair of grating units 10 of the drop filter 80 are tuned to reflect optical channels centered at wavelengths ⁇ a, ⁇ 3 , while the other gratings units are tuned to pass the remaining channels centered at wavelengths ⁇ , ⁇ 4 , ... ⁇ > ⁇ .
• the grating units 10 of the add filter 110 are tuned to pass the added signal 115, having an optical channel centered at ⁇ 2 . Consequently, the ROADM 150 drops optical channels centered at wavelengths ⁇ 2 , ⁇ 3, and adds the added optical signal 115 having a channel centered at wavelengths
• the output signal 119 therefore, includes optical channels centered at ⁇ , ⁇ 2 , ⁇ 4 , , , , ⁇ .
• FIG. 11 illustrates a reconfigurable optical add/drop multiplexer (ROADM)
• the add filter 100 of FIG. 5 is optically connected in series with the drop filter 90.
• the drop and add filters 90,100 functions substantially the same, as discussed hereinbefore.
• Components similar to the drop filter 90 of FIG. 4, the add filter 100 of FIG. 5 and the ROADM 1 0 of FIG. 11 have the same reference number.
• each of the grating units 10 of the drop filter 90 are tuned to pass optical channels centered at wavelengths ⁇ 2 ,X 3 ⁇ while the other gratings 5 units are tuned to reflect the remaining channels centered at wavelengths ⁇ , ⁇ 4, , .. ⁇ ,
• the grating units 10 of the add filter 100 are tuned to reflect the added signal 102, having an optical channel centered at ⁇ 2 . Consequently, the ROADM 160 drops optical channels centered at wavelengths ⁇ Xs, and adds the added optical signal 102 having a channel centered at wavelengths ⁇ 2 .
• the output signal 108 therefore, in includes optical channels centered at X;, ⁇ -,. ⁇ *, ... >w.
• FIG, 12 illustrates a reconfigurable optical add/drop multiplexer (ROADM) 170 that effectively combines the tunable drop filter 90 of FIG, 4 and the tunable add filter 110 of FIG. 6, wherein the add filter 110 is optically connected in series with the drop filter 90.
• the drop and add filters 90,110 functions substantially the same, as is discussed hereinbefore, Components similar to the drop filter 90 of FIG. 4, the add filter 110 of FIG, 6 and the ROADM, 170 of FIG, 12 have the same reference number.
• each of the grating units 10 of the drop filter 90 are tuned to pass optical channels centered at wavelengths ⁇ a. ⁇ a, while the other gratings units are tuned to reflect the remaining channels centered at wavelengths , , , , , ⁇ .
• Each of the grating units 10 of the add filter 1 10 are tuned to pass the added signal
• the ROADM 170 drops optical channels centered at wavelengths X 2 .X., and adds the added optical signal 115 having a channel centered at wavelengths ⁇ 2 , The output
• 25 signal 119 therefore, includes optical channels centered at ⁇ , ⁇ 2 , ⁇ t, ... ⁇ n,
• FIG. 13 illustrates a reconfigurable optical add/drop multiplexer (ROADM) 170 is substantially similar to he ROADM 160 of FIG, 12, which effectively combines the tunable drop filter 90 of FIG, 4 and the tunable add filter 110 of FIG. 6. Effectively, the ROADM has substituted the pair of 3-port circulators 12, 13 with a single 4-port circulator 181.
• the ROADM 180 of FIG. 13 operates substantially the same as the ROADM 170 of FIG. 12, as discussed hereinbefore.
• Components similar to the drop filter 90 of FIG.4, the add filter 110 of FIG. 6 and the ROADM 170 of FIG, 12 have the same reference number.
• the present invention also contemplates other ROADM configurations by optically connecting in series in various combinations of any one of the tunable drop filters 80,90 of FIGs. 3 and 4 respectively, with any one of the tunable add filters 120,130 of FIGs. 7 and 8 respectively.
• the grating units 1 are interconnected to a 4-port circulator, one will appreciate that it is within the scope of the present invention that any other optical directing device or means may be substituted for the circulator 12,13, such as an optical coupler, optical splitter or free space.

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• 2001
  • 2001-03-06 WO PCT/US2001/007165 patent/WO2001067137A2/en not_active Application Discontinuation
  • 2001-03-06 EP EP01937156A patent/EP1261888A2/en not_active Withdrawn
  • 2001-03-06 AU AU2001262920A patent/AU2001262920A1/en not_active Abandoned
  • 2001-03-06 CA CA002402309A patent/CA2402309A1/en not_active Abandoned
  • 2001-03-06 JP JP2001566055A patent/JP2003530586A/ja active Pending
  • 2001-03-06 KR KR1020027011705A patent/KR20030034050A/ko not_active Application Discontinuation

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