OPTICAL COMPONENT MOUNTING AND INTERCONNECT APPARATUS
TECHNICAL FIELD This invention relates to optoelectronic modules, and, more particularly, to subassemblies for mounting optical components in optoelectronic modules.
BACKGROUND ART ' In optical-to-electrical and electrical-to-optical (hereinafter "optoelectronic") modules used in the various communications fields, one of the most difficult problems that must be solved is the electrical interconnection of the various components and the shielding of the module to prevent radiation, (e.g., electromagnetic interference
(EMI)) into or out of the module. Providing this efficient interconnection and shielding requires very precise assembly procedures. Here it will be understood by those skilled in the art that the term "light", as used throughout this disclosure, is a generic term which includes any electromagnetic radiation that can be modulated and transmitted by optical fibers or other optical transmission lines.
Much of the optoelectronic module fabrication difficulty and expense is due to mounting and shielding difficulties of optical components, such as lasers, light emitting diodes, photodiodes, etc. Generally, there are two types of lasers that are used in optoelectronic modules, edge emitting lasers and surface emitting lasers. Edge emitting lasers emit light in a path parallel to the mounting surface while surface emitting lasers emit light perpendicular to the mounting surface. The light from either of the lasers must then be directed into an optical fiber for transmission to a remotely located, light receiver (i.e., a photodiode or the like).
Lens systems are used at both ends of the optical fiber to direct light from a light-generating component
into the optical fiber and to direct light from the optical fiber onto a light-sensing component. The apparatus used to mount the optical components and the lens systems can have a substantial effect (i.e. cost, complexity, operating life and characteristics, etc.) on the construction of the optical systems and the assembly procedures for the optical systems. Also, the mounting structure for the optical components and the lens system must be very rugged and stable so that alignment is not disturbed by use or temperature changes. Further, the entire module must be shielded from external signals and the like to prevent radiation to other external devices or modules .
It would be highly advantageous, therefore, to remedy the foregoing and other deficiencies inherent in the prior art .
Accordingly, it is an object the present invention to provide new and improved optical component mounting and interconnect apparatus.
DISCLOSURE OF THE INVENTION Briefly, to achieve the desired objects of the instant invention in accordance with a preferred embodiment thereof, optoelectronic component mounting and interconnect apparatus are disclosed. The apparatus includes an optoelectronic mounting plate with a substantially parallepiped-shaped base plate having opposed major surfaces and opposed edges extending between the major surfaces. A plurality of electrical contact pads are positioned on one of the major surfaces and electrically insulated from each other with one of the electrical contact pads being designed to have an optoelectronic device physically and electrically mounted thereon. One of the opposed edges is formed to mount the optoelectronic mounting plate on a supporting surface.
In a preferred embodiment, a support plate is physically attached to the opposed edge designed for that purpose. The support plate has electrical traces electrically thereon, which are connected to at least some of the electrical contact pads. Also, in one preferred embodiment the optoelectronic component is a laser that is physically and electrically connected to one of the electrical contact pads with a second terminal of the laser connected to a second contact pad by wire bonding or the like.
BRIEF DESCRIPTION OF THE DRAWINGS
The foregoing and further and more specific objects and advantages of the instant invention will become readily apparent to those skilled in the art from the following detailed description of a preferred embodiment thereof taken in conjunction with the drawings, in which:
FIG. 1 is a sectional view of an optical/electrical module in accordance with the present invention; FIG. 2 is a sectional view of optical component mounting plate in accordance with the present invention;
FIG. 3 is a perspective view of the optical component mounting plate illustrated in FIG. 2;
FIG. 4 is an exploded view of the optical component mounting plate and a support plate;
FIG. 5 is an exploded view in perspective of a package assembly in accordance with the present invention;
FIG. 6 is a side elevational view of the optical component mounting plate fixedly attached to the support plate with a monitor photodiode positioned on the support plate;
FIG. 7 is a side elevational view of the optical component mounting plate fixedly attached to the support plate with the monitor photodiode positioned on the mounting plate;
FIG. 8 is a simplified sectional view of another embodiment of a package assembly in accordance with the present invention;
FIG. 9 is a sectional view of a package assembly including an optical component mounting plate and support plate assembly with a TO window cap in accordance with the present invention;
FIG. 10 is a simplified sectional view of a module including the package assembly illustrated in FIG. 9; FIG. 11 is a sectional view of another embodiment of a package assembly in accordance with the present invention;
FIG. 12 is a sectional view of another embodiment of the package assembly in accordance with the present invention;
FIG. 13 is a sectional view of another embodiment of a package assembly in accordance with the present invention;
FIG. 14 is a sectional view of another embodiment of a package assembly in accordance with the present invention; and
FIG. 15 is a sectional view of another embodiment of a package assembly in accordance with the present invention.
BEST MODES FOR CARRYING OUT THE INVENTION
Referring to FIG. 1, a sectional view of either an optical-to-electrical or electrical-to-optical
(hereinafter referred to as optoelectronic) module 10 in accordance with the present invention. It will be understood by those skilled in the art that modules of the type discussed herein generally include a pair of channels, one of which receives electrical signals, converts the electrical signals to optical (light) beams by way of a laser or the like and introduces them into one
end of an optical fiber, which then transmits the modulated optical beams to external apparatus.
The second channel of the module receives modulated optical beams from an optical fiber connected to the external apparatus, conveys the modulated optical beams to a photo diode or the like, which converts them to electrical signals. In the following description, the apparatus and methods can generally be used in either of the channels but, since the optical portions of the two channels are substantially similar, only one channel will be discussed with the understanding that the description applies equally to both channels.
Module 10 of FIG. 1 includes a receptacle assembly 11 and an optoelectronic package assembly 12 aligned and affixed together, as will be disclosed in more detail below. Receptacle assembly 11 is designed to receive an optical fiber 14 in communication therewith, in a manner that will become clear presently. While optical fiber 14 is illustrated as a bare, unsupported fiber for simplicity, it will be understood that optical fibers are generally terminated in a ferrule or other structure specifically designed for plugging into receiving openings and that such structures are intended to be included herein. In this embodiment, optical fiber 14 is a single mode fiber including a glass core 15 and a cladding layer 16. Receptacle assembly 11 includes an elongated cylindrical ferrule 20 defining a fiber receiving opening 21 at one end and a mounting flange 22 at the opposite end. Ferrule 20 has a radially outward directed step 24 formed in the outer periphery to operate as a stop for a resilient sleeve 25. Sleeve 25 has an inwardly directed flange formed adjacent one end so as to engage step 24 and prevent relative longitudinal movement between ferrule 20 and sleeve 25. Sleeve 25 also includes radially outwardly directed ribs or protrusions 26 in the outer periphery
which are designed to frictionally engage the inner periphery of a mounting housing 30. Thus, to easily and conveniently mount module 10 in housing 30, ferrule 20 with sleeve 25 engaged thereover is press-fit into the circular opening in housing 30 and frictionally holds module 10 in place. Preferably, sleeve 25 is formed, completely or partially, of some convenient resilient material and may be electrically conductive or non- conductive as required in the specific application. Progressing from end 21 toward end 22, ferrule 20 has two radially outwardly directed steps 32 and 33. Step 32 provides a surface or stop for the mounting of an optical spacer 35 and step 33 provides a surface or a stop for the positioning of an optical lens assembly 36. In this preferred embodiment, lens assembly 36 is formed of plastic and may be, for example, molded to simplify manufacturing of module 10.
It should be understood that the term "plastic" is used herein as a generic term to describe any non-glass optical material that operates to transmit optical beams of interest therethrough and which can be conveniently formed into lenses and the like. For example, in most optical modules used at the present time the optical beams are generated by a laser that operates in the infra-red band and any materials that transmit this light, including some oxides and nitrides, come within this definition.
Lens assembly 36 defines a central opening for the transmission of light therethrough from an end 37 to an opposite end 38. A lens 39 is integrally formed in the central opening a fixed distance from end 37. Lens assembly 36 is formed with radially outwardly projecting ribs or protrusions in the outer periphery so that it can be press-fit into ferrule 20 tightly against spacer 35. Thus, lens assembly 36 is frictionally held in place within ferrule 20 and holds spacer 35 fixedly in place. Also, lens 39 is spaced a fixed and known distance from
spacer 35. In this preferred embodiment, optical fiber 14 in inserted into ferrule 20 so that glass core 15 buts against spacer 35, which substantially reduces or suppresses return reflections. Optoelectronic package assembly 12 includes a base or support plate 40 and a mounting plate 42 positioned thereon. One or more spacer rings 43 may be positioned on plate 42 to provide sufficient distance for components mounted thereon. In this example a laser 45 is mounted on the upper surface of mounting plate 42 and positioned to transmit light generated therein to a lens block 46 along a z-direction in an x-y-z coordinate system as illustrated in FIG. 1. Alternatively, laser 45 could be a photodiode or the like. Lens block 46 is mounted on mounting plate 42 by some convenient means, such as outwardly extending ears (not shown) .
A ring 47 is positioned on spacer rings 43 and a cap or cover 48 is affixed to ring 47. Generally, the entire assembly, including plate 40, mounting plate 42, spacer rings 43, ring 47 and cover 48 are fixedly attached together by some convenient means, such as welding, gluing, etc. so that laser 45 is enclosed in a hermetically sealed chamber. However, a hermetic seal is not necessary in many embodiments in which the laser or photodiode used is either separately sealed or is not sensitive to atmospheric conditions.
A window 50 is sealed in cover 48 so as to be aligned with lens block 46. Lens block 46 redirects light from laser 45 at a ninety degree angle out through window 50 and may include one or more lenses or optical surfaces, as will be explained in more detail below. Further, lens block 46 may be molded from plastic for convenience in manufacturing .
Optoelectronic package assembly 12 is affixed to receptacle assembly 11 with flange 22 of ferrule 20 butting against the upper surface of cover 48. Further,
optoelectronic package assembly 12 is optically aligned with receptacle assembly 11 so that light from laser 45 is directed into core 15 of optical fiber 14. This alignment can be accomplished in different ways but one reliable method is known as active alignment. In this process, laser 45 is activated and receptacle assembly 11 is positioned approximately over optoelectronic package assembly 12. The light in optical fiber 14 is measured and the alignment is adjusted for maximum light. When maximum light is measured alignment has been achieved and receptacle assembly 11 is fixed to optoelectronic package assembly 12 by some convenient means, such as welding or adhesive .
Array processing is critical to minimize manufacturing cost. Previous optical solutions have the laser oriented 90 degrees to the optical fiber, so a mirror/lens system is required to redirect the light as illustrated in FIG. 1. The problem with this arrangement is the number of degrees of freedom available to redirect the light into an optical fiber. The more degrees of freedom (DOF) in the optical system, the more difficult it is to align the optical system. Further, some of the degrees of freedom are coupled. For example, when trying to align an optical block, movement along one DOF cannot be differentiated from movement along another DOF. In particular, a translation along the z-axis has the same effect as rotation along θx (See FIG. 1) .
One solution is to rotate the laser so that it emits light directly into the optical fiber. This eliminates the number of degrees of freedom and makes optical alignment between the laser and the optical fiber easier and cheaper. Further, by eliminating certain degrees of freedom, the coupling effect is minimized. Also, the system can be designed to use ball lenses which are low cost and commonly found in optical systems.
Better thermal stability can also be achieved because of the fewer DOF' s and because the thermal mismatch is substantially along the z-axis, which is not as sensitive as the thermal mismatch along the x- and y-axes. Turning now to FIGS. 2 and 3, sectional and perspective views of an optical component mounting plate
49 in accordance with the present invention are illustrated. In this example, for purposes of explanation, mounting plate 49 is used to mount a laser but it will be understood that other optoelectronic components may be included in addition to or instead of the laser. In this embodiment, mounting plate 49 includes a substantially parallepiped or box-shaped base plate 62 and contact pads 52, 54, and 56 positioned on at least one major surface of base plate 62. Contact pads 52, 54, and 56 are electrically isolated from each other, as illustrated in FIG. 3, and each include connected to a conductive (generally plated or metalized) castellations
61 in opposed upper and lower edges of base plate 62 extending from one major side of base plate 62 to the opposed major side. It will be understood that base plate
62 could be formed of any convenient relatively stiff dielectric or insulative material, such as ceramic or the like and contact pads 52, 54, and/or 56 can include gold (Au) , gold-tin (AuSn) , platinum (Pt) , or the like to provide suitable electrical conductivity.
In this embodiment, base plate 62 is designed to allow the placement of electrical components, such as a resistor 58 and/or a laser 60, positioned thereon. It will be understood that laser 60 can include a semiconductor laser or a similar light emitting device, wherein laser 60 can be placed active side up or down. Further, it will be understood that other electrical components could be used and the use of a resistor and laser in this embodiment is for illustrative purposes only.
In this embodiment, resistor 58 is positioned on and in electrical communication with contact pad 52 and laser
60 is positioned on and in electrical communication with contact pad 54. Also, one side of laser 60 is connected to one side of resistor 58 for receiving DC power and to contact pad 56 for receiving RF signals. It will be understood that while three contact pads (i.e. contact pads 52, 54, and 56) are illustrated in this embodiment for simplicity and ease of discussion, it is anticipated that any number of contact pads could be formed depending on the desired application.
In the preferred embodiment, laser 60 is positioned over a castellation 61 such that light 51 emitted from laser 60 can be directed in the plane of the paper (e.g. an edge emitting laser, as illustrated in FIG. 2) or into the paper (a vertical cavity surface emitting laser) without substantial interference from base plate 62. Thus, it can be seen that laser 60 can be either an edge emitting laser or a vertical cavity surface emitting laser. A lower edge 57 (in FIG. 2) of base plate 62 is capable of being positioned on a support (not shown) and laser 60 is positioned proximate to an upper edge 59 of base plate 60. Also in the preferred embodiment, contact pads 52, 54, and 56, and the electrical components (i.e. resistor 58 and laser 60) are designed and positioned such that bonding wires can be conveniently used to electrically connect the various components.
For example, in some embodiments, it is desirable to electrically connect resistor 58 to laser 60 through a bonding wire 53. Further, in some embodiments, it is desirable to electrically connect laser 60 to contact pad 56 through a bonding wire 55. It will be understood that multiple bonding wires could be used in some embodiments and that the use of a single bonding wire 53 and a single bonding wire 55 in this embodiment is for simplicity and ease of discussion.
Turn now to FIG. 4 which illustrates an exploded view of mounting plate 49 and a support plate 64. Support plate 64 can be formed of any convenient supporting material, such as a ceramic, and can include conductive lines and vias. For example, in the preferred embodiment, support plate 64 includes contacts 65, 66, 67, 68, and 69 wherein contacts 65 and 68 are electrically connected through a conductive via 70 or conductive castellation.
Mounting plate 49 can be fixedly placed on support plate 64 such that the contact pads on mounting plate 49 are aligned and in electrical communication with the contact pads on support plate 64 for minimum connector length and, therefore, to provide high speed operation.
For example, in FIG. 4, a contact pad 63 (which can be, for example, a current return path) positioned on base plate 62 is aligned with contact pad 66 and contact pad 52 is aligned with contact pad 68. Mounting plate 49 can be attached and fixedly held to plate 64 using any convenient means, such as glue, an epoxy, solder, or the like. It will be understood that the electrical connections and physical placement of contacts 65, 66, 67, 68, and 69 and via 70 are shown for illustrative purposes only and other configurations are possible.
Turn now to FIG. 5 which illustrates an exploded view in perspective of an optoelectronic package assembly 71 in accordance with the present invention. In this embodiment, optoelectronic package assembly 71 includes support plate 64 fixedly attached to mounting plate 49 as discussed previously. A monitor photodiode 72 is positioned on the upper surface of support plate 64 to monitor the power output of laser 60. Monitor photodiode 72 can be positioned on support plate 64 as illustrated in FIGS. 5 and 6 or monitor photodiode 72 can be positioned on mounting plate 49 as illustrated in FIG. 7 by using an epoxy 34 or a similar material. Epoxy 34 can be formed to substantially increase the optical coupling efficiency of
laser 60 and monitor photodiode 72. Monitor photodiode 72 is positioned to detect light 44 emitted from laser 60.
Light 44 can be emitted directly into monitor photodiode
72 (See FIG. 7) or light 44 can be reflected off another surface, such as base plate 62, (See FIGS. 5 and 6) and into monitor photodiode 72.
In this embodiment and with reference to FIG. 5, an optical focusing system, which in this example includes a lens support 74 with a lens support structure 73, is positioned proximate to laser 60. Lens support 74 and lens support structure 73 are capable of holding a focusing lens (not shown) fixedly in place relative to laser 60 to interact with light 51. The focusing lens can be, for example, a ball grid array or similar lens which could be held in place using a vacuum system (i.e. vacuum lens holder), epoxy, or the like.
Here it will be understood that lens support structure 73 and lens support 74, or other lens structures, can be formed as an integral part of mounting plate 49 and or support plate 64 (FIG. 4), or any of the other structures described herein. Forming the lens structure as a part of the laser mounting structure (e.g. mounting plate 49 or support plate 64 in FIG. 4) can substantially facilitate focusing of light from the laser into an optical fiber. This configuration can be especially useful in end fire' designs, i.e. those that have the optical axis of the laser and the optical fiber on axis. This arrangement has the immediate benefit that the lens and laser structure are mechanically rigid and locally associated with each other, compared to other arrangements where the lens and laser are mounted on separate structures. Misalignments due to thermal mismatches or mechanical distortions will have little effect on the critical coupling between the lens and the laser, where typically a one micron movement will result in 50% of the power launched into the fiber being lost.
In the preferred embodiment, a lid 76 with a window
75 is positioned proximate to lens support 74 to provide hermetic sealing of laser 60 with support plate 64.
However, it will be understood that laser 60 is not required to be hermetically sealed in some applications and the use of hermetic sealing in this embodiment is for illustrative purposes only.
Turn now to FIG. 8 which illustrates an embodiment of a module 82. As illustrated in FIG. 8, mounting plate 49 can be positioned on spacer ring 43 in a manner similar to module 10 illustrated in FIG. 1. In this embodiment, laser 60 is capable of emitting light 51 directly into optical lens system 36 as illustrated. Hence, lens block 46 (See FIG. 1) is no longer needed to redirect light 51 and, consequently, fewer components are necessary.
Turn now to FIG. 9 which illustrates a optoelectronic package assembly 80 with a TO window cap 83 positioned on the upper surface of support plate 64. TO window cap 83 includes a window 81 which allows light 51 to travel therethrough. TO window cap 83 can be fixedly attached to support plate 64 using resistance welding (projection welding), laser welding, soldering, or the like. In this embodiment, contact 63 on mounting plate 49 is electrically connected to a contact pad 85 on the rear or lower surface of support plate 64 through a conductive via 84 and contact 54 on mounting plate 49 is electrically connected to a contact pad 87 on the rear or lower surface of support plate 64 through a conductive via 86. Pads 85 and 87 provide outside or external electrical communication with contacts 63 and 54, respectively. It will be understood that package assembly 80 can include substantially any desired number of contact pads and the use of two contact pads (i.e. contact pads 85 and 87) in this embodiment is for illustrative purposes only. Turn now to FIG. 10 which illustrates an optoelectronic module 90 which includes package assembly
80 with TO window cap 83. It will be understood that module 80 is similar in design and operation to module 10 illustrated in FIG. 1. However, other configurations are possible. Module 90 is designed so that package assembly 80 can be aligned with optical lens assembly 36 and held fixedly in place.
Turn now to FIG. 11 which illustrates another optoelectronic package assembly 100 in accordance with the present invention. In this embodiment, mounting plate 49 is positioned on support plate 64, as previously described, and a plurality of conductive vias 106 extend from the upper surface of support plate 64 to the lower or rear surface. A ring 101 is positioned on the upper surface of support plate 64 and extends around the outer periphery. A ring 102 is positioned on ring 101, and a ring 103 is positioned on ring 102 to form an enclosure 99. Enclosure 99 is formed to substantially surround mounting plate 49 as illustrated. A lid 104 with window
81 is positioned adjacent to ring 103 to provide a path for light 51 to flow into or out of enclosure 99. Here it will be understood that lid 104 may be formed of material transparent to the wavelength of light of interest (i.e. light 51) so that a separate window need not be included, if desired, It will be understood that rings 101, 102, and 103 can be formed of Kovar or a similar material with suitable thermoelectric properties. Further, it will be understood that package assembly 100 can include one or more rings and the use of three rings (i.e. rings 101, 102, and 103) in this embodiment is for illustrative purposes only. In addition, it will be understood that in the preferred embodiment rings 101, 102, and 103 are generally elliptical in shape. However, rings 101, 102, and 103 can have other suitable shapes, such as rectangular or the like.
In the preferred embodiment, vias 106 are formed to provide electrical communication between laser 60 and, for example, a flex lead 107. Flex lead 107 is electrically connected to a PCB board 108 which typically includes control electronics or the like. Further, it will be understood that in some embodiments, vias 106 can be formed to fit small diameter spring loaded contact pins if desired.
Turn now to FIG. 12 which illustrates a package assembly 110 in accordance with the present invention. In this embodiment, electrical communication between laser 60 and PCB board 108 is accomplished by forming a contact 106 on the upper surface of support plate 64, so as to extend between enclosure 99 and the exterior, so that contact 106 is positioned between support plate 64 and ring 101. However, it will be understood that contact 106 can include other configurations, such as one or more mid- layers in a multi-layer laminated ceramic structure (e.g. support plate 64). Flex lead 107 can then be electrically connected to contact 106 using solder or the like.
Turn now to FIG. 13 which illustrates another embodiment of a package assembly 111 that utilizes rings 101, 102, and 103. In this embodiment, an opening 114 is formed through support plate 64. Mounting plate 49 is designed to extend through opening 114 with an upper end positioned in enclosure 99 and a lower end extending externally of enclosure 99. Mounting plate 49 can be held fixedly in place using an epoxy solder, a braze or glass frit seal, or the like, such that light 51 is emitted through window 81. In this embodiment, base plate 62 is designed such that driver circuitry 105 can be positioned directly on contact 106. Base plate 62 can also be designed such that driver circuitry 105 can be positioned on contact 106 and, in addition or alternatively, a flex lead 107, electrically connected to a PCB board 108 which typically includes control electronics or the like, can be
attached to contact or contacts 106. Because of the novel construction of package assembly 111, flex lead 107 can be made shorter to reduce noise and increase speed.
Turn now to FIG. 14 which illustrates a package assembly 112 that utilizes TO window cap 83 with end 115 and side 116. In this embodiment, an opening 114 is formed through a header material layer 109, which can include Kovar, ceramic, or a similar material. Mounting plate 49 is positioned to extend through opening 114 and into the enclosure formed by TO window cap 83 such that light 51 is directed through window 81 positioned in end 115. Mounting plate 49 can be held fixedly in place using an using an epoxy solder, a braze or glass frit seal, or the like, to provide hermetic sealing. In this embodiment, base plate 62 is designed such that driver circuitry 105 can be positioned directly on contact 106. Further, contact 106 is electrically isolated from TO window cap 83 to reduce cross-talk and noise in package assembly 112. In addition or alternatively flex lead 107, electrically connected to a PCB board 108 which typically includes control electronics or the like, can be attached to contact or contacts 106. Thus, flex lead 107 can be made shorter to reduce noise and increase speed.
Turn now to FIG. 15 which illustrates a package assembly 113 that utilizes TO window cap 83 with end 115 and side 116. In this embodiment, mounting plate 49 is positioned on one major surface of a supporting plate 64, generally as described above. TO window cap 83 is mounted on the major surface of supporting plate 64 so as to surround and hermetically seal optoelectronic components mounted on mounting plate 49. A window 81 is formed in side 116 of TO window cap 83 so as to be aligned with any optoelectronic components mounted on mounting plate 49. In this embodiment, supporting plate 64 is designed such that driver circuitry 105 can be positioned directly on a contact 106 on the major surface. In addition or
alternatively, a flex lead 107, electrically connected to a PCB board 108 which typically includes control electronics or the like, can be attached to contact or contacts 106 external to the enclosure formed by TO window cap 83. Thus, flex leabl 107 can be made shorter to reduce noise and increase speed.
Thus, new and improved optical component mounting and interconnect apparatus has been disclosed. The optical component mounting and interconnect apparatus allows light to be directed directly into an optical fiber system so that optical alignment is substantially simplified. Further, several embodiments of the optical component mounting and interconnect apparatus positioned in package modules have been disclosed wherein the apparatus allows high speed electrical communication of the laser with outside control circuitry.
Various changes and modifications to the embodiments herein chosen for purposes of illustration will readily occur to those skilled in the art. To the extent that such modifications and variations do not depart from the spirit of the invention, they are intended to be included within the scope thereof which is assessed only by a fair interpretation of the following claims.
Having fully described the invention in such clear and concise terms as to enable those skilled in the art to understand and practice the same, the invention claimed is :