Abstract:
A method and structures for protectively enclosing and sealing optoelectronic modules having emitter or detector diode arrays aligned with optical fiber facets in optoelectronic transmitters and receivers. A non-hermetic enclosure provides mechanical protection of the components during alignment and assembly of the module. A substantially hermetic enclosure provides additional protection of optoelectronic components against airborne contaminants or moisture. The protective enclosures physically encompass the diode array chip with its delicate wire bonds and also provide a liquid containment dam for easier application of resin for protective encapsulation of the diode array chip. Dual resin encapsulation may include a first resin layer chosen for transparency and a harder setting covering layer. These protective variants can be implemented in different combinations offering varying degrees of protection of the optical components.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     1. Field of the Invention  
         [0002]     This invention pertains generally to the field of optoelectronic data transmitter/receiver modules and in particular concerns protective sealing of optical assemblies in such modules.  
         [0003]     2. State of the Prior Art  
         [0004]     Optoelectronic transmitter/receiver modules are used for communicating over optical fiber links as opposed to electrical cables. Optical transmission has advantages over electrical conductors, such as relative immunity from interference, low loss transmission over long distances, and high data rate capacity, among still others. Optoelectronic devices serve to interface electronic circuits, in which the signals are generated or processed, to optical fiber cables for transmission to other electronic circuits.  
         [0005]     Optoelectronic transmitters convert electrical signals to optical signals for transmission via optical fiber, while optoelectronic receivers perform the opposite operation of converting optical signals received via optical fiber to electrical signals. A transmitter and a receiver may be packaged together in a transceiver module. Multichannel optoelectronic modules transmit and receive signals simultaneously over multiple parallel fibers or channels, and depending on the application, four, eight or more parallel data channels may be used. For example, a four channel transceiver module requires eight optical fibers, four fibers for transmission and four fibers for reception. Flat ribbon cable is commercially available in different widths containing varying numbers of optical fibers for interconnecting multichannel modules.  
         [0006]     Optoelectronic modules, whether transmitter, receiver or transceiver modules, are usually packaged in a module housing containing a printed circuit board on which are mounted electronic circuits and devices for electronic signal processing and an optical assembly which interfaces the electronic circuits of the module to an optical fiber link. This optical assembly normally includes a semiconductor diode array mounted in optical alignment with the fiber facets of an optical fiber array supported in a fiber block. In a transmitter module the diode array includes light emitter diodes which are typically laser diodes, although LEDs may be substituted in some applications. The laser or LED diodes convert drive current supplied by the module&#39;s electronic circuits to a light output which is carried by the optical fibers. In a receiver module the diode array includes photo detector diodes. Light signals delivered by the optical fibers illuminate the photo detector diodes which convert these light signals to electrical signals. Transceiver modules have both a laser diode array chip and a photo detector diode array chip, and each chip is aligned with a corresponding subset of the fiber facets of the fiber block. For simplicity of explanation, the following description is limited to an optoelectronic module with a single diode array, which may be either a PE array or a PD array unless otherwise stated, and for convenience may be referred to as a PD/PE array.  
         [0007]     Each diode array, whether emitter or detector, is typically manufactured on a single semiconductor chip where the diodes are arranged on the chip as an evenly spaced linear array on a common surface or edge of the chip. Due to differences in manufacturing processes, laser diode arrays and photo detector arrays are made on separate chips. These semiconductor chips are small and delicate, and are supported by bonding, as with epoxy adhesive, to a submount of appropriate material, such as aluminum nitride or aluminum oxide. The submount also carries electrical conductors, usually applied as printed circuit traces, for interconnecting the diodes of the array to the electronic circuits of the optoelectronic module. This interconnection is made by wire bond connections of very thin wire between the diode array chip and the conductive traces on the submount. The wire bonds can be made with conventional wire bonding machines. Each wire bond is a small arc of bare wire welded at each end to the electrodes or terminals which are electrically connected by the wire bond. The arc of the wire bond rises to some height above the electrodes, the height depending on the particular wire bonding machine used.  
         [0008]     The optical fiber array of the module includes a number of relatively short fiber lengths supported between two substrates of the fiber block. Each fiber length of the fiber array terminates in an end facet on an end face of the fiber block. Each facet is illuminated by a corresponding light emitter diode (in a transmitter) or itself illuminates a corresponding photo detector diode (in a receiver). The opposite, outer ends of the optical fiber array are optically coupled by industry standard optical connectors to an external optical fiber cable, such as a flat ribbon cable, which interconnects the optoelectronic module to another optoelectronic module.  
         [0009]     The diode array chip with its wire bonds is mechanically delicate and susceptible to mechanical damage or breakage while being handled in the process of alignment and assembly of the module. The diode chips are also vulnerable to degradation by airborne pollutants, while the fiber facets are adversely affected by condensation of moisture.  
         [0010]     Optoelectronic communications modules are used in a wide range of operating environments, depending on the application. In some cases the equipment containing the modules is installed in protected, air conditioned rooms, where the modules are sheltered in a controlled environment and are readily accessible for maintenance and replacement if needed. In these cases a lesser degree of hardening and reliability of the modules is needed. In other applications, such as long haul communications, the modules may be installed in equipment exposed the outdoor environment in harsh climates, and in remote or difficult to access locations such as on mountaintops or undersea cable installations. In the latter cases, a high degree of hardening and reliability of the modules is desirable due to the high cost of repairs.  
         [0011]     For this reason, optoelectronic modules are often packaged in relatively costly, hermetically sealed module housings. Lower cost alternate solutions have been sought for protective sealing of optoelectronic modules, particularly for less critical applications. One lower cost technique has been to encapsulate the optoelectronic components in transparent resin. A coating of transparent resin is applied over the components and, after the resin sets and hardens, it provides a relatively durable, chemically and mechanically resistant encapsulating layer.  
         [0012]     A difficulty encountered in making such resin seals is that the resins tend to be fluid and runny in their initial uncured state, and when first applied to the optoelectronic components, the epoxy resin has a tendency to run off the component before hardening. Thicker paste resins have been used in a one step encapsulation process. Most paste resins, however, have inferior transparency and light transmission characteristics and may become too hard when set, which poses a risk of damage to the diode array chip and its delicate wire bonds. In the past this problem has been addressed by a two step encapsulation process. First, a thicker epoxy formulation, which itself may be undesirable as an encapsulating epoxy, is applied to the submount around the diode array chip to form a raised containment barrier or dam for the more fluid encapsulating epoxy resin. After the barrier epoxy has set, the more fluid encapsulating epoxy is applied over the component. This is an awkward, time consuming and labor intensive procedure, and a simpler, more expedient technique is needed.  
       SUMMARY OF THE INVENTION  
       [0013]     This invention discloses method and structures for protectively enclosing and sealing the optical assembly generally comprising the emitter or detector diode arrays and fiber facets in optoelectronic transmitters and receivers. The protective enclosures described can be implemented to different degrees of protection of the optical components. In one form of the invention a non-hermetic enclosure provides mechanical protection of the components during alignment and assembly of the module. In another form of the invention the enclosure may be substantially hermetic for additional protection of the optoelectronic components against airborne contaminants or moisture. The hermetic or non-hermetic enclosures, in addition to physically enclosing and protecting the diode array chip with its delicate wire bonds, also provides a liquid containment dam during application of sealing resin for protective encapsulation of the diode array chip, avoiding the need for the two step application of epoxy described in the preceding section. For still greater protection the resin encapsulation may include two resin layers, a first inner layer chosen for characteristics such as transparency or setting hardness or both, and an hard setting, second covering layer. These protective variants can be implemented in different combinations, such as a non-hermetic enclosure for mechanical protection of resin encapsulated components, or fully implemented protection including double layered resin encapsulation contained in a hermetic enclosure.  
         [0014]     In yet another form of the invention, a fluid containment dam is provided which encompasses the optical components to be encapsulated in resin so as to prevent run-off of the initially liquid sealing resin, but where the containment dam need not otherwise cover or fully enclose the optical components. In this embodiment, the containment dam may take the form of a wall supported on the submount and encompassing at least the diode array chip, and the wall has sufficient height to contain resin to a depth sufficient to submerge the diode array chip in the sealing resin.  
         [0015]     The protective and fluid containment structures described also facilitate the process of optically aligning and assembling the diode array chip to the fiber block during assembly of the optoelectronic modules and by increasing the contact area between the bonded elements of the optical assembly serve to strengthen the resulting assembly. Protective structures are disclosed which are suitable for edge emitting laser diode chips, surface emitting laser diode chips, LEDs, and photodetector diode chips. In the following descriptions, the term diode array refers to arrays of light emitting diodes, including laser diode array or LED arrays, or arrays photo detector diodes. References to laser diode arrays are interchangeable with photo detector diode arrays. In some embodiments reference is made to edge emitting laser diode arrays. Laser diodes are commercially available in edge emitting configurations and in surface emitting configurations. Photo detector diode arrays, on the other hand, are generally made on chip surfaces rather than along chip edges, such that structures described below in connection with surface emitting diodes are also suitable for use with photo detector array chips. Structures described for use with edge emitting diodes are primarily for edge emitting laser diode arrays only. It should be understood, however, that by appropriate mounting of the diode array chips to their submount, the optical assembly structures disclosed herein can be adapted for use with either edge emitting or surface emitting diodes or with photo detector diodes.  
         [0016]     Various embodiments of the invention are now summarized below.  
         [0017]     In one embodiment of this invention, the optoelectronic module has an optical fiber array terminating in fiber facets on an end face of an optical fiber block, a submount joined to the end face, and an edge emitting laser diode array bonded to the submount in optical alignment with the fiber facets. The diode array chip is electrically connected by wire bonds to conductors on the submount, which in turn are operatively connected to electronic circuits of the module. A protective cap is joined to either or both the submount and to the end face for enclosing the array including the wire bonds and a portion of the fiber block including the facets. The cap may be joined in hermetic sealing relationship to the submount and to the fiber block so as to define a chamber containing the diode array and the fiber facets. The cap has a cap bottom bonded to the submount and encompassing the diode array, and a cap end bonded to the optical fiber block and encompassing the fiber facets. The cap may be a one piece cap, or a two piece cap having a cap side wall portion and a separate cap cover bonded to the side wall portion. The diode array may be encapsulated in sealing resin substantially transparent to light wavelengths passing between the diode array and the fiber facets, such as silicone resin. The sealing resin may also encapsulate the fiber facets on the end face of the fiber block. The cap may have an injection hole for introducing the sealing resin in an initially fluid uncured state into the chamber such that cap serves as a containment dam for containing the initially fluid resin. The sealing resin may include layers of different resins, such as a relatively pliant inner resin layer encapsulating the diode array and a relatively hard outer resin layer covering the inner resin.  
         [0018]     In another embodiment of the invention, the optoelectronic module has optical fibers terminating in fiber facets on an end face of an optical fiber block, a surface emitting laser diode array or photo detector diode array bonded to a submount; and a spacer interposed between and bonded to the submount and to the end face for enclosing the diode array and a portion of the fiber block including the fiber facets. The diode array has a top surface which faces the fiber facets on the end face, and the diode elements of the array are arranged on the top surface with wire bonds between the top surface and the submount. The spacer has a spacer width between the submount and the fiber block sufficient to accommodate the combined height of the diode array and the wire bonds. The spacer may be open or may be a closed frame hermetically bonded to the submount and to the fiber block for defining a sealing chamber containing the diode array and the fiber facets. In either case the diode array and the wire bonds may be encapsulated in sealing resin substantially transparent to light transmissions between the diode array and the fiber facets. The spacer may have an opening for admitting the resin into the chamber, and the opening may be sealed with the resin thereby to seal the chamber.  
         [0019]     This invention also contemplates a method of sealing an optical assembly for use in an optoelectronic transmitter or receiver module, comprising the steps of providing an optical fiber block supporting one or more optical fibers each terminating in a fiber facet on an end face of the block to define a fiber facet array, providing a submount having a top surface and a side surface; bonding a diode array chip to the top surface of the submount; providing a cap having an end surface, affixing the cap to the submount, optically aligning the diode array with the fiber facet array, and bonding the submount to the optical fiber block. Preferably, the cap has an end surface and the cap end surface is also bonded to the fiber block.  
         [0020]     The combined submount side surface and the cap end surface provide a larger area of contact with the fiber block to facilitate optical alignment and better bonding of the substrate with the diode array to the fiber block with the fiber facets.  
         [0021]     The cap may have three side walls and a cap top, with the end face of the fiber block providing a fourth wall and the submount providing a bottom, thereby to define a chamber containing the laser diode array and the fiber facet array. The cap cooperates with the fiber block to define a fluid containment enclosure encompassing the diode array chip and the wire bonds; and the method may further comprising the step of applying liquid sealing resin in the fluid containment enclosure to encapsulate the diode array chip. The cap may have a hole through the cap top for admitting initially liquid resin into the chamber, and the hole may be sealed with resin.  
         [0022]     The cap may have a cap sidewall portion and a separate cap top, and the step of affixing may include the step of affixing the cap sidewall portion to the submount to thereby define with the end face a fluid containment enclosure for containing liquid epoxy resin applied to the diode array, and then affixing the cap top to the cap sidewall thereby to define the chamber.  
         [0023]     The method of this invention may also be understood as having the steps of providing an optical fiber block supporting a number of optical fibers each terminating in a fiber facet on an end face of the block to define a fiber facet array, providing a submount, bonding a diode array chip to the submount, affixing a containment dam to the submount for defining a fluid containment enclosure encompassing the diode array chip; assembling the submount, the containment dam and the optical fiber block with the diode array chip in optical alignment with the fiber facet array, and applying liquid sealing resin to encapsulate the diode array chip. The step of assembling may include bonding the containment dam between the submount and the fiber block, or bonding the containment dam to the submount and then bonding both the submount and the containment dam to the fiber block. The containment dam may have one or more end surfaces and the step of assembling comprises bonding the one or more end surfaces to the fiber block.  
         [0024]     The submount may have a side surface for bonding to the fiber block and the containment dam may have one or more end surfaces, such that the step of affixing comprises the step of aligning the one or more end surfaces in coplanar relationship with the side surface, and the step of bonding comprises bonding both the side surface and the one or more end surfaces to the fiber block, such as to the end face of the fiber block.  
         [0025]     The containment dam may cooperate with the optical fiber block to make a closed chamber containing the diode array and the fiber facet array. For example, the containment dam may feature a cap having three side walls and a cap top, the end face providing a fourth wall and the submount providing a bottom thereby to define a closed chamber containing the diode array and the fiber facets. The cap top may be unitary with the cap side walls, and a hole may be provided through the cap, such as through the cap top, for admitting the liquid sealing resin into the closed chamber. In the case where the cap has a cap side wall and a separate cap top, the step of affixing a containment dam may include the step of affixing the cap side wall to the submount and to the fiber block and thereby define the fluid containment enclosure. The method may further include the step of affixing a cap top to the cap sidewall thereby to define a closed chamber containing the diode array chip and the fiber facet array.  
         [0026]     The containment dam may be at least partly defined by a cap having a plurality of cap side walls and a cap top such that the cap cooperates with the optical fiber block to make a closed chamber containing the diode array and the fiber facet array. Alternatively, the containment dam may be at least partly defined by a spacer interposed between opposing surfaces of the substrate and the optical fiber block. The spacer may have first and second end surfaces, and in such case the step of affixing comprises the step of affixing the first of the end surfaces to the submount and the step of assembling comprises the step of bonding the second of the end surfaces to the optical fiber block, such as to the end face of the optical fiber block.  
         [0027]     The spacer can be a closed frame in which case the step of applying the liquid epoxy to the diode array is performed after affixing the spacer frame to the submount about the diode array and the wire bonds, and then performing the assembling step by bonding the frame to the fiber block.  
         [0028]     Also, the spacer may be a frame having a side opening through the frame and the step of applying liquid epoxy is performed after the aforementioned steps of affixing and assembling by introducing liquid epoxy through the side opening of the spacer frame. The side opening may then be sealed with epoxy resin.  
         [0029]     In more general terms the optoelectronic module of this invention has a housing module with electronic transmitter or receiver circuits in the housing module, an optical fiber block having optical fibers terminating in fiber facets on an end face of the block, an emitter/detector diode array mounted on a submount in optical alignment with the fiber facets and operatively connected to the electronic transmitter or receiver circuits, and chamber defining means bonded to the submount and to the fiber block for enclosing the diode array and at least a portion of the end face including the fiber facets.  
         [0030]     In one form of the invention the submount is also bonded to the fiber block such that both the submount and the chamber defining means are both bonded to the fiber block. The submount may have a side surface and the chamber defining means may have one or more end surfaces coplanar with the side surface such that both the side surface and one or more of the end surfaces contact the end face, such that alignment of the diode array to the fiber facets is facilitated and both the side surface and one or more of the end surfaces are bonded to the fiber block for increased mechanical strength. In another form of the invention the chamber defining means is intermediate to the submount and the fiber block and the submount is supported to the fiber block by the chamber defining means.  
         [0031]     In either form of the invention the chamber defining means may be bonded in substantially sealing engagement to the submount, and one or more of the end surfaces is bonded in substantially sealing engagement with the end face such that the diode array and the fiber facets are enclosed in a sealed chamber. The chamber defining means may also define a fluid containment dam about the diode array including the wire bonds, and the diode array is encapsulated in sealing resin contained by the dam.  
         [0032]     The chamber defining means is selected from the group comprised of a cap enclosure and a spacer enclosure. In one case the chamber defining means is a cap where the one or more end surfaces is an end surface, which may be shaped as an inverted U relative to the submount. In another case the chamber defining means is a spacer such as a frame, which may be rectangular, with either a closed perimeter or an open perimeter, and opposing end surfaces.  
         [0033]     The invention is also a method of making an optical assembly for use in a transmitter or receiver module comprising the steps of providing an optical fiber block supporting an optical fiber array, each fiber terminating in a fiber facet on an end face of the fiber block to define a fiber facet array, providing a submount and a containment dam, bonding a diode array chip to the submount, bonding the containment dam to the submount, and bonding one or both of the containment dam and submount to the fiber block with the diode array chip in optical alignment with the fiber facet array.  
         [0034]     The containment dam may include a number of side walls on a top surface of the submount, the side walls terminating in end surfaces joined to the end face of the fiber block to define a closed containment perimeter about the diode array and wire bonds with the submount providing a bottom. For example, a side wall portion with three side walls may be joined to the fiber block such that the end face provides a fourth wall and the substrate provides a bottom. A separate cap top may be applied to the side wall portion and against the end face to make a protective cap enclosing the diode array, the wire bonds and the fiber facets. The side wall portion of the containment dam may be U-shaped, terminating in two of the aforementioned end surfaces, which may be coplanar with each other. The two end surfaces may also be coplanar with a side surface of the submount such that the end surfaces and the bonding surface are all bonded to the end face of the fiber block. The containment dam may be installed with or without the cap cover. An open top containment dam may be provided by installing only the side wall portion, and encapsulating the diode array in resin contained by the dam. The resin encapsulation may be hardened with a layer of hard setting resin applied over an inner layer of sealing resin.  
         [0035]     These and other improvements, features and advantages will be better understood by reference to the following detailed description of the preferred embodiments and accompanying drawings.  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0036]      FIG. 1  shows a typical optoelectronic module with a protective cap enclosure according to this invention;  
         [0037]      FIG. 2  shows the fiber facet array on the end face of the optical fiber block;  
         [0038]      FIG. 3  is an exploded view of an optical assembly with a one-piece protective cap, a submount with diode array chip and an optical fiber block;  
         [0039]      FIG. 4A  illustrates in side view the bonding of the submount to the optical fiber block with the diode array in optical alignment with the fiber facets of the fiber block;  
         [0040]      FIG. 4B  depicts installation of the one-piece protective cap by bonding to the submount and to the end face of the fiber block to make a chamber enclosing the diode array and fiber facets;  
         [0041]      FIG. 4C  illustrates a one-piece cap perforated with a resin injection hole and shows resin encapsulation of the diode array and fiber facets inside the cap and sealing of the injection hole with the resin;  
         [0042]      FIG. 5  is a view as in  FIG. 3  but showing a two piece cap having a side wall portion and a separate cap top;  
         [0043]      FIG. 6A  illustrates in side view the cap sidewall bonded to the submount while encompassing the diode array, prior to assembly to the optical fiber block;  
         [0044]      FIG. 6B  shows the submount and cap side wall bonded to the end face of the fiber block with the diode array in optical alignment with the fiber facets of the fiber block and defining a fluid containment dam around the diode array chip;  
         [0045]      FIG. 6C  shows how the diode array chip is encapsulated in a layer of resin applied inside the containment dam;  
         [0046]      FIG. 6E  shows the cap top affixed to the cap side wall and to the end face to make a chamber enclosing the encapsulated diode array chip;  
         [0047]      FIG. 6F  shows the two piece cap of  FIG. 5  installed as in the sequence of  FIGS. 6A, 6B  and  6 D, but omitting the resin application of  FIGS. 6D and 6E , to make a protective cap enclosure containing the diode array chip and fiber facet array without resin encapsulation;  
         [0048]      FIG. 7  illustrates a sealing arrangement suitable for surface emitting laser diode chips, LED chips and photodetector chips using a spacer interposed between the chip submount and the optical fiber block;  
         [0049]      FIG. 8A  is a side view of the diode array chip bonded to the chip submount and wire bonded to electrodes on the submount;  
         [0050]      FIG. 8B  shows how the spacer is bonded to the submount and the spacer width is greater than the combined height of the diode array chip and the wire bonds to define a fluid containment submount;  
         [0051]      FIG. 8C  illustrates bonding of the spacer to the fiber block so as to assemble the chip submount to the fiber block and shows how the spacer provides a protective enclosure containing the diode array chip and fiber facets without resin encapsulation;  
         [0052]      FIG. 8D  depicts the application of sealing resin inside the fluid containment dam defined by the spacer in  FIG. 8B  before assembly to the fiber block;  
         [0053]      FIG. 8E  shows the submount and spacer assembled to the fiber block such that the resin encapsulated diode array chip is protected in the chamber defined by the spacer between the submount and the fiber block;  
         [0054]      FIG. 8F  shows an open spacer having a resin injection port such that sealing resin may be introduced for encapsulating the diode array chip after the submount and spacer have been assembled to the fiber block to make a protective enclosure containing the chip;  
         [0055]      FIG. 8G  shows the open spacer of  FIG. 8F  assembled between the submount and fiber block to make an open protective chamber for the diode array chip without resin encapsulation; and  
         [0056]      FIG. 8H  shows the assembly of  FIG. 8G  after encapsulation of the diode array chip in sealing resin, and also shows how the injection port of the spacer is sealed by the resin. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0057]     With reference to the accompanying drawings in which like elements are designated by like numerals,  FIG. 1  shows a typical optoelectronic module, generally designated by numeral  10 , which has an optical assembly  14  according to one embodiment of this invention.  
         [0058]     Module  10  has a module housing  11  including a housing bottom  13  and a housing cover  15 . A printed circuit board  18  mounted on the housing bottom carries electronic circuits  20  which process signals transmitted or received by the module  10 . External package leads  21  interconnect the electronic circuits  20  to other circuits external to the module  10 . The optical assembly  14  interfaces the electronic circuits  20  to an optical fiber pigtail  24  terminated in a suitable optical connector (not shown). The optical assembly  14  as seen in  FIG. 1  has a submount  24 , a protective cap  30  and an optical fiber block  28 . The optical assembly  14  also includes a semiconductor diode array chip  26  mounted on submount  24  and covered in  FIG. 1  by cap  30 , but shown in  FIG. 3  and other Figures.  
         [0059]     As seen in  FIG. 2 , the optical fiber block  28  includes an upper substrate  28   a  and a lower substrate  28   b , an end face  32  and an opposite outer end  34 . Fiber block  28  contains an array of mutually parallel optical fibers  38  contained between substrates  28   a ,  28   b  in parallel V-grooves  28   c  extending from end face  32  to opposite end  34 . Each optical fiber  38  terminates in a fiber facet  40  on end face  32 , forming a linear array of fiber facets  40 , as shown in  FIG. 2 . In  FIG. 1  the fiber block  28  is mounted in an opening  36  in the module housing bottom  13  such that the end face  32  is interior to the module housing  11  and the opposite end  34  together with optical fiber pigtail  24  is exterior to the housing  11 . The fibers  38  in the fiber block  28  are continuous with fibers in pigtail  24 . The upper substrate  28   a  may be of glass or glass ceramic which is molded or cut so as to form the parallel V-grooves  28   c  in a bottom surface of this substrate. Alternatively, silicon may be used and chemically etched to make the V-grooves. The lower substrate  28   b  may have a planar upper surface bonded to the grooved bottom surface of upper substrate  28   a  by suitable means such as an adhesive. Lower substrate  28   b  may be of the same materials, or of a heat dissipating material such as Aluminum Nitride (AlN), or of aluminum oxide (Al 2 O 3 ) in applications where heat dissipation is not an issue.  
         [0060]      FIG. 3  shows in exploded view the optical assembly  14  including a one-piece protective cap  30 , chip submount  24  with bonded LE/LD diode array chip  26  and optical fiber block  28 . The submount  24  has a top surface  24   a  and a side surface  24   b . The chip  26  may be an edge emitting laser diode array chip with a number of laser diodes spaced along a relatively narrow emitting edge  25  and with the diodes facing facets  40  on the fiber block  28 . The relatively wider underside of the diode array chip  26  is bonded, as by means of epoxy adhesive, to the top surface  24   a  with emitting edge  25  of the diode array slightly recessed from the side surface  24   b  to avoid contact between the diodes of chip  26  and the end face  32 . The submount  24  may be of a heat dissipating material, such as Aluminum Nitride, to act as a heat sink for the diode chip  26 , or of aluminum oxide (Al 2 O 3 ) if the LE/LD diode array chip  26  does not require a heat sink and heat dissipation is not an issue. The diode array chip  26  has various chip electrodes which are connected to conductive traces  42  on the submount surface  24   a  by means of wire bonds  44  of very fine wire applied by conventional wire bonding machinery. Traces  42  may be applied by a thin film printing technique so that the traces have a small thickness above the submount surface  24   a . The submount conductors  42  are in turn connected to printed circuit board  18  by suitable conductors such as wire bonds  16 , as in  FIG. 1 .  
         [0061]     Submount  24  is assembled to fiber block  28  as indicated in  FIG. 4A . This assembly includes optical alignment of the laser diode chip  26  to the fiber facets  40 . Alignment is normally performed with the aid of a suitable mechanical manipulator under optical magnification. Active alignment is performed by applying power to the laser diodes arrayed along emitting edge  25  of chip  26  while monitoring light output of the optical fibers  38  at the end connector of pigtail  22 . Ultraviolet (UV) setting epoxy resin is applied to side surface  24   b  and the side surface is brought into contact with end face  32 . The submount  24  is positioned relative to the fiber block  28  so as to achieve a desired degree of optical alignment of the laser diodes with optical fibers  38 . The submount and fiber block can then be temporarily bonded and joined to each other by ultraviolet illumination of the UV setting resin. More permanent bonding of submount  24  to fiber block  28  may be made by any appropriate bonding technology known in the field, such as epoxy bonding or laser welding, for example.  
         [0062]     As shown in  FIG. 4B , protective cap  30  is bonded to both submount  24  and to end face  32  so as to enclose the diode array chip  26  as well as a portion of end face  32  which includes fiber facets  40 . The one piece cap  30  has three sidewalls  30   c  and an integral cap top  30   d . The bottoms of the three side walls together define a U-shaped cap bottom  30   a . The end surfaces of two side walls  30   c  together with cap end surface  30   b  of the cap top  30   d  define a U-shaped cap end surface  30   b . Cap bottom  30   a  is bonded to top surface  24   a  encompassing chip  26 , and cap end surface  30   b  is bonded to end face  32  encompassing the array of fiber facets  40 . The cap  30  provides the three side walls  30   c  and cap top  30   d , the submount top surface  24   a  provides a floor and the end face  32  supplies a fourth wall to define an enclosing chamber  50  containing the diode array chip  26  and fiber facets  40 .  
         [0063]     It may be convenient to install the cap  30  after the submount  24  and fiber block  28  have been aligned and assembled. However, the cap  30  may also be affixed to either one of the submount  24  or the fiber block  28  prior to the alignment procedure, and affixed to the other of the submount  24  or the fiber block  28  after alignment.  
         [0064]     Cap  30  may be bonded, as by appropriate epoxy adhesive or other suitable bonding methods, in hermetic or near hermetic sealing relationship to both submount  24  and end face  32 , thereby to provide a substantially hermetic chamber  50 . Substantially hermetic sealing of the chip  26  and facets  40  by the cap  30  in chamber  50  suffices for many applications as a substitute for conventional hermetic sealing of the entire module housing  12 . In such case, in the module  10  of  FIG. 1  it may suffice to fasten the housing cover  15  to housing bottom  13  by means of a non-hermetic crimp fastening  17 , as opposed to hermetic welding of the housing cover to bottom  15 .  
         [0065]     For applications where a lesser degree of reliability is acceptable, the cap  30  may be affixed or bonded to either or both the submount  24  and fiber block  28  in non-hermetic fashion, in which case the cover provided by cap  30  offers protection against mechanical damage to chip  30  and wire bonds  44 , particularly when the parts are handled during alignment and bonding of optical assembly  14 .  
         [0066]      FIG. 4C  shows the completed optical assembly  14  of  FIG. 1  with a one piece protective cap  30 ′ which is similar to cap  30  of  FIG. 3  except that cap  30 ′ is perforated by a resin injection hole  48  through the cap top  30   d  for introducing sealing resin in an initially fluid uncured state into the chamber where  50 . In this case, the cap  30 ′ also serves as a containment dam for the fluid sealing resin. Preferably, sufficient sealing resin is introduced through hole  48  to at least cover the chip  26  and wire bonds  44 . When cured, the sealing resin hardens to encapsulate the chip  26  and its wire bonds  44  within a generally transparent solid resin mass  52 . The resin mass  52  may cover and encapsulate the chip  26  and also the fiber facets  40  so as to fill the space therebetween. The resin mass  52  may extend to form a plug  54  of resin rising from the interior of chamber  50  to seal injection hole  48 , as also shown in  FIG. 4C . The sealing resin is chosen for good transparency at the wavelengths emitted by the laser diodes of chip  26 . In cases where the chip  26  and wire bonds  44  are especially delicate, the sealing resin is also selected to be relatively soft setting, to reduce the risk of damage to the chip  26  and wire bonds  44  which might be caused by a hard setting resin. One suitable sealing resin is silicone resin, which is substantially transparent at the wavelengths of interest and sets to a relatively pliable resilient cured state.  
         [0067]     In another embodiment of the invention illustrated in  FIGS. 5 and 6 A through  6 D, a two piece protective cap  30 ″ has a cap side wall portion  54   a  and a separate cap cover  54   b . The side wall portion is generally U-shaped with two side walls  56   a  joined at one end by a transverse end wall  56   b . The opposite ends of the two side walls have free ends which terminate in end surfaces  56   c . The two end surfaces  56   c  are preferably flat and coplanar with each other. The side wall portion  54   a  also has a top surface  56   d  and a bottom surface  56   e.    
         [0068]     The presently preferred sequence of assembly of this embodiment is illustrated in  FIGS. 6A  to  6 D. As shown in  FIG. 6A , the bottom  56   e  of the side wall portion  54   a  is bonded to top surface  24   a  of submount  24  such that the chip  26  lies between the side walls  56   a  and the end surfaces  56   c  are coplanar with side surface  24   b . The submount side surface  24   b  and side wall end surfaces  56   c  are then bonded as with epoxy adhesive to end face  32  of fiber block  28 , as depicted in  FIG. 6B , after positioning submount  24  to optically align the diodes of chip  26  with corresponding fiber facets  40  on end face  32 , as described above in connection with  FIG. 4A . The end surfaces  56   c  are added to the side surface  24   b  to augment the contact area between the submount  24  and the end face  32 . The larger contact area facilitates the alignment process by stabilizing the two parts relative to each other during alignment, as well as providing a larger bonding area for greater mechanical strength of the completed assembly  14 . The end face  32  closes the open end of the U-shaped side wall portion  54   a  to define a fluid containment dam into which may be applied liquid sealing resin for encapsulating the diode array chip  26 .  
         [0069]     Assembly may be completed with or without resin encapsulation of the diode array chip  26 .  FIG. 6C  illustrates the resin encapsulation stage. In  FIG. 6C  a sealing resin is applied to cover the chip  26  in a first resin layer  58 . This resin application is preferably a soft setting resin substantially transparent at the diode chip&#39;s operating wavelengths. After the first resin layer  58  has set to encapsulate chip  26 , an optional second resin layer  58   a  is applied over the first resin layer  58 . The second resin layer  58   a  may be a hard setting epoxy which after curing provides a harder protective shell over the softer first resin layer  58 . Assembly may stop at this stage, so that the optical assembly  14  is protected by resin encapsulation as in  FIG. 6C , either a single resin layer  58  or double resin layer  58 ,  58   a , but without a cap cover or other non-resin enclosure of the chip  26 .  
         [0070]     An additional level of protection illustrated in optical assembly  14 ′ of  FIG. 6D  may be provided by bonding cap top  54   b  to top surface  56   d  of the side wall portion  54   a  to cover and enclose the interior of the side wall portion  54   a , and to define a chamber  50  containing the diode array chip  26  and the fiber facets  40  on end face  32 . One edge or end surface  56   f  of the cap top  54   b  may be bonded to the end face  32  to complete a hermetic seal of chamber  50 . The height or thickness of the side wall portion  54   a  measured between top and bottom surfaces  56   d ,  56   e  is at least slightly greater than the height of wire bonds  44  above submount surface  24   a  and also rises above the array of fiber facets  40  on end face  32  so as to include the facets  40  in chamber  50 .  
         [0071]      FIG. 6E  shows an alternate implementation of the invention in optical assembly  14 ″ wherein the two piece protective cap  30 ″ is installed without resin sealing of the chip  26 . The cap  30 ″ may be bonded in hermetic sealing relationship to submount  24  and fiber block  28  to define a hermetic chamber  50  containing chip  26  and facets  40 .  
         [0072]      FIG. 7  shows another embodiment of the invention where a LE/LD diode array  60  is bonded to top surface  62   a  of submount  62 . In the case of a LE diode array, the chip  60  may be a surface emitting laser diode array or a light emitting diode (LED) array. A spacer  64  is interposed between and affixed to submount  62  and to end face  32  of fiber block  28  for enclosing diode array  60  and a portion of the end face  32  including fiber facets  40 . Diode array chip  60  has an array of diode elements along top surface  60   a  which faces end face  32  of the fiber block  28 . The diode elements are electrically connected to conductive traces  68  on submount  62  by wire bonds  66  arcing between chip electrodes provided on top surface  60   a  of the diode array chip and conductors  68 . The submount  62  may be of a heat dissipating material, such as Aluminum Nitride, to act as a heat sink for the diode chip  60 , or Aluminum Oxide, among other possible choices of material.  
         [0073]     The spacer  64  of  FIG. 7  is in the shape of a rectangular frame defining a four sided closed perimeter of sufficient interior aperture to accommodate and encompass the diode array chip  60  between its four sides.  FIG. 8A  illustrates how diode chip  60  and wire bonds  66  rise above submount top surface  62   a . The spacer  64  has opposite end surfaces  64   a ,  64   b . End surface  64   a  is bonded to submount top surface  62   a , as in  FIG. 8B . The width of spacer  64  between end surfaces  64   a ,  64   b  is greater than the combined height of the diode chip  60  and wire bonds  66  above submount top surface  62   a  as illustrated in  FIG. 8B , such that both the chip  60  and wire bonds  66  are contained below the upper end surface  62   b  of spacer  64 .  
         [0074]     Further assembly of the submount  62  to the fiber block  28  includes optical alignment of the submount bonded chip  60  to the fiber facets  40 , and assembly of the spacer  64 , together with submount  62 , to the fiber block  28 . The assembly may proceed with or without resin sealing of the diode chip  60 .  
         [0075]     In  FIG. 8C  submount  62  and spacer  64  are assembled to fiber block  28  by bonding end surface  64   b  to end face  32  such that the array of fiber facets  40  is encompassed within the interior aperture defined by the perimeter of spacer  64 . This step is normally performed with the aid of a mechanical manipulator due to the small size of the parts and the relatively high degree of precision required to achieve optimal alignment of the diode array chip  60  and fiber facets  40 . In one form of the assembly, the spacer  64  is bonded in hermetic relationship to both submount  62  and to end face  32  to define a hermetic chamber  70  for sealing the diode array chip  60  and the fiber facets  44 . Hermetic bonding is achieved by appropriate selection and application of adhesive or other known bonding techniques.  
         [0076]     In  FIG. 8D  the diode chip  60  is encapsulated in a resin seal  72  applied as initially liquid sealing resin selected as in previously described embodiments for transparency to light transmissions between the diode array  60  and fiber facets  40 . As seen in  FIG. 8D  the closed interior perimeter  65  of spacer  64  defines a fluid containment dam around chip  60  with submount  62  as a bottom, where the chip  60 , including top face  60   a  and preferably also wire bonds  66 , can be submerged in sealing resin  72 . After the sealing resin  72  cures to a relatively solid state, assembly can proceed as in  FIG. 8E  with bonding of the end surface  64   b  to end face  32  thereby to assemble the submount  62 , the spacer  64  and the fiber block  28  into a unitary optical assembly  80 . Hermetic bonding of the spacer  64 , to both submount  62  and fiber block  28 , defines a hermetically sealed chamber  70  which supplements the epoxy encapsulation  72  for a higher degree of protection of the optical components. A double resin seal can be provided, for still greater protection, by applying a harder setting epoxy layer  74  over the inner sealing resin encapsulation  72 , before assembling the spacer  64  to the fiber block  28 . In this case the harder setting epoxy layer  74  is selected for sufficient optical transparency at the operating wavelengths of the chip  60 .  
         [0077]     Turning now to  FIG. 8F , the open spacer  64 ′ is similar to the closed frame spacer  64  of  FIG. 7 , but has a break in the frame perimeter defining a resin injection port  82  such that resin may be introduced for encapsulating the diode array chip  60  after the submount  62  and spacer  64 ′ have been optically aligned and assembled to the fiber block  28  to make a protective enclosure containing the chip  60 .  FIG. 8G  shows the open spacer  64 ′ assembled between the submount  62  and fiber block  28  to make an open protective chamber  70 ′ for the diode array chip  60 . For non-critical applications the assembly  80 ′ of  FIG. 8G  may be installed in an optoelectronic module such as module  12  of  FIG. 1  without further sealing or encapsulation. The chamber  70 ′ may be non-hermetic or open to some degree, yet provides mechanical protection to the diode chip  60  and wire bonds  66  against mechanical damage during handling, for example. For higher reliability requirements  FIG. 8H  illustrates the additional step of encapsulating the diode array chip  62  in sealing resin  84  introduced through the resin injection port  82  and also shows how the injection port  82  is itself sealed by a plug  86  of the resin.  
         [0078]     The protective cap  30 ,  30 ′ and  30 ″ of  FIGS. 3 through 6 E and the spacer  64 ,  64 ′ of  FIGS. 7 through 8 H can be made of various materials. By way of example, these elements may be fabricated of glass epoxy, plastic, glass and from suitable metals or metal alloys, among still other possible materials. Appropriate materials will be apparent to those having only ordinary knowledge of this field, and for this reason this invention is not limited to specific materials for these components.  
         [0079]     The following commercially available resin and adhesive products have been found suitable for use with this invention:  
                                       Silicone sealing               resin   Shin-Etsu Chemical Co., Ltd.   Product #KJR9017                   Epoxy   Epoxy Technology, Inc.   Product #301-2                  
 
         [0080]     It will be appreciated that in each of the several described embodiments this invention provides a unitary, integrated optical assembly with scalable degrees of protective sealing appropriate to different applications and environments.  
         [0081]     While several embodiments of the invention have been described and illustrated for purposes of clarity and example, it should be understood that still other changes, modifications and substitutions to the disclosed embodiments will be apparent to those having only ordinary skill in the art without thereby departing from the scope of the invention, which is defined by the following claims.