Abstract:
In an optical communication module, a fiber submount is mated with an optics assembly to optically align an optical fiber retained in a groove in the fiber submount with an optics element of the optics assembly. The fiber submount has a resiliently biased latch portion that engages the optics assembly to provide a resilient retaining force between the optics assembly and the fiber submount. The force retains the optics element in optical alignment with the fiber optical axis.

Description:
BACKGROUND 
     In an optical communication system, it is generally necessary to couple an optical fiber to an opto-electronic transmitter, receiver or transceiver device and to, in turn, couple the device to an electronic system such as a switching system or processing system. These connections can be facilitated by modularizing the device. Such optical modules include a housing in which are mounted opto-electronic elements, optical elements, and electronic elements. In a transceiver module, the opto-electronic elements commonly include one or more light sources, such as lasers, and one or more light detectors, such as photodiodes. The optical elements commonly include lenses and, in modules in which the optical paths are not linear, reflectors that redirect the optical beams. Electronic elements commonly include digital signal driver circuits for driving the lasers or other light sources and digital signal receiver circuits for processing the output of photodiodes or other light detectors. 
     Various optical transceiver module configurations are known. For example, a configuration commonly referred to as “Small Form Factor Pluggable” or SFP refers to a transceiver module having an elongated housing with a rectangular cross-sectional shape, where the rear of the module has an electrical connector that plugs into a bay of a front-panel cage, and the front of the module has an optical fiber cable extending from it or an optical connector that accepts an optical fiber plug. 
     Accurate alignment among optical fibers, opto-electronic elements, and optical elements is important for proper operation of an optical communication module. Three methods for achieving such alignment are known: active alignment, visual alignment, and passive alignment. In active alignment, a light source is activated, and the signal coupling between the light source and target (i.e., photodiode or optical fiber) is electronically monitored while repositioning the elements with respect to each other until a measured signal indicates maximum coupling efficiency. Active alignment is generally a tedious and uneconomical process because it involves a closed-loop control system, including a set of actuators, an efficient peak search algorithm, and attendant instrumentation. 
     Visual alignment also functions as a closed loop system but relies on visual cues, such as fiducials or position of the light beam (monitored through an infrared camera), instead of monitoring the magnitude output of the light source. The primary drawbacks to visual alignment are that capital equipment costs escalate rapidly with required placement accuracy, and the throughput can be comparable to that of an active alignment system. 
     Passive kinematic alignment involves mating elements through accurate physical features. A common example of this is placing a fiber into a silicon submount with an etched V-shaped groove. As silicon is a rigid material in which a V-shaped groove can be very accurately formed by etching, the fiber diameter and accurate dimensions of the V-shaped groove allow for very accurate positional control of the fiber. 
     A variant of passive alignment is optical self-alignment, in which a force inherent to the system pulls the elements together into proper alignment. An example of optical self-alignment would be the use of surface tension of solder to align a die-attach component such as a laser. 
     The primary advantages of using passive alignment techniques are the reduction in system and equipment investment and a general reduction in process complexity. The primary obstacle is that the inherent part (e.g., a silicon fiber submount) costs quickly escalate as the required accuracy of part features increases. 
     SUMMARY 
     Embodiments of the present invention relate to an optical communication module and method in which a fiber submount in the module is mated with an optics assembly in the module to optically align an optical fiber retained in the fiber submount with an optics element of the optics assembly. 
     In an exemplary embodiment, the optical communication module comprises a module housing, a fiber submount within the module housing, and an optics assembly within the module housing. The fiber submount has a surface with at least one fiber-receiving groove aligned along a fiber optical axis extending between a rearward end of the fiber submount and a forward end of the fiber submount. The forward end of the fiber submount has a resiliently biased latch portion. The optics assembly has a forward end mated with the forward end of the fiber submount. The optics assembly also has at least one optics element. Each optics element has an optical axis coaxially aligned with a fiber optical axis. The resiliently biased latch portion of the fiber submount provides a resilient retaining force between the optics assembly and the fiber submount. The force retains the optics element in optical alignment with the fiber optical axis. 
     In the exemplary embodiment, a method for retaining an optical fiber in alignment with an optics element in the above-described optical communication module includes mounting an end of an optical fiber in the fiber-receiving groove, mating a forward end of the optics assembly with a forward end of the fiber submount, and engaging a resiliently biased latch portion at the forward end of the fiber submount with the optics assembly to provide a resilient retaining force that retains the optics element in optical alignment with the fiber optical axis. 
     Other systems, methods, features, and advantages will be or become apparent to one with skill in the art upon examination of the following figures and detailed description. It is intended that all such additional systems, methods, features, and advantages be included within this description, be within the scope of the specification, and be protected by the accompanying claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention can be better understood with reference to the following drawings. The components in the drawings are not necessarily to scale, emphasis instead being placed upon clearly illustrating the principles of the present invention. 
         FIG. 1  is a perspective view of an optical communication module, in accordance with an exemplary embodiment of the present invention. 
         FIG. 2  is a perspective view of the optical communication module of  FIG. 1 , with the cover removed to reveal the interior structure. 
         FIG. 3  is a perspective partially exploded view of the fiber submount, optics assembly and printed circuit board of the optical communication module of  FIGS. 1-2 . 
         FIG. 4  is similar to  FIG. 3 , showing the assembled fiber submount, optics assembly and printed circuit board. 
         FIG. 5  is a top plan view of the fiber submount. 
         FIG. 6  is a perspective partially exploded view of the fiber submount and cover, with the optical fibers retained therein. 
         FIG. 7  is a partially exploded front elevation view of the fiber submount and cover. 
         FIG. 8  is similar to  FIG. 7 , showing the assembled fiber submount and cover. 
         FIG. 9  is a perspective view illustrating mating of the fiber submount and optics assembly. 
         FIG. 10  is a perspective view of the optics assembly. 
         FIG. 11  is a top plan view illustrating mating of the fiber submount and optics assembly. 
         FIG. 12  is similar to  FIG. 7 , showing the fiber submount and optics assembly in a fully mated position. 
     
    
    
     DETAILED DESCRIPTION 
     As illustrated in  FIGS. 1-2 , in an illustrative or exemplary embodiment of the invention, an optical communication module  10  includes a housing  12  and a handle  14 . An optical fiber cable  16  extends from an end of housing  12 . As illustrated in  FIG. 2 , within a portion of housing  12  are a printed circuit board  18 , a fiber submount  20  and an optics assembly  22 . The ends of two optical fibers  24  and  26  of optical fiber cable  16  are retained within fiber submount  20  in a manner described below. A nose portion  28  of housing  12  connects handle  14  ( FIG. 1 ) to the remainder of housing  12  via a pivot pin  30 . Although not shown for purposes of clarity, printed circuit board  18  includes electrical conductors and electronic devices, such as one or more integrated circuit chips, which communicate electrical signals via an array of electrical contact fingers  32  on printed circuit board  18 . The configuration of housing  12  and the manner in which fiber submount  20  and optics assembly  22  are mounted therein are intended to be exemplary only, and in other embodiments (not shown) such a fiber submount and optics assembly can be mounted in any other suitable manner in any other type of optical communication module housing. 
     As illustrated in  FIGS. 3-4 , fiber submount  20  and optics assembly  22  together define a structure having a substantially flat or card-shaped profile that mounts on the upper surface of printed circuit board  18 . That is, the lower surfaces of fiber submount  20  and optics assembly  22  are substantially coplanar and lay flat on the upper surface of printed circuit board  18 . A light source  34  ( FIG. 3 ), such as a laser, and a light detector  36 , such as a photodiode, are mounted on the surface of printed circuit board  18 . As described in further detail below, in operation, a transmit optical beam  38  is communicated between light source  34  and optics assembly  22 , and a receive optical beam  40  is communicated between optics assembly  22  and light detector  36 . Although not shown for purposes of clarity, the bottom or lower surface of optics assembly  22  has a recess or cavity that accommodates light source  34  and light detector  36 . Although the exemplary optical communication module  10  includes two opto-electronic devices comprising light source  34  and light detector  36 , other embodiments can include any other type and number of opto-electronic devices. Accordingly, although the exemplary optical communication module  10  is a transceiver having both light source  34  and light detector  36 , in other embodiments such an optical communication module can be an optical transmitter having one or more light sources and no light detectors or, in still other embodiments, an optical receiver having one or more light detectors and no light sources. 
     As illustrated in  FIG. 5 , fiber submount  20  has a rearward end  42  and a forward end  44 . Four V-shaped fiber-receiving grooves  46  are formed in a surface  48  on the top side of fiber submount  20  and extend to forward end  44 . Although in the exemplary embodiment there are four V-shaped fiber-receiving grooves  46 , in other embodiments there can be any other number of such grooves. 
     Forward end  44  includes two resiliently biased latch portions comprising resiliently deflectable arms  50 . Resiliently deflectable arms  50  extend forward of forward end  44  and have hooked ends  52 . Although in the exemplary embodiment the resiliently biased latch portions comprise resiliently deflectable arms  50 , in other embodiments such resiliently biased latch portions can comprise any other suitable type of latching structure having resilient (i.e., spring-like) bias force-producing properties. Also, in the exemplary embodiment it should be noted that resiliently deflectable arms  50  are unitary with the remaining portions of fiber submount  20 . That is, resiliently deflectable arms  50  and the remaining portions of fiber submount  20  are portions of the same unitary piece of plastic. For example, fiber submount  20 , including its resiliently deflectable arms  50 , can be formed by injection molding or a similar process for forming one-piece parts. 
     As illustrated in  FIGS. 6-8 , the ends of optical fibers  24  and  26  are received in respective V-shaped fiber-receiving grooves  46 . A cover  54  is mounted over surface  48  in which V-shaped fiber-receiving grooves  46  are formed. The underside of cover  54  contacts or rests upon optical fibers  24  and  26 , thereby retaining them within V-shaped fiber-receiving grooves  46  in the manner shown in  FIG. 8 . 
     In accordance with an exemplary method for retaining optical fibers  24  and  26  in optical alignment in optical communication module  10 , a method step comprises mounting the ends of optical fibers  24  and  26  in V-shaped fiber-receiving grooves  46  and securing them with cover  54  in the manner described above. As illustrated in  FIGS. 9 and 11 , a further method step comprises mating a forward end  56  of optics assembly  22  with forward end  44  of fiber submount  20  by orienting optics assembly  22  and fiber submount  20  as shown and moving them closer to each other in the direction of the arrows. As indicated in  FIG. 9 , this direction corresponds to a z-axis in a coordinate system having three mutually perpendicular axes x, y, and z. As illustrated in  FIGS. 9-11 , forward end  56  of optics assembly  22  has two substantially cylindrical projections  58 , while forward end  44  of fiber submount  20  has two cavities or bores  60  ( FIG. 9 ) having a shape complementary to the shape of projections  58 . As fiber submount  20  and optics assembly  22  are moved closer together, two ramp-shaped protrusions  62  on the sides of optics assembly  22  deflect resiliently deflectable arms  50  outwardly (substantially in the x-axis direction) in a camming manner, as indicated in broken line in  FIG. 12 . As fiber submount  20  and optics assembly  22  are moved nearly into the fully mated position, hooked ends  52  of resiliently deflectable arms  50  slide over and behind protrusions  62 . The outward (substantially x-axis) flexure of resiliently deflectable arms  50  generates a correspondingly inward (substantially x-axis) force that urges hooked ends  52  inwardly behind protrusions  62 . 
     When fiber submount  20  and optics assembly  22  are in the fully mated position shown in solid line in  FIG. 12 , hooked ends  52  engage the rear portions of protrusions  62 , thereby retaining fiber submount  20  and optics assembly  22  against relative movement in the z-axis direction. Also, in the fully mated position projections  58  of optics assembly  22  extend into bores  60  of fiber submount  20 . There is a nominal fit between the corresponding or mating surfaces of projections  58  and optics assembly  22 . The term “nominal fit” is well understood in the art as meaning that there is a minute amount of clearance between the mating surfaces. However, the opposing forces exerted by resiliently deflectable arms  50  in the x-axis direction inhibit assembly shift and promote centering of projections  58  within bores  60 . Note that when fiber submount  20  and optics assembly  22  are in the fully mated position, the end of optical fiber  24  is aligned along an optical axis (in the z-axis direction) with a first reflective element  64  of optics assembly  22 , and the end of optical fiber  26  is similarly aligned along another optical axis with a second reflective element  66  of optics assembly  22 . Reflective elements  64  and  66  can be, for example, total internal reflection (TIR) mirrors formed in a surface angled at 45 degrees with respect to the y and z axes. As such reflective elements are well understood in the art, they are not described in further detail herein. Although in the exemplary embodiment optics assembly  22  includes first and second reflective elements  64  and  66 , in other embodiments such an optics assembly can include any other type and number of optics elements, such as, for example, lenses. 
     Note that the optical axis along which the end of optical fiber  24  is aligned corresponds to the nominal direction from which light can enter the end face of optical fiber  24 . Likewise, the optical axis along which the end of optical fiber  26  is aligned corresponds to the nominal direction from which light can be emitted from the end face of optical fiber  26 . 
     In operation, an optical beam  68  emitted from the end face of optical fiber  26  enters an optical port  70  ( FIGS. 10-11 ) at forward end  56  of optics assembly  22  and impinges upon second reflective element  66 . Second reflective element  66  redirects optical beam  68  at a 90-degree angle. The redirected beam emerges from beneath optics assembly  22  as receive optical beam  40  ( FIG. 3 ). As described above with regard to  FIG. 3 , receive optical beam  40  impinges upon light detector  36 . Light detector  36  converts the optical signal into an electrical signal. Circuitry (not shown) on printed circuit board  18  processes this electrical signal, and the resulting electrical signals are output via electrical contact fingers  32 . Similarly, as described above with regard to  FIG. 3 , circuitry (not shown) on printed circuit board  18  processes (e.g., amplifies) electrical signals received via electrical contact fingers  32  and drives light source  34 . Light source  34  emits transmit optical beam  38  in response to these electrical signals. Transmit optical beam  38  impinges upon first reflective element  64  ( FIGS. 10-11 ), which redirects transmit optical beam  38  at a 90-degree angle. The redirected beam  72  emerges from another optical port  74  in forward end  56  of optics assembly  22 . Optical ports  70  and  74  can include lenses for focusing or collimating the respective beams  72  and  68 . The above-described latching action and associated retaining forces retain optics elements  64  and  66  in optical alignment with the optical axes of the ends of respective optical fibers  24  and  26 . 
     One or more illustrative embodiments of the invention have been described above. However, it is to be understood that the invention is defined by the appended claims and is not limited to the specific embodiments described.