Patent Publication Number: US-11652129-B1

Title: Compact annular field imager optical interconnect

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of U.S. application Ser. No. 16/882,513, entitled COMPACT ANNULAR FIELD IMAGER OPTICAL INTERCONNECT, filed on May 24, 2020, which is a continuation of U.S. application Ser. No. 16/532,116, filed on Aug. 5, 2019, entitled COMPACT ANNULAR FIELD IMAGER OPTICAL INTERCONNECT, which is a continuation of U.S. application Ser. No.: 14/213,014, filed on Mar. 14, 2014, entitled LOW PROFILE OPTICAL INTERCONNECT, now U.S. Pat. No. 10,373,998, issued on Aug. 6, 2019, which claims priority to U.S. Provisional Applications Nos. 61/792,886, filed Mar. 15, 2013 and 61/783,507, filed Mar. 14, 2013, the entire contents of all of which are incorporated herein by reference and for all purposes. 
    
    
     STATEMENT OF FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
     This invention was made with U.S. Government support from the U.S. Army under Contract W31P4Q-09-D-0004. The U.S. Government has certain rights in the invention. 
    
    
     BACKGROUND 
     These teachings generally relate to optical interconnects and signal routing. 
     Current signal routing from one circuit board to another within an electronics enclosure typically uses an electrical path through a common backplane and backplane connectors. Routing signals through the backplane is often difficult on densely populated circuit boards and limits layout freedom. 
     There is a need for a signal routing solution that frees board layout and reduces the number of connections to the backplane and traces run to the backplane. 
     SUMMARY 
     Various embodiments of the present teachings disclose optoelectronic modules that reduce the need to route signals through connectors or to the backplane by routing signals optically between boards. 
     For a better understanding of the present invention, together with other and further objects thereof, reference is made to the accompanying drawings and a detailed description. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1    illustrates a relay lens system as used in these teachings. 
         FIG.  2    illustrates an embodiment of the modules of these teachings as mounted on two adjacent boards. 
         FIG.  3    shows embodiments of (a) an emitter die and (b) a detector die in these teachings. 
         FIG.  4    shows an embodiment of the detector die in these teachings with the wirebonds attached. 
         FIG.  5    shows embodiments of various imagers in these teachings. 
         FIG.  6    shows embodiments of detector dies with different variations on detector element size and number in these teachings. 
         FIG.  7    illustrates an embodiment of the optical system in these teachings. 
         FIG.  8    shows an embodiment of the module in these teachings. 
         FIG.  9    shows another embodiment of the module in these teachings. 
         FIG.  10    shows the embodiment of the module illustrated in  FIG.  8    with the housing transparent to show a wirebond protection feature of these teachings. 
         FIG.  11    shows an exploded view of the embodiment of the module of these teachings illustrated in  FIG.  8   . 
         FIG.  12    shows a molded-housing embodiment of the module of these teachings. 
         FIG.  13    shows an embodiment of the directly board-mounted module of these teachings. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Reference is made to  FIG.  1   , which illustrates an imaging relay lens system  11  including a pair of lenses  10  and  12  used to reimage an object array  16  to an image array  14 . See, for example, U.S. Pat. Nos. 6,635,861, 7,015,454, 7,446,298, and 8,171,625, which are incorporated herein by reference in their entirety and for all purposes. 
     The system  11  in  FIG.  1    is designed to substantially tolerate misalignments between a first imager assembly  2  (comprising a housing  6 , an imager  12 , and an object array  16 ), and a second imager assembly  4  (comprising a housing  8 , an imager  10 , and an image array  14 ), making a connectorless opto-electronic data transmission scheme possible. The first imager assembly  2  and the second imager assembly  4  are each herein referred to as a “module,” which refers to an assembly or component that contains, but is not limited to, a housing, an imager, and an image or object array. An array may include optoelectronic components, waveguides, or other sources of electromagnetic radiation, or detectors of electromagnetic radiation. The object array  16  includes a single emitter or an array of emitters, and the image array  14  includes a single detector or an array of detectors. Herein, “emitter” refers to a source of light including, but not limited to, VCSELs, LEDs, optical fibers, and optical waveguides. Herein, a “detector” refers to a target for said light, including, but not limited to, waveguides, photodiodes, optical fibers, and optical to electrical converters. Herein, an “imager” refers to an optical device or element capable of substantially transmitting light emitted by a source, such as but not limited to a refractive lens, a gradient index (GRIN) rod, a reflective optical assembly, a diffractive lens, etc. 
     In operation, electromagnetic radiation (typically in the ultraviolet, visible, and/or infrared bands, herein referred to generally as light) emitted or reflected by a given object (either real or virtual, herein referred to generally as emitters) located at the object plane (in this embodiment, but not limited to, an object array  16 ) is incident on a first imager  12 , in this embodiment, comprising, but not limited to, a gradient index (GRIN) rod lens, which is capable of substantially receiving a portion of the light emanating from the object array  16  and substantially collimating the light. The light is then incident on a second imager  10 , in this embodiment, comprising, but not limited to, a gradient index (GRIN) rod lens, which is capable of substantially receiving the light from the first imager  12  and substantially focusing the light to a image array  14 . The first imager  12  and second imager  10  are affixed to housings  6  and  8  respectively. 
     Reference is made to  FIG.  2   , wherein an embodiment of an optical system  20  is shown, where the first imager assembly  2  and second imager assembly  4  are embodied as modules  24  and  25 , acting together in connectorless pairs of Optical Data Pipes (ODPs). ODPs transmit data from a first circuit board  18  to a second circuit board  22  directly without the need to route signals through connectors on a common backplane and without the need for any common electrical or mechanical connection of the circuit boards  18  and  22  provided the ODP modules are oriented and positioned within the acceptable relative misalignment determined by the imager and array designs. In various embodiments, the ODP modules  24  and  25  may be a transmitter module, a receiver module, or a bi-directional transceiver module, depending on design choices. These modules can be electrically connected to the mounts or circuit boards  18  and  22 , and operated as discrete opto-electronic devices. 
     Reference is made to  FIG.  3 ( a )  which illustrates an embodiment of the object array  16  as illustrated in  FIG.  1   , comprising an optoelectronic transmitter die  36  including an array of emitters  44  (shown as an array of small circles) and an array of wirebond pads  38  (shown as an array of small squares). Reference is made to  FIG.  3 ( b )  which illustrates an embodiment of the image array  14  as illustrated in  FIG.  1   , comprising an optoelectronic receiving die  32  including an array of detectors  42  (shown as an array of large circles) and an array of wirebond pads  38  (shown as an array of small squares). 
     Reference is made to  FIG.  4   , which illustrates the image array  32  illustrated in  FIG.  3   b   , where the receiving die  32  is electrically connected with an interposer (not shown) by means of wire bonds  46 , connected to the array of wirebond pads  38  on the die  32 . The array of wire bond pads  38  are shown merely for exemplary purposes and not for limiting the arrangement. Alternative means are possible to electrically connect the die with the interposer using, for example, flip chip technology. 
     Reference is made to  FIG.  5   , which illustrates a comparison of relative sizes according to related embodiments. Two embodiments of advanced imagers  52  and  54  are shown alongside a Gradient Index (GRIN) lens  48 , where  FIG.  5 ( a )  illustrates the GRIN lens  48  with a die  32  (the same die as in  FIG.  4   ),  FIG.  5 ( b )  illustrates a more compact imager  52  with a die  32 , and  FIG.  5 ( c )  illustrates an even smaller imager  54  with a die  56  having an array with a reduced number of emitters or detectors (herein referred to generally as channels). Further details regarding the advanced imager options are illustrated in  FIG.  6 ( a ) , where compact imager  52  is above an array of detectors  42  on die  32  illustrated in  FIG.  3   b   . The smaller imager  54  can be used by reducing the number of detectors  42 , as shown in  FIG.  6 ( b )  on the die with fewer channels  56 , or by maintaining the number of channels (and detectors) but using reduced-size detectors  58  on die  62  as shown in  FIG.  6 ( c ) . 
     A schematic view of a compact annular field imaging relay lens  70  is provided in  FIG.  7    with an optical ray trace shown for a pair of object elements within the annular field. In operation, light originating from a first source element  64  in an annular source array  71  is incident upon a first half relay lens  73  comprising a catadioptric element where the light is refracted by a first optical surface  74 , which is substantially capable of receiving a portion of the light, and substantially transmitted to a first reflective surface  66 , which is substantially capable of receiving the light refracted by the first optical surface  74 . The light is then reflected by the first reflective surface  66  and transmitted to a second reflective surface  68 , which is capable of substantially receiving the light reflected by the first reflective surface  66 . The light is then reflected by the second reflective surface  68  and transmitted to a second optical surface  82 , which is substantially capable of receiving the light reflected by the second reflective surface  68 , where the light is refracted and transmitted towards a second half relay lens  83 , which is oriented substantially symmetric to the first half relay lens  73  about the plane  81  separating the two lenses  73  and  83 . 
     The light is then incident upon the second half relay lens  83  comprising a catadioptric element where it is refracted by a first optical surface  82 , which is substantially capable of receiving the light, and substantially transmitted to a first reflective surface  68 , which is substantially capable of receiving the light refracted by the first optical surface  82 . The light is then reflected by the first reflective surface  68  and transmitted to a second reflective surface  66 , which is substantially capable of receiving the light reflected by the first reflective surface  68 . The light is then reflected by the second reflective surface  66  and transmitted to a second optical surface  74 , which is substantially capable of receiving the light reflected by the second reflective surface  66 , where it is refracted and imaged to a first detecting element  86  in an annular detecting array  91 . 
     In a similar fashion, a second source element  84  in the annular source array  71  is substantially reimaged by the pair of compact annular field imaging relay lenses  73  and  83  to a second detecting element  88  in the annular detecting array  91 , and likewise all source elements in the annular source array  71  are substantially reimaged to respective detecting elements in the annular detecting array  91 . In practice, the half relay lenses  73  and  83  can include any combination of refractive, reflective, or catadioptric elements. 
       FIG.  8    shows an ODP module  80  in accordance with an embodiment of the present disclosure. As shown in  FIG.  8   , ODP module  80  includes an imager  96 , which is capable of substantially focusing light onto an array of detectors on an optoelectronic die  108 , substantially collimating light emitted from an array of emitters on an optoelectronic die  108 , or any combination thereof (including bi-directionally focusing and collimating light between arrays including both detectors and emitters); an imager housing  116  (in this embodiment, comprising an imager housing base  98  and an imager housing insert  94 ) to position, hold and protect the imager  96 , and provide protection for the opto-electronic die  108  and wire bonds  112 ; an optoelectronic die  108  with an array of detectors, emitters, or both; and an interposer  102 . 
     In this embodiment, the interposer  102  is a printed circuit board. It is appreciated that in other instances, interposer  102  may be, for example, a thick film ceramic circuit card, a co-fired ceramic circuit card, or any substrate capable of routing electrical signals. In this embodiment the die  108  is electrically connected by, but not limited to, wire-bonds  112  to the interposer  102  and affixed with epoxy  104 . The imager is affixed with epoxy  114  within the imager housing  116  and the imager housing  116  in turn is affixed to the interposer  102 . In other embodiments, components affixed to each other with epoxy may be affixed by other means, including, but not limited to, heat staking, molding, crimping, pressing, and welding. 
       FIG.  9    shows the module  80  of  FIG.  8    as being mounted to an application circuit board  118 . This particular embodiment  90  has the following features: an imager  96  is recessed from the front surface of the imager housing  124  to prevent damage to the imager  96 , should the two opposing ODP modules  90  contact each other because of flexing of the application PCBs or for some other reason; a two-piece housing where the imager housing insert  94  is threaded into the imager housing base  98  to provide a focus adjustment during initial alignment. 
     In this embodiment  90 , the interposer  102  substantially conducts electrical signals between the optoelectronic die  108  and the circuit board  118  on which interposer  102  is mounted via surface mount technology, in this case for example, but not limited to, a Land Grid Array  106  (called out in  FIG.  8   , but too thin to be seen in this section) or Ball Grid Array. Other surface mount technologies that could be used include, but are not limited to, column grid arrays, micro-ball grid arrays, and Low-profile Quad Flat Package (LQFP). The module  80  can have other means of electrical connection such as but not limited to discrete wires, flexible printed circuits, or pin arrays. The module  80  can also be mounted to substrates other than printed circuit boards, and can be mechanically affixed to the substrate with an epoxy  122  as shown in  FIG.  9   , or by another means such as, but not limited to, heat staking, welding, or soldering. 
     Other embodiments include, but are not limited to, the previously listed embodiment  80  with substitutions such as, but not limited to, any or all of the following: a flip-chip die instead of a wire-bonded die  108 ; a single-piece or multi-piece housing, instead of a two-piece housing  116 ; and a through-hole pin array, any surface mount technology, or wire-bonds for electrically connecting to the application circuit board or mount instead of using a land grid or ball grid array. 
     Further, as shown in  FIG.  10   , a partially transparent view of the embodiment  80  shown in  FIG.  8   , and, as shown in  FIG.  11   , an exploded view of the embodiment  90  shown in  FIG.  9   , a means of allowing for in-plane alignment of the imager  96  to the object array or image array (in this embodiment an optoelectronic die  108 ) can limit travel sufficiently to prevent damage to the wire-bonds during the alignment process. The wirebond protection is embodied in the posts  128  on the imager housing base  98  and oversized notches  126  in the interposer  102  that accept the posts  128 . When the posts  128  hit the sides of the notches  126 , as illustrated in  FIG.  10   , the housing  116  has reached the limit of its travel. Yet another embodiment includes an imager/housing assembly that incorporates datum geometry that substantially fixes the imager in the correct location with respect to the emitter/detector array. 
       FIG.  12    shows an embodiment of a module of these teachings  120  that has an injection-molded housing  132  molded around the imager  138 . Once the imager  138  is focused and aligned to the die  108 , the housing  132  and interposer  142  can be bonded together. 
     In another embodiment of a module of these teachings, as shown in  FIG.  13   , an ODP module  130  includes a die mounted and wire bonded directly to the application circuit board  118 , with the interposer being eliminated. The housing  116 , in turn, is bonded directly to the application circuit board  118 . The bonded assembly of the housing  116  and imager  96  can be actively aligned to the board-mounted die, or placed in a datum geometry that substantially fixes the bonded housing  116  and imager  96  assembly in the correct location with respect to the object array, image array, or any combination thereof. 
     Note that while housings discussed herein are shown as part of the imager and housing assemblies, the functions performed by the housings (for example, but not limited to, protection, mounting features, and tooling features) can be incorporated into the imagers. Herein, where the term “housing” is used to refer to the component or components containing or holding an imager, it should be taken to also mean those features on an integrated housing-imager, such as, but not limited to, a molded optical element with housing features that serve the same purpose. 
     Note that herein, “transmitting elements”, also known as “transmitters” and “emitters,” can refer to any number of devices, such as but not limited to, optical waveguides, optical fibers, and VCSELS. Herein, “receiving elements,” also known as “receivers,” can refer to any number of devices, such as, but not limited to, optical waveguides, optical fibers, and optoelectronic detectors. The term “optoelectronic detectors” (or simply “detectors”) refers to elements that produce an electrical signal in response to incident light. 
     As used herein, the singular forms “a,” “an,” and “the” include the plural reference unless the context clearly dictates otherwise. Except where otherwise indicated, all numbers expressing quantities of ingredients, reaction conditions, and so forth used in the specification and claims are to be understood as being modified in all instances by the term “about.” 
     For the purpose of better describing and defining the present invention, it is noted that terms of degree (e.g., “substantially,” “about,” and the like) may be used in the specification and/or in the claims. Such terms of degree are utilized herein to represent the inherent degree of uncertainty that may be attributed to any quantitative comparison, value, measurement, and/or other representation. The terms of degree may also be utilized herein to represent the degree by which a quantitative representation may vary (e.g., ±10%) from a stated reference without resulting in a change in the basic function of the subject matter at issue. 
     Although embodiments of the present teachings have been described in detail, it is to be understood that such embodiments are described for exemplary and illustrative purposes only. Various changes and/or modifications may be made by those skilled in the relevant art without departing from the spirit and scope of the present disclosure as defined in the appended claims.