Patent Publication Number: US-2023152531-A1

Title: Optical waveguide positioning feature in a multiple waveguides connector

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application is a divisional filing of U.S. application Ser. No. 15/763,506, filed Mar. 27, 2018, now allowed, which is a national stage filing under 35 C.F.R. 371 of PCT/US2016/055122, filed Oct. 3, 2016, which claims the benefit of U.S. Provisional Application No. 62/240,009, filed Oct. 12, 2015, the disclosures of which are incorporated by reference in their entireties herein. 
    
    
     TECHNICAL FIELD 
     This disclosure relates generally to optical connector assemblies and methods related to optical connector assemblies. 
     BACKGROUND 
     Optical connectors can be used for optical communications in a variety of applications including telecommunications networks, local area networks, data center links, and internal links in computer devices. There is interest in extending optical communication to applications inside smaller consumer electronic appliances such as laptops and even cell phones. Expanded optical beams may be used in connectors for these systems to provide an optical connection that is less sensitive to dust and other forms of contamination and so that alignment tolerances may be relaxed. Generally, an expanded beam is a beam that is larger in diameter than the core of an associated optical waveguide (usually an optical fiber, e.g., a multi-mode fiber for a multi-mode communication system). The connector is generally considered an expanded beam connector if there is an expanded beam at a connection point. The expanded beam is typically obtained by diverging a light beam from a source or optical fiber. In many cases, the diverging beam is processed by optical elements such as a lens or mirror into an expanded beam that is approximately collimated. The expanded beam is then received by focusing of the beam via another lens or mirror. 
     BRIEF SUMMARY 
     Embodiments are directed to a coupling unit including a light coupling element comprising an attachment area for receiving and permanently attaching to a plurality of optical waveguides. One or more grooves are provided at the attachment area. Each groove is configured to receive an optical waveguide and defined by a bottom surface, a first region, a second region, and an opening. The first region is defined between the bottom surface and the second region. The first region in cross section has substantially parallel sidewalls separated by a spacing. The second region is disposed between the first region and the opening. A width of the opening is greater than the spacing. 
     Some embodiments are directed to a coupling unit including a light coupling element comprising an attachment area for receiving and permanently attaching to a plurality of optical waveguides. One or more grooves are provided at the attachment area. Each groove is configured to receive an optical waveguide having a width. Each groove has a first region and a bottom surface, the first region in cross section having substantially parallel sidewalls separated by a spacing. Each groove has a longitudinal transition section comprising a first end and a second end. The first end has a sidewall spacing greater than the width of the optical waveguide, and the second end has a sidewall spacing less than the width of the optical waveguide. 
     Other embodiments are directed to a coupling unit including a light coupling element comprising an attachment area for receiving and permanently attaching to a plurality of optical waveguides. One or more grooves are provided at the attachment area. Each groove is configured to receive an optical waveguides having a width. Each groove has a first region and a bottom surface, the first region in cross section having substantially parallel sidewalls separated by a spacing. Each groove has two or more sections along a longitudinal direction wherein each section has a different sidewall spacing than adjoining sections, and wherein at least one of the sections has a sidewall spacing less than a width of the optical waveguides. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG.  1    shows an optical cable subassembly  100  in accordance with some embodiments; 
         FIGS.  2 A and  2 B  are cutaway views of a portion of an optical cable subassembly focusing on the light redirecting member according to some embodiments; 
         FIG.  3    illustrates a side view of two optical cable subassemblies showing mated light coupling units attached to optical waveguides at light coupling unit attachment areas in accordance with embodiments described herein; 
         FIGS.  4 A,  4 B, and  4 C  provide several views of portions of an optical connector assembly in accordance with some embodiments; 
         FIG.  5    depicts an embodiment of an inner housing including four optical cable subassemblies installed in the inner housing; 
         FIG.  6 A  illustrates an inner housing having retainer mounts comprising a group of four pegs disposed within the shared passageway in accordance with some embodiments; 
         FIG.  6 B  illustrates the inner housing of  FIG.  6 A  after the optical cable subassemblies have been installed; 
         FIG.  7 A  illustrates an inner housing having retainer mounts, each retainer mount comprising a group of two pegs disposed within a shared passageway in accordance with some embodiments; 
         FIG.  7 B  illustrates the position of the optical cable subassemblies in the mated position within the inner housing of  FIG.  7 A ; 
         FIG.  8 A  shows an example of a jig made to facilitate fabrication of an optical cable subassembly in accordance with some embodiments; 
         FIG.  8 B  illustrates a process of making an optical connector assembly in accordance with some embodiments; 
         FIGS.  9 A,  9 B, and  9 C  illustrate a lateral cross sectional view, a perspective view, and a longitudinal cross sectional view, respectively, of a cable retainer in accordance with some embodiments; 
         FIGS.  10 A and  10 B  are cross sectional views that illustrate a version of a unitary, single piece cable retainer in accordance with some embodiments; 
         FIG.  11 A  is a perspective view of an embodiment of a unitary, single piece cable retainer in accordance with some embodiments; 
         FIG.  11 B  shows an optical cable subassembly that includes the cable retainer of  FIG.  11 A ; 
         FIG.  11 C  illustrates a single cable retainer attached to multiple optical waveguides in accordance with some embodiments; 
         FIGS.  12 ,  13 , and  14    illustrate cable retainers that are multi-piece structures in accordance with various embodiments; 
         FIGS.  15 A and  15 B  illustrate closed and open views of a cable retainer having a single piece construction with two portions that can move relative to one another in accordance with some embodiments; 
         FIGS.  16 A and  16 B  depict a retainer comprising a C-shaped collet piece in accordance with some embodiments; 
         FIGS.  17 A,  17 B, and  17 C  provide an example of a collet-type cable retainer in accordance with some embodiments; 
         FIGS.  18 A and  18 B  illustrate a collet-type retainer comprising a collet piece and a tapered piece in accordance with some embodiments; 
         FIG.  19    shows a cable retainer that includes surface features to facilitate alignment of the individual optical waveguides in accordance with some embodiments; 
         FIG.  20    depicts a cable retainer having rounded exit surfaces in accordance with some embodiments; 
         FIG.  21    depicts an optical cable subassembly comprising a keyed peg cable retainer in accordance with some embodiments; 
         FIG.  22    and  FIG.  23    depict portions of optical cable subassemblies with optical waveguides disposed within a variable width adhesive attachment space of the cable retainer in accordance with some embodiments; 
         FIG.  24 A  is a cross sectional diagram of an optical cable subassembly that includes a boot in accordance with some embodiments; 
         FIGS.  24 B and  24 C  depict an optical cable subassembly including a cable retainer that is shaped so that the optical waveguides bend within the cable retainer in accordance with some embodiments; 
         FIG.  25    illustrates an embodiment wherein the cable retainer includes an extension that extends inside the boot in accordance with some embodiments; 
         FIG.  26    shows mating optical connector assemblies having male and female covers on the outer housings that extend over the light coupling units in accordance with some embodiments; 
         FIG.  27    provides a side view of mating hermaphroditic connector assemblies which includes separate, removable covers in accordance with some embodiments; 
         FIG.  28    provides a side view of mating hermaphroditic connector assemblies having hinged covers in accordance with some embodiments; 
         FIGS.  29 A and  29 B  depict side views of hermaphroditic connector assemblies having spring actuated retractable covers in accordance with various embodiments; 
         FIGS.  30  and  32    illustrate various features provided on a first major surface of an LCU in accordance with various embodiments; 
         FIGS.  31  and  33    illustrate various features provided on a second major surface of the LCU shown in  FIGS.  30  and  32   ; 
         FIGS.  34  and  36    illustrate various features provided on a first major surface of an LCU in accordance with various embodiments; 
         FIGS.  35  and  37    illustrate various features provided on a second major surface of the LCU shown in  FIGS.  34  and  36   ; 
         FIG.  38    illustrates various features provided on a surface of an LCU in accordance with various embodiments; 
         FIG.  39    illustrates various features provided on a surface of an LCU in accordance with other embodiments; 
         FIG.  40 A  illustrates a mating interface between two LCUs that does not incorporate a particulate contaminant capture feature of the present disclosure; 
         FIG.  40 B  illustrates a particulate contaminant at a mating interface between two LCUs that does not incorporate a particulate contaminant capture feature of the present disclosure; 
         FIG.  40 C  illustrates particulate contaminants trapped by particulate contaminant capture features of the present disclosure provided at mating interfaces between two LCUs;  FIG.  41    illustrates an LCU that incorporates a compound groove having a centering arrangement in accordance with various embodiments; 
         FIG.  42    illustrates various details of the compound groove shown in  FIG.  41   , the groove configured to receive an optical waveguide; 
         FIG.  43    illustrates a longitudinal transition section of the groove shown in  FIG.  41   ; 
         FIG.  44    is a top view of an LCU attachment area comprising a forward adhesive cavity in accordance with various embodiments; 
         FIG.  45    is a side view of the LCU attachment area shown in  FIG.  44   ; 
         FIG.  46    is a top view of an LCU attachment area comprising lateral adhesive cavities in accordance with various embodiments; 
         FIG.  47    is a side view of the LCU attachment area shown in  FIG.  46   ; 
         FIG.  48    is a top view of an LCU attachment area comprising a shared forward adhesive reservoir in accordance with various embodiments; 
         FIGS.  49 - 55    illustrate a process for installing a waveguide in a compound groove of an LCU attachment area in accordance with various embodiments; 
         FIG.  56    illustrates an alignment error that can occur when installing a waveguide in a compound groove; 
         FIG.  57    shows a groove having a recessed bottom surface and a porch region according to various embodiments that facilitate reduction of the alignment error illustrated in  FIG.  56   ; 
         FIGS.  58 - 60    show a groove having two separate sections, including an angular alignment section and a longitudinal transition section comprising centering surfaces in accordance with various embodiments; 
         FIG.  61    shows an LCU that incorporates a compound groove having a positioning arrangement in accordance with various embodiments; and 
         FIG.  62    illustrates an optical ferrule having fiducials in accordance with some embodiments. 
     
    
    
     The figures are not necessarily to scale. Like numbers used in the figures refer to like components. However, it will be understood that the use of a number to refer to a component in a given figure is not intended to limit the component in another figure labeled with the same number. 
     DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS 
     Embodiments described herein involve optical cable subassemblies, optical connectors and related methods. Optical cables and connectors used in many applications may make use of one waveguide or arrays of multiple parallel waveguides (typically 4, 8 or 12 or more parallel waveguides). The individual waveguides are typically made of glass with a protective buffer coating, and the parallel waveguides are enclosed by a jacket. Optical cables and connectors including multiple waveguide cables and connectors are useful for connecting optical waveguides to optical waveguides or to optoelectronic components for in-line interconnects and/or printed circuit board (PCB) connections, e.g., backplane connections. 
     One type of connector is an expanded beam connector, in which light is coupled between waveguides in a beam that is larger in diameter than the core of an associated optical waveguide and typically somewhat less than the waveguide-to-waveguide pitch. The waveguides may comprise optical fibers, e.g., a multi-mode fibers for a multi-mode communication system. These expanded beam optical connectors can have non-contact optical coupling and can require reduced mechanical precision when compared with conventional optical connectors. 
       FIG.  1    shows an optical cable subassembly  100  in accordance with some embodiments. The optical cable subassembly  100  includes one or more optical waveguides  110  and a light coupling unit  120  (also referred to herein as an optical ferrule). The term optical waveguide is used herein to refer to an optical element that propagates signal light. An optical waveguide comprises at least one core with a cladding, wherein the core and cladding are configured propagate light within the core, e.g., by total internal reflection. An optical waveguide may be, for example, a single or multi-mode waveguide, a single core fiber, a multi-core optical fiber, or a polymeric waveguide. A waveguide may have any suitable cross sectional shape, e.g., circular, square, rectangular etc. 
     In some embodiments, discussed in greater detail below, the optical cable subassembly includes a cable retainer  130 . The optical waveguides are permanently attached to the light coupling unit  120  at a light coupling unit (LCU) attachment area  108 . In embodiments that include a cable retainer  130 , the optical waveguides  110  are attached to the retainer  130  at the retainer attachment area  131 . 
     The light coupling unit  120  is configured to mate, e.g., hermaphroditically, with another light coupling unit. The light coupling unit  120  illustrated in  FIG.  1    includes a mechanical mating tongue  116  and light redirecting member  112 . In some embodiments, the mechanical mating tongue  116  can have a tapering width along at least a portion of a length of the tongue portion as shown in the illustrations. The mechanical mating tongue  116  can extend outwardly from a front of a connector housing (not shown in  FIG.  1   ). 
     The light coupling unit (LCU) attachment area  108  includes plurality of grooves  114  each groove being configured to accommodate a different optical waveguide of the optical waveguides  110 . The grooves are configured to receive an optical waveguide and each optical waveguide  110  is permanently attached to a respective groove  114  at the light coupling unit attachment area  108 , e.g., using an adhesive. 
       FIGS.  2 A and  2 B  are cutaway views of a portion of an LCU focusing on the light redirecting member.  FIG.  2 A  illustrates the attachment of several optical waveguides  204  to light coupling unit  220 . Optical fibers  204  are aligned in grooves  214  to which they are permanently attached. The exit end of optical fibers  204  is situated so as to be able to direct light emanating from the optical fiber into the input side or face of light redirecting member  212 . Light redirecting member  212  includes an array of light redirecting elements  213 , at least one for each optical waveguide  204  attached to light coupling unit  220 . For example, in various embodiments each light redirecting element  213  comprises one or more of a prism, a lens, and a reflecting surface. Light redirecting member  212  includes an array of light redirecting elements  213 , one for each optical waveguide of the optical waveguides (optical fibers)  204 . 
       FIG.  2 B  is a cutaway view of a portion of an LCU that includes just one light redirecting element  213 , one waveguide alignment member, e.g., groove  214 , and one optical fiber  204 . In this illustration, optical fiber  204  is aligned in groove  214  and may be permanently attached to it. At the point of attachment, the fiber buffer coating and protective jacket (if any) have been stripped away to allow only the bare optical fiber to lie aligned and permanently affixed to groove  214 . Light redirecting element  213  includes light input side  222  for receiving input light from first optical waveguide (optical fiber)  204  disposed and aligned at first waveguide alignment member  214 . Light redirecting element  213  also includes light redirecting side  224  that may include a curved surface for receiving light from the input side along an input direction and redirecting the received light along a different redirected direction. The light redirecting element  213  also includes output side  226  that receives light from light redirecting side  224  of light redirecting element  213  and transmits the received light as output light along an output direction toward a light redirecting member of a mating light coupling unit. 
       FIG.  3    illustrates a side view of two optical cable subassemblies  301  and  302  showing mated light coupling units  310  and  320  attached to optical waveguides  311 ,  321  at light coupling unit attachment areas  313 ,  323 . A cable retainer  331 ,  332  is optionally attached to the optical waveguides  311 ,  321 , at a retainer attachment area  341 ,  342 . The light coupling units  310 ,  320  may be oriented at a predetermined mating angle, α, with respect to a mating direction. A bend  312 ,  322  in the optical waveguides  311 ,  321  between the light coupling unit attachment area  313 ,  323  and the retainer attachment area  341 ,  342  (or other attachment area, e.g., in a connector housing) provides a predetermined amount of spring force to maintain the light coupling units  310 ,  320  in the mated position. 
     Additional information regarding features and operation of light coupling units, optical cable subassemblies and optical connectors is discussed in commonly owned U.S. Patent Application 61/710,077 filed on Oct. 5, 2012 which is incorporated herein by reference in its entirety. 
       FIGS.  4 A through  4 C  provide several views of portions of an optical connector assembly  401 . The optical connector assembly  401  comprises an inner housing  419  (shown in  FIGS.  4 B and  4 C ) that can hold one or more optical cable subassemblies  402 . The inner housing  419  and a portion of one or more optical cable subassemblies  402  are disposed within an outer housing  418  (shown in  FIG.  4 A ).  FIGS.  4 B and  4 C  illustrate one optical cable subassembly  402  placed within the inner housing  419 , however, the inner housing  419  in this example is capable of holding two optical cable subassemblies. In general, the inner and outer housings can be configured to hold any convenient number of optical cable subassemblies. 
     The inner and outer housings,  419 ,  418 , respectively, have a mating end  451  and a non-mating end  452 . One or more passageways  461 ,  462  are disposed between the mating end  451  and the non-mating end  452  of the inner housing  419 . Each passageway  461 ,  462  is dimensioned to receive and contain a section of an optical cable subassembly. Optical cable subassembly  402  is shown within passageway  461 . The walls  461   a,    461   b,    462   a,    462   b  of the passageways  461 ,  462  between the retainer mount  411  and the mating end  451  can be configured to support the optical cable subassembly  402  while the optical cable subassembly  402  is in an unmated position. The walls  461   c,    461   d,    462   c,    462   d  of the passageways  461 ,  462  between the retainer mount  411  and the non-mating end  452  may be configured to support the optical cable subassembly  402  while the optical cable subassembly  402  is in an unmated position or is in a mated position. 
     In various embodiments, the passageways within the inner housing may have any shape and may have a smaller or a larger volume relative to the volume occupied by the inner housing than the example passageways  461 ,  462  shown in  FIGS.  4 A through  4 C . The volume of a passageway is sufficient to allow the optical waveguides of the optical cable subassembly to develop the predetermined bend that provides the mating spring force. The bend  490  provides a spring force at the mating angle of the light coupling unit  471  that maintains the light coupling unit  471  in optical communication with a mating light coupling unit  491  when the light coupling unit  471  is mated with a light coupling unit  491  of a mating optical connector assembly  481  as illustrated by  FIG.  4 C . 
     The walls  461   a,    461   b,    461   c,    461   d,    462   a,    462   b,    462   c,    462   d  of the passageways  461 ,  462  may have any convenient shape, and are shown in  FIG.  4 C  as curved walls in the forward section  455   a  of the inner housing (between the retainer mounts  411 ,  412  and the mating end  451 ). The curved walls  461   a,    461   b,    462   a,    462   b  of passageways  461 ,  462  accommodate a gentle −z direction bend  490  of the optical waveguides  405 . In some implementations, when the light coupling unit  471  is mated with a mating light coupling unit, the light coupling unit  471  and the optical waveguides  405  “float” within the inner housing  419  such that neither the optical waveguides  405  nor the light coupling unit  471  touch the curved walls  464   a,    464   b  or other surfaces of the passageway  461  in forward section  455   a  of the inner housing  419 . 
     The inner housing  419  optionally includes one or more support features  485  at the mating end  451  that support the optical waveguides  405  and/or the light coupling unit  471  so that the light coupling unit  471  is in a position for mating. In some embodiments, the position for mating may be angled with respect to the mating direction of the optical connector assembly  401  as shown in  FIG.  4 A . The light coupling unit  471  is in a mating position before it mates with another light coupling unit after which (in some embodiments) the light coupling unit is in the “floating” mated position. In some embodiments, when in the mated position, the light coupling unit  471  floats above support feature  485   b  and below support feature  485   a.  In the example illustrated in  FIGS.  4 A- 4 C , the support features  485  comprise dual support arms that extend outwardly from the passageways  461 ,  462 . 
     The inner housing  419  includes retainer mounts  411 ,  412  in passageways  461 ,  462 . Retainer mount  411  is configured to couple with the cable retainer  421  of the optical cable subassembly  402 . The section of the inner housing  419  that includes the retainer mounts  411 ,  412  and the mating end  451 , as indicated by arrow  455   a,  is referred to herein as the forward section of the inner housing  419 . In the embodiment illustrated in  FIGS.  4 A through  4 C , the mating end  451  includes light coupling unit support features  485   a,    485   b.  The section of the inner housing  419  that extends just behind retainer mounts  411 ,  412  and includes the non-mating end  452 , indicated by arrow  455   b,  is referred to herein as the rear section  455   b  of the inner housing  419 . Coupling the cable retainer  421  to the retainer mount  411  within the inner housing  419  fixes the position of the retainer attachment area  403  of the optical cable subassembly  402  within the inner housing  419 , or at least fixes the position of the retainer attachment area  403  within the forward section  455   a  of inner housing  419 , when the optical cable subassembly  402  is in the mated position. 
     In some embodiments, when the cable retainer  421  is installed in the retainer mount  411  and the optical cable subassembly  402  is in the unmated position, there may be some movement (e.g., along the x and or z axes shown in  FIG.  4 B ) of the cable retainer  421 . When the optical cable subassembly  402  mates with a compatible optical cable subassembly and is in the mated position, the position of the retainer attachment area  403  of the optical cable subassembly  402  is fixed by the interaction of the cable retainer  421  and the retainer mount  411 . Fixing the position of the retainer attachment area  403  provides for developing the spring force in the optical waveguides such that the light coupling unit  471  in the mated position is able to float. The light coupling unit and the optical waveguides are held away from the passageway walls  461   a,    461   b  and/or the supports  485  by the spring force of the optical waveguides  405  and the optical waveguides  487  of a mating optical cable subassembly  482  of a mating connector assembly  481  (as shown in  FIG.  4 C ). In some embodiments, when the cable retainer  421  is coupled with the retainer mount  411 , the retainer attachment area  403  may be the only point of attachment of the optical cable subassembly  402  to the inner housing  419  that fixes the position of the optical cable subassembly  402 . In the mated position, the cable retainer  421  and the retainer mount  411  support the optical cable subassembly  402  and attach the optical cable subassembly  402  to the inner housing  419 , fixing the position of the retainer attachment area  403  within the inner housing  419 . 
     As illustrated in  FIG.  4 B , the retainer mount  411 ,  412  can be a slot in the passageway  461 ,  462  dimensioned to hold the cable retainer  421 ,  422  within the inner housing  419 . The optical waveguides  405  of the optical cable subassembly  402  bend, e.g., downwards in the passageway  461  in the orientation of  FIGS.  4 A- 4 C , in response to a force applied by a mating LCU. In some embodiments, the section of optical waveguides enclosed within the cable retainer  411  may be disposed at an angle with respect to the mating direction of the inner housing  419  when the optical cable subassembly  402  is installed in the inner housing  419 . 
       FIG.  5    depicts an embodiment of an inner housing  519  including four optical cable subassemblies  502  installed in the inner housing  519 . In this embodiment, the cable retainers  521  are installed in complementary retainer mounts  511  disposed near the non-mating end  552  of the inner housing  519 . Each of the optical cable subassemblies  502  include a strain relief boot  545  disposed outside the inner housing  519 . In this embodiment, the cable retainer  521  of each optical cable subassembly  502  is arranged between the strain relief boot  545  and the light coupling unit  571 . The cable retainer  521  includes an extension  561   a  that extends into the strain relief boot  545 . In this example, the cable retainer  521  and complementary retainer mount  511  are arranged so that the section of the optical waveguides within the cable retainer  521  is disposed about parallel with a mating direction of the optical connector. 
     The cable retainer and retainer mount can take on various complementary shapes.  FIGS.  4 A- 4 C and  5    illustrate the retainer mount as a slot with the cable retainer dimensioned to fit within the slot.  FIGS.  6 A,  6 B and  7 A and  7 B  illustrate x-z plane cross sectional views of inner housings  619 ,  719  with retainer mounts  611 ,  711  comprising groups of pegs  612 ,  712  that extend laterally (along the y-axis) within a passageway  661 ,  761 . In these embodiments, optical cable subassemblies  605 ,  705  are disposed within a passageway  661 ,  761  of the inner housing  619 ,  719  that is shared by multiple optical cable subassemblies  605 ,  705 . The cable retainers  621 ,  721  have holes  622  or slots  722  that fit the pegs  612 ,  712  such that when the optical cable subassembly  605 ,  705  is installed within the inner housing  619 ,  719 , the retainer attachment area  603 ,  703  is at a fixed position within the passageway  661 ,  761  of the inner housing, at least when the light coupling unit  671 ,  771  is in the mated position. 
       FIG.  6 A  illustrates an inner housing  619  having retainer mounts  611 , each retainer mount comprising a group of four pegs  612  disposed within the shared passageway  661 . The cable retainers  621  of the optical cable subassembly  605  comprise holes  622  that fit the pegs  612 .  FIG.  6 B  illustrates the inner housing  619  after the optical cable subassemblies  605  have been installed. The light coupling unit support features  685  comprise indentations in the sidewalls of the passageway  661  of the inner housing  619  which are dimensioned to receive the light coupling units  671  and to support the light coupling units  671  at least when the light coupling units  671  are in the position for mating. Other support features (not shown) in inner housing  619  may be provided to position the optical cable assembly. 
       FIG.  7 A  illustrates an inner housing  719  having retainer mounts  711 , each retainer mount comprising a group of two pegs  712  disposed within the shared passageway  761 . The cable retainers  721  (shown in  FIG.  7 B ) of the optical cable subassemblies  705  comprise slots  722  that fit the pegs  712 .  FIG.  7 A  illustrates the retainer mounts  711  prior to insertion of the optical cable subassemblies  705 .  FIG.  7 B  illustrates the optical cable subassemblies  705  installed in the shared passageway  761  of the inner housing  719 . As also illustrated in  FIGS.  6 A and  6 B , the light coupling unit support features  785  shown in  FIGS.  7 A and  7 B  comprise indentations in the sidewalls of the passageway  761  of the inner housing  719  that are dimensioned to receive the light coupling units  771 . 
       FIGS.  6 A,  6 B,  7 A, and  7 B  depict cable retainers comprising holes or slots and retainer mounts comprising pegs, however, it will be appreciated that the reverse could also be implemented wherein the cable retainers comprise pegs and the holes or slots are disposed in the housing. 
     An optical cable subassembly may be formed by attaching one or more optical waveguides at the attachment area of a light coupling unit, the light coupling unit attachment area configured for receiving and permanently attaching to the optical waveguides. The optical waveguides are also attached to a cable retainer comprising a retainer attachment area for receiving and attaching to the optical waveguides. In some embodiments, attaching the optical waveguides to the cable retainer comprises inserting the waveguides, e.g., a linear array of waveguide, into a channel of the cable retainer by motion primarily along a direction parallel to the plane of the array of waveguides, and orthogonal to the direction of the waveguide axes. In some embodiments, attaching the optical waveguides to the cable retainer comprises inserting the waveguides, e.g., a linear array of waveguides, into a channel of the cable retainer by motion primarily along a direction perpendicular to the plane of the array of waveguides, and orthogonal to the direction of the waveguide axes. 
     A length of the optical waveguides between the light coupling unit attachment area and the retainer attachment area is configured to allow a bend to develop in the optical waveguides that provides a predetermined mating spring force at a predetermined angle and location of the light coupling unit. In some embodiments, the optical cable subassembly includes a boot that may be attached to the optical waveguides such that the cable retainer is disposed between the light coupling unit and the boot. In some embodiments, the boot may be configured to attach to the optical cable in a way that provides strain relief for the optical cable. 
       FIG.  8 A  shows an example of a jig  800  made to facilitate fabrication of an optical cable subassembly  801  including precise positioning of the retainer  821  on the optical waveguides  803 . The light coupling unit  871  is first attached to the end of the optical waveguides  803 , with the fibers aligned to the optical features of the light coupling unit with v-grooves, or other appropriate means. A cable retainer  821  is inserted into a socket  811  in the jig  800 , and the optical waveguides  803  with light coupling unit  871  attached is then inserted into a groove  802  in the jig  800  and the groove or other feature  822  in the cable retainer  821 . The optical waveguides  803  are gently pulled axially until the light coupling unit  871  rests against a mechanical stop  872  in the jig  800 . Adhesive is then applied to the interior of the cable retainer  821 , attaching the waveguides  803  to the cable retainer  821 . 
     In some embodiments, the cable retainer may be attached to the optical waveguides first. Then the optical waveguides may be stripped and cleaved to a precise length before being attached to the light coupling unit. In yet other embodiments, the optical waveguides may be first stripped and cleaved before the cable retainer is attached at a precise distance from the cleaved end. The light coupling unit may be subsequently attached. 
     The cable retainer may be attached to the optical waveguides by any suitable means, including adhesive bonding to the jacket of the optical waveguides and/or to the optical waveguide buffers, adhesive bonding to bare fiber in a section where the jacket and buffer have been removed, mechanical clamping or crimping of the retainer onto the optical waveguides, welding or soldering to a metallized section of the fiber, or any combination of the above techniques. A strain relief boot may be attached to the cable retainer before the cable retainer is assembled into the connector housing. 
       FIGS.  8 B,  4 B and  4 A  illustrate a process of making an optical connector assembly in accordance with some embodiments. After the optical cable subassembly  801  is fabricated, e.g., as discussed above, the length of the optical waveguides between the light coupling unit attachment area  809  and the retainer attachment area  822  is L as shown in  FIG.  8 B . The optical cable subassembly  801  is installed into a connector inner housing  819  as indicated by dashed line  899 . In some embodiments, the optical cable subassembly  801  is configured to be installed in and subsequently removed from the housing  819  without damage to the inner housing  819  or to the subassembly  801 . The retainer  821  is coupled to a complementary retainer mount  811  in the housing  819  such that the cable retainer  821  coupled with the complementary retainer mount  811  fixes a position of the optical cable subassembly  801  within the housing  819  at least when the optical cable subassembly  801  is in the mated position. The optical waveguides  803  are inserted into a passageway  861  of the inner housing  819  wherein the passageway  861  is shaped to constrain the optical waveguides to bend within the housing  819  between the light coupling unit attachment area  809  and the retainer attachment area  822 . As shown in  FIGS.  4 B and  4 A , after the optical cable subassembly  402  is inserted into the housing  419 , the straight-line distance, d, between the light coupling unit attachment area  409  and the retainer attachment area  403  is less than L due to the bend that develops in the optical waveguides  405  when the optical cable subassembly  402  is installed in the connector inner housing  419 . After the optical cable subassembly  402  is installed in the connector inner housing  419 , an outer housing  420  is disposed over the inner housing  419  as illustrated in  FIG.  4 A . 
     The cable retainer and the complementary retainer mount can take on a variety of shapes, a few of which are illustrated by  FIGS.  9  through  25   .  FIGS.  9 A through  9 C  illustrate a lateral cross sectional view, a perspective view, and a longitudinal cross sectional view, respectively, of cable retainer  900  in accordance with some embodiments. In the illustrated embodiment of  FIGS.  9 A through  9 C , the cable retainer  900  comprises a block  901  having an attachment surface  902  upon which the optical waveguides  905  are bonded by an adhesive layer  906 . As shown in  FIGS.  9 A through  9 C , the adhesive layer  906  may be disposed between the block surface  902  and the optical waveguides  905 . In this example, and other examples where an adhesive is used to attach the optical waveguides to the cable retainer, the adhesive may be applied to the jacket, the buffer coating, and/or the cladding of the optical waveguides. In some configurations, the adhesive may be applied over the optical waveguides and/or along the sides of the optical waveguides.  FIGS.  9 A through  9 C  provide an example of a unitary, single piece cable retainer. 
       FIGS.  10 A and  10 B  are cross sectional views that illustrate another version of a unitary, single piece cable retainer. In the illustrated embodiment, the cable retainer  1000  comprises a U-shaped piece  1001  having sidewalls  1007  and an attachment surface  1002  between the sidewalls  1007 . In the embodiment of  FIG.  10 A , the optical waveguides  1005  are attached to the attachment surface  1002  by an adhesive layer  1006  disposed between the attachment surface  1002  and the optical waveguides  1005 . In the embodiment of  FIG.  10 B , the adhesive  1006  is disposed under and over the optical waveguides  1005 , e.g., substantially filling the interior of the U-shaped piece  1001 . 
       FIG.  11 A  is a perspective view of an embodiment of a unitary, single piece cable retainer  1100  and  FIG.  11 B  shows an optical cable subassembly  1190  that includes the cable retainer  1100 . In the illustrated embodiment, the cable retainer  1100  comprises a C-shaped piece  1101  having attachment surfaces  1103   a,    1103   b.  In some embodiments, the optical waveguides  1105  may be adhesively attached to one or both of the attachment surfaces  1103   a,    1103   b.  The C-shaped piece  1101  can have an inner volume  1107  that is shaped to facilitate placement of adhesive between the optical waveguides  1105  and one or both of the inner attachment surfaces  1103   a,    1103   b.    
       FIG.  11 B  depicts an optical cable subassembly  1190  comprising a light coupling unit  1191  attached to the optical waveguides  1105  at light coupling unit attachment area  1192 . The optical waveguides  1105  are attached to the cable retainer  1100  at a retainer attachment area  1103 . As shown in  FIG.  11 B , the cable retainer  1100  may be attached to the buffer coatings  1106  of the individual optical waveguides  1105   a - 1105   l.  The jacket  1194  that encloses the optical waveguides  1105  has been stripped back but is still visible in  FIG.  11 B . In alternative embodiments, the retainer  1100  may be attached to the jacket of the optical waveguides rather than the buffer coatings. In some embodiments, both the jacket and the buffer coatings may be stripped back and the retainer is attached to the cladding of the individual optical waveguides  1105   a - 1105   l.    
     In some embodiments, as illustrated by  FIG.  11 C , a single cable retainer  1150  may be configured for attachment to two or more waveguides or waveguide arrays  1161 ,  1162 . 
     If the retainer is attached to the jacket of the optical waveguides, the waveguides may move axially within the jacket and/or within their individual buffer coatings. If the jacket is stripped back and the retainer is attached to the buffer coatings, the axial movement of the optical waveguides is decreased relative to the embodiment wherein the retainer is attached to the jacket. Attaching the retainer to the cladding of the optical waveguides provides the least amount of axial movement of the waveguides and so is desirable in some circumstances. 
     In some embodiments, the cable retainer may be a multi-piece structure with separate pieces as illustrated by  FIGS.  12 - 14   .  FIG.  12    illustrates a cross section in the x-y plane of a cable retainer  1200  comprising two separate pieces including a first piece  1201  having a surface  1202  facing the optical waveguides  1205  and a second piece  1211  having a surface  1212  facing the optical waveguides  1205 . The first and second pieces  1201 ,  1211  are configured to attach together so that the optical waveguides  1205  are disposed between the first piece  1201  and the second piece  1211 . In some embodiments, the first piece  1201  and the second piece  1211  may operate together as a clamp so that the optical waveguides  1205  are held in place by friction between the optical waveguides  1205  and surfaces  1202 ,  1212  of the first and second pieces  1201 ,  1211 . In some embodiments, the first piece  1201  and second piece  1210  may be attached together by a mechanical fastener  1220 , e.g., one or more screws, rivets, clips, etc. In some embodiments, the first and second pieces  1202 ,  1212  may be adhesively attached together. Additionally or alternatively, the optical waveguides  1205  may be adhesively attached to one or both surfaces  1202 ,  1212  of the first and second pieces  1201 ,  1211 . In some embodiments, the first and/or second pieces may be attached together by latch parts (not shown in  FIG.  12   ) disposed on the first and second pieces and configured to latch the first and second pieces together. 
       FIG.  13    provides another example of a cable retainer  1300  comprising two separate pieces including a first U-shaped piece  1301  and a second plate-shaped piece  1311 . As illustrated in the x-y cross sectional diagram of  FIG.  13   , the first and second pieces  1301 ,  1311  may be attached together by one or more of mechanical fasteners  1320 , adhesive  1306 , latching parts (not shown in  FIG.  13   ), etc. In some embodiments, the optical waveguides  1305  may be adhesively attached to the U shaped piece  1301  in a manner similar to that described above in connection with  FIGS.  10 A or  10 B  before the first  1301  and second  1311  pieces are attached together. 
     The cable retainer may comprise two separate U-shaped pieces  1401 ,  1411  as shown in the x-y cross sectional diagram of  FIG.  14   . In this embodiment, the cable retainer  1400  comprises first  1401  and second  1411  U-shaped pieces wherein the second U-shaped piece  1411  fits inside the first U-shaped piece  1401 . The first and second pieces  1401 ,  1411  may attach together and grip and hold the optical waveguides  1405  due to a snap fit or press fit that provides friction between the inner surfaces  1403  of the sides of the first piece  1401  and the outer surfaces  1413  of the sides of the second piece  1411 . Gripping of the fiber may be improved by adding a compliant (e.g. elastomeric) pad or grommet  1407  inside the U-shaped pieces which is pressed into contact with the optical waveguides. The compliant structure may allow more secure gripping without damage to the waveguides, or inducing micro-bending loss. Additionally or alternatively, the first and second pieces  1401 ,  1411  may be attached together by mechanical fasteners  1420 , by adhesive  1406 , or by latching parts (not shown in  FIG.  14   ). In some configurations, the optical waveguides  1405  may be adhesively attached to the attachment surface  1402  of the first piece  1401  and/or the attachment surface  1412  of the second piece  1411 . 
     In some implementations, as illustrated in the cross sectional diagrams of  FIGS.  15 A and  15 B , the cable retainer  1500  may have a single piece construction with two portions that can move relative to one another.  FIGS.  15 A and  15 B  show, in x-y cross section, closed and open views, respectively, of a hinged cable retainer  1500  that includes a first portion  1501  and a second portion  1511  connected by a hinge  1550  that allows the first and second portions  1501 ,  1511  to move relative to one another. The hinge may comprise a “living hinge” comprising a thin flexible hinge made from the same material as the retainer pieces. As above, gripping of the fiber may be improved by adding a compliant (e.g. elastomeric) pad or grommet inside the U-shaped pieces which is pressed into contact with the optical waveguides. 
     In some embodiments, in the closed position, the optical waveguides  1505  are clamped and held between the first and second portions  1501 ,  1511  by friction. In some embodiments, the cable retainer  1500  includes complementary latch parts  1507   a,    1507   b,  e.g., on a side of the cable retainer opposite the hinge  1550  as shown in  FIGS.  15 A and  15 B , to facilitate clamping the optical waveguides  1505  between the first and second portions  1501 ,  1511 . Alternatively or additionally, the optical waveguides  1505  may be adhesively attached to the first and/or second portions  1501 ,  1511 . 
     In some embodiments, illustrated by  FIGS.  16 A,  16 B,  17 A,  17 B,  17 C and  18   , the retainer may comprise a collet with fingers configured to grip the optical waveguides when the collet is pushed into a slot or sleeve. To ensure a strong mechanical bond to the glass waveguides, the shapes of the collet and the collet slot or sleeve may be tapered such that when the collet is inserted into the inner housing, the collet is compressed, causing it to clamp the optical waveguides. Gripping of the fiber may be improved by adding a compliant (e.g. elastomeric) pad or grommet inside the U-shaped pieces which is pressed into contact with the optical waveguides. 
     In some embodiments, illustrated by  FIGS.  16 A and  16 B , the retainer  1621  includes a C-shaped collet piece  1601  with two or more collet fingers  1691 ,  1692  that can flex in the z direction under force F. The optical waveguides  1605  are positioned within the collet piece  1601  and the collet fingers  1691 ,  1692  extend laterally in the y-direction across waveguides  1605 . The retainer mount (shown in  FIG.  16 B ), is a tapered slot  1611  formed in the passageway  1661  of an inner housing  1619  (only a portion of the inner housing  1619  is shown in  FIG.  16 B ) such that when the cable retainer  1621  is inserted into the retainer mount  1611  the inner surfaces  1611   a,    1611   b  of the slot  1611  exert a force on the outer surfaces  1621   a,    1621   b  of the fingers  1691 ,  1692 , causing the fingers  1691 ,  1692  to flex toward and grip the optical waveguides  1605  between the fingers  1691 ,  1692 . In some embodiments, the optical waveguides  1605  may be additionally affixed to the cable retainer  1621  by an adhesive, or other means. 
       FIGS.  17 A through  17 C  provide another example of a collet-type cable retainer  1700 .  FIG.  17 A  provides an x-z side view of the of the retainer  1700 ,  FIG.  17 B  shows a y-z end view of the retainer  1700 , and  FIG.  17 C  shows an x-z side view of the retainer  1700  disposed in a slot  1711  in an inner housing  1719 . 
     The retainer  1700  includes a collet piece  1701  with two or more fingers  1791 ,  1792  that can flex in the z direction under force F. The optical waveguides  1705  are positioned within the collet piece  1701  so that the fingers  1791 ,  1792  extend longitudinally in the x-direction along waveguides  1705 . The retainer mount (shown in  FIG.  17 C ), is a slot  1711  formed in the passageway of an inner housing  1719  (only a portion of the passageway and inner housing  1719  is shown in  FIG.  17 C ) such that when the cable retainer  1700  is inserted into the retainer mount  1711 , the inner surfaces  1711   a,    1711   b  of the slot  1711  exert a force on the outer surfaces  1721   a,    1721   b  of the fingers  1791 ,  1792  of the cable retainer  1700 , causing the fingers  1791 ,  1792  to flex toward and grip the optical waveguides  1705  between the fingers  1791 ,  1792 . In some embodiments, the optical waveguides  1705  may additionally affixed to the cable retainer  1700  by an adhesive 
     In yet another example of a collet type retainer, the retainer  1800  illustrated in  FIGS.  18 A and  18 B  includes a tapered collet piece  1801  and a tapered sleeve piece  1811 . The collet piece  1801  includes two or more fingers  1802 ,  1803  configured to flex under force F. The optical waveguides  1805  are inserted through the collet piece  1801  and through the sleeve piece  1811  which are initially separated as shown in  FIG.  18 A . When the collet piece  1801  is inserted into the tapered sleeve  1811 , as shown in  FIG.  18 B , the sleeve  1811  applies a force on the fingers  1802 ,  1803  causing the fingers  1802 ,  1803  to flex toward and grip the optical waveguides  1805  between the fingers  1802 ,  1803 . In some embodiments, the optical waveguides  1805  may alternatively or additionally affixed to the collet piece  1801  by an adhesive. In various embodiments, the inside of the sleeve may be tapered, or both the inside of the sleeve and outside of the collet may be tapered. 
     In some embodiments, e.g., wherein the retainer is configured to attach to the optical waveguides by a friction grip, the optical waveguides may slide longitudinally along the x-axis through the retainer until the appropriate length of the optical waveguides is reached. When the appropriate length is reached, the optical waveguides are fixedly attached to the retainer by a clamping action of the retainer. Initially allowing the optical waveguides to slide until the retainer clamps and grips the waveguides, thus fixing the position of the retainer on the waveguides, may facilitate fabrication of the optical cable subassembly and/or optical connector assembly in some circumstances. 
     In some embodiments, the cable retainer may include surface features that facilitate alignment of the individual optical waveguides. One example of a cable retainer with surface features is shown in  FIG.  19   .  FIG.  19    depicts a cross sectional y-z view of a retainer  1900  comprising a block  1901  having an attachment surface  1902  for attaching to an optical waveguides which are not shown in  FIG.  19   . The attachment surface  1902  includes grooves  1907 , e.g., U, V, and/or Y shaped grooves, wherein each groove  1907  is dimensioned to accommodate one optical waveguide. The grooves  1907  facilitate alignment of the individual optical waveguides in the retainer  1900 . The optical waveguides  1905  may be gripped by the retainer and/or adhesively attached to the retainer  1900 . 
     In some embodiments, one or both exit surfaces of one or both ends of the cable retainer may have a particular shape, e.g., rounded, squared, beveled, etc. Rounded or beveled exit surfaces may be used to accommodate a bend in the optical waveguides.  FIG.  20    illustrates a cross section in the x-z plane of an optical cable subassembly  2000  comprising a light coupling unit  2010 , one or more optical waveguides  2020 , and a cable retainer  2030 . The cable retainer  2030  comprises a retainer piece  2001  having first end  2001   a  and a second end  200 lb. At the first end  2001   a,  the retainer piece  2001  has first exit surface  2011  with a rounded edge and a second exit surface  1612  with a rounded edge. The first and exit surfaces  2021 ,  2022  at the second end  1601   b  of the retainer piece  1601  have square edges. In some embodiments, the cable retainer piece (or multiple pieces) may include grooves or recess features that provide a bonding space for adhesive, as illustrated by features  2005  of  FIG.  20   . Bonding spaces  2005  as shown in  FIG.  20   , for example, may be used in any of the cable retainers described herein that rely on adhesive bonding to secure the optical waveguides to the retainer. These bonding spaces can improve the strength of the adhesive bond to the cable retainer by increasing the surface area of the bonded region, and/or by creating a mechanical interlock between the adhesive and the cable retainer. The bonding spaces can also be used to control the flow of excess adhesive and prevent it from contaminating the outside surface of the cable retainer, thus interfering with its intended fit into the retainer mount. 
       FIG.  21    depicts an optical cable subassembly  2100  comprising a light coupling unit  2110 , a plurality of optical fibers  2105  and a keyed cable retainer  2130 . The cable retainer  2130  includes a peg, e.g., a cylindrical peg, having a first side or portion  2101 , a second side or portion  2111 , wherein the first side  2101  includes a key  2102 . The optical waveguides  2105  are attached between the first side  2101  and the second side  2111 . The optical waveguides  2105  may be held in the cable retainer  2130  between the first and second sides  2101 ,  2111  by adhesive  2106  and/or friction grip. When an adhesive is used, the cable retainer  2130  includes an adhesive slot  2117  between the retainer sides or portions  2101 ,  2111  where the optical waveguides  2105  are adhesively attached to the cable retainer  1230 . The cable retainer  2130  is configured to fit into a complementary keyed slot of the inner housing (not shown in  FIG.  21   ). 
     In some embodiments, the cable retainer can serve as both a strain relief and an optical waveguide retainer. In these embodiments, the cable retainer includes first and second regions, a first region of the cable retainer, which is the strain relief section, is attached to the jacket of the plurality of the optical waveguides. A second region of the cable retainer is attached to the cladding and/or buffer coating of the optical waveguides. To facilitate attaching to both the jacket and the cladding and/or buffer coatings, some embodiments, illustrated by  FIGS.  22  and  23   , include an adhesive attachment space wherein the width (along the z axis) of the adhesive attachment space between the pieces or portions of the cable retainer that adhesively attach to the optical waveguides may vary. An example of a variable width attachment space  2217  is shown in  FIG.  22   .  FIG.  22    depicts a portion of an optical cable subassembly  2200  including optical waveguides  2205  and a cable retainer  2230 . The optical waveguides  2205  are disposed within the variable width adhesive attachment space  2217  of the cable retainer  2230 . The adhesive attachment space includes a first region  2217   a,  having a width s 1 , and a second region  2217   b,  having a width s 2 , wherein s 1  is less than s 2 . 
     The first region  2217   a  of the adhesive attachment space  2217  is configured to adhesively attach to first regions  2205   a  of the optical waveguides  2205  that have the jacket  2208  stripped away from the optical waveguides  2205 . In the first regions  2205   a  of the optical waveguides  2205 , the buffer coating  2207  of the optical waveguides  2205  is exposed and adhesive  2206  is disposed between the buffer coating  2207  and the inner surfaces  2217   a,    2217   b  of the adhesive attachment space  2217  of the cable retainer  2230 . The height s 1  of the adhesive attachment space  2217  at the opening  2217   c  of the adhesive attachment space  2217  is relatively narrow which controls the angle of the optical waveguides  2205  at the opening  2217   c.    
     The second region  2217   b  (strain relief region) of the adhesive attachment space  2217  is configured to adhesively attach to second regions  2205   b  of the optical waveguides  2205 . In the second regions  2205   b  of the optical waveguides  2205 , the jacket  2208  of the optical waveguides  2205  has not been stripped away from the optical waveguides  2205 . In the second region  2205   b  of the optical waveguides  2205 , adhesive  2206  is disposed between the jacket  2208  of the optical waveguides  2205  and the inner surfaces  2218   a,    2218   b  of the adhesive attachment space  2217  of the cable retainer  2230 . 
     In other embodiments (not shown) the width of the adhesive attachment space  2217  does not substantially vary. 
     Another example of a cable retainer having a strain relief section facilitated by a variable height attachment space  2317  is shown in  FIG.  23   .  FIG.  23    depicts a portion of an optical cable subassembly  2300  including optical waveguides  2305  and a cable retainer  2330 . The optical waveguides  2305  are disposed within the variable width adhesive attachment space  2317  of the cable retainer  2330 . The adhesive attachment space includes a first region  2317   a,  having a height s 3 , and a second region  2317   b  (the strain relief section) having a height s 4 , where s 4  is greater than s 3 . 
     The first region  2317   a  of the adhesive attachment space  2317  is adhesively attached to regions of the optical waveguides that have the jacket removed and/or to regions of the optical waveguides that have both the jacket  2308  and the buffer coating  2307  stripped away exposing the cladding  2309  of the optical waveguides  2305 . In the first region  2317   a,  adhesive  2306  is disposed between the buffer coating  2307  and/or cladding  2309  of the optical waveguides  2305  and the inner surfaces  2317   a,    2317   b  of the adhesive attachment space  2317  of the cable retainer  2330 . 
     In some implementations, bonding the cable retainer  2330  to the cladding  2309  of the optical waveguides may provide a more reliable bond and/or may reduce the amount of longitudinal movement of the individual optical waveguides within their buffer coating  2307  and/or the jacket  2308  of the optical waveguides. 
     The second (strain relief) region  2317   b  of the adhesive attachment space  2317  is configured to adhesively attach to a region of the optical waveguides  2305  where the jacket is intact. In the second region  2317   b,  adhesive  2306  is disposed between the jacket  2308  of the optical waveguides  2305  and the inner surfaces  2317   a,    2317   b  of the adhesive attachment space  2317  of the cable retainer  2330 . 
     In other embodiments (not shown) the width adhesive attachment space  2317  does not substantially vary. 
     In some embodiments, the optical cable subassembly includes a boot that covers a portion of the optical waveguides. The boot is often positioned outside the connector housing at or near the non-mating end of the connector housing. The cable retainer is positioned between the boot and the light coupling unit. The boot may be made of a flexible material which protects the optical waveguides from breakage or damage due to overflexing. 
       FIG.  24 A  is a cross sectional diagram of an optical cable subassembly  2400  that includes a light coupling unit  2410 , one or more optical waveguides  2420 , a cable retainer  2430 , and a boot  2440 . In the illustrated embodiment, the boot  2440  and the cable retainer  2430  are spaced apart along the optical waveguides  2420 . Each optical waveguide  2420  has a cladding  2409  surrounding an optical core with a buffer coating  2407  disposed over the cladding  2409 . A jacket  2408  is disposed over the optical waveguides  2420 . In some sections  2420   a,    2420   b  of the optical waveguides  2420 , the jacket  2408 , the buffer coating  2407 , or both are stripped away to facilitate attachment of the optical waveguides  2420  at the light coupling unit attachment area  2411  and/or the retainer attachment area  2431 . 
     In some embodiments, the optical cable subassembly may include a cable retainer that is shaped or angled such that the optical waveguides are bent or angled within the retainer.  FIG.  24 B  depicts an optical cable subassembly  2490  comprising a light coupling unit  2491 , a boot  2494  and a cable retainer  2493  disposed between the light coupling unit  2491  and the boot  2494 . The cable retainer  2493  is shaped so that the optical waveguides  2492  include a bend  2495  within the cable retainer  2493 . 
       FIG.  24 C  depicts an optical cable subassembly comprising a light coupling unit  2481 , a boot  2484  and a cable retainer  2483  disposed between the light coupling unit  2481  and the boot  2484 . The cable retainer  2483  is shaped so that the portion  2485  of the optical waveguides  2482  within the cable retainer  2483  is angled. 
     In some embodiments, as shown in  FIG.  25   , the boot and the cable retainer may be overlapping and/or may be attached together.  FIG.  25    illustrates an embodiment wherein the cable retainer  2530  includes an extension  2531  that extends through the passageway  2561  of the inner housing, outside the inner connector housing  2519 , and inside the boot  2540 . 
     In various embodiments, the optical connector assembly may include a protective cover to protect the light coupling units from damage or contamination.  FIGS.  26  through  29    illustrate several protective cover configurations.  FIG.  26    shows mating optical connector assemblies  2601 ,  2602  having male  2610  and female  2620  protective covers on the outer housings that extend over the light coupling units  2671 . In the illustrated embodiment, the protective covers are fixed on the connectors, and do not move during mating, e.g., the female cover does not move relative to the female connector. 
       FIG.  27    provides a side view of mating hermaphroditic connector assemblies  2701 ,  2702  having inner  2719 ,  2729  and outer housings  2718 ,  2728 . The light coupling units  2771 ,  2772  are shown disposed within the inner housings  2719 ,  2729 . Each connector assembly  2701 ,  2702  includes a separate, removable protective cover  2703 ,  2704  that is disposed over the mating end of the outer housing  2718 ,  2728 . The protective covers  2603 ,  2704  are configured to be manually removed before the connector assemblies  2701 ,  2702  are mated. 
       FIG.  28    provides a side view of mating hermaphroditic connector assemblies  2801 ,  2802  having inner  2819 ,  2829  and outer housings  2818 ,  2828 . The light coupling units  2871 ,  2872  are shown disposed within the inner housings  2819 ,  2829 . Each connector assembly  2801 ,  2802  includes a protective cover  2803 ,  2804  coupled to the outer housing  2718 ,  2728  by a hinge  2705 ,  2706 . The protective covers  2803 ,  2805  are moved via the hinges  2805 ,  2806  to expose the light coupling units  2871 ,  2872  before the connector assemblies  2801 ,  2802  are mated. 
       FIGS.  29 A and  29 B  depict side views of hermaphroditic connector assemblies  2901 ,  2902  having spring actuated retractable protective covers.  FIG.  29 A  shows the position of the protective cover  2903  of connector assembly  2901  prior to mating.  FIG.  29 B  shows the position of protective covers  2903 ,  2904  after mating. The hermaphroditic connector assemblies  2901 ,  2902  have inner  2919 ,  2929  and outer housings  2918 ,  2928 . The light coupling units  2971 ,  2972  are shown disposed within the inner housings  2919 ,  2929 . Each connector assembly  2901 ,  2902  includes a retractable protective cover  2903 ,  2904  actuated by a spring  2905 ,  2906 . The protective covers  2903 ,  2905  are pushed back, compressing the springs  2905 ,  2906  as the connector assemblies  2901 ,  2902  are mated. 
     Expanded-beam optical interconnect devices, such as single mode light coupling units, are sensitive to angular errors on the order of 0.1 degrees. For example, the planar interface between light coupling units of the present disclosure can be about 3 mm long. If a single 50 μm diameter dust particle is trapped in the interface between two mated light coupling units, the dust particle would generate an angular error of 1 degree or larger, thereby decreasing optical transmission efficiency. Embodiments are directed to a light transmitting surface, such as a mating surface of a light coupling unit, that incorporates a series of grooves, posts or other features or patterns configured to capture particulate contaminates, such as dust, when the mating surface contacts a corresponding mating surface of a mating light coupling unit. In order to make mating between light transmitting surfaces less sensitive to dust, a series of small lands with grooves between them (or posts with spacing therebetween) can be added to the planar sections of the light transmitting surface so that there is a place for the dust or other particulate contaminate to fall into. Although the following discussion is directed to a light coupling unit or units, it is understood that any light transmitting surface or surfaces are contemplated. 
     Turning now to  FIGS.  30 - 34   , there are illustrated different views of an LCU  3000  which incorporates a feature for capturing particulate contaminants in accordance with various embodiments. The LCU  3000  illustrated in  FIGS.  30  and  32    includes a first major surface  3001  on which an LCU attachment area  3002  is provided. The LCU  3000  further includes sidewalls  3022  and rear wall  3024 . The LCU attachment area  3002  is shown positioned between the sidewalls  3022  and includes a plurality of substantially parallel first grooves  3010  oriented along a first direction. A light redirecting member  3004  is provided at the end of each of the first grooves  3010 . The first grooves  3010  are configured to receive an optical waveguides (not shown). The first major surface  3001  also includes a mating tongue  3012  that projects outwardly from the LCU attachment area  3002 . The mating tongue  3012  includes a first surface  3013  and an opposing second surface  3015 . Adjacent the LCU attachment area  3002  is the rear wall  3024  which includes a coupling member  3014 . The coupling member  3014  is configured to receive a mating tongue  3012  of a mating light coupling unit. 
       FIGS.  31  and  33    illustrate various features of the LCU  3000  provided on a second major surface  3021 , the second major surface  3021  opposing the first major surface  3001  shown in  FIGS.  30  and  32   . The second major surface  3021  is configured to be a mating surface of the LCU  3000 . The second major surface  3021  includes the second surface  3015  of the mating tongue  3012  which, in the embodiment shown in  FIGS.  31  and  33   , is substantially planar. The second major surface  3021  also includes a plurality of substantially parallel second grooves  3020  and an optically transmitting window  3016  disposed between the second grooves  3020  and the second surface  3015  of the mating tongue  3012 . The second grooves  3020  are oriented along a direction different from the first direction of the first grooves  3010  provided at the LCU attachment area  3002  on the first major surface  3001 . The second grooves  3020  are oriented along a direction different from the mating direction, D M . The second grooves  3020  have a pitch different from that of the first grooves  3010 . 
     In the embodiment shown in  FIGS.  31  and  33   , the second surface  3015  of the mating tongue  3012  is substantially planar. In other embodiments, the second surface  3015  of the mating tongue  3012  includes a plurality of the substantially parallel second grooves  3020 . The second grooves  3020  on the second surface  3015  of the mating tongue  3012  are oriented along a direction different from the mating direction, D M . 
     As discussed above, the second major surface  3021  is configured to be a mating surface of the LCU  3000 . In particular, the second major surface  3021  is adapted to slide against the mating surface of a mating light coupling unit when moved in a mating direction, D M  (see  FIG.  31   ). The interior surfaces of the sidewalls  3022  have a shape configured to receive the shape of a mating tongue  3012  of a mating light coupling unit. In the embodiment shown in  FIGS.  31  and  33   , the interior surfaces of the sidewalls  3022  have a curvature that matches the curvature of the mating tongue  3012  of the mating light coupling unit. It is understood that the interior surfaces of the sidewalls  3022  can instead be polygonal or include polygonal features in addition to curved features. 
     In the embodiment shown in  FIGS.  31  and  33   , the optically transmitting window  3016  is recessed into the second major surface  3021 . More particularly, the optically transmitting window  3016  is recessed below the second surface  3015  of the mating tongue  3012  and below the lands  3023  of the second grooves  3020 . Recessing the optically transmitting window  3016  into the second major surface  3021  prevents potentially damaging contact with a mating tongue  3012  of a mating light coupling unit when the LCU  3000  is connected to a mating light coupling unit. 
     According to various embodiments, the second grooves  3020  on the second major surface  3021  are configured to capture particulate contaminants (e.g., dust) between the second major surface  3021  and a mating surface of a mating light coupling unit. For example, as the mating tongue  3012  of the mating light coupling unit is received by the coupling member  3014 , any particulate contaminants on the mating tongue  3012  of the mating light coupling unit or on a land  3023  of the second grooves  3020  are pushed into and captured by a recess of the second grooves  3020 . Capturing of particulate contaminants within the recesses of the second grooves  3020  prevents the above-described angular errors from occurring when mating a pair of light coupling units. 
     In the embodiment shown in  FIGS.  31  and  33   , the second grooves  3020  on the second major surface  3021  are oriented transverse to the first direction of the first grooves  3010  on the first major surface  3001 . In some embodiments, the second grooves  3020  are oriented substantially perpendicular to the first direction of the first grooves  3010 . In other embodiments, the second grooves  3020  can be oriented at an angle of about 45° with respect to the first direction of the first grooves  3010 . In further embodiments, the second grooves  3020  can be oriented at an angle between about 30° and 60° with respect to the first direction of the first grooves  3010 . Although the second grooves  3020  are shown in  FIGS.  31  and  33    to be substantially parallel and straight, the second grooves  3020  can have some degree of curvature while maintaining a substantially parallel relationship. For example, the second grooves  3020  can have a generally chevron shape or other curved shape. 
     The second grooves  3020  can have cross-sections that comprise polygonal surfaces and/or curvilinear surfaces. In some embodiments, the second grooves  3020  have a V-shaped cross section. In other embodiments, the second grooves  3020  have a U-shaped cross section. The second grooves  3020  comprise a series of lands  3023  and a recess between adjacent lands  3023 . In some embodiments, the lands  3023  have a width smaller than a width of the recesses. For example, the width of the lands  3023  can be less than about half the width of the recesses. By way of further example, the width of the lands  3023  can be less than about one-fourth the width of the recesses. In other embodiments, the lands  3023  have a width larger than a width of the recesses. In further embodiments, the width of the lands  3023  is less than about 75 μm. The lands  3023  may be coplanar with any mating surface, such as a mating surface that does not have lands. It is noted that if the lands  3023  are narrower than the recesses, and there is a linear pattern where the lands  3023  are parallel on the two mating parts, the lands  3023  can fall into the recesses and jam. Accordingly, if the lands  3023  are linear and not sufficiently parallel, they will not cause jamming. 
       FIGS.  34 - 37    illustrate an LCU  3000  having a groove configuration on the second major surface  3021  in accordance with various embodiments. The LCU  3000  shown in  FIGS.  34  and  36    includes a first major surface  3001  having many of the features shown in  FIGS.  30  and  32   . The LCU  3000  shown in  FIGS.  34  and  36    includes a second major surface  3021  having features differing from those shown in  FIGS.  31  and  33   . More particularly, and with reference to  FIGS.  35  and  37   , the second surface  3015  of the mating tongue  3012  includes a plurality of substantially parallel second grooves  3020 . In this embodiment, the second major surface  3021  includes a first region  3030  comprising at least some of the second grooves  3020  and a second region  3032  comprising at least some of the second grooves  3020 , wherein the second region  3032  includes the second surface  3015  of the mating tongue  3012 . 
     The second grooves  3020  on the second major surface  3021  are oriented along a direction different from the first direction of the first grooves  3010  of the LCU attachment area  3002 . In the embodiment shown in  FIGS.  35  and  37   , the second grooves  3020  are oriented at an angle of about 45° with respect to the first direction of the first grooves  3010 . In general, the second grooves  3020  can be oriented at an angle between about 30° and 60° with respect to the first direction of the first grooves  3010 . A diagonal orientation of the second grooves  3020  serves to reduce chattering that can occur during light coupling unit mating where the second grooves  3020  are oriented perpendicular to the direction of mating, D M . Although the second grooves  3020  are shown in  FIGS.  35  and  37    to be substantially parallel and straight, the second grooves  3020  can have some degree of curvature while maintaining a substantially parallel relationship. 
     In the embodiment illustrated in  FIGS.  35  and  37   , an optically transmitting window  3016  is situated between the first region  3030  and the second region  3032 . The upper surface of the optically transmitting window  3016  is flush with the lands  3023  of the second grooves  3020  in the first and second regions  3030  and  3032 . Positioning the optically transmitting window  3016  to be flush with the lands  3023  of the second grooves  3020  facilitates clearing of any particulate contaminants from the optically transmitting window  3016  when connecting the LCU  3000  to a mating light coupling unit. When connecting a pair of light coupling units, for example, the second grooves  3020  on region  3032  of the mating tongue  3012  of a mating light coupling unit slidably contacts the optically transmitting window  3016  of the LCU  3000 , thereby pushing any particulate contaminates off of the optically transmitting window  3016 . 
     Because the optically transmitting window  3016  comes into contact with the mating tongue  3012  of a mating light coupling unit, it is desirable that the optically transmitting window  3016  have enhanced hardness. More particularly, the optically transmitting window  3016  can have a hardness greater than that of the lands  3023  of the second grooves  3020 . For example, the optically transmitting window  3016  can include a coating having a hardness greater than that of the lands  3023  of the second grooves  3020 . The coating on the optically transmitting window  3016  can be an antireflective coating, for example. 
       FIG.  38    illustrates an LCU  3000  having a pattern of small posts  3025  on the second major surface  3021  in accordance with various embodiments. The LCU  3000  shown in  FIG.  38    includes a first major surface (not shown) having many of the features shown in previous figures (e.g., one or more grooves configured to receive one or more optical waveguides). The LCU  3000  shown in  FIG.  38    includes a second major surface  3021  having a field of small posts  3025  that extend normal from the second major surface  3021 . Top surfaces of the posts  3025  define lands. The spacing between the posts  3025  allows dust and other particulate contaminants to be captured within recesses between the posts  3025 . In some embodiments, the posts  3025  are arranged in rows and columns In other embodiments, the posts  3025  are arranged in a staggered pattern or other distribution. The second surface  3015  of the mating tongue  3012  is preferably planar, which becomes a mating surface for posts of a mating LCU. 
       FIG.  39    illustrates an LCU  3000  having a waffle pattern  3027  on the second major surface  3021  in accordance with various embodiments. The LCU  3000  shown in  FIG.  39    includes a first major surface (not shown) having many of the features shown in previous figures. The LCU  3000  shown in  FIG.  39    includes a second major surface  3021  having a waffle pattern  3027  extending over the second major surface  3021  except for the optically transmitting window  3016 . In some embodiments, the waffle pattern  3027  can cover the region of the second major surface  3021  that excludes the mating tongue  3012  and the optically transmitting window  3016 . The lands (raised portions) of the waffle pattern  301  are arranged to contact corresponding lands or planar surfaces of a waffle pattern or planar surface provided on a mating LCU. The waffle pattern  3017  of  FIG.  39    has a rectangular pattern. In other embodiments, patterns such as hexagonal patterns, diamond patterns, or irregular patterns may be used. 
       FIGS.  40 A- 40 C  illustrate coupling between two LCUs  3000 A and  3000 B along a mating interface  3030 . The mating interface  3030  includes a first mating interface  3030 A between a mating tongue surface  3012 A of LCU  3000 A and a mating surface  3003 B of LCU  3000 B. The mating interface  3030  also includes a second mating interface  3030 B between a mating tongue surface  3012 B of LCU  3000 B and a mating surface  3003 A of LCU  3000 A. In  FIG.  40 A , the mating interface  3030  of the two LCUs  3000 A and  3000 B does not include a particulate contaminant capture feature of the present disclosure. In the absence of particulate contaminants at the mating interface  3030 , the optical transparent portions  3016 A and  3016 B are in proper optical alignment. 
       FIG.  40 B  shows a dust particle  3032  trapped at the second mating interface  3030 B between the mating surface  3003 A of LCU  3000 A and the tongue mating surface  3012 B of LCU  3000 B. As was discussed previously, presence of a single 50 μm diameter dust particle trapped in the interface  3030  between the two mated LCUs  3000 A and  3000 B can generate an angular error of 1 degree or larger at the optical interface  3016 A/ 3016 B. 
       FIG.  40 C  shows coupling between two light coupling units  3000 A and  3000 B each incorporating a particulate contaminant capture feature in accordance with various embodiments.  FIG.  40 C  illustrates a dust particle  3032 A captured within one of the second grooves  3020 A at a second mating interface  3030 B between LCU  3000 A and LCU  3000 B. More particularly, the dust particle  3032 A is captured within a recess of one of the grooves  3020 A at the second mating interface  3030 B between the mating surface  3003 A of LCU  3000 A and the mating tongue surface  3012 B of LCU  3000 B. 
       FIG.  40 C  also illustrates a dust particle  3032 B captured within one of the second grooves  3020 B at a first mating interface  3030 A between LCU  3000 A and LCU  3000 B. More particularly, the dust particle  3032 B is captured within a recess of one of the grooves  3020 B at the first mating interface  3030 A between the mating surface  3003 B of LCU  3000 B and the mating tongue surface  3012 A of LCU  3000 A. Because the dust particles  3032 A and  3032 B are trapped within the particulate contaminant capture features, proper optical alignment at the optical interface  3016 A/ 3016 B between LCU  3000 A and LCU  3000 B is maintained. 
     Attachment of optical waveguides or fibers to optical or optoelectronic devices is often done with V-shaped grooves (i.e., V-grooves). The waveguides is forced into the bottom of the groove (typically a 90° angle V-groove) with a clamping mechanism. Typically, an index-matching adhesive is then applied to permanently hold the waveguides in the V-groove. This scheme has several challenges. The clamping mechanism must provide sufficient force to bend the waveguides to seat them in and thus align them with the grooves, yet have sufficient compliance to contact each waveguide of a ribbon of waveguides. It must also allow access for the application of the adhesive without itself becoming bonded to the waveguides. The position of the clamping mechanism over the V-grooves makes it difficult to observe the positions of the waveguides, or to use a light-cured adhesive. Use of U-shaped grooves (i.e., U-grooves) with flat bottoms and vertical sidewalls have several challenges. Issues with the ease of capture of the waveguides and with the positional error associated with the clearance required for the groove width have not been previously addressed. 
     Embodiments are directed to a light coupling unit having one or a multiplicity of grooves configured to receive and permanently attach to one or a multiplicity of optical waveguides. In one embodiment, a portion of a groove provides nearly vertical sidewalls that allow an optical waveguide to be bent laterally into the correct position. The groove can be formed wider at the top, providing a substantially Y-shaped cross-section (i.e., Y-groove) that facilitates capturing an optical waveguide into the groove. As was discussed previously, the optical waveguides can be single-mode optical waveguides, multi-mode optical waveguides, or an array of single-mode or multi-mode optical waveguides. In some embodiments, the waveguides are single-mode or a multi-mode polymer optical waveguide. 
     In another embodiment, a portion of a groove provides nearly vertical sidewalls that allow an optical waveguide to be bent laterally into the correct position. This portion of the groove can be made slightly wider than the diameter of the optical waveguide to provide clearance for initial capture of the optical waveguide. Once in contact with and approximately parallel to the bottom of the groove, the end of the optical waveguide is slid axially into a location where the width of the groove gradually narrows to less than the diameter of the optical waveguide. Here the tip of the optical waveguide stops, and is correctly positioned. The groove, according to some embodiments, can be formed wider at the top, providing a substantially Y-shaped cross-section that facilitates capturing an optical waveguide into the groove. 
     Embodiments of the disclosure can provide several advantages over conventional approaches. For example, like V-grooves, Y-grooves can be molded in the same mold insert as the light redirecting members (e.g., mirror lenses) of a light coupling unit. The waveguides can be easily and very quickly positioned in the Y-grooves. The waveguides can be precisely positioned without the use of a clamp over the grooves (see  FIGS.  49 - 55   ), which allows for direct observation of the waveguides in the grooves and the use of light-cured adhesive to rapidly and reliably attach the waveguides in the Y-grooves. 
       FIG.  41    illustrates a portion of an LCU  4100  in accordance with various embodiments. The LCU  4100  shown in  FIG.  41    includes a single LCU attachment area  4102 . Although a single LCU attachment area  4102  is shown in  FIG.  41   , it is understood that a multiplicity of attachment areas  4102  can be provided on the LCU  4100  for receiving and permanently attaching to a multiplicity of optical waveguides. The LCU attachment area  4102  includes a Y-groove  4110  having an entrance  4111 , a terminal end  4113 , and a central plane  4112  (see  FIG.  42   ) extending between the entrance  4111  and the terminal end  4113 . The central plane  4112 , as shown in  FIG.  42   , is a plane bisecting a bottom surface  4125  of the Y-groove  4110  and extending perpendicularly from the bottom surface  4125 . The Y-groove  4110  is configured to receive an optical waveguide, such as the generally cylindrical waveguide  4105  shown in  FIG.  42   . 
     The LCU  4100  includes a light redirecting member  4104  and an intermediate section  4108  between the light redirecting member  4104  and the terminal end  4113 . In some embodiments, the terminal end  4113  comprises an optically clear member, such as a lens, or is formed from optically transparent material. The intermediate section  4108  is formed from an optically transparent material. The light redirecting member  4104  includes an output side  4106  through which light exits from (or enters into) the light directing member  4104 . 
     According to some embodiments, and with reference to  FIGS.  41  and  42   , the Y-groove  4110  is a compound groove formed by a generally U-shaped lower portion  4120  and an expanded upper portion making the compound groove generally Y-shaped. It is understood that the terms U and Y modifying the term groove serve to connote an approximate shape of these grooves for purposes of convenience and not of limitation. 
     As is best seen in  FIG.  42   , the Y-groove  4110  is defined by a first region  4120 ′, a second region  4130 ′, an opening  4140 , and a bottom surface  4125 . The first region  4120 ′ is defined between the bottom surface  4125  and the second region  4130 ′. The first region  4120 ′ includes substantially parallel sidewalls  4122  separated by a spacing, S. The sidewalls  4122  can have a draft of one or a few degrees (e.g., &lt;about 10 degrees) in a direction off vertical, and as such, may be considered to be substantially parallel to one another. For example, the sidewalls  4122  can be normal to the bottom surface  4125  to within about 5 degrees. The sidewalls  4122  can have a slight outward slope or draft to facilitate mold release of the sidewalls  4122  during fabrication. In this case, the substantially vertical sidewalls  4122  form a draft angle, α, with a plane  4112  extending perpendicular from the bottom surface  4125 . 
     The second region  4130 ′ is disposed between the first region  4120 ′ and the opening  4140 . The opening  4140  is defined between top surfaces  4127  of the Y-groove  4110 . A width, W, of the opening  4140  is greater than the spacing, S, between the sidewalls  4122 . As can be seen in  FIG.  42   , the first region  4120 ′ defines the U-shaped lower portion  4120  of Y-Y-groove  4110  and the second region  4130 ′ defines the expanded upper portion  4130 . 
     The second region  4130 ′ includes sidewalls  4132  that extend outwardly from the central plane  4112  of the Y-groove  4110 . In  FIG.  42   , the sidewalls  4132  comprise linear sidewalls, which may be considered chamfered sidewalls. In other embodiments, the sidewalls  4132  may be non-linear, such as by having some degree of curvature. The sidewalls  4132  extend between the first region  4120 ′ and the opening  4140 , with a spacing between the sidewalls  4132  progressively increasing from the first region  4120 ′ to the opening  4140 . 
     According to some embodiments, a width, W, of the opening  4140  is greater than the spacing, S, of the first region  4120 ′ by a distance equal to about half of the spacing, S. In other embodiments, the width, W, of the opening  4140  is greater than the spacing, S, by a distance greater than half of the spacing, S. A height of the sidewalls  4122  of the first region  4120 ′ can be greater than about 50% of the height of the waveguide  4105 . For example, a height of the sidewalls  4120  of the first region  4120 ′ can range between about 50% and 75% of the height of the optical waveguide  4105 . In some embodiments, the height of the sidewalls  4122  of the first region  4120 ′ can be greater than about 62.5 to 65 μm but less than a height of an optical waveguide  4105 . In other embodiments, the height of the sidewalls  4122  of the first region  4120 ′ can be greater than about 75 μm but less than a height of an optical waveguide  4105 . In the embodiment shown in  FIG.  42   , the overall height of the Y-groove  4110  is about equal to the height of the waveguide  4105  (e.g., about 125 μm). In some embodiments, the overall height of the Y-groove  4110  can be less than or greater than the height of the waveguide  4105 . A cover  4135  (optional) may be configured to cover the optical waveguides  4105  and grooves  4110  of the LCU  4100 . 
     As can be seen in  FIG.  42   , spacing between the sidewalls  4122  of the first region  4120 ′ in a region of closest approach to the optical waveguide  4105  is larger than the width of the waveguide by a predetermined clearance. In some embodiments, the predetermined clearance can be less than about 1 μm. In other embodiments, the predetermined clearance can be between about 1 and 3 μm. In further embodiments, the predetermined clearance can be between about 1 and 5 μm. For example, an optical waveguide  4105  can have a width of about 125 μm, and the spacing separating the sidewalls  4122  of the first region  4120 ′ can include a clearance of about 1 to 5 μm. 
     In embodiments that employ a waveguide  4105  comprising multi-mode fiber, the predetermined clearance can be between about 1 and 5 μm. For example, the predetermined clearance can be equal to about 0.8 to 4% of the width of an optical waveguide  4105  that comprises multi-mode fiber. In embodiments that employ a waveguide  4105  comprising single mode fiber, the predetermined clearance can be between about 0 and 2 μm. For example, the predetermined clearance can be equal to about 0 to 1.6% of a width of an optical waveguide  4105  that comprises single mode fiber. In some cases, the clearance may be less than 0, so that the waveguide  4105  deforms the Y-groove  4110  when placed in it (e.g., via an interference fit). 
     The waveguide  4105  shown in  FIGS.  42  and  43    includes a core  4107  surrounded by cladding  4109 . It is important that the core  4107  be optically aligned with the light redirecting member (see  4104  in  FIG.  41   ) when the waveguide  4105  is permanently bonded in place within the Y-groove  4110  using an optical (index-matched) bonding material. In some embodiments, the Y-groove  4110  includes a centering arrangement by which the waveguide  4105  is forcibly guided laterally toward a central plane  4112  of the Y-groove  4110  when the waveguide  4105  is installed in the Y-groove  4110 . In addition to centering the core  4107  along a central plane  4112  of the Y-groove  4110 , the centering arrangement serves as a stop that limits axial displacement of the waveguide  4105  within the Y-groove  4110 . As such, a compound Y-groove  4110  according to some embodiments includes a centering arrangement in combination with a U-groove alone or a Y-groove. 
       FIGS.  41  and  43    show a Y-groove  4110  that incorporates a centering arrangement defined by a longitudinal transition section  4115  comprising a first end  4115 ′ and a second end  4115 ″. The first end  4115 ′ has a width equal to the spacing, S, between the sidewalls  4122  of the first region  4120 ′. The second end  4115 ″ has a width less than a width of the optical waveguide  4105 . The sidewall spacing progressively reduces within the transition section  4115 , such as by the sidewalls angling inwardly in the transition section  4115 . The transition section  4115  comprises centering sidewalls  4126  which can originate from terminal ends of sidewalls  4122  and project inwardly toward the central plane of the Y-groove  4110 . The centering sidewalls  4126  may be considered chamfered sidewalls of the Y-groove  4110 . The sidewalls  4122  and centering sidewalls  4126  of the transition section  4115  can comprise substantially planar sidewall surfaces or non-planar sidewall surfaces. 
     The centering sidewalls  4126  form an angle, β, with the sidewalls  4122  that can range between about 5 and 45 degrees. The longitudinal transition section  4115  need not be very long relative to the overall length of the Y-groove  4110 . For example, length of the Y-groove  4110  can be between 200 μm and 2000 μm, and the centering sidewalls  4126  can extend from the sidewalls  4122  by a distance of about 2 μm to 50 μm. The centering sidewalls  4126  can have the same height as that of the sidewalls  4122 . 
     As the waveguide  4105  is displaced axially within the Y-groove  4110  toward the light redirecting member  4104 , the terminal end  4103  of the waveguide  4105  contacts the centering sidewalls  4126  and is guided toward the central plane of the Y-groove  4110  so that the central axis of the waveguide  4105  is centered within the Y-groove  4110 . A gap  4129  is defined between terminal ends of the centering sidewalls  4126 . The gap  4129  is sufficiently wide to allow unimpeded passage of light emanating from the core  4107  of the waveguide  4105 . The length of the centering sidewalls  4126  and width of the gap  4129  are preferably sized to accommodate the core and cladding dimensions of the waveguide  4105 . With the terminal end  4103  of the waveguide  4105  properly centered within the Y-groove  4110  by the centering arrangement, the cladding  4109  is in contact with the centering sidewalls  4126 , and the core  4107  is aligned with the center of the gap  4129 . It is understood that the centering arrangement shown in  FIG.  43    may be implemented in a U-groove, or in a compound U-groove such as a Y-groove. 
       FIG.  44    shows a top view of an LCU attachment area  4102  of an LCU  4100  in accordance with various embodiments. The LCU attachment area  4102  illustrated in  FIG.  44    shows the terminal end  4103  of the waveguide  4105  centered within the Y-groove  4110 . The embodiment of the Y-groove  4110  illustrated in  FIG.  44    includes an alignment feature between the entrance  4111  and the longitudinal transition section  4115  of the Y-groove  4110 . The alignment feature includes a protruded section  4124  of the groove sidewalls  4122 . The spacing between opposing protruded sections  4124  is slightly greater than the width of the waveguide  4105  and less than the spacing between opposing sidewalls  4122 . The protruded sections  4124  of the alignment feature serve to provide angular alignment of the waveguide  4105  with respect to the central plane of the Y-groove  4110  when the waveguide end  4103  is positioned in the transition section  4115  of the Y-groove  4110 . In some embodiments, the alignment feature formed by protruded sections  4124  is located at or near the groove entrance  4111 . 
     In the embodiment illustrated in  FIG.  44   , the edges of the terminal end  4103  of the waveguide  4105  are shown slightly embedded in the centering walls  4126  of the transition section  4115 . In this embodiment, the cladding  4109  of the waveguide  4105  is formed of a material (e.g., glass) that is harder than the material used to form the centering walls  4126 . A deformation  4128  in the centering walls  4126  can be formed by applying an axially directed force to the waveguide  4105  when the terminal end  4103  of the waveguide  4105  rests against the centering walls  4126  at its centered position. The deformation  4128  helps to maintain proper centered positioning of the waveguide  4105  within the Y-groove  4110  when optical bonding material is applied to permanently bond the waveguide  4105  within the Y-groove  4110 . 
     The embodiment of the Y-groove  4110  shown in  FIG.  44    incorporates a bonding region  4123  defined between the sidewalls  4122  of the Y-groove  4110  and the outer periphery of the waveguide  4105 . The bonding region  4123  can be filled with bonding material (e.g., optical bonding material) which, when cured, permanently bonds the waveguide  4105  within the Y-groove  4110 . In some embodiments, the bonding region  4123  is defined as a volume between the waveguide  4105 , the planar bottom surface  4125 , and the sidewalls  4122 . In other embodiments, a depression or trough can be formed along a portion of the sidewalls  4122  where the bottom surface  4125  meets the sidewalls  4122  so as to increase the volume of bonding material captured within the Y-groove  4110 . 
       FIG.  44    also shows a forward adhesive cavity  4131  configured to receive a volume of optical bonding material which, when cured, serves to increase the strength (e.g., integrity) of the bond between the terminal end  4103  of the waveguide  4105  and the LCU attachment area  4102 . The forward adhesive cavity  4131  can be configured to receive a volume of material other than an adhesive, such as an index gel or oil, for example. In some embodiments, the adhesive cavity  4131  is configured to transmit light from an end of the waveguide  4105 . As is shown in  FIG.  45   , the forward adhesive cavity  4131  can include a depression  4131 ′ formed into the bottom surface  4125  of the LCU attachment area  4102 . The depression  4131 ′ serves to increase the total volume of the forward adhesive cavity  4131  for receiving an optical bonding material, thereby enhancing the strength/integrity of the bond between the terminal end  4103  of the waveguide  4105  and the LCU attachment area  4102 .  FIG.  45    also shows the entrance  4111  of the Y-groove  4110  at a location  4133  where the bottom surface  4125  of the groove  110  transitions from a slope to a plateau. 
       FIG.  46    shows the bonding regions  4123  and forward adhesive cavity  4131  illustrated in  FIG.  44    and, in addition, shows a lateral adhesive cavity  4121  extending laterally from each sidewall  4122  of the Y-groove  4110 . The lateral adhesive cavities  4121  can be extended portions of the bonding regions  4123 . The lateral adhesive cavities  4121  provide a volume for receiving additional bonding material near the sides of the terminal end  103  of the waveguide  4105 , which increases the strength/integrity of the bond between the Y-groove  4110  and the waveguide  4105 . As is shown in  FIG.  47   , the lateral adhesive cavity  4121  can include a depression  4121 ′ formed into the bottom surface  4125  of the LCU attachment area  4102 . The depression  4121 ′ serves to increase the total volume of the lateral adhesive cavity  4121  for receiving an optical bonding material, thereby enhancing the strength/integrity of the bond between the waveguide  4105  and the Y-groove  4110 . The lateral adhesive cavity  4121  can be configured to receive a volume of material other than an adhesive, such as an index gel or oil, for example. 
       FIG.  48    illustrates an LCU attachment area  4102  comprising a multiplicity of grooves  4110  each having a waveguide  4105  disposed therein. In  FIG.  48   , two grooves  4110  are illustrated with respective waveguides  4105  in contact with centering surfaces  4126  at a centered position within the grooves  4110 .  FIG.  48    shows an adhesive reservoir  4131 ″ located adjacent the forward adhesive cavities  4131 . The adhesive reservoir  4131 ″ is a volume of the LCU attachment area  4102  that is shared between two or more of the forward adhesive cavities  4131 . In this regard, the adhesive reservoir  4131 ″ is fluidically coupled to two or more of the forward adhesive cavities  4131 . The adhesive reservoir  4131 ″ provides a volume for receiving additional bonding material near the terminal ends  4103  of the waveguides  4105 , which increases the strength/integrity of the bond between the waveguide  4105  and the LCU attachment area  4102 . The adhesive reservoir  4131 ″ can be configured to receive a volume of material other than an adhesive, such as an index gel or oil, for example. 
       FIGS.  49 - 55    illustrate a process for installing a waveguide  4105  in a Y-groove  4110  of an LCU attachment area  4102  in accordance with various embodiments. In some embodiments, the installation process can be monitoring using microscopes with digital cameras to provide views (e.g., top view, side view) similar to those shown in  FIGS.  49  and  50   . The waveguide  4105  to be positioned within the Y-groove  4110  is shown extending from a buffer  4116  which encompasses the waveguide  4105 . The buffer  4106  is typically a polymer sheath which serves to protect the waveguide  4105 . 
     The waveguide  4105  is initially positioned over the expanded region (i.e., upper region) of Y-groove  4110  with the terminal end  4103  pointed downwards at a small angle (e.g., 5°-20°).  FIGS.  49  and  50    illustrate a typical example in which the waveguide  4105  is initially misaligned within the Y-groove  4110 . The upper expanded region of Y-groove  4110  includes angled side surfaces  4132  which serve to capture the waveguide  4105  and funnel the waveguide  4105  into the U-groove region (i.e., lower region) of the Y-groove  4110 . As the terminal end  4103  of the waveguide  4105  is lowered, the terminal end  4103  contacts the capturing sidewall  4132  on one side of the Y-groove region, which guides the terminal end  4103  into the bottom region (i.e., U-groove region) of the Y-groove  4110 , forcing the waveguide  4105  to bend and/or move laterally. 
     As the waveguide  4105  is lowered into the Y-groove  4110  (see  FIG.  51   ), the terminal end  4103  is bent upward by the bottom surface  4125  of the Y-groove  4110 . Simultaneously, the Y-groove  4110  continues to bend and/or move the waveguide  4105  laterally so that the waveguide  4105  is constrained by the near-vertical sidewalls  4122  of the U-groove region of the Y-groove  4110  (see  FIG.  52   ). When the waveguide  4105  is approximately horizontal (i.e., tangent to the bottom surface  4125  of the Y-groove  4110 ), as is shown in  FIG.  53   , the waveguide  4105  is pushed forward into the longitudinal transition section  4115  of the Y-groove  4110  (see  FIG.  54   ) until the terminal end  4103  contacts a centering surface  4126  (see  FIG.  55   ). The centering surface  4126  pushes the terminal end  4103  of the waveguide  4105  laterally as needed until the terminal end  4103  is in contact with the centering surfaces  4126  on both sides of the Y-groove  4110 , thereby precisely centering the terminal end  4103  of the waveguide  4105  in the Y-groove  4110 , as is best seen in  FIG.  55   . 
     The final angle of the waveguide  4105  as it is centered by the centering surfaces  4126  is typically horizontal, and may be controlled by any suitable mechanical means, optionally guided by optical inspection of a side view, such as the view shown in  FIG.  53   .  FIG.  56    illustrates an alignment error that can occur if the waveguide  4105  is lowered too much such that it makes contact with the rear edge  4125 ′ of the bottom surface  4125  of the Y-groove  4110 . In this scenario, the terminal end  4103  of the waveguide  4105  is levered up out of the Y-groove  4110 . This misalignment is greatly reduced by recessing the most of the bottom surface  4125  of the Y-groove  4110 , leaving only a relatively short porch region  4125 ″ ( FIG.  57   ) at the terminal end  4113  of the Y-groove  4110 . 
     As can be seen in  FIG.  57   , the majority of the bottom surface  4125 ″′ is recessed relative to the porch region  4125 ″ adjacent the terminal end  4113  of the Y-groove  4110 . In some embodiments, the recessed section  4125 ″′ of the bottom surface  4125  of the Y-groove  4110  can extend from the entrance  4111  of the Y-groove  4110  towards the terminal end  4113  and cover more than about one-half of the surface area of the bottom surface  4125 . For example, the recessed section  4125 ″′ can extend from the entrance  4111  of the Y-groove  4110  to within a distance from the terminal end  4113 , the distance being less than about two times a height of the waveguide  4105  received by the Y-groove  4110 . Typically, at least a portion of the recessed section  4125 ″′ will be filled with cured optical adhesive, so that the waveguide  4105  is well supported. 
     A compound Y-groove  4110  comprising a lower U-groove and an expanded upper groove can be fabricated with injection molding of a thermoplastic (e.g., UItem). Such materials have a much larger coefficient of thermal expansion than that of glass optical fibers. Therefore, there is concern over stresses caused by thermal excursions, such as may occur in operation in a computer chassis. These stresses may lead to optical misalignment due to warping of the part containing the Y-groove  4110 , or even to failure of the adhesive used to bond the waveguide  4105 . To minimize such stresses, it is desirable to minimize the length of the Y-groove  4110  that is filled with adhesive. However, sufficient groove length is required to constrain the angle of the waveguide  4105 . The required length of the Y-groove  4110  depends on the angular tolerance of the optics system and on the extra width of the Y-groove  4110  included to provide clearance for the waveguide  4105 . 
       FIGS.  58 - 60    show a Y-groove  4110  with two separate sections  4110   a  and  4110   b.  Near the terminal end  4103  of the waveguide  4105 , a short section includes the longitudinal transition section  4115  and the centering surfaces  4126 . This section  4110   a  may be filled with index-matching adhesive. A separate section  4110   b  is placed some sufficient distance (e.g., 0.5 mm) from the section  4110   b,  such that it provides accurate angular alignment of the waveguide  4105  but is not filled with adhesive. This design minimizes stresses associated with thermal expansion (by minimizing the bond length) without compromising angular alignment. 
       FIG.  61    illustrates a portion of an LCU  6100  in accordance with various embodiments. The LCU  6100  shown in  FIG.  61    includes a single LCU attachment area  6102 . Although a single LCU attachment area  6102  is shown in  FIG.  61   , it is understood that a multiplicity of attachment areas  6102  can be provided on the LCU  6100  for receiving and permanently attaching to a multiplicity of optical waveguides. The LCU attachment area  6102  includes a groove  6110  having an entrance  6111  and a terminal end  6113 . The groove  6110  is configured to receive an optical waveguide, such as the generally cylindrical waveguide  4105  shown in  FIG.  42   . 
     The LCU  6100  includes a light redirecting member (not shown in  FIG.  61   , but see  4104  in  FIG.  41   ) and an intermediate section  6108  between the light redirecting member and the terminal end  6113 . In some embodiments, the terminal end  6113  comprises an optically clear member, such as a lens, or is formed from optically transparent material. The intermediate section  6108  is formed from an optically transparent material. The light redirecting member includes an output side through which light exits from (or enters into) the light directing member. 
     According to some embodiments, the groove  6110  is a compound groove formed by a generally U-shaped lower portion  6123  and an expanded upper portion  6127 ,  6132  making the compound groove generally Y-shaped (Y-groove), as has been described in detail hereinabove. The groove  6110  includes a longitudinal transition section  6115  that includes a single centering sidewall  6126 . Within the longitudinal transition section  6115 , the spacing between sidewalls  6122  and  6122 ′ reduces from a width equal to that of the optical waveguide  6105  plus a clearance to a width less than the width of the optical waveguide  6105 . In the embodiment illustrated in  FIG.  61   , one of the sidewalls  6122  is substantially planar between the entrance  6111  and terminal end  6113  of the groove  6110 . The opposing sidewall  6122 ′ includes a sidewall portion that is substantially parallel to sidewall  6122  and transitions to the centering sidewall  6126  that angles inwardly in the transition section  6115 . The centering sidewall  6126  may be considered chamfered sidewall of the groove  6110 . 
     In  FIG.  61   , the groove  6110  includes a centering sidewall  6126  only on one side of the groove  6110 . As such, the single centering sidewall  6126  may be considered a positioning sidewall  6126 . During assembly, the optical waveguide  6105  is slid along the planar sidewall  6122  until the positioning sidewall  6126  pins the optical waveguide  6105  at its installed location within the groove  6110 , as is shown in  FIG.  61   . At this location, the positioning sidewall  6126  prevents further longitudinal advancement of the terminal end  6103  of the optical waveguide  6105  within the groove  6110 . One advantage to the embodiment shown in  FIG.  61    is that the angle of the optical waveguide  6105  can be well controlled during assembly, since it can be bent parallel to the sidewall  6122 . In some embodiments, the positioning sidewall  6126  need not pinch the optical waveguide  6105 , but can instead serve as a conventional stop, such as by defining the end of the groove  6110  or some other barrier, as long as the optical waveguide  6105  can be bent against the sidewall  6122  during assembly. 
       FIG.  62    shows one side  6201  of an optical ferrule  6200 , e.g., a molded optical ferrule, a molded plastic optical ferrule, that includes fiducials  1221 - 1224 . Ferrule  6200  is configured to receive one or more optical waveguides and includes one or more features. Each feature corresponds to a different optical waveguide. The ferrule  6200  also includes one or more fiducials, wherein the one or more fiducials correspond to the one or more features. According to some implementation, the features of the optical ferrule  6200  are optical elements configured to be on an optical path of a light ray propagating within the ferrule and the one or more fiducials correspond to the one or more optical elements. 
     The ferrule  6200  includes elements  6203 , e.g., grooves, U-shaped, V-shaped, or Y-shaped grooves configured for receiving and securing an optical waveguide. Ferrule  6200  includes one or more light affecting elements  6205  configured for affecting characteristics of light from the optical waveguide while propagating the light within the optical ferrule  6200 . According to some embodiments, each light affecting element  6205  of the ferrule  6200  comprises a light redirecting feature  6205   a  that may include a curved lens  6206  and a planar surface  6207  disposed proximate to and/or at least partially surrounding the lens  6206 . The light affecting element  6205  further includes an intermediate surface  6205   b,  e.g., a planar surface, disposed between the receiving element  6203  and light redirecting feature  6205   a.  Optical ferrule  6200  includes multiple receiving and securing elements  6203  and multiple light affecting elements  6205 , however, some unitary optical ferrules can include a single receiving and securing element and a single light affecting element with an intermediate surface disposed therebetween. 
     The optical ferrule includes one or more alignment features, including feature  6211  configured to control translation of the ferrule  6200  along a first lateral axis  121 . Features  6211  shown in the example optical ferrule  6200  are forward stops that engage with forward stops of a mating ferrule to set the mated distance between light affecting elements of the optical ferrule and light affecting elements of the mating ferrule. The forward stops  6211 , when engaged with forward stops of the mating ferrule, also control rotation of the optical ferrule  6200  around the thickness axis  123 . 
     The optical ferrule  6200  includes alignment features  6212 ,  6213  wherein alignment feature  6212  is a pin that fits into a compatible socket of a mating ferrule. Alignment feature  6213  is a socket that fits a pin of the mating ferrule. The pin  6212  includes spaced apart portions  6212   a  and  6212   b.  The pin  6212  and socket  6213  control translation of the optical ferrule  6200  along the second lateral axis  622  and may also control rotation of the optical ferrule  6200  around the thickness axis  623 . Pin  6212  may be designed such that only the sides of the pin  6212  can come into contact with the mating socket, providing a lateral stop on either side of the pin  6212  and thereby controlling translation along the second lateral axis  122 . The pin  6212  is designed to be slightly narrower that the socket  6213  to allow for manufacturing tolerances. Optionally, compliant features (not shown) could be designed into the pin and/or socket to allow for manufacturing tolerances. In some embodiments, the compliant features may provide flexible alignment. The pin or the socket, or both, can be fitted with compliant side features that facilitate centering the pin in the socket. 
     Additional information regarding optical ferrules having alignment features is provided in commonly owned and concurrently filed U.S. patent application Ser. No. ______, having the title “Optical Ferrules” and identified by Attorney Docket Number 76982US002 which is incorporated herein by reference. Additional information regarding optical ferrules, frames, and connectors that employ flexible alignment features is provided in commonly owned and concurrently filed U.S. patent application Ser. No. ______, having the title “Ferrules, Alignment Frames and Connectors” and identified by Attorney Docket Number 75767US002 which is incorporated herein by reference. 
     The planar mating surface  6217  of optical ferrule  6200  controls translation of the ferrule  6200  along the thickness axis  123  and rotation of the ferrule  6200  along the first and second lateral axes  121 ,  122 . An optical output window  6214  is disposed, e.g., recessed, in the planar mating surface  6217 . 
     Optical ferrules and the molds used to make the optical ferrules according to various embodiments, including those illustrated herein, involve molded features, e.g., plastic molded features, configured to provide for propagation of light within the ferrule and between the ferrule and a mating ferrule that is aligned with the ferrule. For example, the light affecting elements may comprise lenses, e.g., curved lenses, configured to redirect light propagating in the ferrule. As previously described, the optical ferrules can include a planar mating surface having optical output window that is transparent to the propagating light, wherein the light propagating in the optical ferrule exits the optical ferrule after being transmitted by the optical output window. 
     In some embodiments, one or more fiducials may be molded into the ferrule wherein the fiducials correspond to the ferrule features. For example, a mold side may be fabricated by one or more tools and each fiducial may be a divot (or other feature) that indicates a location of the tool used form a mold feature. 
     One fiducial may correspond to a plurality of ferrule features or one fiducial may correspond to a single ferrule feature. For example, in implementations that include multiple light affecting elements, multiple fiducials may be used wherein each of the fiducials corresponds to one of the light affecting elements. In some embodiments, as shown in  FIG.  62   , two or more fiducials  6221 ,  6222  may correspond to a light redirecting feature  6205   a,  e.g., each light redirecting feature  6205   a  may be disposed between two fiducials  6221 ,  6222 . 
     According to some implementations, at least one fiducial may correspond to at least a single receiving element. In implementations that include multiple receiving elements, multiple fiducials may be used, wherein each of the fiducials corresponds to one of the receiving elements. For example, as shown in  FIG.  62   , two or more fiducials  6223 ,  6224  may correspond to one of the receiving elements  6203 , e.g., each receiving element  6203  may be disposed between two fiducials  6223 ,  6224 . Fiducials that correspond to one feature (or type of feature) may have the same shape or may differ in shape from fiducials that correspond to another feature (or type of feature). 
     Additional information regarding ferrules, alignment frames, and connectors that may be used in conjunction with the approaches described herein is provided in the following commonly owned and concurrently filed U.S. Patent Applications which are incorporated herein by reference: U.S. Patent Application Ser. No. 62/239,998, having the title “Connector with Latching Mechanism” and identified by Attorney Docket Number 76663US002; U.S. Patent Application Ser. No. 62/240,069, having the title “Optical Ferrules” and identified by Attorney Docket Number 76982US002; U.S. Patent Application Ser. No. 62/240,066, having the title “Ferrules, Alignment Frames and Connectors,” and identified by Attorney Docket Number 75767US002; U.S. Patent Application Ser. No. 62/240,008, having the title “Optical Cable Assembly with Retainer,” identified by Attorney Docket Number 76662US002; U.S. Patent Application Ser. No. 62/240,000, having the title “Dust Mitigating Optical Connector,” identified by Attorney Docket Number 76664US002; U.S. Patent Application Ser. No. 62/240,010, having the title “Optical Coupling Device with Waveguide Assisted Registration,” identified by Attorney Docket Number 76660US002; U.S. Patent Application 62/239,996, having the title “Optical Ferrules and Optical Ferrule Molds,” identified by Attorney Docket Number 75985US002; U.S. Patent Application 62/240,002 having the title “Optical Ferrules with Waveguide Inaccessible Space,” identified by Attorney Docket Number 76778US002; U.S. Patent Application 62/240,003, having the title “Configurable Modular Connectors,” identified by Attorney Docket Number 76907US002; and U.S. Patent Application 62/240,005, having the title “Hybrid Connectors,” identified by Attorney Docket Number 76908US002. 
     Embodiments described in this disclosure include:
     Item 1. A coupling unit, comprising:   

     a light coupling element comprising an attachment area for receiving and permanently attaching to a plurality of optical waveguides; and 
     one or more grooves provided at the attachment area, each groove configured to receive an optical waveguide and defined by:
         a bottom surface, a first region, a second region, and an opening;   the first region defined between the bottom surface and the second region, the first region in cross section having substantially parallel sidewalls separated by a spacing; and   the second region disposed between the first region and the opening, wherein a width of the opening is greater than the spacing.       Item 2. The coupling unit of item 1, wherein the second region comprises substantially planar sidewalls.   Item 3. The coupling unit of item 1, wherein the second region comprises non-planar sidewalls.   Item 4. The coupling unit of item 1, wherein:   

     the second region comprises sidewalls extending between the first region and the opening; and 
     a spacing between the sidewalls of the second region progressively increases from the first region to the opening.
     Item 5. The coupling unit of item 1, wherein the bottom surface is planar.   Item 6. The coupling unit of item 1, wherein at least a central region of the bottom surface is planar.   Item 7. The coupling unit of item 1, wherein the width of the opening is greater than the spacing by a distance equal to about half of the spacing.   Item 8. The coupling unit of item 1, wherein the width of the opening is greater than the spacing by a distance greater than half of the spacing.   Item 9. The coupling unit of item 1, wherein a height of the sidewalls of the first region is greater than about 50% of a height of the optical waveguide.   Item 10. The coupling unit of item 1, wherein a height of the sidewalls of the first region ranges between about 50% and 75% of a height of the optical waveguide.   Item 11. The coupling unit of item 1, wherein a height of the grooves is greater than a height of the optical waveguides.   Item 12. The coupling unit of item 1, wherein a height of the grooves is less than a height of the optical waveguides.   Item 13. The coupling unit of item 12, further comprising a cover configured to extend over the optical waveguides and the grooves.   Item 14. The coupling unit of item 1, wherein the spacing between the sidewalls in a region of closest approach to the optical waveguide is less than a width of the optical waveguide by a predetermined amount, resulting in an interference fit.   Item 15. The coupling unit of item 1, wherein the spacing between the sidewalls in a region of closest approach to the optical waveguide is greater than a width of the optical waveguide by a predetermined clearance.   Item 16. The coupling unit of item 15, wherein the predetermined clearance is less than about 1 μm.   Item 17. The coupling unit of item 15, wherein the predetermined clearance is between about 1 and 3 μm.   Item 18. The coupling unit of item 15, wherein the predetermined clearance is between about 1 and 5 μm, and the optical waveguide comprises a multi-mode fiber.   Item 19. The coupling unit of item 18, wherein the width of the optical waveguide corresponds to a diameter of the fiber.   Item 20. The coupling unit of item 15, wherein the predetermined clearance is equal to about 0.8 to 4% of a width of the optical waveguide, and the optical waveguide comprises a multi-mode fiber.   Item 21. The coupling unit of item 20, wherein the width of the optical waveguide corresponds to a diameter of the fiber.   Item 22. The coupling unit of item 15, wherein the predetermined clearance is between about 0 and 2 μm, and the optical waveguide comprises a single mode fiber.   Item 23. The coupling unit of item 22, wherein the width of the optical waveguide corresponds to a diameter of the fiber.   Item 24. The coupling unit of item 15, wherein the predetermined clearance is equal to about 0 to 1.6% of a width of the optical waveguide, and the optical waveguide comprises single mode fiber.   Item 25. The coupling unit of item 24, wherein the width of the optical waveguide corresponds to a diameter of the fiber.   Item 26. The coupling unit of item 1, wherein:   

     an optical waveguide has a width of about 125 μm; and 
     the spacing separating the sidewalls of the first region includes a clearance for the optical waveguide of about 1 to 5 μm.
     Item 27. The coupling unit of item 1, wherein a height of the sidewalls of the first region is greater than about 62 μm.   Item 28. The coupling unit of item 1, wherein a height of the sidewalls of the first region is greater than about 75 μm.   Item 29. The coupling unit of item 1, wherein the sidewalls of the first region deviate from parallel by an angle of less than 10 degrees.   Item 30. The coupling unit of item 1, wherein the sidewalls of the first region are normal to the bottom surface to within about 5 degrees.   Item 31. The coupling unit of item 1, wherein:   

     the light coupling element comprises a plurality of optical elements aligned relative to the one or more grooves; and 
     each of the optical elements is in optical alignment with one of the optical waveguides.
     Item 32. The coupling unit of item 1, wherein:   

     the light coupling element comprises a plurality of light redirecting members aligned relative to the one or more grooves; and 
     each of the light redirecting members is in optical alignment with one of the optical waveguides.
     Item 33. The coupling unit of item 1, wherein the bottom surface of each groove comprises one or more recessed sections.   Item 34. The coupling unit of item 1, wherein:   

     the bottom surface of each groove comprises a recessed section; and 
     a majority of the bottom surface includes the recessed section.
     Item 35. The coupling unit of item 1, wherein:   

     each groove has an entrance and a terminal end; 
     the bottom surface of each groove comprises a recessed section; and 
     the recessed section extends from the entrance toward the terminal end and covers more than about one-half of a surface area of the bottom surface.
     Item 36. The coupling unit of item 35, wherein the recessed section extends from the entrance to within a distance from the terminal end, the distance being less than two times a height of the waveguide received by the groove.   Item 37. The coupling unit of item 1, wherein each groove has an entrance end and a terminal end, and the coupling unit further comprising a terminal wall at the terminal end.   Item 38. The coupling unit of item 1, wherein each groove comprises a terminal end and a cavity proximate the terminal end, the cavity configured to receive a volume of a material and configured to transmit light from an end of the optical waveguide.   Item 39. The coupling unit of item 38, further comprising a reservoir proximate the terminal end and fluidically coupled to the cavities of two or more grooves.   Item 40. The coupling unit of item 1, wherein each groove comprises a terminal end and an adhesive cavity proximate the terminal end, the adhesive cavity configured to receive a volume of an optical bonding material and configured to transmit light from an end of the optical waveguide.   Item 41. The coupling unit of item 40, further comprising an adhesive reservoir proximate the terminal end and fluidically coupled to the adhesive cavities of two or more grooves.   Item 42. The coupling unit of item 1, wherein each groove comprises:   

     an entrance and a terminal end; and 
     a lateral cavity between the entrance and the terminal end and situated lateral of opposing sides of the waveguide, the lateral cavity configured to receive a volume of a material.
     Item 43. The coupling unit of item 1, wherein each groove comprises:   

     an entrance and a terminal end; and 
     a lateral adhesive cavity between the entrance and the terminal end and situated lateral of opposing sides of the waveguide, the lateral adhesive cavity configured to receive a volume of a bonding material.
     Item 44. A coupling unit, comprising:   

     a light coupling element comprising an attachment area for receiving and permanently attaching to a plurality of optical waveguides; 
     one or more grooves provided at the attachment area, each groove configured to receive an optical waveguide having a width; 
     each groove having a first region and a bottom surface, the first region in cross section having substantially parallel sidewalls separated by a spacing; and 
     each groove having a longitudinal transition section comprising a first end and a second end, the first end having a sidewall spacing greater than the width of the optical waveguide, and the second end having a sidewall spacing less than the width of the optical waveguide.
     Item 45. The coupling unit of item 44, wherein the sidewall spacing progressively reduces within the transition section.   Item 46. The coupling unit of item 44, wherein the spacing between the sidewalls decreases in one direction along the groove in the transition section.   Item 47. The coupling unit of item 44, wherein:   

     sidewalls of the second end of the transition section define a gap therebetween; and 
     the gap is sufficiently large to allow light from a core of the optical waveguide to pass substantially unimpeded.
     Item 48. The coupling unit of item 44, wherein the transition section comprises substantially planar sidewalls.   Item 49. The coupling unit of item 44, wherein the transition section comprises non-planar sidewalls.   Item 50. The coupling unit of item 44, wherein a terminal end of the optical waveguide contacts the sidewalls of the transition section.   Item 51. The coupling unit of item 44, wherein:   

     the parallel sidewalls comprise a first sidewall and a second sidewall; 
     the first sidewall is planar; 
     the second sidewall comprises a section that angles inwardly toward a central plane of the groove in the transition section; and 
     the section of the second sidewall is configured to force a terminal end of the optical waveguide against the first sidewall.
     Item 52. The coupling unit of item 51, wherein the section of the second sidewall is configured to prevent further longitudinal advancement of the terminal end of the optical waveguide within the groove.   Item 53. The coupling unit of item 44, wherein contact between the optical waveguide and the sidewalls of the transition section guides the optical waveguide laterally to a predetermined position.   Item 54. The coupling unit of item 53, wherein the predetermined position is a central plane of the groove.   Item 55. The coupling unit of item 53, wherein the predetermined position is offset from a central plane of the groove.   Item 56. The coupling unit of item 44, wherein:   

     the optical waveguide comprises a core and cladding surrounding the core; 
     the cladding contacts the sidewalls of the transition section; and 
     the core is positioned relative to a gap between terminal ends of the sidewalls of the transition section.
     Item 57. The coupling unit of item 56, wherein the optical waveguide is a single-mode fiber or a multi-mode optical fiber.   Item 58. The coupling unit of item 56, wherein the optical waveguide is a single-mode polymer optical waveguide or a multi-mode polymer optical waveguide.   Item 59. The coupling unit of item 44, wherein the plurality of optical waveguides comprises an array of single-mode optical waveguides or an array of multi-mode optical waveguides.   Item 60. The coupling unit of item 44, wherein:   

     the light coupling element comprises a plurality of optical elements aligned relative to the one or more grooves; and 
     contact between the optical waveguide and the sidewalls of the transition section guides a core of the optical waveguide laterally into optical alignment with the optical element.
     Item 61. The coupling unit of item 44, wherein:   

     the light coupling element comprises a plurality of light redirecting members aligned relative to the one or more grooves; and 
     contact between the optical waveguide and the sidewalls of the transition section guides a core of the optical waveguide laterally into optical alignment with the light redirecting member.
     Item 62. The coupling unit of item 44, wherein the bottom surface of each groove comprises at least one recessed section.   Item 63. The coupling unit of item 44, wherein:   

     the bottom surface of each groove comprises a recessed section; and 
     a majority of the bottom surface includes the recessed section.
     Item 64. The coupling unit of item 44, wherein:   

     each groove has an entrance and a terminal end; 
     the bottom surface of each groove comprises a recessed section; and 
     the recessed section extends from the entrance toward the terminal end and covers more than about one-half of a surface area of the bottom surface.
     Item 65. The coupling unit of item 44, further comprising:   

     a second region and an opening, the second region disposed between the first region and the opening; 
     wherein a width of the opening is greater than the spacing between the sidewalls of the first region.
     Item 66. The coupling unit of item 65, wherein the second region comprises substantially planar sidewalls.   Item 67. The coupling unit of item 65, wherein the second region comprises non-planar sidewalls.   Item 68. The coupling unit of item 65, wherein:   

     the second region comprises sidewalls extending between the first region and the opening; and 
     a spacing between the sidewalls of the second region progressively increases from the first region to the opening.
     Item 69. The coupling unit of item 65, wherein the width of the opening is greater than the spacing by a distance equal to about half of the spacing.   Item 70. The coupling unit of item 65, wherein the width of the opening is greater than the spacing by a distance greater than half of the spacing.   Item 71. The coupling unit of item 44, wherein a height of the sidewalls of the first region is greater than about 50% of a height of the optical waveguide.   Item 72. The coupling unit of item 44, wherein a height of the sidewalls of the first region ranges between about 50% and 75% of a height of the optical waveguide.   Item 73. The coupling unit of item 44, wherein a height of the grooves is greater than a height of the optical waveguide.   Item 74. The coupling unit of item 44, wherein a height of the grooves is less than a height of the optical waveguide.   Item 75. The coupling unit of item 44, further comprising a cover configured to extend over the optical waveguides and the grooves.   Item 76. The coupling unit of item 44, wherein the spacing between the sidewalls in a region of closest approach to the optical waveguide is greater than a width of the optical waveguide by a predetermined clearance.   Item 77. The coupling unit of item 44, wherein the spacing between the sidewalls in a region of closest approach to the optical waveguide is less than a width of the optical waveguide by a predetermined amount, resulting in an interference fit.   Item 78. The coupling unit of item 77, wherein the predetermined clearance is less than about 1 μm.   Item 79. The coupling unit of item 77, wherein the predetermined clearance is between about 1 and 3 μm.   Item 80. The coupling unit of item 77, wherein the predetermined clearance is between about 1 and 5 μm, and the optical waveguide comprises multi-mode fiber.   Item 81. The coupling unit of item 80, wherein the width of the optical waveguide corresponds to a diameter of the waveguide.   Item 82. The coupling unit of item 77, wherein the predetermined clearance is equal to about 0.8 to 4% of a width of the optical waveguide, and the optical waveguide comprises multi-mode fiber.   Item 83. The coupling unit of item 77, wherein the width of the optical waveguide corresponds to a diameter of the fiber.   Item 84. The coupling unit of item 77, wherein the predetermined clearance is between about 0 and 2 μm, and the optical waveguide comprises single mode fiber.   Item 85. The coupling unit of item 84, wherein the width of the optical waveguide corresponds to a diameter of the fiber.   Item 86. The coupling unit of item 77, wherein the predetermined clearance is equal to about 0 to 1.6% of a width of the optical waveguide, and the optical waveguide comprises single mode fiber.   Item 87. The coupling unit of item 86, wherein the width of the optical waveguide corresponds to a diameter of the fiber.   Item 88. The coupling unit of item 44, wherein:   

     an optical waveguide has a width of about 125 μm; and 
     the spacing separating the sidewalls of the first region includes a clearance for the optical waveguide of about 1 to 5 μm.
     Item 89. The coupling unit of item 44, wherein a height of the sidewalls of the first region is greater than about 62.5 to 65 μm.   Item 90. The coupling unit of item 44, wherein a height of the sidewalls of the first region is greater than about 75 μm.   Item 91. The coupling unit of item 44, wherein the sidewalls of the first region deviate from parallel by an angle of less than 10 degrees.   Item 92. The coupling unit of item 44, wherein:   

     the light coupling element comprises a plurality of optical elements aligned relative to the one or more grooves; and 
     each of the optical elements is in optical alignment with one of the optical waveguides.
     Item 93. The coupling unit of item 44, wherein:   

     the light coupling element comprises a plurality of light redirecting members aligned relative to the one or more grooves; and 
     each of the light redirecting members is in optical alignment with one of the optical waveguides.
     Item 94. The coupling unit of item 44, wherein the bottom surface of each groove comprises one or more recessed sections.   Item 95. The coupling unit of item 44, wherein:   

     the bottom surface of each groove comprises a recessed section; and 
     a majority of the bottom surface includes the recessed section.
     Item 96. The coupling unit of item 44, wherein:   

     each groove has an entrance and a terminal end; 
     the bottom surface of each groove comprises a recessed section; and 
     the recessed section extends from the entrance toward the terminal end and covers more than about one-half of a surface area of the bottom surface.
     Item 97. The coupling unit of item 96, wherein the recessed section extends from the entrance to within a distance from the terminal end, the distance being less than two times a height of the waveguide received by the groove.   Item 98. The coupling unit of item 44, wherein each groove has an entrance end and a terminal end, and the coupling unit further comprising a terminal wall at the terminal end.   Item 99. The coupling unit of item 44, wherein each groove comprises a terminal end and a cavity proximate the terminal end, the cavity configured to receive a volume of a material and configured to transmit light from an end of the optical waveguide.   Item 100. The coupling unit of item 99, further comprising a reservoir proximate the terminal end and fluidically coupled to the cavities of two or more grooves.   Item 101. The coupling unit of item 44, wherein each groove comprises a terminal end and an adhesive cavity proximate the terminal end, the adhesive cavity configured to receive a volume of an optical bonding material and configured to transmit light from an end of the optical waveguide.   Item 102. The coupling unit of item 101, further comprising an adhesive reservoir proximate the terminal end and fluidically coupled to the adhesive cavities of two or more grooves.   Item 103. The coupling unit of item 44, wherein each groove comprises:   

     an entrance and a terminal end; and 
     a lateral cavity between the entrance and the terminal end and situated lateral of opposing sides of the waveguides, the lateral cavity configured to receive a volume of a material.
     Item 104. The coupling unit of item 44, wherein each groove comprises:   

     an entrance and a terminal end; and 
     a lateral adhesive cavity between the entrance and the terminal end and situated lateral of opposing sides of the waveguides, the lateral adhesive cavity configured to receive a volume of a bonding material.
     Item 105. A coupling unit, comprising:   

     a light coupling element comprising an attachment area for receiving and permanently attaching to a plurality of optical waveguides; 
     one or more grooves provided at the attachment area, each groove configured to receive an optical waveguides having a width; 
     each groove having a first region and a bottom surface, the first region in cross section having substantially parallel sidewalls separated by a spacing; and 
     each groove having two or more sections along a longitudinal direction wherein each section has a different sidewall spacing than adjoining sections, wherein at least one of the sections has a sidewall spacing less than a width of the optical waveguides.
     Item 106. The coupling unit of item 105, wherein the spacing between the sidewalls progressively reduces at at least one section.   Item 107. The coupling unit of item 105, wherein the at least one section is at an end of the groove.   Item 108. The coupling unit of item 105, wherein the sidewalls angle inwardly toward a central plane of the first region of the groove between the first and second sections.   Item 109. The coupling unit of item 105, wherein only one of the sidewalls angles inwardly toward a central plane of the first region of the groove between the first and second sections.   Item 110. The coupling unit of item 105, wherein contact between the optical waveguide and both sidewalls of the transition section guides the optical waveguide laterally to a predetermined position.   Item 111. The coupling unit of item 110, wherein the predetermined position is a central plane of the groove.   Item 112. The coupling unit of item 105, wherein:   

     a first sidewall is planar; 
     a second sidewall within the at least one section angles inwardly toward a central plane of the first region of the groove; and 
     contact between the optical waveguide and the angled section of the second sidewall guides the optical waveguide laterally to a predetermined position.
     Item 113. The coupling unit of item 112, wherein the predetermined position is offset from a central plane of the groove.   

     Unless otherwise indicated, all numbers expressing feature sizes, amounts, and physical properties used in the specification and claims are to be understood as being modified in all instances by the term “about.” Accordingly, unless indicated to the contrary, the numerical parameters set forth in the foregoing specification and attached claims are approximations that can vary depending upon the desired properties sought to be obtained by those skilled in the art utilizing the teachings disclosed herein. The use of numerical ranges by endpoints includes all numbers within that range (e.g. 1 to 5 includes 1, 1.5, 2, 2.75, 3, 3.80, 4, and 5) and any range within that range. 
     Various modifications and alterations of the embodiments discussed above will be apparent to those skilled in the art, and it should be understood that this disclosure is not limited to the illustrative embodiments set forth herein. The reader should assume that features of one disclosed embodiment can also be applied to all other disclosed embodiments unless otherwise indicated. It should also be understood that all U.S. patents, patent applications, patent application publications, and other patent and non-patent documents referred to herein are incorporated by reference, to the extent they do not contradict the foregoing disclosure.