Patent Publication Number: US-9897763-B2

Title: Transceiver interface having staggered cleave positions

Description:
TECHNICAL FIELD 
     The present invention relates to an optical connector for connecting sets of optical waveguides such as optical fiber ribbons. 
     BACKGROUND 
     Optical fiber connectors are used to connect optical fibers in a variety of applications including: the telecommunications network, local area networks, data center links, and for internal links in high performance computers. These connectors can be grouped into single fiber and multiple fiber designs and also grouped by the type of contact. Common contact methods include: physical contact wherein the mating fiber tips are polished to a smooth finish and pressed together; index matched, wherein a compliant material with an index of refraction that is matched to the core of the fiber fills a small gap between the mated fibers&#39; tips; and air gap connectors, wherein the light passes through a small air gap between the two fiber tips. With each of these contact methods a small bit of dust tips of the mated fibers can greatly increase the light loss. 
     Another type of optical connector is referred to as an expanded beam connector. This type of connector allows the light beam in the source connector to exit the fiber core and diverge within the connector for a short distance before the light is collimated to form a beam with a diameter substantially greater than the core. In the receiving connector the beam is then focused back to its original diameter on the tip of the receiving fiber. This type of connector is less sensitive to dust and other forms of contamination. 
     The optical cables used in many applications make use of fiber ribbons. These ribbons are comprised of a set of coated fibers joined together in a line (typically 4, 8 or 12 fibers in a line). The individual glass fibers with their protective coatings are typically 250 microns in diameter and the ribbons typically have a fiber to fiber pitch of 250 microns. This 250 micron spacing has also been used in optical transceivers with a variety of designs spacing the active optical devices at the same 250 micron spacing. 
     Currently available expanded beam multiple fiber connectors typically limit the beam diameter to 250 microns to match the ribbon pitch. In order to achieve a beam diameter greater than the fiber pitch, current connectors require the fiber ribbon to be manually split into single fibers before mounting the fibers on the connector. 
     In general, single fiber optical connectors include a precision cylindrical ferrule for aligning and contacting optical fiber end faces with each other. The optical fiber is secured in the central bore of the ferrule so that the fiber&#39;s optical core is centered on the ferrule axis. The fiber tip is then polished to allow physical contact of the fiber core. Two such ferrules can then be aligned with each other using an alignment sleeve with the polished fiber tips pressed against each other to achieve a physical contact optical connection from one fiber to another. Physical contact optical connectors are widely used. 
     Multiple fiber connectors often use a multiple fiber ferrule such as the MT ferrule to provide optical coupling from the source fibers to the receive fibers. The MT ferrule guides the fibers in an array of molded bores to which the fibers are typically bonded. Each ferrule has two additional bores in which guide pins are located to align the ferrules to each other and thus align the mated fibers. 
     A variety of other methods have also been used to make fiber to fiber connections. Included are V-groove alignment systems such as found in Volition™ optical fiber cable connectors, and bare fiber alignment in an array of precise bores. Some connecting concepts such as described in, for example, U.S. Pat. Nos. 4,078,852; 4,421,383, and 7,033,084 make use of lenses and/or reflecting surfaces in optical fiber connections. Each of these connecting concepts describes single purpose connection systems, such as an in line connector or a right angle connector. 
     It would be advantageous to provide an expanded beam connector that can terminate fiber ribbons without separating the fibers and also provide a beam with a diameter greater than the fiber-to-fiber pitch. 
     SUMMARY 
     The disclosure generally relates to sets of optical waveguides such as optical fiber ribbons, and fiber optic connectors useful for connecting multiple optical fibers such as in optical fiber ribbon cables. In particular, the disclosure provides an efficient, compact, and reliable optical waveguide connector that incorporates a optically transmissive substrate combining the features of optical waveguide alignment, along with redirecting and shaping of the optical beam. 
     In one aspect, the present disclosure provides an optical construction that includes: an optically transmissive substrate having: a first major surface including a plurality of waveguide alignment features; an opposing second major surface including a plurality of microlenses staggered relative to one another; and a plurality of optical waveguides with angle cleaved end faces disposed adjacent the first major surface. The angle cleaved end faces are staggered relative to one another, each angle cleaved end face of an optical waveguide in the plurality of optical waveguides corresponding to a different microlens and being oriented so that light exiting each optical waveguide is directed by the angle cleaved end face to the corresponding microlens through the substrate. In another aspect, the present disclosure also provides an optical connector including the optical construction. In still another aspect, the present disclosure also provides a transceiver including the optical construction. 
     In another aspect, the present disclosure provides an optical construction that includes: a first major surface having a first plurality of waveguide alignment features; a first plurality of optical waveguides with angle cleaved end faces disposed adjacent the first major surface, the angle cleaved end faces being staggered relative to one another; a second major surface opposite the first major surface and comprising a second plurality of waveguide alignment features; and a second plurality of optical waveguides with angle cleaved end faces disposed in adjacent the second major surface, the angle cleaved end faces being staggered relative to one another. Each optical waveguide in the first plurality of optical waveguides corresponds to a different optical waveguide in the second plurality of optical waveguides, the angle cleaved faces of corresponding optical waveguides being so oriented that light exiting one optical waveguide enters the corresponding optical waveguide. In another aspect, the present disclosure also provides an optical connector including the optical construction. In still another aspect, the present disclosure also provides a transceiver including the optical construction. 
     In yet another aspect, the present disclosure provides an optical construction that includes: an optically transmissive substrate having a first major side including a first floor surface; a first staircase formed on the first floor surface and including at least a first step comprising a first tread; a second major side opposite the first major side and having a second floor surface; a second staircase formed on the second floor surface and including at least a first step having a first tread. The optically transmissive substrate further includes a first plurality of staggered microlenses disposed on the second floor surface and forming rows of microlenses; a second plurality of staggered microlenses disposed on the first tread of the second staircase and forming rows of microlenses, wherein the substrate, the first and second staircases and the microlenses form a unitary construction. The optical construction further includes a first plurality of optical waveguides with angle cleaved end faces disposed on the first floor surface, the angle cleaved end faces being staggered relative to one another; and a second plurality of optical waveguides with angle cleaved end faces disposed on the first tread of the first staircase, the angle cleaved end faces being staggered relative to one another, wherein each angle cleaved end face of an optical waveguide in the first and the second plurality of optical waveguides corresponds to a different microlens so that light exiting each optical waveguide is directed by the angle cleaved end face to the corresponding microlens through the substrate. In another aspect, the present disclosure also provides an optical connector including the optical construction. In still another aspect, the present disclosure also provides a transceiver including the optical construction. 
     The above summary is not intended to describe each disclosed embodiment or every implementation of the present disclosure. The figures and the detailed description below more particularly exemplify illustrative embodiments. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Throughout the specification reference is made to the appended drawings, where like reference numerals designate like elements, and wherein: 
         FIG. 1A  shows a cut-away perspective view of a fiber optic connector; 
         FIG. 1B  shows a cut-away perspective view of a fiber optic connector; 
         FIG. 1C  shows a perspective view of a fiber optic connector; 
         FIG. 2A  shows a top perspective schematic view of an optically transmissive substrate; 
         FIG. 2B  shows a bottom perspective schematic view of an optically transmissive substrate; 
         FIG. 3A  shows a top perspective schematic view of an optically transmissive substrate; 
         FIG. 3B  shows a bottom perspective schematic view of an optically transmissive substrate; 
         FIG. 4  shows a cross-sectional schematic view of an optical connection; 
         FIGS. 5A-5C  show schematic views of optical fiber and microlens positioning; and 
         FIG. 6  shows a cross-sectional schematic view of an optical connection. 
     
    
    
     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 
     This application is related to U.S. Pat. No. 9,207,413, which is incorporated by reference. 
     The present disclosure relates sets of optical waveguides such as optical fiber ribbons, and fiber optic connectors useful for connecting multiple optical fibers such as in optical fiber ribbon cables. The description that follows is directed toward connections of optical fibers and optical fiber ribbon cables; however, it is to be understood that the present disclosure is similarly directed to connections of optical waveguides including, for example, planar optical waveguides that can be fabricated from polymeric materials or glasses. 
     There are a number of optical fiber connector features that users of optical fibers desire, which are not found in currently available products. These features include low cost, robust performance against contamination, easy cleaning, compact designs, and the ability to rapidly and repeatedly connect multiple optical fibers with a single connector. A rapidly growing application for high capacity interconnections is between equipment racks in data centers where data rates of 10 Gb/s are common, and link lengths are relatively short (typically a few to 100 meters). In such applications, multiple single fiber connectors are often ganged together. Accordingly, described herein is a multiple fiber connecting technique and article which can significantly reduce the cost of multi-fiber connecting. 
     In both single fiber and multi-fiber device interfaces it is often desirable to maintain a low profile interface. This is often accomplished by routing the fiber parallel to the circuit board and using a reflective surface to turn the light so that the beam is perpendicular to the board at the chip interface. It is also common to make use of small lenses to improve the coupling efficiency between the device and the fiber. In the case of ribbon fiber interfaces, these lenses have a center to center distance of 250 um to match with the spacing in the ribbon. Often an MT ferrule is also included as part of the transceiver package with the ferrule&#39;s alignment pins being used to align the fibers to the lenses. 
     In one particular embodiment, the present disclosure provides a general purpose connecting element for multi-fiber optical connectors that include an optically transmissive substrate that makes use of angled reflecting surfaces and a microlens array to redirect and focus or collimate the optical beams. The redirected beams emerge from the element perpendicular to a planar mating surface. The microlens elements can be located in a pocket and can be slightly recessed from the mating surface. The connecting elements also include mechanical features to facilitate alignment of the microlens arrays of the two mated parts. In one particular embodiment, the reflecting surfaces may be cleaved end surfaces that can be aligned at an angle to the optical axis of the optical fiber. In some cases, the reflective surface may be coated with a reflecting material such as a metal or metal alloy to redirect the light. In some cases, the reflective surface may instead enable Total Internal Reflection (TIR) to facilitate redirecting the light. 
     The optically transmissive substrate can be encased in a connector housing that can provide support for the optical cable, ensure alignment of interlocking components of the connector element, and provide protection from the environment. Such connector housings are well known in the art, and can include, for example, alignment holes, matching alignment pins, and the like. The same connecting element can be used in a variety of connecting configurations. It can also be used to interface optical fibers to optical devices such as VCSELs and photodetectors using a board mounted alignment ring. It is to be understood that although the disclosure provided herein describes light travelling in one direction through the fiber and the connector, one of skill in the art should realize that light could also travel in the opposite direction through the connector, or could be bi-directional. 
     The relatively simple design used for both the optically transmissive substrate and the connector housing, eliminates the use of fine core pins such as in an MT ferrule molding, and as a result, the cost and complexity of the molded, cast, or machined part is reduced. Furthermore, a general purpose connecting element described herein can be used in a variety of applications, thereby allowing both development costs and manufacturing costs to be spread across higher volume, decreasing the cost per part. Still further, the use of an expanded optical beam from focusing or collimating microlenses can also provide for improved resistance to transmission losses due to dirt or other impurities. 
     In one particular embodiment, the unique interface defined herein can be used for making internal links within high performance computers, servers, or routers. Additional applications in mating to optical back planes can also be envisioned. Some of the prominent features of the connecting elements can include: a molded (or cast, or machined) component having a generally planar mating surface, and a recessed area (pocket) within the mating surface; convex microlens features located on the floor of the pocket with the apex of these microlens features being within the pocket volume so that when two elements are mated with their mating surfaces in contact, a small gap exists between the microlens features; optical fiber alignment features useful to align the optical fibers axes generally within about 15 degrees of parallel to the mating surface; and reflecting surfaces to redirect the optical beam from each fiber so that they are perpendicular to the mating surface. Each optical beam is centered over one of the microlens features; and mechanical alignment features facilitate the alignment of two connecting elements so that their mating surfaces are in contact and their microlenses are aligned. 
     In one particular embodiment, the microlens features may collimate the light beam from the fiber. Generally, collimated light can be useful for making fiber-to-fiber connections, since the light beam is generally expanded upon collimation, which makes the connection less susceptible to contamination by foreign material such as dust. In one particular embodiment, the microlens features may instead focus the beam so as to create a beam “waist” in the plane of the mating surface. Generally, focused beams can be useful for making fiber-to-circuit connections such as to a sensor or other active device disposed on a circuit board, since the light beam can be concentrated to a smaller region for greater sensitivity. In some cases, particularly for optical fiber-to-fiber connections, collimation of the light beam may be preferred, since the collimated light beams are more robust against dirt and other contamination, and also provide for greater alignment tolerances. 
     In one particular embodiment, the optical fibers can be aligned using waveguide alignment features, such as within molded vee-groove features in the optically transmissive substrate, with the vee-grooves being parallel to the mating surface; however, vee-grooves are not required for alignment in all cases. As described herein, optional parallel vee-grooves are included, but it is to be understood that other techniques for alignment and securing of the optical fibers would also be acceptable. Furthermore, vee-grooved alignment may not be suitable in some cases and other techniques may be preferred, for example, when the optical waveguide is a planar optical waveguide. In some cases, the alignment of the optical waveguides and/or optical fibers can instead be accomplished by any of the techniques known to one of skill in the art of optical alignment using any suitable waveguide alignment feature. 
     A variety of mechanical feature sets may be used to align a pair of connecting elements. One feature set includes a pair of precisely positioned holes into which alignment pins are placed, similar to the alignment technique used for MT ferrules. In one particular embodiment, if the holes diameters and locations are similar to that of the MT connector, then one of the connecting elements described herein could (with an appropriate set of microlenses) intermate with an MT ferrule. 
     Coupling the light from optical fiber to optical fiber, from semiconductor light sources to optical fibers, and the related coupling light from optical fibers to photodetector chips, has been done in a wide variety of ways. Achieving the desired low loss and low cost has been challenging. This is especially so when the fibers are grouped into industry standard ribbons. These ribbons contain a number of coated fibers (typical numbers are 8 or 12) having an outside diameter of about 250 um. The fibers are then laminated between a pair of thin polymer films to make a flat ribbon. Another technique for fabricating ribbons is to use an extrusion process wherein the individual coated fibers are guided through an extrusion die with a polymeric matrix material. 
     The present disclosure provides an improvement on previous multifiber interfaces, including transceiver interfaces, by providing a fiber ribbon that includes individual fibers cleaved at more than one length to allow greater space between optical devices reducing electrical interference and also allowing the use of lenses having a larger diameter to allow more effective optical coupling. In one particular embodiment, the individual fibers can be cleaved at more than one length that results in a staggered pattern of the cleaved ends. The staggered pattern can include several rows of fiber ends, each row including fibers cleaved at the same length, whereas adjacent rows include adjacent fibers that are cleaved at a different length. 
     The present disclosure relates in part to optical transceiver interfaces used in communication and computer networks for both external and internal links. The transceivers may be located on a motherboard, daughter board, blade, or may be integrated into the ends of an active optical cable. 
     With the ever increasing data rates, it becomes increasingly difficult to package sensitive photodetectors close to the higher power semiconductor lasers without electromagnetic interference problems. Furthermore, as bit rates increase the beam divergence of vertical cavity surface emitting lasers (VCSELs) increases. These issues make it desirable to increase the device spacing and the lens diameter. 
     In some cases, to minimize Fresnel loss, it can be desirable to have only a single air gap between the devices and the fiber cores. To achieve this, the present disclosure provides that the fibers can be adhesively attached to the optically transmissive substrate along their bottom side with an index matching adhesive. 
     Given this configuration and the numerical aperture of the fiber, a 500 um lens allows the lens block to be manufactured without extremely fine sections which would be difficult to mold. Cleave patterns other than the two rows shown here are also possible and would enable even larger lens diameter and device spacing. 
       FIG. 1A  shows a cut-away perspective view of a fiber optic connector  100  according to one aspect of the disclosure. Fiber optic connector  100  includes a connector housing  110  having an optional cover support  115 , an optional cover (not shown) that fits within the optional cover support  115  to protect the optical components of the fiber optic connector  100  from the environment, and an alignment feature  150 . An optically transmissive substrate  120  having a plurality of optional parallel vee-grooves  126  for accepting individual optical fibers  132  from an optical ribbon cable  130  is secured within connector housing  110 . The individual optical fibers  132  each include a cleaved end  136  disposed in a staggered orientation forming at least a first optical fiber row  135   a  and a second optical fiber row  135   b . It is to be understood that any desired number of optical fiber rows can staggered relative to each other, as described elsewhere. In operation, each of the cleaved ends  136  associated with each of the individual optical fibers  132  re-direct light through optically transmissive substrate  120  and out through a microlens  128  disposed on lower surface  122 . The microlenses  128  can be disposed in a cavity  140  such that the lens surface is indented from the bottom of the connector housing  110 . The cleaved ends  136  can be laser cleaved optical fibers that forms an oblique angle with the axis of the fiber, as described elsewhere. In some cases, the cleaved optical fibers can be coated with a reflector such as a metal or metal alloy. In some cases, the cleaved optical fibers can instead re-direct light by total internal reflection (TIR). 
     Optically transmissive substrate  120  can be fabricated from any suitably transparent and dimensionally stable material including, for example, polymers such as a polyimide. In one particular embodiment, optically transmissive substrate  120  can be fabricated from a dimensionally stable transparent polyimide material such as, for example, Ultem 1010 Polyetherimide, available from SABIC Innovative Plastics, Pittsfield Mass. In some cases, the individual optical fibers  132  can be adhesively secured in the optional parallel vee-grooves  126 . In one particular embodiment, an index matching gel or adhesive may be inserted between the optically transmissive substrate  120  and the individual optical fibers  132 . By eliminating any air gap in this area, Fresnel losses may be greatly reduced. 
       FIG. 1B  shows a cut-away perspective view of a fiber optic connector  101  attached to a circuit board  170 . The housing components shown in  FIG. 1A  have been removed in  FIG. 1B  to more clearly show the relationship of the optical ribbon cable  130 , the individual optical fibers  132 , the cleaved ends  136 , and the optional vee-grooves of the optically transmissive substrate  120 . As described elsewhere, each of the first row  135   a  and second row  135   b  of cleaved ends  136  of optical fibers  132  are associated with a first row and a second row of microlenses (not shown). The microlenses (and thus the cleaved ends  136 ) can be aligned by alignment features  150  and alignment ring  160 , to any desired optical device (not shown, but located under optically transmissive substrate  120 ) positioned on circuit board  170 . 
       FIG. 1C  shows a perspective view of the fiber optic connector  100  of  FIG. 1A  connected to a second fiber optic connector  100 ′. Second fiber optic connector  100 ′ can be identical to the fiber optic connector  100 , and forms an optical connection  102 , as described elsewhere. Optional cover  117  is disposed optional cover support  115  (shown in  FIG. 1A ) to protect the optical components of the fiber optic connector  100  from the environment. Alignment features  150  serve to ensure that light from optical ribbon cable  130  and second optical ribbon cable  130 ′ are coupled efficiently, with a minimum of losses. 
       FIG. 2A  shows a top perspective schematic view of an optically transmissive substrate  220 , according to one aspect of the disclosure. Optically transmissive substrate  220  includes a first surface  224  having a plurality of optional parallel vee-grooves  226 , and an opposing second surface  222 . A plurality of input optical fibers (two are shown as first input optical fiber  232   a  and a second input optical fiber  232   b ) are positioned along optional parallel vee-grooves  226 , and may be adhered to the optional parallel vee-groove  226 , as described elsewhere. Each of the input optical fibers  232   a ,  232   b , are cleaved at an oblique angle to the axis of the input optical fibers  232   a ,  232   b , forming a first cleaved end  236   a  and a second cleaved end  236   b  within a first cleaved end row  235   a , such that injected light is re-directed into the optically transmissive substrate  220 . In some cases, the light can be re-directed at an angle perpendicular to the axis of the input optical fibers  232   a ,  232   b.    
       FIG. 2B  shows a bottom perspective schematic view of the optically transmissive substrate  220  of  FIG. 2A . Optically transmissive substrate  220  includes the first surface  224  and the opposing second surface  222  having a plurality of microlenses  228   a ,  228   b ,  228   c ,  228   d , that are disposed within a microlens pocket  240 . Each of the plurality of microlenses  228   a ,  228   b ,  228   c ,  228   d  are aligned with a cleaved end  236   a ,  236   b , in first cleaved end row  235   a  described above, and are disposed to receive re-directed light from the respective optical fiber  232   a ,  232   b . Each of the microlenses have a microlens diameter D 1 , and are disposed within microlens pocket  240  with a center-to-center spacing L 1 . The center-to-center spacing L 1  typically is no greater than the spacing between adjacent optical fibers, and results in a restriction on the maximum microlens diameter D 1  that can be utilized in the connector, as described elsewhere. The depth of microlens pocket  240  serves to keep each of the microlenses below the level of opposing second surface  222 . It is to be understood that optically transmissive substrate  220  can include any desired number of optional parallel vee-grooves  226 , cleaved ends  236   a - 236   b , rows of cleaved ends  235   a , microlenses  228   a - 228   d , and input optical fibers  232   a ,  232   b.    
       FIG. 3A  shows a top perspective schematic view of an optically transmissive substrate  320 , according to one aspect of the disclosure. Optically transmissive substrate  320  includes a first surface  324  having a plurality of optional parallel vee-grooves  326  that are aligned with a plurality of light re-directing features  335   a ,  335   b ,  335   c ,  335   d , and an opposing second surface  322 . A plurality of input optical fibers (two are shown as first input optical fiber  332   a  and a second input optical fiber  332   b ) are positioned along optional parallel vee-grooves  326 , and may be adhered to the optional parallel vee-groove  326 , as described elsewhere. Each of the input optical fibers  332   a ,  332   b , are cleaved at an oblique angle to the axis of the input optical fibers  332   a ,  332   b , forming a first cleaved end  336   a  within a first cleaved end row  335   a , and a second cleaved end  336   b  within a second cleaved end row  335   b , such that injected light is re-directed into the optically transmissive substrate  320 . In some cases, the light can be re-directed at an angle perpendicular to the axis of the input optical fibers  332   a ,  332   b.    
       FIG. 3B  shows a bottom perspective schematic view of the optically transmissive substrate  320  of  FIG. 3A . Optically transmissive substrate  320  includes the first surface  324  and the opposing second surface  322  having a plurality of staggered microlenses  328   a ,  328   b ,  328   c ,  328   d , that are disposed within a microlens pocket  340 . Each of the plurality of staggered microlenses  328   a ,  328   b ,  328   c ,  328   d  are aligned with a cleaved end  336   a ,  336   b  in a first and second row  335   a ,  335   b , described above, and is disposed to receive light from the respective optical fibers  332   a ,  332   b . Each of the staggered microlenses  328   a ,  328   b ,  328   c ,  328   d  have a staggered microlens diameter D 2 , and are disposed within microlens pocket  340  with a center-to-center spacing L 1  corresponding to the separation of the optical fibers, and the center-to-center spacing L 1  of adjacent microlenses  328   a - 328   d  can be the same as the center-to-center spacing L 1  described with reference to  FIG. 2B . However, each of the staggered microlenses  328   a ,  328   b ,  328   c ,  328   d  have a staggered spacing L 2  corresponding to the separation of the microlenses, and the staggered spacing L 2  is larger than the center-to-center spacing L 1 . As a result, the maximum microlens diameter D 2  that can be utilized in the connector is greater for the staggered spacing L 2  shown in  FIG. 3B , as compared to the maximum microlens diameter D 1  that can be utilized in the microlens spacing L 1 , as described elsewhere. 
     As a result of staggering the cleaved ends  336   a ,  336   b , the plurality of staggered microlenses  328   a ,  328   b ,  328   c ,  328   d , enable an increase in the microlens diameter D 1  to the staggered microlens diameter D 2 . A larger staggered microlens diameter D 2  is preferred. The depth of microlens pocket  340  serves to keep each of the microlenses below the level of opposing second surface  322 . It is to be understood that optically transmissive substrate  320  can include any desired number of optional parallel vee-grooves  326 , cleaved ends  336   a - 336   b , rows of cleaved ends  335   a ,  335   b , microlenses  328   a - 328   d , number of rows of microlenses  328   a - 328   d , number of microlenses  328   a - 328   d  in each row, and input optical fibers  332   a ,  332   b.    
     In contrast with the embodiment shown in  FIGS. 2A-2B , the microlens locations shown in  FIG. 3B  are not defined as a single row. In this case two rows of microlenses are shown with two microlenses in each row. When used with optical fiber ribbons having a 250 micron fiber-to-fiber spacing, this allows the microlenses to approach 500 microns in diameter. The use of 500 micron diameter collimating microlenses possible with the staggered fiber/microlens embodiment shown in  FIGS. 3A-3B , allows an alignment tolerance that is less stringent than is required with 250 micron diameter microlenses possible with the embodiment shown in  FIGS. 2A-2B , and much less stringent than needed for physical contact connectors using conventional MT ferrules. It is to be understood that any of the optical connectors described herein can include staggered cleaved ends and correspondingly staggered microlenses as described with reference to  FIGS. 3A-3B , and it may be preferable to include the staggered configurations wherever possible. Generally, the described staggered microlens designs can enable an expanded-beam optical fiber connector that can be used for a ribbonized collection of fibers, wherein the optical beam diameter exiting the microlenses is greater than the fiber-to-fiber separation (that is, pitch) in the ribbon, and the fibers do not need to be singulated in order to accomplish the connection. 
       FIG. 4  shows a cross-sectional schematic view of an optical connection  401  that includes a first optical connector  400  connected to a second optical connector  400 ′, according to one aspect of the disclosure. In  FIG. 4 , the cross-sectional view is near the optical axis (that is, center) of a pair of optical fibers in communication through the connector. In one particular embodiment, second optical connector  400 ′ can be identical to the first optical connector  400 , and forms the optical connection  401 , similar to the optical connection  101  shown in  FIG. 1B . 
     First optical connector  400  includes a first connector housing  410  and a first optically transmissive substrate  420  secured within the first connector housing  410 . The first optically transmissive substrate  420  includes a first upper surface  424  and an opposite first lower surface  422 . A first optical fiber  432  is secured within a first optional parallel vee-groove  426  on first upper surface  424 , between the first optically transmissive substrate  420  and the first connector housing  410 . The first connector housing  410  further includes an optional first cover support  415 , and an optional first cover  417  that can serve to protect the components in the first optical connector  400 . 
     First optical fiber  432  includes a first light re-directing feature  435  including a first cleaved end  436  of first optical fiber  432 . First optical fiber  432  can be held in position and aligned by resting in the first optional parallel vee-groove  426 , which can be directly molded into first optically transmissive substrate  420 . First optical fiber  432  can be in direct contact with first upper surface  424  such that first gap  434  is eliminated. In some cases, an adhesive can be used to affix the first optical fiber  432  to the first optional parallel vee-groove  426  and an index-matching adhesive or gel can fill the first gap  434 , if present. 
     First optically transmissive substrate  420  further includes a first microlens  428  disposed on the first lower surface  422 , positioned such that a central light ray  490  travelling through the first optical fiber  432  that intercepts and is reflected from the first cleaved end  436 , is directed toward the optical center of the first microlens  428 . In one particular embodiment, shown in  FIG. 4 , first cleaved end  436  can be disposed such that central light ray  490  intercepts first cleaved end  436  at a reflection angle θr equal to about 45 degrees. In some cases, first cleaved end  436  can be a TIR surface. In some cases, first cleaved end  436  can instead be a mirrored reflective surface. 
     In a similar manner, second optical connector  400 ′ includes a second connector housing  410 ′ and a second optically transmissive substrate  420 ′ secured within the second connector housing  410 ′. The second optically transmissive substrate  420 ′ includes a second upper surface  424 ′ and an opposite second lower surface  422 ′. A second optical fiber  432 ′ is secured within a second optional parallel vee-groove  426 ′ on second upper surface  424 ′, between the second optically transmissive substrate  420 ′ and the second connector housing  410 ′. The second connector housing  410 ′ further includes an optional second cover support  415 ′, and an optional second cover  417 ′ that can serve to protect the components in the second optical connector  400 ′. 
     Second optical fiber  432 ′ includes a second light re-directing feature  435 ′ including a second cleaved end  436 ′ of second optical fiber  432 ′. Second optical fiber  432 ′ can be held in position and aligned by resting in the second optional parallel vee-groove  426 ′, which can be directly molded into second optically transmissive substrate  420 ′. Second optical fiber  432 ′ can be in direct contact with second upper surface  424 ′ such that second gap  434 ′ is eliminated. In some cases, an adhesive can be used to affix the second optical fiber  432 ′ to the second optional parallel vee-groove  426 ′ and an index-matching adhesive or gel can fill the second gap  434 ′, if present. 
     Second optically transmissive substrate  420 ′ further includes a second microlens  428 ′ disposed on the second lower surface  422 ′, positioned such that a central light ray  490  travelling through the second optical fiber  432 ′ that intercepts and is reflected from the second cleaved end  436 ′, is directed toward the optical center of the second microlens  428 ′. In one particular embodiment, shown in  FIG. 4 , second cleaved end  436 ′ can be disposed such that central light ray  490  intercepts second cleaved end  436 ′ at a reflection angle θr equal to about 45 degrees. In some cases, second cleaved end  436 ′ can be a TIR surface. In some cases, second cleaved end  436 ′ can instead be a mirrored reflective surface. 
     A first and a second alignment feature  450 ,  450 ′ in first and second connector housing  410 ,  410 ′, respectively, serve to ensure that light from the first optical fiber  432  and the second optical fiber  432 ′ are coupled efficiently, with a minimum of losses. First and second alignment features  450 ,  450 ′ can include any suitable feature to ensure alignment of the first and second optical connectors  400 ,  400 ′, and the features shown in  FIG. 4  are for illustrative purposes only. 
     A first optical fiber separation distance S 1  can be measured between the optical axis of the first optical fiber  432  and the first microlens  428 . A second optical fiber separation distance S 1 ′ can be measured between the optical axis of the second optical fiber  423 ′ and the second microlens  428 ′. A microlens separation distance S 2  can be measured between the surfaces of the first and second microlenses  428 ,  428 ′. In some cases, each of the first optical fiber separation distance S 1  and the second optical fiber separation distance S 1 ′ will be the same, and can range from about 1 mm to about 2 mm, or about 1.5 mm. The microlens separation distance S 2  can range from about 0.1 mm to about 1 mm, or about 0.5 mm. 
     A light beam  490  travelling through first optical fiber  432  is reflected from first cleaved end  436  in a direction perpendicular to the optical axis of first optical fiber  432 . Light beam  490  then passes through first microlens  428  which can be a collimating microlens or a focusing microlens, as described elsewhere. Light beam  490  then enters second optically transmissive substrate  420 ′ through second microlens  428 ′, is reflected from second cleaved end  436 ′ and enters second optical fiber  432 ′ in a direction parallel to the optical axis of the second optical fiber  432 ′. 
       FIGS. 5A-5C  show schematic views of optical fiber and microlens positioning, according to one aspect of the disclosure. In  FIG. 5A , each of the optical fibers  532  in ribbon cable  530  have an uncoated fiber diameter fl equal to about 125 microns, and a fiber-to-fiber spacing dl equal to about 125 microns. In one particular embodiment, for two rows of microlenses  528  shown in the figure, the staggered cleaved ends  536  of optical fibers  532  can be separated by a fiber length difference L 1  equal to about 433 microns, and the maximum diameter D 1  of the microlenses  528  can be about 500 microns. 
     In  FIG. 5B , each of the optical fibers  532  in ribbon cable  530 ′ have an uncoated fiber diameter fl equal to about 125 microns, and a fiber-to-fiber spacing dl equal to about 125 microns. In one particular embodiment, for three rows of microlenses  528  shown in the figure, the staggered cleaved ends  536  of optical fibers  532  can be separated by a fiber length difference L 2  equal to about 707 microns, and the maximum diameter D 2  of the microlenses  528  can be about 750 microns. 
     In  FIG. 5C , each of the optical fibers  532  in ribbon cable  530 ″ have an uncoated fiber diameter fl equal to about 125 microns, and a fiber-to-fiber spacing dl equal to about 125 microns. In one particular embodiment, for four rows of microlenses  528  shown in the figure, the staggered cleaved ends  536  of optical fibers  532  can be separated by a fiber length difference L 3  equal to about 968 microns, and the maximum diameter D 3  of the microlenses  528  can be about 1000 microns. 
       FIG. 6  shows a cross-sectional schematic view of an optical connection  601  that includes a first optical connector  600  connected to a second optical connector  600 ′, according to one aspect of the disclosure. In  FIG. 6 , the cross-sectional view is near the optical axis (that is, center) of two pairs of optical fibers in communication through the connector. In one particular embodiment, second optical connector  600 ′ can be identical to the first optical connector  600 , and forms an optical connection  601 , similar to the optical connection  101  shown in  FIG. 1B . In some cases, second optical connector  600 ′ can instead be a mirror image to the first optical connector  600 . 
     First optical connector  600  includes a first connector housing  610  and a first optically transmissive substrate  620  secured within the first connector housing  610 . The first optically transmissive substrate  620  comprises a staircase that includes a first floor surface  624 , a first step  625 , and a first tread  627 . The first optically transmissive substrate  620  further comprises a second floor surface  622  opposite the first floor surface  624  and a second tread  621  opposite the first tread  627 . A first optical fiber  632  is secured within a first optional parallel vee-groove  626  on first floor surface  624 , between the first optically transmissive substrate  620  and the first connector housing  610 . A second optical fiber  631  is secured within a second optional parallel vee-groove  629  on the first tread  627 , and is also secured within first connector housing  610 . The first connector housing  610  further includes an optional first cover support  615 , and an optional first cover  617  that can serve to protect the components in the first optical connector  600 . 
     First optical fiber  632  includes a first light re-directing feature  635  including a first cleaved end  636  of first optical fiber  632 . First optical fiber  632  can be held in position and aligned by resting in the first optional parallel vee-groove  626 , which can be directly molded into first optically transmissive substrate  620 . First optical fiber  632  can be in direct contact with first floor surface  624  such that first gap  634  is eliminated. In some cases, an adhesive can be used to affix the first optical fiber  632  to the first optional parallel vee-groove  626  and an index-matching adhesive or gel can fill the first gap  634 , if present. 
     Second optical fiber  631  includes a second light re-directing feature  637  including a second cleaved end  638  of second optical fiber  631 . Second optical fiber  631  can be held in position and aligned by resting in the second optional parallel vee-groove  629 , which can be directly molded into first optically transmissive substrate  620 . Second optical fiber  631  can be in direct contact with first tread  627  such that second gap  639  is eliminated. In some cases, an adhesive can be used to affix the second optical fiber  631  to the second optional parallel vee-groove  629  and an index-matching adhesive or gel can fill the second gap  639 , if present. 
     First optically transmissive substrate  620  further includes a first microlens  628  disposed on the second floor surface  622 , positioned such that a light ray travelling through the first optical fiber  632  that intercepts and is reflected from the first cleaved end  636 , is directed toward the optical center of the first microlens  628 . First optically transmissive substrate  620  still further includes a second microlens  623  disposed on the second tread  621 , positioned such that a light ray travelling through the second optical fiber  631  that intercepts and is reflected from the second cleaved end  638 , is directed toward the optical center of the second microlens  623 . 
     In a similar manner, second optical connector  600 ′ includes a second connector housing  610 ′ and a second optically transmissive substrate  620 ′ secured within the second connector housing  610 ′. The second optically transmissive substrate  620 ′ comprises a staircase that includes a third floor surface  624 ′, a second step  625 ′, and a third tread  627 ′. The second optically transmissive substrate  620 ′ further comprises a fourth floor surface  622 ′ opposite the third floor surface  624 ′ and a fourth tread  621 ′ opposite the third tread  627 ′. A third optical fiber  632 ′ is secured within a third optional parallel vee-groove  626 ′ on third floor surface  624 ′, between the second optically transmissive substrate  620 ′ and the second connector housing  610 ′. A fourth optical fiber  631 ′ is secured within a fourth optional parallel vee-groove  629 ′ on the third tread  627 ′, and is also secured within second connector housing  610 ′. The second connector housing  610 ′ further includes an optional second cover support  615 ′, and an optional second cover  617 ′ that can serve to protect the components in the second optical connector  600 ′. 
     Third optical fiber  632 ′ includes a third light re-directing feature  635 ′ including a third cleaved end  636 ′ of third optical fiber  632 ′. Third optical fiber  632 ′ can be held in position and aligned by resting in the third optional parallel vee-groove  626 ′, which can be directly molded into second optically transmissive substrate  620 ′. Third optical fiber  632 ′ can be in direct contact with third floor surface  624 ′ such that third gap  634 ′ is eliminated. In some cases, an adhesive can be used to affix the third optical fiber  632 ′ to the third optional parallel vee-groove  626 ′ and an index-matching adhesive or gel can fill the third gap  634 ′, if present. 
     Fourth optical fiber  631 ′ includes a fourth light re-directing feature  637 ′ including a fourth cleaved end  638 ′ of fourth optical fiber  631 ′. Fourth optical fiber  631 ′ can be held in position and aligned by resting in the fourth optional parallel vee-groove  629 ′, which can be directly molded into second optically transmissive substrate  620 ′. Fourth optical fiber  631 ′ can be in direct contact with third tread  627 ′ such that fourth gap  639 ′ is eliminated. In some cases, an adhesive can be used to affix the fourth optical fiber  631 ′ to the fourth optional parallel vee-groove  629 ′ and an index-matching adhesive or gel can fill the fourth gap  639 ′, if present. 
     Second optically transmissive substrate  620 ′ further includes a third microlens  628 ′ disposed on the fourth floor surface  622 ′, positioned such that a light ray travelling through the third optical fiber  632 ′ that intercepts and is reflected from the third cleaved end  636 ′, is directed toward the optical center of the third microlens  628 ′. Second optically transmissive substrate  620 ′ still further includes a fourth microlens  623 ′ disposed on the fourth tread  621 ′, positioned such that a light ray travelling through the fourth optical fiber  631 ′ that intercepts and is reflected from the fourth cleaved end  638 ′, is directed toward the optical center of the fourth microlens  623 ′. 
     A first and a second alignment feature  650 ,  650 ′ in first and second connector housing  610 ,  610 ′, respectively, serve to ensure that light from the first optical fiber  632  and the fourth optical fiber  431 ′ are coupled efficiently, and also that light from the second optical fiber  631  and the third optical fiber  632 ′ are coupled efficiently, with a minimum of losses. First and second alignment features  650 ,  650 ′ can include any suitable feature to ensure alignment of the first and second optical connectors  600 ,  600 ′, and the features shown in  FIG. 6  are for illustrative purposes only. 
     A first optical fiber separation distance S 1  can be measured between the optical axis of the first optical fiber  632  and the first microlens  628 . A second optical fiber separation distance S 1 ′ can be measured between the optical axis of the fourth optical fiber  631 ′ and the fourth microlens  623 ′. A first microlens separation distance S 2  can be measured between the surfaces of the first and fourth microlenses  628 ,  623 ′. Similarly, a third optical fiber separation distance S 3  can be measured between the optical axis of the second optical fiber  631  and the second microlens  623 . A fourth optical fiber separation distance S 3 ′ can be measured between the optical axis of the third optical fiber  632 ′ and the third microlens  628 ′. A second microlens separation distance S 4  can be measured between the surfaces of the second and third microlenses  623 ,  628 ′. 
     In some cases, each of the first through fourth optical fiber separation distances S 1 , S 1 ′, S 3 , S 3 ′, can be the same, and can range from about 1 mm to about 2 mm, or about 1.5 mm. In some cases, each of the first and second microlens separation distance S 2 , S 4 , can be the same, and can range from about 0.1 mm to about 1 mm, or about 0.5 mm. In one particular embodiment, each of the connection path lengths through the connector can be the same, such that the first-fourth optical fiber path length S 1 +S 2 +S 1 ′ is equal to the second-third optical fiber path length S 3 +S 4 +S 3 ′. 
     A first light beam  690  travelling through first optical fiber  632  is reflected from first cleaved end  636  in a direction perpendicular to the optical axis of first optical fiber  632 . First light beam  690  then passes through first microlens  628  which can be a collimating microlens or a focusing microlens, as described elsewhere. First light beam  690  then enters second optically transmissive substrate  620 ′ through fourth microlens  623 ′, is reflected from fourth cleaved end  638 ′ and enters fourth optical fiber  631 ′ in a direction parallel to the optical axis of the fourth optical fiber  631 ′. 
     In a similar manner, a second light beam  691  travelling through second optical fiber  631  is reflected from second cleaved end  638  in a direction perpendicular to the optical axis of second optical fiber  631 . Second light beam  691  then passes through second microlens  623  which can be a collimating microlens or a focusing microlens, as described elsewhere. Second light beam  691  then enters second optically transmissive substrate  620 ′ through third microlens  628 ′, is reflected from third cleaved end  636 ′ and enters third optical fiber  632 ′ in a direction parallel to the optical axis of the third optical fiber  632 ′. 
     In one particular embodiment, an antireflective (AR) coating can be applied to portions of the optically transmissive substrate, the optical fiber, or to both the optically transmissive substrate and the optical fiber, in order to further reduce reflective (that is, Fresnel) losses. In some cases, an AR coating can be applied in the region proximate each of the gaps between the optical fiber and the optically transmissive substrate (for example, the first through fourth gaps  634 ,  639 ,  634 ′,  639 ′). In some cases, an AR coating can also be applied to the surface of the microlenses. In one particular embodiment, an index matching gel or an index matching adhesive can be disposed in the region surrounding the gaps between the optically transmissive substrate and the optical fiber, also to reduce reflective losses. 
     Following are a list of embodiments of the present disclosure. 
     Item 1 is an optical construction comprising: an optically transmissive substrate comprising: a first major surface comprising a plurality of waveguide alignment features; an opposing second major surface comprising a plurality of microlenses staggered relative to one another; and a plurality of optical waveguides with angle cleaved end faces disposed adjacent the first major surface, the angle cleaved end faces being staggered relative to one another, each angle cleaved end face of an optical waveguide in the plurality of optical waveguides corresponding to a different microlens and being oriented so that light exiting each optical waveguide is directed by the angle cleaved end face to the corresponding microlens through the substrate. 
     Item 2 is the optical construction of item 1, wherein the waveguide alignment features comprise parallel grooves. 
     Item 3 is the optical construction of item 1 or item 2, wherein the optical waveguides comprise optical fibers. 
     Item 4 is the optical construction of item 1 to item 3, wherein the staggered microlenses form spaced apart first and second rows of microlenses and the staggered angle cleaved end faces form spaced apart first and second rows of angle cleaved end faces. 
     Item 5 is the optical construction of item 1 to item 4, wherein each of the angle cleaved end faces comprise a total internal reflection (TIR) surface. 
     Item 6 is the optical construction of item 1 to item 5, wherein each of the angle cleaved end faces comprise a reflective material coating. 
     Item 7 is the optical construction of item 6, wherein the reflective material coating comprises a metal or a metal alloy. 
     Item 8 is the optical construction of item 1 to item 7, wherein each microlens includes a diameter greater than a separation distance between adjacent optical waveguides. 
     Item 9 is the optical construction of item 1 to item 8, further comprising an antireflective coating disposed on each microlens. 
     Item 10 is an optical construction comprising: a first major surface comprising a first plurality of waveguide alignment features; a first plurality of optical waveguides with angle cleaved end faces disposed adjacent the first major surface, the angle cleaved end faces being staggered relative to one another; a second major surface opposite the first major surface and comprising a second plurality of waveguide alignment features; and a second plurality of optical waveguides with angle cleaved end faces disposed adjacent the second major surface, the angle cleaved end faces being staggered relative to one another; wherein each optical waveguide in the first plurality of optical waveguides corresponds to a different optical waveguide in the second plurality of optical waveguides, the angle cleaved faces of corresponding optical waveguides being so oriented that light exiting one optical waveguide enters the corresponding optical waveguide. 
     Item 11 is the optical construction of item 10, wherein the waveguide alignment features comprise parallel grooves. 
     Item 12 is the optical construction of item 10 or item 11, wherein the optical waveguides comprise optical fibers. 
     Item 13 is the optical construction of item 10 to item 12, wherein corresponding optical waveguides are associated with one or more corresponding microlenses for directing light between the angle cleaved end faces of the corresponding optical waveguides. 
     Item 14 is the optical construction of item 10 to item 13, wherein the staggered angle cleaved end faces of each of the first and second pluralities of optical waveguides form spaced apart first and second rows of angle cleaved end faces. 
     Item 15 is the optical construction of item 10 to item 14, wherein each of the angle cleaved end faces comprise a total internal reflection (TIR) surface. 
     Item 16 is the optical construction of item 10 to item 15, wherein each of the angle cleaved end faces comprise a reflective material coating. 
     Item 17 is the optical construction of item 16, wherein the reflective material coating comprises a metal or a metal alloy. 
     Item 18 is the optical construction of item 10 to item 17, wherein each microlens includes a microlens diameter greater than a separation distance between adjacent optical waveguides. 
     Item 19 is the optical construction of item 10 to item 18, further comprising an antireflective coating disposed on each microlens. 
     Item 20 is an optical construction, comprising: an optically transmissive substrate comprising: a first major side comprising a first floor surface; a first staircase formed on the first floor surface and comprising at least a first step comprising a first tread; a second major side opposite the first major side and comprising a second floor surface; a second staircase formed on the second floor surface and comprising at least a first step comprising a first tread; a first plurality of staggered microlenses disposed on the second floor surface and forming rows of microlenses; a second plurality of staggered microlenses disposed on the first tread of the second staircase and forming rows of microlenses, wherein the substrate, the first and second staircases and the microlenses form a unitary construction; a first plurality of optical waveguides with angle cleaved end faces disposed on the first floor surface, the angle cleaved end faces being staggered relative to one another; and a second plurality of optical waveguides with angle cleaved end faces disposed on the first tread of the first staircase, the angle cleaved end faces being staggered relative to one another, wherein each angle cleaved end face of an optical waveguide in the first and the second plurality of optical waveguides corresponds to a different microlens so that light exiting each optical waveguide is directed by the angle cleaved end face to the corresponding microlens through the substrate. 
     Item 21 is the optical construction of item 20, wherein the waveguide alignment features comprise parallel grooves. 
     Item 22 is the optical construction of item 20 or item 21, wherein the optical waveguides comprise optical fibers. 
     Item 23 is the optical construction of item 20 to item 22, wherein a separation distance between each angle cleaved end face of the optical waveguide and the corresponding microlens is a constant. 
     Item 24 is the optical construction of item 20 to item 23, wherein each of the angle cleaved end faces comprise a total internal reflection (TIR) surface. 
     Item 25 is the optical construction of item 20 to item 24, wherein each of the angle cleaved end faces comprise a reflective material coating. 
     Item 26 is the optical construction of item 25, wherein the reflective material coating comprises a metal or a metal alloy. 
     Item 27 is the optical construction of item 20 to item 26, further comprising an antireflective coating disposed on the microlenses. 
     Item 28 is an optical connector comprising the optical construction of item 1 to item 27. 
     Item 29 is a transceiver comprising the optical construction of item 1 to item 28. 
     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 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. 
     All references and publications cited herein are expressly incorporated herein by reference in their entirety into this disclosure, except to the extent they may directly contradict this disclosure. Although specific embodiments have been illustrated and described herein, it will be appreciated by those of ordinary skill in the art that a variety of alternate and/or equivalent implementations can be substituted for the specific embodiments shown and described without departing from the scope of the present disclosure. This application is intended to cover any adaptations or variations of the specific embodiments discussed herein. Therefore, it is intended that this disclosure be limited only by the claims and the equivalents thereof.