Patent Publication Number: US-2016246015-A1

Title: Multiple-beam microlen

Description:
This application claims the benefit of U.S. Provisional Application No. 61/823,558, filed May 15, 2013 and U.S. Provisional Application No. 61/823,588, filed May 15, 2013, which are herein incorporated by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a multiple-beam microlens for transference of light between cores of a multi-core fiber (MCF) and optical devices or single core fibers. More particularly, the present invention relates a microlens, or interconnected microlenses forming a microlens array, with each microlens designed to directly couple light from the cores of a MCF to optical devices and/or single core fibers. 
     2. Description of the Related Art 
     For applications such as high-performance computing, storage area networks, local area networks, data centers, and others, there is an ever-increasing need for higher-speed optical communication links having higher density in the links, and having higher port density at the ends. “Parallel optical communication” is known in the prior art. In a parallel optical communication system, multiple optical fibers are closely grouped, and terminated in a single connector, typically in a single row or in two rows, such as presented by an MT ferrule or an MPO connector. Typical spacing of the fiber ends at the ferrule&#39;s end face or connector face is 250 μm, center-to-center. Each fiber has a single core at its center, which relays an optical data stream in parallel to the data streams being relayed by the other fiber ends presented by the ferrule/connector end face. 
     An optoelectronic transducer (OET) is a device which converts an electrical data stream to an optical data stream or converts an optical data stream to an electrical data stream. For converting high-speed data streams from electrical to optical, the most prevalent OET is a semiconductor laser, and for parallel optical communications, that is usually a vertical-cavity surface-emitting laser, or VCSEL. For converting high-speed data streams from optical to electrical, the most prevalent OET is a p-i-n photodiode, or PIN. To achieve low cost, a microlens array formed of a molded plastic is typically used to couple light between an array of OETs and an array of fibers, such as the array of fiber ends presented at a ferrule/connector end face in a parallel optical communication system. 
     Packaging of optoelectronic transducers (OETs) to a circuit board or other structure, and coupling of light beams between OETs and optical fiber ends for higher performance and higher density is a continuing challenge.  FIG. 1  illustrates two channels of one end of a parallel optical communication link, in accordance with the prior art. The following description is for an array of optical data streams transmitted by an array of OETs  104 ,  104 ′, such as VCSELs, coupled to an array of single core fibers, such as first and second fibers  112 ,  112 ′ by a microlens array  100 . Each of the first and second fibers  112 ,  112 ′ includes a cladding layer  114 ,  114 ′ surrounding a central core  116 ,  116 ′. The description of the upper channel is the same as for the other channels, such as the lower channel in  FIG. 1  having the same reference numerals followed by a prime (′) symbol. Therefore, only the upper channel of  FIG. 1  will be described in detail hereinafter. 
     A first OET  104 , a single microlens (upper microlens in  FIG. 1 ) of the microlens array  100 , and a first fiber  112  are essentially collinear, as shown by a central axis  102  of the first OET and microlens overlaying a central axis  118  of the first fiber  112 . The OET  104  is mounted to a board  144 . A Light beam  120  is emitted from the OET  104 , collected by a first microlens surface  106 , and then relayed through microlens material  108  to a second microlens surface  110 . The second microlens surface  110  focuses the light  120  onto an end face  103  of the first fiber  112 , more particularly onto an end of the core  116  in the center of the first fiber  112 , as presented on a ferrule/connector end face  146 . 
     It should be understood that OETs  104  and  104 ′ mounted to the board  144  may comprise transmitters, such as a VCSELs for transmitting light to the cores  116  and  116 ′ of the first and second fibers  112  and  112 ′ or may be a receivers, such as PIN photodiodes. In the latter case, the light is transmitted from the fiber core  116  of the first fiber  112  to the OET  104  via the microlens element. It is also common for a single row of OETs  104 ,  104 ′, . . . mounted on the board surface  144  to comprise both VCSELs and PINs, e.g. four of each, to form the basis of a transceiver, which performs both transmit and receive operations on optical data streams. 
     In combination, first microlens surface  106 , microlens material  108 , and second microlens surface  110  constitute a single microlens element of a microlens array  100  for a first communication channel. Similarly, first microlens surface  106 ′, microlens material  108 , and second microlens surface  110 ′ constitute a single microlens element of the microlens array  100  for a second communication channel. The diameter (D) of the microlens element is smaller than 250 um to allow for manufacturing and correspondence to the typical core-to-core spacing of the single fiber ends presented by an array-type connector. In other words, the distance between central axis  118  and central axis  118 ′ of the fibers  112  and  112 ′ in  FIG. 1  is approximately 250 um. Hence, the microlens diameter D is smaller than 250 um. Spacing (S) between the OET  104  and a forward edge  142  of first microlens surface  106  is usually more than 350 um, which easily accommodates packaging features, such as wirebonds, which may project 150 um or more above the surface of the OETs  104  or board  144 . The thickness (T) of the microlens elements, measured from the forward edge  142  of the first microlens surface  106  to the forward edge  143  of the second microlens surface  110 , is about 1 mm. 
     The potential for high-speed, high-density optical communications using multi-core fibers (MCF) is known. See for example, U.S. Pat. Nos. 5,734,773 and 6,154,594 and U.S. Published Applications 2011/0229085, 2011/0229086 and 2011/0274398, each of which is herein incorporated by reference. The use and speed of multi-mode multi-core fiber (MMMCF), sometimes referred to as multi-core multi-mode fiber (MCMMF), has been demonstrated and published (Lee et al., Journal of Lightwave Technology, vol. 30, No. 6, Mar. 15, 2012). The communication link described by Lee et al. used a MCMMF to relay six optical data streams, each at 20 Gb/s, from six VCSELs to six PIN photodiodes. 
     The coupling means between the OETs and the cores of the MCFs was simple “butt coupling,” wherein the OETs and cores are located close enough to one another that light is transferred between with sufficient efficiency. Butt coupling suffers from inefficient transfer, and the required close proximity of the cores to the OETs often causes problems with wirebonds or other packaging features used in connection with the OETs. For reasons such as these, butt coupled packages are almost completely absent from commercial, high-speed optical communications products. 
     The cores of a MCF are positioned much more closely than the prevalent 250 um spacing (axis  118  to axis  118 ′ in  FIG. 1 ) of single core fibers in a parallel optical communication link. In the demonstration published by Lee et al., the cores of the MCF were 39 um apart. Extending the approach of  FIG. 1  to Lee et al.&#39;s configuration would require microlenses about 35 um in diameter, i.e., the distance between axis  102  and  102 ′ in  FIG. 1  would need to be about 35 um. Further, the space S in  FIG. 1  would need to be about 60 um. The small space S precludes the use of conventional low-cost wirebonding technology in connection with the OET  104 . Furthermore, optical beams having such small diameters will diffract significantly while propagating even over small distances, and the thickness T of the lens array  100  would have to be less than about 650 um, preferably about 500 um, thus having potential issues in manufacturing and in structural stability for the lens array  100 . 
     SUMMARY OF THE INVENTION 
     The Applicant has discovered a need in the art for an improved system to couple light between closely-spaced OETs and cores of a MCF. More particularly, the Applicant has developed a coupling system with the properties of high coupling efficiency, adequate space S between OETs and the first surface of the microlens to accommodate a wide range of OET packaging features, e.g., wirebondings, and a microlens thickness T sufficient for mechanical stability and manufacturability. 
     These and other objects are accomplished by a single microlens element to couple multiple optical data signals between multiple OETs and multiple cores of a MCF. Further, at least one OET and at least one core of a MCF are substantially removed from the microlens element&#39;s axis and the MCF axis, possibly by different amounts. Preferably, multiple OETs are positioned approximately equidistant from the microlens axis. Optionally, the microlens element is connected to other microlens elements to form a microlens array. 
     The Applicant has also appreciated that some applications, i.e. patching, link testing, link monitoring, cross connects, etc. require the optical cores of a MCF to be separated and routed to different termination points. It would be desirable to provide an easy and effective way of routing one or more individual cores of a MCF to different locations. 
     It is an object of the present invention to address one or more of the needs in the prior art, as appreciated by the Applicant. 
     Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present invention will become more fully understood from the detailed description given hereinbelow and the accompanying drawings which are given by way of illustration only, and thus, are not limits of the present invention, and wherein: 
         FIG. 1  is a side view of a lens optical coupling arrangement between single core fibers and OETs, in accordance with the prior art; 
         FIG. 2  is a side view of a lens optical coupling arrangement between cores of a MCF and OETs, in accordance with the present invention; 
         FIG. 3A  is a side view of a lens optical coupling arrangement between cores of a MCF and OETs illustrate a non-telecentric configuration, in accordance with the present invention; 
         FIG. 3B  is a close up of the end surface of the MCF of  FIG. 3A ; 
         FIG. 4  is a side view of a lens optical coupling arrangement model used to generate test data for the present invention; 
         FIG. 5  is a diagram illustrating performance data of the multi-beam microlens element design of  FIG. 4 ; and 
         FIG. 6  is a side view of a lens optical coupling arrangement between cores of a MCF and cores of plural single core fibers, in accordance with the present invention. 
     
    
    
     DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION 
     The present invention now is described more fully hereinafter with reference to the accompanying drawings, in which embodiments of the invention are shown. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. 
     Like numbers refer to like elements throughout. In the figures, the thickness of certain lines, layers, components, elements or features may be exaggerated for clarity. Broken lines illustrate optional features or operations unless specified otherwise. 
     The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. It will be further understood that terms, such as those defined in commonly used dictionaries, should be interpreted as having a meaning that is consistent with their meaning in the context of the specification and relevant art and should not be interpreted in an idealized or overly formal sense unless expressly so defined herein. Well-known functions or constructions may not be described in detail for brevity and/or clarity. 
     As used herein, the singular forms “a”, “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “comprises” and/or “comprising,” when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof. As used herein, the term “and/or” includes any and all combinations of one or more of the associated listed items. As used herein, phrases such as “between X and Y” and “between about X and Y” should be interpreted to include X and Y. As used herein, phrases such as “between about X and Y” mean “between about X and about Y.” As used herein, phrases such as “from about X to Y” mean “from about X to about Y.” 
     It will be understood that when an element is referred to as being “on”, “attached” to, “connected” to, “coupled” with, “contacting”, etc., another element, it can be directly on, attached to, connected to, coupled with or contacting the other element or intervening elements may also be present. In contrast, when an element is referred to as being, for example, “directly on”, “directly attached” to, “directly connected” to, “directly coupled” with or “directly contacting” another element, there are no intervening elements present. It will also be appreciated by those of skill in the art that references to a structure or feature that is disposed “adjacent” another feature may have portions that overlap or underlie the adjacent feature. 
     Spatially relative terms, such as “under”, “below”, “lower”, “over”, “upper”, “lateral”, “left”, “right” and the like, may be used herein for ease of description to describe one element or feature&#39;s relationship to another element(s) or feature(s) as illustrated in the figures. It will be understood that the spatially relative terms are intended to encompass different orientations of the device in use or operation in addition to the orientation depicted in the figures. For example, if the device in the figures is inverted, elements described as “under” or “beneath” other elements or features would then be oriented “over” the other elements or features. The device may be otherwise oriented (rotated 90 degrees or at other orientations) and the descriptors of relative spatial relationships used herein interpreted accordingly. 
       FIG. 2  illustrates two channels of one end of a parallel optical communication link, in accordance with the present invention. The following description is for an array of optical data streams transmitted by an array of OETs  204 ,  224 ,  204 ′ and  224 ′, such as VCSELs, coupled to first and second MCFs  201  and  201 ′ by a microlens array  200 . Each of the first and second MCFs  201  and  201 ′ include cladding layers  202  and  202 ′ surrounding plural cores, such as cores  216  and  236  for the first MCF  201  and cores  216 ′ and  236 ′ for the second MCF  201 ′. The description of the upper channel is the same as for the other channels, such as the lower channel in  FIG. 2  having the same reference numerals followed by a prime (′) symbol. Therefore, only the upper channel of  FIG. 2  will be described in detail hereinafter. 
       FIG. 2  shows an embodiment of the present invention, wherein first microlens surface  206 , microlens material  208  and second microlens surface  210  constitute a first microlens element of a microlens array  200  for plural communication channels associated with the first MCF  201 . Similarly, first microlens surface  206 ′, microlens material  208 , and second microlens surface  210 ′ constitute a second microlens element of the microlens array  200  for plural communication channels associated with the second MCF  201 ′. In many cases, multiple microlens elements, e.g. four, eight, twelve or any other number, are fabricated by injection molding of a single piece of plastic to form the microlens array  200 . 
     A preferred plastic to form the microlens array  200  is known as Ultem, although other plastics, glasses, semiconductors, or optical materials may be used instead. Although refractive microlens elements are illustrated in the drawings, the present invention may also employ diffractive lenses, gradient-index lenses, or other types or combinations of lenses. 
     In  FIG. 1 , each microlens element facilitates a single channel of communication. By contrast, in  FIG. 2 , each microlens element facilitates plural channels of communication, i.e., the channels represented by the number of cores within a single MCF  201  or MCF  201 ′.  FIG. 2  shows the MCF  201  having two cores  216  and  236  communicating to two OETs  224  and  204 , respectively, via a single microlens element. Showing only two cores  216  and  236  and two OETs  204  and  224  is only to simplify  FIG. 2 . In practice, any number of cores and OETs may be employed per microlens element, such as four, six or eight cores/OETs per microlens element. 
     The OETs  204  and  224  are mounted to a board  244 . A Light beam  220  emitted from the first OET  204  is collected by the first microlens surface  206 , and then relayed through microlens material  208  to the second microlens surface  210 . The second microlens surface  210  focuses the light  220  onto an end face  203  of the first MCF  201 , more particularly onto an end of the second core  236  which extends along an axis  15 , offset from a central axis  19  of the first MCF  201 , as presented on a ferrule/connector end face  246 . A Light beam  240  emitted from the second OET  224  is collected by the first microlens surface  206 , and then relayed through microlens material  208  to the second microlens surface  210 . The second microlens surface  210  focuses the light  240  onto an end of the first core  216  which extends along an axis  17 , offset from the central axis  19  of the first MCF  201 . 
     It should be understood that first and second OETs  204  and  224  mounted to the board  244  may comprise transmitters, such as VCSELs for transmitting light to the second and first cores  236  and  216  of the first MCF  201 , or may be a receivers, such as PIN photodiodes. In the latter case, the light is transmitted from the first and second cores  216  and  236  of the MCF  201  to the second and first OETs  224  and  204  via the microlens element. The OETs  204  and  224  mounted on the board surface  244  may comprise both VCSELs and PINs, e.g. two of each, to form the basis of a transceiver, which performs both transmit and receive operations on optical data streams of the MCF  201 . 
     Although  FIG. 2  shows two clusters of OETs, with OETs  204  and  224  in the first cluster, and OETs  204 ′ and  224 ′ in the second cluster, additional OET clusters, microlens elements, and MCFs may be contained in the same transceiver package. A preferred embodiment comprises a single chip containing four clusters of VCSELs mounted to board  244  and another single chip containing four clusters of PIN photodiodes mounted to board  244 . A microlens array  200  comprising one piece of material, e.g. molded plastic, has eight microlens elements, i.e., one microlens element for each OET cluster. Further, eight MCFs are included, with one MCF end align with each microlens element. The MCFs could be presented by an array type ferrule/connector, such as an MT ferrule or MPO connector. 
     If each MCF had four cores, each cluster would contain four VCSELs or four PIN photodiodes or some combination of VCSELs and PIN photodiodes totally four. If each MCF had eight cores, each cluster would contain eight VCSELs or eight PIN photodiodes or some combination of the two devices totally eight, such as four and four. 
     The diameter D 1  of the microlens element is preferably smaller than 250 um to allow for manufacturing and correspondence to the typical center-to-center spacing of the MCF fiber ends  203 ,  203 ′ presented by an array-type connector. In other words, the distance between central axis  19  and central axis  19 ′ of the MCF fibers  201  and  201 ′ in  FIG. 2  is approximately 250 um, hence the microlens element diameter D 1  is smaller than 250 um. 
     Spacing S 1  between the OETs  204 ,  224 ,  204 ′,  224 ′ and a forward edge  242  of the first microlens surface  206  is usually more than 220 um, which easily accommodates packaging features such as wirebonds, which may project 150 um or more above the surface of the OETs  204 ,  224 ,  204 ′ and  224 ′ or board  244 . The thickness T 1  of the microlens elements, measured from the forward edge  242  of the first microlens surface  206  to the forward edge  243  of the second microlens surface  210 , is about 0.88 mm. 
     In  FIG. 2 , the first core  216  of the MCF  201  has a core axis  17  substantially distanced from the MCF central axis  19  and the second core  236  of the MCF  201  has a core axis  15  substantially distanced from the MCF central axis  19 . Preferably, the distances between each core axis  17  and  15  and the MCF central axis  19  are approximately equal. The first OET  204  has an axis  11  coincident to the direction of its central emitted or received beam in light  220 , e.g., chief ray. The second OET  224  has an axis  13  coincident to the direction of its central emitted or received beam in light  240 , e.g., chief ray. Preferably, the axis  11  of the first OET  204  is distanced from the central axis  18  of the group or cluster of OETs  204  and  224  by an amount which is approximately equal to a distance between the axis  13  of the second OET  224  and the central axis  18 . 
     In  FIG. 2 , the central axis  19  of the MCF  201  coincides with, e.g., overlies, the central axis  18  of the group or cluster of OETs  204  and  224  communicating with MCF  201 . However, it is possible to achieve several of the advantages of the present invention even if the central axis  19  of the MCF  201  is not coinciding with the central axis  18  of the group or cluster of OETs  204  and  224 . 
     The ability of the prior art microlenses element of  FIG. 1  to relay an optical beam between an OET  104  and a single, central core  116  of the fiber  112  is substantially degraded when the axis  102  of the OET  104  is substantially distanced from the axis  118  of the microlens element and/or core  116 . However, with the configuration of the present invention in  FIG. 2 , the shapes of the first and second microlens surfaces  206  and  210  are modified to optimize the performance of the microlens element at a given off-axis distance. Performance at other off-axis distances will be less-than optimal, including the prior-art on-axis configuration. 
     For this reason, it is preferable that the axes  11  and  13  of all OETs  204  and  224  associated with a microlens element are substantially the same distance from the microlens axis, which coincides with the central axis  19  of the MCF  201 . Further, it is preferable that the axes  17  and  15  for all cores  216  and  236  associated with a MCF  201  are substantially the same distance from the microlens axis, which coincides with the central axis  19  of the MCF  201 . 
     When the magnification of the microlens element is unity, e.g., 1.0, the axes  11  and  13  of OETs  204  and  224  and axes  17  and  15  of the cores  216  and  236  are all approximately the same distance from microlens/MCF central axis  19 , which overlies the central axis  18  of the cluster of OETs  204  and  224 . More generally, when the microlens element has a magnification M, the off-axis distances will be different by a factor of M. The example of  FIG. 2  has a magnification of approximately 1.5 in the left-to-right direction and approximately 1/1.5 (or ⅔) in the right-to-left direction. Also note that the microlens element “inverts” the positions of the optical data streams  220  and  240 , e.g., the first OET  204  above the microlens/MCF central axis  19  is coupled with the second core  236  below the microlens/MCF axis  19 . Conversely, the second OET  224  below the microlens/MCF central axis  19  is coupled with the first core  216  above the microlens/MCF axis  19 . 
     An often-desirable feature of a microlens element communication system is that it be “doubly telecentric.” A beam on either side of a lens is telecentric when its chief ray, or central ray, propagates parallel to the lens axis, e.g., approaches the microlens surface parallel to the central axis  19  of the microlens element. When the OET  204  is a VCSEL, and assuming the VCSEL chip surface  244  is perpendicular to microlens/MCF central axis  19  (as shown in  FIG. 2 ), the beam is naturally telecentric, as shown by the central ray propagating parallel to microlens/MCF central axis  19 . Similarly, when the beam exits the second microlens surface  210 , the central chief ray will again propagate parallel to microlens/MCF central axis  19 , and thus be telecentric. 
     Preferably, the microlens element is designed to have telecentric, or nearly-telecentric, properties on both sides. This condition results in the most efficient fiber coupling, and the greatest tolerance to lateral and longitudinal displacement of the first core  216 . Absent a limiting aperture inside the microlens element, in order for the microlens element to be doubly telecentric, its thickness T 1  must be optimized in combination with the shapes of the first and second microlens surfaces  206  and  210 . 
       FIG. 3 a    illustrates a modified embodiment of the present invention, wherein the light beams are telecentric on the OET side of the microlens element, but are slightly non-telecentric on the fiber side of the microlens element. More specifically, the end faces of the first and second cores  216 A and  236 A are polished at a slight angle, e.g. 4°, angling away from the center of the MCF  201 A. For example, the polished angle may be referred to as a facet angle α1 measured between a line  260  flat against the end face  203 A of the MCF  201 A relative to a line  246  perpendicular to the central axis  19  of the MCF  201 A (best seen in  FIG. 3B , where the angle has been exaggerated for clarity of illustration). 
     Preferably, the incident angles above and below the central axis  19  of the MCF  201 A have a radial symmetry, e.g. angled away from the central axis  19  of the MCF  201 A, and may be produced with an approximately-spherical polish on the end  203 A of the MCF  201 A. Of course, the other communication channels of the parallel communication system are similar polished. For example, with the second communication channel, the end faces of the first and second cores  216 A′ and  236 A′ are polished at a slight angle, e.g. 4°. All other structural elements of the embodiment of  FIG. 3A  may be the same as the embodiment of  FIG. 2 . However,  FIG. 3A  differs from  FIG. 2  by illustrating that the center axis  11  of the OET  204  may be coincident with the center axis  17  of the first core  216 A, and the center axis  13  of the second OET  204  may be coincident with the center axis  15  of the second core  236 A. As noted in the embodiment of  FIG. 2 , typically these center axis will be offset relative to each other, however in some embodiments, depending upon such factors as the diameter of the first and second cores  216 A and  236 A and the magnification of the microlens element, the central axes  11  and  13  may coincide with the with the central axes  17  and  15 , respectively. 
     In prior preferred embodiments, the incident angle α2 and the facet angle α1 were optimized, such that the chief ray  262  entered the first core  216  along the central axis  17  of the core  216 , e.g., the incident angle α2 was approximately zero degrees, e.g., telecentric. The prior preferred configurations of the present invention maximized coupling efficiency and tolerance. 
       FIG. 3B  is a close up view showing the vicinity of the end face  203 A of the first MCF  201 A in  FIG. 3A . As illustrated in  FIG. 3B , the present invention applies to conditions wherein the incident angle α2 and the facet angle α1 are not optimized. For example, the incident chief ray  262  may be non-telecentric while the fiber end may be flat, or the incident chief ray may be telecentric while the fiber end angled or curved or the incident chief ray may be non-telecentric while the fiber end angled or curved.  FIG. 3B  shows both conditions with the chief ray  262  being non-telecentric by incident angle α2 and the end of the fiber  216 A being angled or curved by facet angle α1. 
     The configuration illustrated in  FIGS. 3 a  and 3 b    is particularly useful for single-mode optical beams, e.g., emitted from a single-mode VCSEL, because the configuration reduces feedback from the end face  203 A of MCF  216 A into the OET  204 , e.g., VCSEL, thus helping to preserve signal quality. Feedback to OET  204  is reduced because the reflection  264  of the chief ray  262  leaves the end face  203 A at reflected angle α3. The previous embodiments, which optimized coupling efficiency/tolerance, also maximized feedback into the OET  204  resulting from reflections at the end face  203  of the first fiber  216  because the reflect angle was approximately zero degrees. Hence, an alternative preferred embodiment, as shown in  FIGS. 3A and 3B , slightly reduces the coupling efficiency/tolerance of  FIG. 2  in order to reduce feedback into the OET  204 . 
     To establish the feasibility of the multi-beam microlens communication system, an optical design was performed, using the Zemax™ lens design/analysis program. As shown in  FIG. 4 , the design includes a light source  204  formed as a point source having a numerical aperture (NA) of 0.27, simulating a VCSEL on the board  144 . The central axis  11  of the point light source  204  is located a distance K 1  away from the central axis  19  of the microlens element and MCF  201 , where K 1  is approximately 39 um. A magnification of the microlens element is set to about 1.5. The central axis  15  of the second core  236  is set a distance K 2  from the central axis  19  of the MCF  201 , where K 2  is approximately equal to 58.5 um. 
     The distance S 2  from the source  204  to the first microlens surface  206  is set to about 220 um. The light beam was approximately collimated inside the microlens material having a refractive index approximating that of Ultem plastic. A thickness T 2  of approximately 880 um exists between the first and second microlens surfaces  206  and  210  resulting in approximate telecentricity, as seen by the central (chief) ray propagating approximately along the central axis  15  of the second core  236  on the MCF side of the second microlens surface  210 . Conic constants and higher-order aspheric coefficients for first and second microlens surfaces  206  and  210  were varied to minimize the root-mean-square radius and the geometrical radius of the light beam at the second core  236  of the MCF  201 . 
       FIG. 5  illustrates the performance of the multi-beam microlens element design with through-focus spot diagrams generated via Zemax™ lens design/analysis program. At the optimal focus location (defocus=0 in  FIG. 5 ), the root-mean-square spot radius is less than 4 um, and the geometrical radius (maximal extent of the traced rays from the spot center) is about 6.3 um. 
       FIG. 6  is a side view of a lens optical coupling arrangement between cores of MCFs  201  and  201 ′ and cores of plural single core fibers  304 ,  324 ,  304 ′ and  324 ′, in accordance with the present invention. In  FIG. 6 , all elements to the right of vertical line  344  are the same as the elements of  FIG. 2  and will not be repeated in detailed herein.  FIG. 6  illustrates how the microlens elements of the microlens array  200  can be used to couple light signals from the first and second cores  216  and  236  of the first MCF  201  into a core  324  of a second single core fiber  324  and a core  306  of a first single core fiber  304 , respectively. 
     In essence, the OETs  204  and  224  in the embodiment of  FIG. 2  have been replaced by the first and second single core fibers  304  and  324 . A central axis  311  of the first single core fiber  304  exactly replaces the central axis  11  of the first OET  204  of  FIG. 2 , and a central axis  313  of the second single core fiber  324  exactly replaces the central axis  13  of the second OET  224  of  FIG. 2 . A central axis  319  of the cluster of single core fibers exactly replaces the central axis  18  of the cluster of OETs in  FIG. 2 . 
     Of course, the cluster of single core fibers could contained more than the two single core fibers depicted in  FIG. 6 . In a preferred embodiment, the number of single core fibers matches the number of cores in the MCF  201 , such as four, six or eight. All of the embodiments and variations discussed above in connection with  FIGS. 2, 3A, 3B, 4 and 5 , such as non-telecentricity, are applicable to the configuration of  FIG. 6 . 
     The configuration of  FIG. 6  is useful in the construction of fiber optic jumpers, patch cords, trunk cables, fanouts and other cable configurations that provide optical connectivity in numerous spaces including local area networks (LANs), wide area networks (WANs), datacenters, vehicles, aircraft and ships. Historically, fanouts and jumpers have used one or more single-core optical fibers to mate with one or more single-core optical fibers presented by a termination. With the MCF  201 , new fanout designs and new jumper designs are needed to deal with the multiple cores  216  and  236  within the MCF  201  because these cores  216  and  236  cannot be simply separated out of the MCF  201  for redirection or separate termination. 
       FIG. 6  shows a configuration to provide fanout cordage (left side of  FIG. 6 ) or jumper cordage (again left side of  FIG. 6 ) mated with one or more MCFs  201 ,  201 ′ presented by a ferrule end face  246 , wherein the cordage is constructed of single-core fibers, e.g.,  304 ,  324 ,  304 ′ and  324 ′, such that terminations at the remote end of the fanout cordage, or at intermediate taps along the jumper cordage, can be made using conventional single core connectors. The Applicant has also appreciated that a jumper with single-core fibers can be used to reorder cores of a MCF from a first end of the jumper to a second end of the jumper. The reordering of the cores may facilitate various connection methods, daisy-chaining patch cords between devices, and/or data security. 
     By the illustrated configuration of  FIG. 6  for connecting multiple cores within one fiber, e.g., a MCF  201 , to multiple fibers with single-cores, e.g., single core fibers  304  and  324 , the single-core fibers can be terminated by traditional envelopes, e.g., LC, SC, ST, for other uses, as shown in Applicant&#39;s co-pending U.S. application Ser. No. 14/170,781, filed Feb. 3, 2014, which is herein incorporated by reference. In the earlier embodiments, it was described how light signals could pass through the microlens element in both directions, e.g., from VCSELs to the MCF  201  or from the MCF  201  to PIN photodiodes. The microlens element in the later embodiments may also pass light signals in both directions, e.g., from the single core fibers  304  and  324  to the MCF  201  or from the MCF  201  to the single core fibers  304  and  324 . 
     The inventive concepts described herein are applicable to any combination of single-mode and multi-mode optical beams, and single-mode and multi-mode fiber cores. The entire lens arrays  200 , or at least the microlens elements, of the present invention may be coated with an anti-reflection coating to improve the lens-to-fiber interface and/or reduce reflected rays from the first and second microlens surfaces  206  and  210 . 
     The present invention has been described above in terms of several preferred embodiments. However, modifications and additions to these embodiments will become apparent to persons of ordinary skill in the art upon a reading of the foregoing disclosure. All such modifications and additions comprise a part of the present invention to the extent they fall within the scope of the several claims appended hereto.