Abstract:
An optical fiber system that enables direct board-to-board optical communication is described. The optical fiber system does not require data transmission through the backplane and, consequently, avoids the complexity and possible communication delays that would be required if data transmissions had to go through the backplane. The optical fiber system includes a positioner that is configured to urge opposite ends of two or more optical fibers respectively toward opposed optical devices that are coupled to facing sides of adjacent printed circuit boards coupled to a common backplane. The optical fiber system may be installed and removed quickly and easily, and may be readily retrofitted into existing computer systems.

Description:
TECHNICAL FIELD 
     This invention relates to fiber optic connectors and optical fiber systems. 
     BACKGROUND 
     Fiber optic connectors couple optical communication channels (e.g., optical fibers) to one or more optical devices (e.g., electro-optic and opto-electric devices). The optical communication channels may be defined by a bundle of glass or plastic fibers (a “fiber optic cable”), each of which is capable of transmitting data independently of the other fibers. Relative to traditional metal connections, optical fibers have a much greater bandwidth, they are less susceptible to interference, and they are much thinner and lighter. Because of these advantageous physical and data transmission properties, efforts have been made to integrate fiber optics into computer system designs. For example, in a local area network, fiber optics may be used to connect a plurality of local computers to each other and to centralized equipment, such as servers and printers. In this arrangement, each local computer has an optical transceiver for transmitting and receiving optical information. The optical transceiver may be mounted on a printed circuit board that supports one or more integrated circuits. Typically, each computer includes several printed circuit boards that are plugged into the sockets of a common backplane. The backplane may be active (i.e., it includes logic circuitry for performing computing functions) or it may be passive (i.e., it does not include any logic circuitry). An external network fiber optic cable may be connected to the optical transceiver through a fiber optic connector that is coupled to the backplane. 
     Other fiber optic applications have been proposed. For example, backplanes have been designed to interconnect the circuit boards of a computer system and thereby enable optical communication between the boards (see, e.g., U.S. Pat. Nos. 4,913,508, 5,134,679, and 5,793,919). These backplanes often are referred to as “optical backplanes.” Typically, an optical backplane includes one or more fiber optic cables that couple to connectors mounted on the edges of the printed circuit boards. 
     SUMMARY 
     The invention features an optical fiber system that enables direct board-to-board optical communication that does not require data transmission through the backplane. In accordance with this inventive optical fiber system, a positioner is configured to urge opposite ends of two or more optical fibers respectively toward opposed optical devices that are coupled to facing sides of adjacent printed circuit boards coupled to a common backplane. 
     Embodiments may include one or more of the following features. 
     The positioner may be configured to support the optical fibers along a curved path between the opposed optical devices. The ends of the optical fibers preferably extend beyond respective ends of the positioner. The positioner preferably is configured to hold the optical fibers in a spaced-apart, substantially parallel planar array. The positioner may be configured to align end portions of the optical fibers in directions oriented at oblique angles relative to respective engagement surfaces of the opposed optical devices. 
     In one embodiment, the positioner includes a flexible and resilient support structure that extends along a substantial length of the optical fibers. The support structure preferably includes a flexible and resilient ribbon matrix. The ribbon matrix may incorporate an elongated resilient member that increases the resiliency of the ribbon matrix. The positioner and the optical fibers preferably form a unitary, elongated fiber optic ribbon having a planar surface bounded by two ends and two sides. The ends of the optical fibers preferably extend beyond respective ends of the fiber optic ribbon. The fiber optic ribbon may preferentially bends in a plane orthogonal to the planar surface upon application of a compressive force between the ends of the fiber optic ribbon. The fiber optic ribbon preferably is elastically bendable. 
     In another embodiment, the optical fibers are incorporated in a multi-fiber fiber optic cable and the positioner is configured to releasably receive the multi-fiber fiber optic cable. The positioner preferably has a support arm configured to guide the optical fibers into alignment with the opposed optical devices. The support arm may include two or more support fingers. The positioner may include a second support arm with two or more support fingers that interleave with the support fingers of the first support arm. The positioner preferably is pivotally coupled to each of the opposed optical devices. 
     The positioner may be characterized by an engaged configuration in which the optical fibers are optically coupled to the opposed optical devices and a disengaged configuration in which the optical fibers are optically de-coupled from the opposed optical devices. The positioner may include a biasing mechanism configured to switch the positioner between the engaged configuration and the disengaged configuration upon application of a centralized pressing force. The biasing mechanism preferably includes a spring coupled between the positioner and one of the opposed optical devices. 
     Among the advantages of the invention are the following. The invention provides an optical fiber system that enables direct board-to-board optical communication without the complexity and possible communication delays that would be required if data transmissions had to go through the backplane. In addition, each inventive optical fiber system may be installed and removed quickly and easily. Furthermore, the invention may be readily retrofitted into existing computer systems. 
     Other features and advantages of the invention will become apparent from the following description, including the drawings and the claims. 
    
    
     DESCRIPTION OF DRAWINGS 
     FIG. 1 is a diagrammatic side view of a computer system that includes a backplane and four printed circuit boards coupled by respective optical fiber systems. 
     FIG. 2A is a diagrammatic top view of an optical fiber system with an integral positioner in a disengaged configuration. 
     FIG. 2B is a diagrammatic cross-sectional front view of the optical fiber system of FIG.  2 A. 
     FIG. 2C is a diagrammatic side view of the optical fiber system of FIG. 2A with the positioner in an engaged configuration. 
     FIG. 3A is an enlarged diagrammatic side view of two printed circuit boards, an optical fiber system, and a fiber optic positioner in a disengaged configuration. 
     FIGS. 3B and 3C are a diagrammatic top view and an enlarged diagrammatic side view of the disengaged positioner of FIG. 3A, respectively. 
     FIG. 3D is an enlarged diagrammatic side view of the two printed circuit boards coupled by the optical fiber system of FIG. 3A, with the positioner in an engaged configuration. 
     FIGS. 3E and 3F are a diagrammatic top view and an enlarged diagrammatic side view of the engaged positioner of FIG. 3D, respectively. 
     FIG. 4A is a diagrammatic cross-sectional side view of an optical device with a plurality of grooves receiving the fibers of a multi-fiber fiber optic cable. 
     FIG. 4B is a diagrammatic cross-sectional front view of the optical device of FIG. 4A receiving the fibers of the multi-fiber fiber optic cable. 
     FIG. 5A is a diagrammatic cross-sectional side view of a retracted fiber optic plug positioned in a socket of an optical device. 
     FIG. 5B is a diagrammatic cross-sectional side view of the fiber optic plug of FIG. 5A in an extended configuration. 
     FIG. 5C is a cross-sectional front view of the extended fiber optic plug of FIG. 5B positioned inside the socket. 
     FIG. 5D is a diagrammatic cross-sectional front view of the optical device of FIG. 5B receiving the optical fibers from the extended fiber optic plug. 
    
    
     DETAILED DESCRIPTION 
     Referring to FIG. 1, a computer system  10  includes a backplane  12  into which printed circuit boards  14 ,  16 ,  18  and  20  are plugged. Optical fiber systems  22 ,  24  and  26  optically couple printed circuit boards  14 - 20 . Each of the printed circuit boards  14 - 20  supports one or more integrated circuits and at least one optical device  28 ,  30 ,  32 ,  34 ,  36 ,  38  (e.g., a fiber optic transceiver) for transmitting and receiving optical data signals over optical fiber systems  22 - 26 . Each of the optical fiber systems  22 - 26  includes a fiber optic positioner that is configured to urge opposite ends of a multi-fiber fiber optic cable respectively toward a pair of opposed optical devices that are mounted on facing sides of a pair of adjacent printed circuit boards. By this arrangement, optical fiber systems  22 - 26  enable direct board-to-board optical communication without requiring data transmission through backplane  12 . 
     The components (e.g., the integrated circuits and the optical devices) supported on the printed circuit boards may be housed in ball grid array (BGA) packages that include die carriers with bottom surfaces supporting a plurality of solder balls (or bumps) that connect to contacts on the surfaces of the printed circuit boards. The BGA packages may include an over molded pad array carrier or a ceramic substrate material that houses the printed circuit board components. In alternative embodiments, the printed circuit board components may be mounted to the printed circuit boards using surface mount technology (SMT) or other mounting technique (e.g., bore soldering or pin through-hole technology). In other embodiments, the integrated circuits and optical devices  28 - 38  may be mounted on single-sided printed circuit boards rather than two-sided printed circuit boards  14 - 20 . 
     Referring to FIGS. 2A-2C, in one optical fiber system  39 , a positioner  40  is a flexible and resilient ribbon matrix that may be formed from, for example, a UV curable acrylate material or other thermoplastic material (e.g., polyvinyl chloride). Positioner  40  encases and holds two or more optical fibers  42  in a spaced-apart, substantially parallel planar array. The optical fibers  42  may be spaced apart by a distance of about 100 μm to about 1,000 μm. As shown in FIG. 2B, each optical fiber  42  includes a core  44  and a cladding  46 . The ends of optical fibers  42  extend beyond positioner  40  so that they may be coupled to an opposed pair of optical devices. In one embodiment, optical fibers  42  extend beyond the ends of positioner  40  by a distance of about 0.5 cm to about 3 cm. The fiber end faces may be flat or angled; if they are angled, however, optical fibers  42  should be oriented in a way that is complementary to the orientation of the input fibers of positioner  40 . In this embodiment, positioner  40  and optical fibers  42  form a unitary fiber optic ribbon cable with sixteen optical communication channels. Other embodiments may include a different number of optical fibers (e.g., 2, 4, 16, 32, 64 or 128 optical fibers). 
     Referring to FIG. 2C, positioner  40  is sufficiently flexible that it can be bent elastically into a curved shape that enables the ends of optical fibers  42  to engage a pair of opposed optical devices. At the same time, the ribbon matrix is sufficiently resilient that it generates an outward restoring force that tends to return optical fiber system  39  back to its original planar shape (FIG.  2 A). This restoring force causes positioner  40  to clamp the ends of optical fibers  42  to the optical inputs of the opposed optical devices. Additional materials may be incorporated into the ribbon matrix to increase its resiliency. For example, one or more resilient wires  48  formed from, for example, metal or plastic, may be embedded along the length of the ribbon matrix to increase the restoring force generated by positioner  40 . 
     In operation, a technician may apply a compressive force between the ends of positioner  40  to cause it to bend into the U-shaped curve shown in FIG.  2 C. Because of the elongated planar shape of the ribbon matrix, positioner  40  preferentially bends in a plane that is parallel to optical fibers  42  and orthogonal to the planar surface of the ribbon matrix. Once the ends of the ribbon matrix have been bent together close enough, the technician may insert optical fiber system  39  between a pair of opposed optical devices and, subsequently, reduce the applied compressive force until optical fiber system  39  engages the opposed optical devices. As shown in FIG. 1, the U-shaped optical fiber system  39  may be inserted between the pair of opposed optical devices so that it extends between the corresponding pair of adjacent printed circuit boards (e.g., optical fiber systems  22  and  26 ) or extend outside of the region between the printed circuit boards (e.g., optical fiber system  24 ). 
     Referring to FIGS. 3A-3F, in another optical fiber system  50 , a positioner  52  is configured to releasably receive a multi-fiber fiber optic ribbon cable  56  (FIG. 3A) and bias it into engagement with a pair of opposed optical devices  58  and  60  (FIG.  3 D). The fibers of ribbon cable  56  extend beyond the surrounding support matrix so that they may be coupled to optical devices  58 ,  60 . The optical fibers may extend beyond the support matrix by a distance of about 0.5 cm to about 3 cm. 
     Positioner  52  includes a pair of cantilevered support arms  62 ,  64  respectively coupled to a plurality of distal support fingers  66 ,  68 . Support fingers  66 ,  68  are interleaved when positioner  52  is in the engaged configuration (FIGS. 3E and 3F) and they are almost end-to-end when positioner  52  is in the disengaged configuration (FIGS.  3 B and  3 C). Support fingers  66 ,  68  include rails (not shown) for guiding multi-fiber fiber optic cable  56  into proper alignment with optical devices  58 ,  60 . Positioner  52  is pivotally mounted to support structures  70 ,  72 , which are coupled to optical devices  58 ,  60 . Dual-position pistons  74 ,  76  are mounted to optical devices  58 ,  60  and are operable to switch positioner  52  between the engaged configuration and the disengaged configuration upon application of a pressing force  78  to a central portion of positioner  52 . Pistons  74 ,  76  include springs  80 ,  82  respectively coupled between cylindrical housings  84 ,  86  and caps  88 ,  90 . Each piston  74 ,  76  operates, for example, like a convention ballpoint pen, and includes a locking mechanism that causes caps  88 ,  90  to engage inner surfaces of housings  84 ,  86  every other time a sufficient pressing force  78  is applied. 
     In operation, a technician may set positioner  52  into the disengaged configuration and load multi-fiber fiber optic ribbon cable  56  onto positioner  52  (FIG.  3 A). At this time, caps  88 ,  90  are locked, springs  80 ,  82  are compressed within housings  84 ,  86  and support arms  62 ,  64  are locked in the disengaged configuration. After the ribbon cable has been seated properly on positioner  52 , the technician may apply a simple pressing force  78  to a centralized portion of the positioner to connect the ribbon cable to optical devices  58 ,  60 . In response to the pressing force, caps  88 ,  90  unlock and the restoring forces of springs  80 ,  82  bias support arms  62 ,  64  into the engaged configuration. 
     In each of the above-described embodiments, the fiber optic positioners are configured to urge opposite ends of a multi-fiber fiber optic cable respectively toward a pair of opposed optical devices. As explained in detail below, the fiber optic positioners also are configured to guide a multi-fiber fiber optic cable into proper alignment with the pair of opposed optical devices. 
     Referring to FIGS. 4A and 4B, in one embodiment, an optical device  100  includes a fiber-supporting surface  102  with a plurality of fiber-receiving grooves  104  and an optical input  106  formed from a fiber guide  108  and a plurality of input optical fibers  110 . Fiber guide  108  and fiber-supporting surface  102  may be formed in the over molded pad array carrier (or the ceramic substrate material) that houses optical device  100 . Fiber guide  108  has a plurality of bores  112  that retain input fibers  110  and align them with grooves  104 . Input fibers  110  may be secured in bores  112  by, for example, an adhesive. In this embodiment, input fibers  110  are substantially straight. In another embodiment, input fibers  110  may be oriented at an oblique angle relative to fiber-supporting surface  102  and, as a result, input fibers  110  would bend or bow resiliently in the regions where they contact fiber-supporting surface  102 . In the engaged configuration, one of the above-described positioners aligns and guides the coupling fibers  114  of the multi-fiber fiber optic cable  116  into grooves  104  at an oblique angle relative to fiber-supporting surface  102  (FIG.  4 A). Coupling fibers  114  resiliently bend or bow in the regions where they contact fiber-supporting surface  102 . In the engaged configuration, the distal ends of coupling fibers  114  abut the distal ends of input fibers  110  to optically couple the multi-fiber fiber optic cable  116  to optical device  100 . By this arrangement, slight differences in the lengths of the coupling fibers  114  may be accommodated by changes in the locations where input fibers  110  bend at fiber-supporting surface  102 . In an alternative embodiment, coupling fibers  114  may abut directly against an active optical device positioned in bore  112 . 
     In this embodiment, grooves  104  are defined by pairs of adjacent side walls  118  that taper in width as they extend away from surface  102 . To accommodate an optical fiber spacing of about 250 μm, side walls  118  may have a base width of about 125 μm and a groove width at surface  102  of about 125 μm. 
     Referring to FIGS. 5A-5D, in another embodiment, the terminal portion of a multi-fiber fiber optic cable  120  includes a fiber-aligning plug  122 , and the over molded pad array carrier (or the ceramic substrate material) that houses an optical device  124  incorporates a mating socket  126 . Socket  126  is configured to receive plug  122  and to align and guide the coupling fibers  128  of fiber optic cable  120  into optical contact with the input fibers  130  of optical device  124 . 
     Plug  122  includes a plug body  132 , a plug cap  134  which is slidable within plug body  132 , and a spring  136  that is coupled between plug body  132  and plug cap  134 . Plug body  132  includes a bore  138  through which optical fiber cable  120  extends. Fiber optic cable  120  may be secured within bore  138  by, for example, an adhesive. The distal portions of coupling fibers  128  extend beyond the distal end of plug body  132  and into a cavity  139  defined by plug cap  134 . Plug  122  is characterized by a retracted configuration in which the distal portions of coupling fibers  128  are contained in plug cap  134  (FIG.  5 A), and an extended configuration in which the distal portions of coupling fibers  128  extend beyond plug cap  134  (FIG.  5 B). Plug body  132  includes a latch  140  that catches on a lug  142  of plug cap  134  to lock plug  122  in the extended configuration; latch  140  may be depressed to release plug cap  134  from plug body  132 , whereby spring  136  biases plug cap  134  away from plug body  132 . Plug  122  and socket  126  also may include a similar locking mechanism (not shown) to secure plug  122  to socket  126 . 
     Plug socket  126  includes a fiber guide  143  and a fiber-supporting surface  144  with a plurality of fiber-receiving grooves  146 . Fiber guide  143  and fiber-supporting surface  144  may be formed in the over molded pad array carrier (or the ceramic substrate material) that houses optical device  124 . Fiber guide  143  has a plurality of bores  150  that hold input fibers  130  and align them with grooves  146 . Input fibers  130  may be secured in bores  150  by, for example, an adhesive. In this embodiment, input fibers  130  are substantially straight. In another embodiment, input fibers  130  may be oriented at an oblique angle relative to fiber-supporting surface  144  and, as a result, input fibers  130  would bend or bow resiliently in the regions where they contact fiber-supporting surface  144 . 
     As shown in FIG. 5C, plug cap  134  includes a plurality of fiber-aligning openings  152  through which coupling fibers  128  extend when plug  122  is in the extended configuration. Plug cap  134  also includes a pair of slots  154  that ride along a pair of alignment rails  156  formed in socket  126 . Plug  122  may be inserted within socket  126  and locked in the extended configuration by compressing spring  136  until latch  140  catches lug  142 . In this position, coupling fibers  128  extend out of openings  152  in plug cap  134  toward fiber supporting socket surface  144 . As shown in FIG. 5D, openings  152  align and guide coupling fibers  128  into grooves  146 . Coupling fibers  128  are oriented at an oblique angle relative to fiber-supporting surface  144  and, as a result, coupling fibers  128  resiliently bend or bow in the regions where they contact fiber-supporting surface  144 . The distal ends of coupling fibers  128  abut the distal ends of input fibers  130  to optically couple multi-fiber fiber optic cable  120  to optical device  124 . By this arrangement, slight differences in the lengths of the coupling fibers  128  may be accommodated by changes in the locations where input fibers  130  bend at fiber-supporting surface  144 . In an alternative embodiment, coupling fibers  114  may abut directly against an active optical device positioned in bore  150 . 
     Other embodiments are within the scope of the claims. 
     For example, the optical fiber receiving surfaces described above are configured to bend the received fibers at only one plane. As a result, the optical fibers form a “C-shape” near the region of contact between the optical fibers and the optical fiber receiving surface. In other embodiments, the optical fibers may be bent at two planes so that the optical fibers form an “S-shape.” 
     The optical fibers also may be arranged in any of the above-described embodiments as a spaced-apart, three-dimensional array of substantially parallel fibers.