Opical fiber systems

Abstract: An optical fiber system (22-26, 39, 50) that enables direct board-to-board optical communication is described. The optical fiber system (22-26, 39, 50) does not require data transmission through the backplane (12) and, consequently, avoids the complexity and possible communication delays that would be required if data transmissions had to go through the backplane (12). The optical fiber system (22-26, 39, 50) includes a positioner (40, 52) that is configured to urge opposite ends of two or more optical fibers (42) respectively toward opposed optical devices (28-38) that are coupled to facing sides of adjacent printed circuit boards (14-20) coupled to a common backplane (12). The optical fiber system (22-26, 39, 50) 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. Patent 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. The Japanese Patent Application Publication JP-A-10-239 535 discloses an optical wiring component and its manufacture approach for connecting between the optical I/O sections of two or more optical components disposed on a printed board. The optical wiring component comprises a plurality of optical fibers that are connected through a binder. According to JP-A-10-239 535 a resilient optical wiring component can be realized. The International Patent Application Publication WO-A-98/40774 discloses an optical fiber connector to connect optical fibers. The optical fiber connector includes means to induce double bends of the optical fibers to increase the contact force of connections between optical fibers arranged in grooves. SUMMARY Optical fibre systems according to the invention are defined in claims 1 and 5. 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 extends 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. In one embodiment the ribbon matrix incorporates an elongated resilient member that increases the resiliency of the ribbon matrix and the positioner and the optical fibers 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 bend 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 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 has first and second support arms configured to guide the optical fibers into alignment with the opposed optical devices. Each support arm includes two or more support fingers. 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. 2A. 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 not in accordance with the invention that has 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 that is not in accordance with the invention. 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. 2A). 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 are 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. 2C. 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. 3D). 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. 3B and 3C). 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. 3A). 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, 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. Input fibers 110 are substantially straight or 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. 4A). 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, 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. 5A), and an extended configuration in which the distal portions of coupling fibers 128 extend beyond plug cap 134 (FIG. 5B). 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. Input fibers 130 are substantially straight or 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.

Claims: An optical fiber system (50), the system comprising: a common backplane (12); a first printed circuit board (14) and a second printed circuit board (16), the first printed circuit board (14) and the second printed circuit board (16) disposed adjacent to one another and each coupled to the common backplane (12); a first optical device (28) coupled to the first printed circuit board (14), the first optical device facing the second printed circuit board (16); a second optical device (30) coupled to the second printed circuit board (16), the second optical device (30) facing the first printed circuit board (14); and a positioner (52) extending between the printed circuit boards and configured elastically to urge opposite ends of two or more optical fibers (42) toward the first optical device (28) and the second optical device (30) to form direct board-to-board optical communication between the first optical device (28) and the second optical device (30), the two or more optical fibers being incorporated in a multi-fiber optic cable (56), wherein the positioner (52) is configured to releasably receive the multi-fiber fiber optic cable (56) and comprises: a first support arm (62, 64) configured to guide the optical fibers (42) into alignment with the opposed optical devices (28, 30); and a second support arm (62, 64) configured to guide the optical fibers (42) into alignment with the opposed optical devices (28, 30); wherein the first support arm (62, 64) includes two or more support fingers (66, 68); the second support arm includes two or more support fingers (66, 68) that interleave with the support fingers (66, 68) of the first support arm (62, 64); and the first and second support arms are respectively pivotally coupled to each of the opposed optical devices (28, 30). The system (50) of claim 1, wherein the positioner (52) has one of an engaged configuration in which the optical fibers (42) are optically coupled to the opposed optical devices (28, 30) and a disengaged configuration in which the optical fibers (42) are optically de-coupled from the opposed optical devices (28, 30). The system (50) of claim 2, wherein the positioner (52) includes a biasing mechanism configured to switch the positioner (52) between the engaged configuration and the disengaged configuration upon application of a centralized pressing force (78). The system (50) of claim 3, wherein the biasing mechanism includes a spring (80, 82) coupled between the positioner (52) and one of the opposed optical devices (28, 30). An optical fiber system (39), the system comprising: a common backplane (12); a first printed circuit board (14) and a second printed circuit board (16), the first printed circuit board (14) and the second printed circuit board (16) disposed adjacent to one another and each coupled to the common backplane (12); a first optical device (28) coupled to the first printed circuit board (14), the first optical device facing the second printed circuit board (16); a second optical device (30) coupled to the second printed circuit board (16), the second optical device (30) facing the first printed circuit board (14); and a position (40) configured elastically to urge opposite ends of two or more optical fibers (42) toward the first optical device (28) and the second optical device (30) to form direct board-to-board optical communication between the first optical device (28) and second optical device (30); wherein the positioner (40) is configured to support the optical fibers (42) along a curved path between the opposed optical devices (28, 30); the positioner (40) comprises a flexible and resilient support structure that extends along a substantial length of the optical fibers; and the support structure comprising a flexible and resilient ribbon matrix that incorporates an elongated resilient member (48) that increases the resiliency of the ribbon matrix. The system (39) of claim 5, wherein the positioner (40) and the optical fibers (42) form a unitary, elongated fiber optic ribbon having a planar surface bounded by two ends and two sides. The system (39) of claim 6, wherein the ends of the optical fibers (42) extend beyond respective ends of the fiber optic ribbon. The system (39) of claim 6, wherein the fiber optic ribbon bends in a plane orthogonal to the planar surface upon application of a compressive force between the ends of the fiber optic ribbon. The system (39) of claim 6, wherein the fiber optic ribbon is elastically bendable. The system (39) of claim 5, wherein the positioner (40) is configured to hold the optical fibers (42) in a spaced-apart, substantially parallel planar array.

Inventors: VAN DOORN SCHELTO, VAN DOORN, SCHELTO
Applicants: INFINEON TECHNOLOGIES CORP, INFINEON TECHNOLOGIES NORTH AMERICA CORP.
Application year: 2001
Main classification: G02B6
IPC codes: G02B6, H05K1