Abstract:
An optical connector for use in multilayer electro-optic circuit boards. An electro-optical back plane circuit board uses both electrical and optical connectors to carry signals in both electrical and light form. The optical connector employs redundant alignment features to provide for reliable connectivity between plug in boards and the electro-optic back plane. A process is of forming the back plane and other multilevel circuit boards so as to embed optical connectors is disclosed.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]    The present application is a continuation of Ser. No. 10/051,418, filed Oct. 30, 2001, which claims priority under 35 U.S.C. § 19(e) from U.S. Provisional Application No. 60/244,390, filed Oct. 31, 2000, both of which are hereby incorporated by reference herein in their entirety, for all purposes. 
     
    
     
       INTRODUCTION  
         [0002]    The present invention relates generally to the field of optical connectors for circuit boards. More particularly, the present invention relates to electro-optical back plane circuit boards that have both electrical and optical connectors.  
         BACKGROUND OF THE INVENTION  
         [0003]    Electronics devices are becoming increasingly integrated with optical systems. This has given rise to the need to integrate electronics and optics together into printed circuit board systems. Currently, this integration is somewhat awkward. Although printed circuit wiring is a fairly mature technology, the mixing of printed circuit wiring with optical conduction paths is still at an awkward stage of development.  
           [0004]    Additionally, the connectors for interfacing optical conduction paths on circuit boards with fibers off-board is still a challenge. Specifically, aligning the off-board optical fibers with the connectors on the board remains a reliability problem.  
           [0005]    Thus, what is needed is a printed circuit board configuration that reliably integrates electrical conduction with optic conduction, including stable optical connectors.  
         SUMMARY OF THE INVENTION  
         [0006]    One aspect of the present invention is an optical connector for use in a multilayer circuit board.  
           [0007]    Another aspect of the present invention is a method for forming an electro-optical multilayer circuit board having embedded optical connectors.  
           [0008]    It is also an aspect of the present invention to embed an optical connector in a multilayer circuit board using a guide plate and pins to align the optical connector with the various layers of the circuit board.  
           [0009]    An additional aspect of the present invention is an electro-optical back plane having both electrical connectors and optical connectors.  
           [0010]    One embodiment of the present invention is an optical connector for use with an electro-optical board. The optical connector includes a right angle interface body that has one or more first optical paths and one or more second optical paths. Each of the first optical paths corresponding to a respective second optical path, and the first optical paths are disposed in a first plane and the one or more second optical paths are disposed in a second plane. The first and second planes being substantially at right angles with respect to one another. The optical connector also includes a female self-alignment body that has a tapered channel substantially aligned with the first plane. The optical connector further includes a tapered male self-alignment body sized to fit closely into the tapered channel of the female self-alignment body, and having one or more third optical paths adapted to align with the first optical paths when the tapered male self-alignment body is engaged with the female self-alignment body. The third optical paths are adapted for connection to one or more optical fibers disposed outside the electro-optical board. The second optical paths are adapted for connection to optical fibers embedded in the electro-optical board.  
           [0011]    Another embodiment of the present invention is a method of integrating into an optical-electrical board an optical connector that includes a right angle interface body, a female self-alignment body having a tapered channel, and an anchor body. The method includes the steps of connecting the right angle interface body to a set of one or more optical fibers, and embedding the right angle interface body and the one or more optical fibers inside the optical-electrical board. The method also includes the steps of forming a hole in the optical-electrical board to expose an upper surface of the embedded right angle interface body, securely fastening the anchor body about the hole, and inserting the female self-alignment body through the anchor body and the hole so as to bring the tapered channel into registration with the embedded right angle interface body.  
           [0012]    Yet another embodiment of the present invention is an electro-optical back plane. The electro-optical back plane includes a fiber management system formed of plural optical fibers, an electrical bus circuit, and a board, wherein the fiber management system and the electrical bus circuit are embedded inside the board. The electro-optical back plane further includes plural optical connectors disposed on the board, each of the optical connectors being coupled to one or more of the plural optical fibers of the fiber management system. Additionally, the electro-optical back plane includes plural electrical connectors disposed on the board, each of the electrical connectors being electrically connected to the electrical bus circuit. Each of the optical connectors includes a right angle interface body embedded into the board for connection to one or more fibers of the fiber management system, an anchor body securely fastened to the surface of the board, and a female self-alignment body having a tapered channel. The female self-alignment body is held by the anchor body so that the tapered channel is in registration with an upper surface of the right angle interface body. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0013]    Additional objects and advantages of the present invention will be apparent in the following detailed description read in conjunction with the accompanying drawing figures.  
         [0014]    [0014]FIG. 1 illustrates a sectional exploded view of parts of an optical connector according to an embodiment of the present invention.  
         [0015]    [0015]FIG. 2 illustrates a perspective view of a right angle interface body according to an embodiment of the present invention.  
         [0016]    [0016]FIG. 3 illustrates a sectional view of the right angle interface body of FIG. 2.  
         [0017]    [0017]FIG. 4 illustrates another sectional view of the right angle interface body of FIG. 2 (orthogonal to the sectional view of FIG. 3).  
         [0018]    [0018]FIG. 5 illustrates an initial pre-assembly schematic view of various lamination layers for composing a multilayer printed circuit board according to an embodiment of the present invention.  
         [0019]    [0019]FIG. 6 illustrates a post-lamination cross sectional view of a multilayer circuit board according to a process embodiment of the present invention.  
         [0020]    [0020]FIG. 7 illustrates a cross sectional view of a multilayer circuit board illustrating a machining step of a process embodiment of the present invention.  
         [0021]    [0021]FIG. 8 illustrates a cross sectional view of a multilayer circuit board illustrating a connector assembly step of a process embodiment of the present invention.  
         [0022]    [0022]FIG. 9 illustrates a cross sectional view of a multilayer circuit board illustrating another connector assembly step of a process embodiment of the present invention.  
         [0023]    [0023]FIG. 10 illustrates a cross sectional detail view (per section line X in FIG. 9) showing the ratcheted interface between an anchor body and a female self-alignment body that form the female connector portion according to an embodiment of the present invention.  
         [0024]    [0024]FIG. 11 illustrates a partial section view of a fully assembled optical connector according to an embodiment of the present invention.  
         [0025]    [0025]FIG. 12 illustrates a schematic view of an electro-optical back plane according to an embodiment of the present invention. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0026]    Referring to FIG. 1, and exploded sectional view of a connector according to an embodiment of the present invention is illustrated. A male connector portion  110  is insertable into a female connector portion  120 . The male and female connector portions  110 ,  120  are tapered to fit together so as to provide a self-aligning function. A micro machined optical conductor assembly  112  in the male connector portion  110  is cause to be brought into precise alignment with another micro machined optical conductor assembly  132  disposed in a right angle interface body  130 . The female connector portion  120  guides the male connector portion  110  into precise registration with the right angle interface body  130 .  
         [0027]    The housing parts of the optical connector are preferably formed of a high Tg material. Polyetherimide resins, and in particular ULTEM® resin (a product of GE), have been found to be a suitable as housing material to embody the invention.  
         [0028]    The right angle interface body  130  is to be embedded inside a multi-layer circuit board. The female connector portion  120  mounts on a surface of the multi-layer circuit board, with a lower portion thereof extending down into the circuit board to engage the right angle interface body  130 . The micro machined optical conductor assembly  132  is disposed above an integrated mirror  134  that provided a 90° transition for light traveling through the connector. This reflected light also travels through an additional micro machined conductor assembly  136  that provides coupling to a plurality of optical fibers  140 , which are embedded inside the multilayer circuit board.  
         [0029]    An optional feature of the optical connector  100  according to this embodiment is a spring-loaded door  122  inside the tapered passageway  124  of the female connector portion  120 . The spring-loaded door  122  provides two functions. First, it prevents debris from falling down n inside the connector and contaminating the optical interface surface  131  on the top of the right angle interface body  130 . Secondly, the spring-loaded door  122  prevents light from being emitted through the tapered passageway  124  of the female connector portion  120  when no male connector portion  130  is inserted therein.  
         [0030]    The female connector portion  120  is securely held to the surface of the multilayer circuit board via locking connectors  124  that are inserted into holes formed through the multilayer circuit board.  
         [0031]    Off-board optical fibers  150  are connected into the male connector portion  110  so as to be in optical communication with the micro machined optical conductor assembly  112 . In addition to the self-aligning feature provided by the matched tapering shape of the male and female connector portions  110 ,  120 , precision of alignment of the optical connector is enhanced by alignment pins  114  extending from the male connector portion that interdigitate with precisely machined alignment holes (not shown in this view) formed in the top side of the right angle interface body  130 .  
         [0032]    Referring to FIG. 2, a perspective view of the right angle interface body  130  is illustrated. The precision alignment holes  138  are disposed on either end of the optical conductor assembly  132 . Plural optical conductors  137  (preferably glass fibers) embedded in a silicon body  139  to form the optical conductor assembly  132 . The optical conductor assembly is principally formed of silicon. MT type optical connector devices have been found to be suitable for embodying these assemblies.  
         [0033]    Referring to FIG. 3, a sectional view of the right angle interface body  130  of FIG. 2 is illustrated. Anchor members  135  extend downward from the bottom side of the right angle interface body  130  to provide enhanced mechanical stability inside the multilayer circuit board.  
         [0034]    Referring to FIG. 4, another sectional view of the right angle interface body  130  of FIG. 2 is illustrated. Extending upwardly from the integrated mirror  134  through the micro machined optical conductor assembly  132  are plural glass fibers  137 .  
         [0035]    Referring to FIG. 5, an initial pre-assembly schematic view is illustrated, showing the relative position of various lamination layers for composing the multi-layer printed circuit board. One layer is an electrical inner layer  502  according to known prior art practices. A registration plate  504  is provided to keep the board structure flat and having alignment holes to align and fix the optical connector during bonding. A prepreg layer  506  for bonding and embedding optical management structures is provided above the laminate layer  504 . About the right angle interface body  530  a laminate layer  508  is provided with the perimeter of the fiber management system  540  being routed out to compensate for thickness differences. An adhesive copper tape  512  is layered onto the top surface of the right angle interface body  530  to protect the glass fibers, alignment holes, and other surrounding structures from later processing steps. The copper tape  512  is adhered to the top surface of the right angle interface body  530  by an adhesive. Preferably, the adhesive can withstand a temperature of at least 210° C. and will not leave behind excessive residue when the copper tape  512  is later removed. Above the additional lamination layers  514 , an outer copper foil  510  is layered on as a top layer. The outer copper foil  510  is preferably about 18 micrometers in thickness.  
         [0036]    The circuit board layers may be formed with any suitable materials that are known in the art. Standard circuit board materials are available from a number of manufacturers including Isola of the U.K., Nelco Products, Inc. of Fullerton, Calif., and Polyclad Laminates of Franklin, N.H.  
         [0037]    Referring to FIG. 6, a cross sectional view of the multilayer circuit board  600  is illustrated, post-lamination. The right angle interface body  530  is shown coupled to a fiber management system  540 , with both being embedded inside a multi-layer printed circuit board  600 . The right angle interface body  530 , a basic alignment component of the entire optical connector, is aligned to the circuit board  600  via a registration plate  504 . The registration plate  504  aligns and fixes the entire optical connector to the electrical pattern of the printed circuit board  600  by fixing the anchor members  539  into the registration plate  504 . The registration plate  504  is aligned to the other layers of the multilayer printed circuit board  600  by using a traditional Lenkheit system.  
         [0038]    The interlocking of the right angle interface body  530  with the registration plate  504  via the anchor members  539  aligns the optical connector both in the x-y plane of the board, as well as along the z axis.  
         [0039]    It is noted that the right angle interface body  530  has angled sidewalls  531 . These angled sidewalls  531  serve a dual purpose. One reason for having the angles sidewalls  531  is to facilitate cleaning around the interface body  530  with a laser that is used to ablate away the board layers above the interface body  530 . The second useful purpose for the angled sidewalls is to provide for good alignment with the female connector portion.  
         [0040]    Referring to FIG. 7, the multilayer printed circuit board  600  is shown after machining steps have been conducted on the board. Holes  602  have been drilled through the board  600  for connecting the female connector portion  920  to the surface of the board. A hole  604  has been machined into the upper surface of the board  600  and so is to expose the right angle interface body  530 . The outer copper foil layer  510  has also been etched to provide conductive runs. At this time the copper tape  512  on the top of the right angle interface body  530  may be pealed off and the top surface of the right angle interface body cleaned  530 . The protective copper tape  512  is left on the top surface of the right angle interface body  530  until the board  600  has been electrically tested and finally inspected.  
         [0041]    Referring to FIG. 8, the first step of assembling the female connector portion is illustrated. An anchor body  822  is securely engaged to the surface of the board  600  by inserting its anchors  824  into the holes  602  drilled in the board  600 .  
         [0042]    Referring to FIG. 9, a second step of assembling the female connector portion is illustrated. A female self-alignment body  924  is forced downward through the anchor body  822  and into the machined out hole  604  in the board  600  until it aligns with the imbedded right angle alignment body  530 .  
         [0043]    Referring to FIG. 10, a detail view of the interface between the anchor body  822  and the female self-alignment body  924  is illustrated. The anchor body  822  engages the female self-alignment body  924  via a one way ratchet  926 .  
         [0044]    Referring to FIG. 11, the fully assembled optical connector  1100  is illustrated in a partial section view. A male self-alignment body  910  is inserted down into the female self-alignment body  920  (formed by the combination of the anchor body  822  and the female self-alignment body  924 ) to guide the male connected portion into precise registration with the top surface of the right angle alignment body  530 . To insure precision of engagement between the optical paths of the male connector portion  910  with the optical paths of the right angle alignment body  530 . the alignment pins  914  of the male connector portion  910  are engaged with the precision machined holes  538  of the right angle alignment body  530 .  
         [0045]    Referring to FIG. 12, an electro-optical back plane  1200  according to an embodiment of the present invention is illustrated. The back plane  1200  has an optical carrier  1210  (preferably a fiber management system) embedded with a number of optical connectors  1220  according to embodiments of the present invention. For interfacing printed circuit boards  1230  to the electro-optical back plane  1200 , optical connectors  1220  are placed adjacent to electrical connectors  1222 . The printed circuit boards  1230  are engaged with the electro-optical back plane  1200  using separate fibers  1224  on the board  1230  slotted into the electro optical back plane  1200  via both the electrical connectors  1222  and their corresponding optical connectors  1220 . Purely optical devices  1250  may also be plugged into the back plane  1200 . For example an optical switch  1252  is shown being connected to optical connectors  1220  alone, as is a splitter coupler device  1254 .  
         [0046]    The present invention has been described in terms of preferred embodiments, however, it will be appreciated that various modifications and improvements may be made to the described embodiments without departing from the scope of the invention.