Abstract:
An automated optical chip holder for use in a pigtailing system precisely positions an optical chip at a predetermined location in three-dimensional space to align the optical chip within the pigtailing system. An adjustable chuck assembly is driven by a stepper motor under PLC control to position optical chip. After alignment, the optical chip is clamped by the adjustable chuck assembly during the pigtailing process to prevent the optical chip from moving out of alignment. This significantly reduces the occurrence of glue-joint failure and misalignment due to retraction stress. The clamp is fabricated using soft resilient materials at the point of contact with the chip. Thus, uniform pressure is exerted on the chip, micro-vibrations are absorbed, damage to the chip is reduced, and the necessity of precision motion control of the chuck assembly is avoided. The design of the automated chip holder allows the optical chip to be loaded and the pigtailed chip to be automatically unloaded using minimal operator involvement. The automated chip holder also accomodates different sized optical chips without altering the size of the chuck assembly holding the device.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates generally to an optical chip holder in a pigtailing system, and particularly to an automated optical chip holder that loads the optical chip and unloads the pigtailed optical chip in an automated mass-pigtailing system. 
     2. Technical Background 
     Optical fibers must be precisely and securely aligned with integrated optical chip waveguides during a pigtailing procedure. Otherwise, light signals propagating through the resulting device will be severely degraded by attenuation and other optical losses. In addition, processes depending on the extensive use of manpower, are undesirable. From an efficiency standpoint, it is most desirable that the entire pigtailing process for loading the optical chip, precision aligning, pigtailing, and unloading be automated and reproducible. 
     One approach that has been considered involves the use of vacuum chucks. Typically, the optical chip is placed on a chuck platform surface having air ducts which communicate to a plenum. Subsequently, the air in the plenum is evacuated and the resulting vacuum force holds the optical chip against the platform surface. However, this approach has several drawbacks. First, vacuum chucks tend to produce air fluctuations that induce small vibrations, perturbing the optical chip. Thus, the stability of the optical chip is not maintained during the curing of the glue. More importantly, retraction stresses during the curing of the glue cause the optical chip&#39;s waveguides to be misaligned with the fiber or fiber array block. As a result, the device has a lower reliability and the resulting optical losses are high. Another drawback associated with this method is the dependency on skilled labor. An operator is required to load the optical chip and unload the pigtailed optical chip manually. Since this is a very delicate operation, the success of the pigtailing process is largely dependent on the experience of the operator. 
     In another approach that has been considered, a slide mechanism is used to hold the optical chip in place. The face of the optical chip substrate is used as a support reference. The slide mechanism slides against the substrate face to clamp it against a support. Although the stability of the optical device is improved, the resulting chip thickness dispersion tends to negatively affect the reproducibility of the process. Like the method described above, this method requires that an operator load the optical chip and unload the pigtailed optical chip manually. Again, since this is a very delicate operation and the success of the pigtailing process is dependent on the experience of the operator. 
     Thus, a need exists for an automated chip holder that precisely, securely, and repeatedly positions and aligns optical chips within the pigtailing system. Further, a need exists for an automated chip holder that automatically loads the optical chip and unload the pigtailed optical chip with minimal operator involvement; one that is suitable for mass-producing pigtailed optical devices. 
     SUMMARY OF THE INVENTION 
     The present invention addresses the problems of the conventional systems discussed above. The automated chip holder of the present invention automatically loads and precisely positions the optical chip at a predetermined position. The chip is clamped in position for pigtailing using soft resilient materials that secure the chip in two dimensions. The resilient clamp materials compensate for irregularities in the hard surfaces of the chuck platform causing the pressure that is exerted on the chip to be more uniformly distributed. Thus, micro-vibrations are substantially reduced and damage to the chip is avoided, resulting in improved manufacturing yields. In addition, the resiliency of the clamp materials will compensate for relatively coarse positional adjustments of the chuck assembly during positioning and alignment. After pigtailing, the pigtailed chip is automatically unloaded with minimal operator involvement. The chip holder accomodates optical chips having various shapes and sizes. 
     One aspect of the present invention is an automated chip holder for positioning an optical chip in a pigtailing system. The optical chip has a registration edge and a registration surface. The automated chip holder positions the optical chip in a three dimensional space characterized by a rectangular coordinate system having an x-axis, y-axis, and z-axis. The automated chip holder includes: a support base having a slide track disposed parallel to the x-axis; a registration member fixed to the support base for defining an alignment position in the three dimensional space; an adjustable chuck assembly slidably disposed on the slide track for moving the optical device between a device interchange position and the alignment position, the adjustable chuck assembly being movable in the x-axis direction and adjustable in the z-axis direction in response to a force directed in the x-axis direction; and a drive unit connected to the adjustable chuck assembly for applying the x-axis force to said adjustable chuck assembly. 
     In another aspect, the present invention includes a method for positioning an optical device in a pigtailing system using an automated chip holder. The optical device includes a registration edge and a registration surface. The automated chip holder includes a support base having a slide track, a registration member fixed to the support base for defining an alignment position in a three dimensional space characterized by a rectangular coordinate system having an x-axis, y-axis, and z-axis. The method for positioning comprising the steps of: providing an adjustable chuck assembly slidably disposed on the slide track for moving the optical device between a device interchange position and the alignment position, the adjustable chuck assembly being movable in the x-axis direction and adjustable in the z-axis direction in response to an x-axis force; and applying the x-axis force to thereby move the optical device from a device interchange position to the alignment position. 
     Additional features and advantages of the invention will be set forth in the detailed description which follows, and in part will be readily apparent to those skilled in the art from that description or recognized by practicing the invention as described herein, including the detailed description which follows, the claims, as well as the appended drawings. 
     It is to be understood that both the foregoing general description and the following detailed description are merely exemplary of the invention, and are intended to provide an overview or framework for understanding the nature and character of the invention as it is claimed. The accompanying drawings are included to provide a further understanding of the invention, and are incorporated in and constitute a part of this specification. The drawings illustrate various embodiments of the invention, and together with the description serve to explain the principles and operation of the invention. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a side elevation view of the automated chip holder of the present invention; 
     FIG. 2 is a rear elevation view of the automated chip holder of the present invention; 
     FIG. 3 is a detail view illustrating the uniform force applied in the z-direction during alignment; 
     FIG. 4 is a detail view of a registration member of the present invention; 
     FIG. 5 is a detail view of a side elevation of an adjustable chuck assembly of the present invention; 
     FIG. 6 is a detail view illustrating the uniform force applied in the x-direction during alignment; 
     FIG. 7 is a detail view of a rear elevation of the adjustable chuck assembly of the present invention. 
     FIG. 8 is a detail view of the device interchange position of the automated chip holder of the present invention; 
     FIG. 9 is a detail view of an alignment position of the automated chip holder of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Reference will now be made in detail to the present preferred embodiment of the invention, an example of which is illustrated in the accompanying drawings. Wherever possible, the same reference numbers will be used throughout the drawings to refer to the same or like parts. An exemplary embodiment of the automated chip holder of the present invention is shown in FIG. 1, and is designated generally throughout by reference numeral  10 . 
     In accordance with the invention, the present invention for an automated chip holder  10  includes an adjustable chuck assembly  40  which moves optical chip  100  to a precise location in three dimensional space. Optical chip  100  is disposed on a resilient pad and adjacent to a resilient wedge to protect the chip from damage during clamping. The resilient material applies uniform clamping forces acting in a horizontal and vertical direction during the pigtailing process. This is an important feature that absorbs micro-vibrations, eliminating chip misalignment due to retraction stresses. There are other advantages associated with using the resilient materials. The incremental movements of the clamp need not be as precise as a clamp having a hard non-resilient surface. If a non-resilient clamp exerts too much force on the chip, it will damage the chip. Thus, the motion control system must be implemented using stricter tolerances to avoid such damage. On the other hand, the resilient material is forgiving and accomodates a chuck assembly having coarser incremental movements when clamping. Thus, the necessity of precision motion control is avoided along with the concomitant cost. Note also, that the resilient wedge is interchangeable allowing the adjustable chuck assembly  40  to accomodate optical chips having various sizes and shapes. 
     As discussed above, automated chip holder  10  positions optical chip  100  at a precise location in three-dimensional space. Movement in the three dimensional space is described throughout in reference to a Cartesian coordinate system having mutually orthogonal x, y, and z axes. The length of automated chip holder  10  corresponds to an x-axis, the width corresponds to a y-axis, and the height corresponds to a z-axis. 
     As embodied herein, and depicted in FIG. 1, automated chip holder  10  includes a support base  12  which functions as a chassis for automated chip holder  10 . Support base  12  includes slide track  14 , which is a raised portion used for guiding adjustable chuck assembly  40  in either direction along the x-axis. Registration member  20  is connected to support base  12  and defines the alignment position of optical chip  100  in three-dimensional space. Adjustable chuck assembly  40  is slidably disposed on support base  12  and carries optical chip  100  between a device interchange position and the alignment position. Adjustable chuck assembly  40  includes a transport member  42  which is movable along the x-axis, and adjustable platform  50  which adjusts the position of optical chip  100  along the z-axis. The device interchange position and the alignment position will be discussed in more detail below. Rotatable screw  62  is connected to adjustable chuck assembly  40 . Rotatable screw  62  drives adjustable chuck assembly  40  in either direction along the x-axis using screw transfer motion. Stepper motor  60  is connected to rotatable screw  62  and is reversible, rotating in either a clockwise or counter-clockwise direction as needed. Programmable Logic Controller (PLC)  64  is connected to stepper motor  62 . The operational sequence of automated holder  10  resides in PLC  64 . 
     In accordance with the invention, the registration member  20  may further include column member  26 , which is fixed to support base  12  and extends in a direction parallel to the z-axis. Column member  26  is connected to cantilvered member  28  and is parallel to support base  12 . Adjustable stop member  30  is disposed on cantilevered member  28  spaced apart from column member  26 . The spacing is variable to accomodate various chip sizes. Surface region  24  of cantilevered member  28  located in the space between stop member  30  and column member  26  is the z-axis alignment reference corresponding to the registration surface  104 . Column surface  22  provides an x-axis alignment reference for aligning registration edge  102  of optical chip  100 . 
     As embodied herein and depicted in FIG. 2, a rear elevation view of the automated chip holder  10  of the present invention includes a cantilevered member  28  that has arms  280  and  282  which form open area  284 . Adjustable stop member  30  includes stop tab  32  which extends downward in the z-axis direction into open area  284 . Adjustable platform  50  includes tongue member  54  which extends upward in the z-axis direction. Optical chip  100  is clamped against surface  24  by adjustable platform  50  as it moves upward along the z-axis, positioning registration surface  104  in z-axis alignment. Resilient pad  524  supports optical chip  100  during clamping and provides uniform clamping forces in a z-direction. Resilient pad  524  compensates for surface irregularities in the adjustable platform which would otherwise generate an uneven pressure distribution. Note that tongue member  54  and stop tab  32  interlock preventing movement of adjustable platform  50  in certain circumstances. 
     As embodied herein and depicted in FIG. 3, the uniform clamping forces applied by resilient pad  524  are approximately equal to 100 grams/mm. The term “uniform force” means that the amplitude of the linear force applied by resilient pad  524  is equal at every point of contact between resilient pad  524  and optical chip  100 . 
     FIG. 4 is a detail view of registration member  20  of the present invention in a plane formed by the x-axis and the y-axis. Arms  280  and  282  of cantilevered member  28  are connected to column member  26  to form a u-shape having open area  284 . Adjustable stop member  30  is disposed on arms  280  and  282  and adjustable along the x-axis to accomodate optical chips of any size. The position of adjustable stop member  30  is fixed for a particular size optical device by set device  34 . Set device  34  may be of any suitable well-known type, but there is shown by way of example, a set screw which is pressed against arm  280 . FIG. 4 also depicts stop tab  32  interlocking with tongue member  54 . In x-axis alignment, registration edge  102  is resiliently pressed against column surface  22  by resilient wedge  522  as transport member  42  advances in the x-axis direction. Column surface  22  is the x-axis reference. In order to reduce the frictional force between optical chip  100  and x-axis reference  22  and to ensure the accuracy of the reference, notch  220  is formed in column member  26 . Thus, the point of contact between optical chip  100  and x-axis reference  22  is reduced to small region. 
     FIG. 5 is a detail view of a side elevation of an adjustable chuck assembly of the present invention. In accordance with the invention, the adjustable chuck assembly  40  may further include transport member  42  and adjustable platform  50 . Transport member  42  is disposed on support base  12  and connected to the rotating screw  62 . It is driven along the x-axis in either direction by the rotation of rotating screw  62 . Transport member  42  includes transport inclined surfaces  46  and  48  for supporting the adjustable platform  50 . Inclined surfaces  46  and  48  are finely polished and coated with teflon to lower the coefficient of friction. Transport stop edge  44  is provided to limit the movement of adjustable platform  50 . 
     Also depicted in FIG. 5, adjustable platform  50  is disposed on transport member  42 . Adjustable platform  50  is removable and is not attached to transport member  42  by any kind of connector or adhesive. It maintains its position on transport member  42  by gravity and frictional force only, allowing it to freely slide on polished inclined surfaces  46  and  48 . Adjustable platform  50  includes stage member  52 , tongue member  54 , and platform stop edge  56 . Stage member  52  is equipped with resilient wedge  522  which, as described above, provides uniform clamping forces in the x-direction during clamping and alignment. Optical chip  100  is disposed on resilient pad  524 . Stage inclined surfaces  526  and  528  are also provided, corresponding to transport inclined surfaces  46  and  48 . Inclined surfaces  526  and  528  are also polished and coated with teflon. The position of optical chip  100  along the z-axis is adjusted by sliding inclined surfaces  526  and  528  over inclined surfaces  46  and  48 . As discussed above, tongue member  54  prevents the adjustable platform  50  from moving along the x-axis when the tongue member  54  is interlocked with the stop tab  32  of the adjustable stop member  30 . Platform stop edge  56  interlocks with transport stop edge  44  to prevent adjustable platform  50  from completely sliding off transport member  42 . 
     As embodied herein and depicted in FIG. 6, the uniform clamping forces applied by resilient wedge  522  are approximately equal to 40 grams/mm. The ratio between the z-direction force and the x-direction force is approximately 5:2. However, the x-direction force can be as little as 10 grams/mm. Again, the term “uniform force” means that the amplitude of the linear force applied by resilient wedge  522  is equal at every point of contact between resilient wedge  522  and optical chip  100 . Resilient wedge  522  compensates for any surface irregularities on platform  52  that would might otherwise generate an uneven pressure distribution on optical chip  100 . 
     FIG. 7 is a detail view of a rear elevation of adjustable chuck assembly  40  of the present invention. Transport member  42  has track guide  16  formed in the bottom surface. Track guide  16  mates with slide track  14  of support base  12 . Stop edge member  56  fits over transport member  42  such that inclined surfaces  526  and  528  rest on inclined surfaces  46  and  48 . This design eliminates movement of chuck assembly  40  along the y-axis. Optical chip  100  is disposed on resilient pad  524 . As depicted, resilient pad  524  is inserted in a groove formed along the edge of stage member  52  and provides the uniform clamping force in the z-direction as discussed above. In one embodiment, the position of optical chip  100  on stage member  52  is predetermined and fixed before adjustable platform  50  is disposed on transport member  42  to thereby establish y-axis alignment. Subsequently, optical chip  100  and adjustable platform  50  are lowered onto transport member  42  as a unit. In another embodiment, adjustable platform  50  is disposed on transport member  42  before loading the optical chip  100 . In this embodiment, a vacuum chuck carries optical chip  100  to adjustable platform  50  and disposes optical chip  100  on adjustable platform  50  at a predetermined position. Thus, in either embodiment, optical chip  100  is automatically aligned with respect to the y-axis when loaded into automated holder  10 . 
     The operation of automated chip holder  10  will now be explained in reference to FIGS. 8 and 9. FIG. 8 is a detail view of chuck assembly  40  in the device interchange position of automated chip holder  10  of the present invention. Adjustable chuck assembly  40  is disposed on support base  12  at a position on the x-axis adjacent to end wall  18  of support base  12 . It is in this position that optical chip  100  is loaded and the pigtailed optical chip is unloaded from the automated chip holder  10 . As discussed above, y-axis alignment is acheived during the loading process. Registration edge  102  is aligned with stage edge  520  by properly selecting the size of resilient wedge  522 . Stage edge  520  is aligned with transport member edge  420  to provide the necessary x-axis clearance between adjustable platform  50  and cantilevered member  28 . Once loading is complete, adjustable platform  50  can be slid forward on transport member  42  until platform stop edge  56  contacts transport stop edge  44 . This would increase the z-axis clearance between registration surface  104  and surface  24 , the z-axis alignment reference. There must be enough clearance to allow tongue member  54  to pass under stop tab  32  of adjustable stop member  30  when the transport member  42  advances toward the alignment position in the x-axis direction. 
     FIG. 9 is a detail view of an alignment position of the automated chip holder of the present invention. Based on the size and thickness of optical chip  100 , stepper motor  60 , under the control of PLC  64  (both not shown), drives transport member  42  from the device interchange position to the x-axis alignment position. Once transport member  42  reaches this position on the x-axis, registration edge  102  is pressed against x-axis alignment reference  22 , and the movement of adjustable platform  50  in the x-axis ceases. At this moment, the x-axis uniform force is exerted on the opposite edge of optical chip  100  by resilient wedge  522 . Since adjustable platform  50  can no longer move in the x-axis, inclined surfaces  46  and  48  slide under inclined surfaces  526  and  528 , forcing adjustable platform  50  to slide up the z-axis toward the z-axis alignment reference, surface  24 . Subsequently, tongue member  54  interlocks with stop tab  32  and registration surface  104  is clamped against surface  24 . When optical chip  100  is resiliently clamped, stepper motor  60  is de-energized and rotatable screw  62  stops turning. The uniform forces that are exerted on optical chip  100  by resilient wedge  522  and resilient pad  528  are maintained by rotatable screw  62  which is fixed in position until the pigtailing process is complete. 
     After pigtailing is completed, the pigtailed optical chip is moved back to the device interchange position shown in FIG.  8 . Stepper motor  60  is re-energized and begins to turn rotatable screw  62  in a reverse direction causing transport member  42  to retract along the x-axis. As transport member  42  moves in a reverse direction along the x-axis, tongue member  54  is pressed against stop tab  32  preventing adjustable platform  50  from moving along the x-axis. Inclined surfaces  46  and  48  slide under inclined surfaces  526  and  528  and adjustable platform  50  moves in the z-direction toward support base  12 . Once tongue member  54  is disengaged from stop tab  32 , adjustable chuck assembly  40  moves as a unit in a reverse x-axis direction toward the device interchange position. Once there, the pigtailed chip is interchanged for an unprocessed chip, and the above described process will be repeated. 
     It will be apparent to those skilled in the art that various modifications and variations can be made to the present invention without departing from the spirit and scope of the invention. Thus, it is intended that the present invention cover the modifications and variations of this invention provided they come within the scope of the appended claims and their equivalents.