Abstract:
An apparatus for aligning a fiber to an optical device includes a base, a fiber holder mounted on the base, the fiber holder holding the fiber during operation of the apparatus, a first movable stage mounted on the base, the first movable stage holding the optical device during operation of the apparatus, a second movable stage mounted on the base, wherein the second movable stage is configured to move parallel to the first movable stage, a fiber positioner attached to the second movable stage, and a processor programmed to control the movement of the first movable stage and the second movable stage, wherein, during operation of the apparatus, the processor moves the first movable stage and the second movable stage towards the fiber.

Description:
CLAIM OF PRIORITY 
     This application claims priority under 35 USC §119(e) to U.S. patent application Ser. No. 60/224,735, filed on Aug. 11, 2000, the entire contents of which are hereby incorporated by reference. 
    
    
     TECHNICAL FIELD 
     This invention relates to aligning a fiber to an optical device. 
     BACKGROUND 
     Fiber optic systems often require aligning an optical fiber (“a fiber”) to couple light to an optical device, such as a laser diode or an electro-optical detector. Fibers and optical devices have very small emitting and receiving areas, sometimes as small as a few microns in diameter. Therefore, achieving an efficient coupling between a fiber and an optical device requires an alignment with sub-micron accuracy. Typically, the alignment is performed manually, by an operator, who adjusts the position of the fiber while observing the fiber with an observation station (i.e., a high-resolution camera or microscope) or while monitoring a measured output signal from the optical device. Manual alignment is very time consuming and the resulting alignment is dependent on the accuracy and skill of the individual operator. 
     SUMMARY 
     According to an aspect of this invention, an apparatus for aligning a fiber to an optical device includes a base, a fiber holder mounted on the base, the fiber holder holding the fiber during operation of the apparatus, a first movable stage mounted on the base, the first movable stage holding the optical device during operation of the apparatus, a second movable stage mounted on the base, wherein the second movable stage is configured to move parallel to the first movable stage, a fiber positioner attached to the second movable stage, and a processor programmed to control the movement of the first movable stage and the second movable stage, wherein, during operation of the apparatus, the processor moves the first movable stage and the second movable stage towards the fiber. 
     One or more of the following features may also be included: during operation of the apparatus, the processor moves the first movable stage and the second movable stage towards the fiber until the end of the fiber is proximate to the optical device, the fiber positioner may include a movable arm having a range of motion orthogonal to the longitudinal axis of the fiber held in the fiber holder, wherein the processor is programmed to control the movement of the movable arm, and wherein, during operation of the apparatus, the processor moves the movable arm and positions an end of the fiber proximate to the optical device, the apparatus may include a signal generation circuit transmitting a test signal to one of the optical device and the fiber, and a signal detection circuit receiving a detected test signal from one of the optical device and the fiber, wherein the processor is programmed to determine the optimum position of the fiber to maximize a strength of the detected signal, the apparatus may include a support member attached to the base, and a camera mounted to the support member, the camera having a focal plane proximate to the end of the fiber, and, wherein the processor is programmed to determine the coordinates of the end of the fiber that is being aligned to the optical device, and, wherein the movable arm further includes a fiber-guide holding device attached to an end of the movable arm, wherein, during operation of the apparatus, the fiber-guide holding device holds the fiber-guide using forces associated with a flow of air, and, wherein the movable arm further includes a fiber-guide holding device attached to an end of the movable arm, wherein the fiber-guide holding device is a clamping device, and, wherein the optical device is mounted within a device box, and wherein the device box has an opening in a side of the device box that is in substantial alignment with the optical device, and apparatus may further include a third movable stage mounted to the support member and holding an adhesive applicator, wherein, during operation of the apparatus, the adhesive applicator holds an adhesive, and wherein the processor is programmed to control the movement of the third movable stage and programmed to control the dispensing of the adhesive proximate to at least one of the fiber, the fiber-guide and the device box, and apparatus may further include an adhesive applicator attached to the second movable stage, wherein, during operation of the apparatus, the adhesive applicator holds an adhesive, and, wherein the processor is programmed to control the dispensing of the adhesive proximate to at least one of the fiber, the fiber-guide and the opening in the side of the device box, and the apparatus may further include a third movable stage mounted to the support member and holding an adhesive applicator, wherein, during operation of the apparatus, the adhesive applicator holds an adhesive, and wherein the processor is programmed to control the movement of the third movable stage and programmed to control the dispensing of the adhesive proximate to at least one of the fiber and the fiber-guide, and, wherein the fiber holder includes a fiber rotator for rotating the fiber about its longitudinal axis, and wherein the processor is programmed to rotate the fiber until the detected test signal is maximized. 
     According to a further aspect of this invention, an apparatus for aligning a fiber to an optical device includes a base, a fiber holder mounted on the base, the fiber holder holding the fiber during operation of the apparatus, a first movable stage mounted on the base, the first movable stage holding the optical device during operation of the apparatus, a support member attached to the base, a camera mounted to the support member, the camera having a focal plane proximate to an end of the fiber that is being aligned to the optical device, and a processor programmed to control the movement of the first movable stage, wherein, during operation of the apparatus, the first movable stage is moved towards the fiber. 
     One or more of the following features may also be included: wherein the processor is programmed to determine the coordinates of the end of the fiber that is being aligned to the optical device, and, wherein the optical device is mounted within a device box, and wherein the device box has a feed-through opening in a side of the device box that is in substantial alignment with the optical device, and the apparatus may further include a signal generation circuit transmitting a test signal to one of the optical device and the fiber, and a signal detection circuit receiving a detected test signal from one of the optical device and the fiber, wherein the processor is programmed to determine the optimum separation distance between the fiber and the optical device to maximize a strength of the detected signal, and, wherein the fiber holder includes a fiber rotator for rotating the fiber about its longitudinal axis, and wherein the processor is programmed to rotate the fiber until the detected test signal is maximized. 
     According to a further aspect of this invention a method of aligning a fiber to an optical device includes holding a fiber in a fixed position, holding an optical device on a first movable stage, holding a fiber-guide on a second movable stage, and moving the optical device and the go fiber-guide towards the fiber, wherein the moving the optical device and the fiber-guide towards the fiber comprises controlling the moving with a processor. 
     One or more of the following features may also be included: wherein the holding a fiber-guide further includes holding the fiber-guide with a movable arm having a range of motion orthogonal to the longitudinal axis of the fiber, and moving the fiber-guide proximate to the optical device under control of the processor, the method may further include transmitting a test signal to one of the fiber and the optical device, receiving a signal from one of the fiber and the optical device, and determining the optimum position of the fiber with the processor, the determining based on a signal strength of the received signal, and, wherein holding a fiber in a fixed position further includes holding an end of the fiber in a focal plane of a camera, the method may further include determining coordinates of the end of the fiber with the processor, the determining the coordinates based on an output signal from the camera, and, wherein holding the fiber-guide further includes holding the fiber-guide with a force associated with a flow of air, and, wherein holding the fiber-guide further includes holding the fiber-guide with a clamping force, and, wherein the optical device is mounted within a device box, wherein the device box has an opening in the side of the device box, and wherein holding the device box further includes holding the device box with the opening in substantial alignment with the longitudinal axis of the fiber, the method may further include dispensing adhesive proximate to one of the fiber-guide, the fiber and the optical device, wherein the dispensing adhesive may further include moving an adhesive applicator under control of the processor, and dispensing adhesive from the applicator under control of the processor, the method may further include rotating the fiber with a fiber rotator under control of the processor, and determining, by the processor, the optimum rotational position of the fiber based on a signal strength of the received signal. 
     According to a further aspect of this invention a method of aligning a fiber to an optical device includes holding a fiber in a fixed position, wherein an end of the fiber is located in a focal plane of a camera, holding an optical device on a first movable stage, moving the optical device towards the fiber, the moving comprises controlling the moving with a processor. 
     One or more of the following features may also be included: determining coordinates of the end of the fiber with the processor, the determining based upon an output signal from the camera, and, wherein the optical device is mounted within a device box, wherein the device box has an opening in the side of the device box, and wherein holding the device box further includes holding the device box with the opening in substantial alignment with the longitudinal axis of the fiber, the method may further include transmitting a test signal to one of the fiber and the optical device, receiving a signal from one of the fiber and the optical device, and determining the optimum position of the fiber with the processor, the determining based on a signal strength of the received signal, the method may further include rotating the fiber with a fiber rotator under control of the processor, and determining, by the processor, the optimum rotational position of the fiber based on a signal strength of the received signal. 
     Embodiments of the invention may have one or more of the following advantages. For example, the use of automated movers reduces the manual handling of a fiber during alignment to an optical device and reduces the time required to perform an alignment. Holding the fiber stationary while moving the optical device into alignment reduces the stresses applied to the fiber, reduces the possibility of damaging the fiber and reduces possible fluctuations in a light beam emitted from the fiber (i.e. the intensity or phase of the emitted light beam). Holding the fiber stationary also reduces the complexity, and therefore the cost, of the apparatus by requiring fewer movable stages. Some of the embodiments include a camera that is held stationary and with a fixed focal plane near the end of the fiber that is being held stationary while the optical device is being aligned with it. This eliminates the need to move the camera to track the end of the fiber during the alignment. In some embodiments a fiber rotator is used to rotate a fiber along its longitudinal axis, therefore setting the polarity of the fiber end to match the polarity of the optical device. This fiber rotator may also include a clamping mechanism for holding the fiber. In some embodiments adhesive is dispensed before or after the fiber is aligned to the optical device. 
     The details of one or more embodiments of the invention are set forth in the accompanying drawings and the description below. Other features, objects, and advantages of the invention will be apparent from the description and drawings, and from the claims. 
     DESCRIPTION OF DRAWINGS 
     FIG. 1A shows a side view of a fiber to optical device alignment system in a start position; 
     FIG. 1B shows the fiber to optical device alignment systems of FIG. 1 in an intermediate position; 
     FIG. 1C show the fiber to optical device alignment system of FIG. 1 in a final alignment position; 
     FIG. 2A shows a side view of a fiber holder with rotating mechanism; 
     FIG. 2B shows a front view of a fiber holder with rotating mechanism; 
     FIG. 3A shows a front view of a fiber-guide holder holding a fiber-guide; 
     FIG. 3B shows a side cross-sectional view of the fiber-guide of FIG. 3A with a fiber inserted; 
     FIG. 3C shows a side view of a second embodiment of a fiber-guide holder clamp holding a fiber-guide; 
     FIG. 3D shows another view of the fiber-guide holder clamp of FIG. 3C; 
     FIG. 4 shows an adhesive applicator and ultra-violet curing light attached to the system of FIG.  1 . 
     Like reference symbols in the various drawings indicate like elements. 
    
    
     DETAILED DESCRIPTION 
     Referring to FIGS. 1A-1C, a fiber to optical device alignment system  100  automatically aligns a stationary optical fiber  112  to an optical device  130  by moving a device box  132 , which contains an optical device  130 , and a capillary-shaped fiber-guide  140  held proximate to the device, towards fiber  112 . System  100  includes a base  110 , a fiber holder  115  mounted on base  110  and an overhead support member  120  mounted on base  110 . Two cameras  125  and  126  are mounted approximately 90° apart from each other to overhead support member  120  and have fixed focal planes proximate to the fiber tip  113  held in fiber holder  115 . System  100  includes a device carrier  138  for holding and moving optical device  130  towards fiber  112  and a fiber-guide holder  142  mounted to a fiber-guide carrier  144  for holding and moving fiber-guide  140  in-line with optical device  130  and fiber  112 . Both device carrier  138  and fiber-guide carrier  144  are constructed from “single-axis stages”, i.e., automated platforms (“stages”) that are movable in a single-axis, in this case, allowing device carrier  138  and fiber-guide carrier  144  to move in the same axis as the longitudinal axis of fiber  112 . Fiber-guide holder  142  includes an extendible arm with a fiber-guide clamp attached to the end of the arm for holding a fiber-guide  140 . The extendible arm moves orthogonally to the longitudinal axis of fiber  112 , therefore, extendible arm can move fiber-guide  140  and fiber tip  113  orthogonally to the surface of optical device  130  facing fiber tip  113  (see FIG.  1 C). 
     The system includes a computer processor  190  that has a memory, executable programs and input/output capabilities. Computer processor  190  is connected to receive inputs from cameras  125  and  126 ; the camera inputs are used by computer processor  190  to determine the location of fiber tip  113  relative to optical device  130 , as will be explained. Computer processor  190  also controls the movements of device carrier  138 , fiber-guide carrier  144  and the extendible arm of fiber-guide holder  142 . 
     Referring to FIGS. 1A-2, to operate system  100 , an operator places device box  132  against an adjustable stop  134  on device carrier  138 . Adjustable stop  134  allows different-sized device boxes to be mounted to device carrier  138 . Device box  132  includes optical device  130  mounted to a support  136  within device box  132  and also includes a feed-through tube  137  in a side of device box  132  that is roughly in-line with optical device  130  and a through-hole  139  in upright  136 . The operator then loads fiber  112  into fiber holder  115  by positioning fiber  112  length-wise into a v-groove  210  formed in the longitudinal center of the bottom of fiber holder  115  (see FIG.  2 ). V-groove  210  is mechanically referenced to optical device  130 , therefore the vertical position of fiber  112  relative to optical device  130  is roughly established. The operator roughly establishes the horizontal position of fiber tip  113  relative to optical device  130  by placing fiber tip  113  in the center of the field of view of cameras  125  and  126  when placing fiber  112  and before clamping fiber  112  into fiber holder  115 . 
     With optical device  130  and fiber  112  loaded on apparatus  100 , computer processor  190  executes an object recognition algorithm that determines the orthogonal coordinates of fiber tip  113  from the inputs received from cameras  125  and  126 . Computer processor  190  then moves device carrier  138  into an “intermediate position” (see FIG.  1 B). When device carrier  138  has moved into the intermediate position, computer processor  190  extends fiber-guide holder  142  into device box  132  to hold the center of fiber-guide  140  in the determined vertical position of fiber  112 . Computer processor  190  then moves device carrier  138  and fiber-guide carrier  144  simultaneously towards fiber  112  until feed-through tube  137  and fiber-guide  140  are slid over fiber tip  113 , thereby moving fiber tip  113  next to optical device  130  (“final position”, see FIG.  1 C). Fiber tip  113  will now be roughly aligned to optical device  130  and close enough to optical device  130  to ensure that some light from fiber  112  will couple into device  130 . At this point, computer processor  190  executes an active feedback algorithm and moves fiber-guide holder  142  so as to more closely align fiber tip  113  and device  130 , as will be explained. 
     Referring again to FIG. 1A, system  100  includes a signal detection and signal generation circuit  195  that is controlled by computer processor  190 . Circuit  195  has two input/output ports  198 B and  199 B connected to fiber  112 , at connector  198 A, and optical device  130 , at connector  199 A, respectively (the connection between  198 A and  198 B is not shown). If optical device  130  is a transmitting device, circuit  195  outputs a generated signal through port  199 A that causes the optical device  130  to output a signal to fiber  112  that is received as a detected signal on port  198 B. However, if optical device  130  is a receiving device, circuit  195  outputs a generated signal through port  198 B and receives a detected signal through port  199 B. At this point, computer processor  190  executes an active feedback control algorithm that moves the fiber-guide  140  and fiber tip  113  to hunt for and converge upon the location of fiber tip  113  that maximizes the detected signal, and therefore, maximizes the coupling of light between the optical device  130  and the fiber tip  113 . 
     Referring to FIGS. 2A and 2B, fiber holder  115  includes a fiber rotator  118  (for example, a “theta-wheel” clamp) that is controlled by computer processor  190 . Fiber rotator  118  holds fiber  112  in a fixed horizontal position relative to base  110  but also may rotate fiber  112  about its longitudinal axis to adjust the orientation of the polarity of fiber tip  113  relative to device  130 . Fiber rotator  118  is mounted near one end of an arm  220 . Arm  220  has a pivot pin  225  in the center of the arm  220  connected to fiber holder  115 , and a linear actuator  230  (for example, a pneumatic cylinder) connected to the opposite end of arm  220  from fiber rotator  118 , allowing fiber rotator  118  to open and close by retracting and extending piston  232 . As discussed previously, v-groove  210  is formed in the longitudinal center of the bottom surface of fiber holder  115  and is used to establish the vertical position of fiber  112  relative to optical device  130 . A servo-motor  250  is connected to fiber rotator  118  through gears  260  and  270 . The servo-motor is coupled to computer processor  190 , and when activated by computer processor  190  servo-motor  250  causes fiber rotator  118  to rotate about its longitudinal axis, thereby rotating fiber  112  and fiber tip  113  about the longitudinal axis of fiber  112 . 
     Referring again to FIG. 2B, in some cases, fiber tip  113 A may require longitudinal alignment to optical device for optimum performance. For example, fiber tip  113 A may be angled to achieve a reduction in possible back reflection from the end of fiber  112  of a light beam leaving fiber  112 . Or, fiber tip  113 A may be “lensed”, i.e., having a lens attached or formed at fiber tip  113 A. In addition, optical device  130  may be mounted at an angle relative to the longitudinal axis of fiber  112  so that any light that might be reflected back off optical device  130  will not re-enter fiber  112 . To minimize the back-reflected light between fiber tip  113  and an angular-mounted optical device  130 , computer processor  190  uses an active feedback control algorithm to rotate fiber  112  and fiber tip  113  until the back-reflected signal is minimized. 
     Referring to FIG. 3A, fiber-guide holder  142  includes upper arm  310  and lower arm  320  connected by pivot joint  322 . Lower arm  320  is a linear actuator that includes piston guide frame  340  and extendible piston  345  with fiber-guide clamp  360  connected to the end of piston  345 . A fiber-guide tray feeder  330  is attached to piston guide frame  340 , which automates the loading of fiber-guides  140 A- 140 N into fiber-guide clamp  360 . More specifically, under control of computer processor  190 , piston  345  extends or retracts, causing fiber-guide clamp  360  to load a successive fiber-guide  140 A- 140 N, with each extension of piston  345 . 
     Referring to FIGS. 3A and 3B, fiber-guide  140  is cylindrically-shaped and has a tapered central region  380  into which fiber  112  is inserted through the wider end and out the narrower end. Fiber-guide clamp  360  has a semi-circular shape that conforms to the outside of fiber-guide  140 . An airflow  365 , up through piston  345  and cylinder  320  holds fiber-guide  140  in clamp  360 . 
     Referring to FIGS. 3C and 3D, an alternative fiber-guide clamp  360 A includes a frame member  362  with an angled portion  364  an opposing arm  389  and a clamping arm  388 . Clamping arm  388  is connected to frame  362  via a pivot pin  387  through angled portion  364 . A closing spring  392  is connected between clamping arm  388  and frame member  362 . A linear actuator  382  with an extendible piston  384  is connected to one end of clamping arm  388  via connecting pin  386 . When air pressure is released from cylinder  382 , piston  384  is retracted into cylinder  382  and clamping arm  388  pivots towards opposing arm  389  to clamp and hold fiber-guide  140  under forces applied by spring  392 . 
     Referring to FIG. 4, system  100  may also include an adhesive applicator  400  and an ultra-violet light  410  to apply to and cure, respectively, an adhesive  432  to fiber  112  and fiber-guide  140  to bond them in position after final alignment of fiber tip  113  to optical device  130 . Adhesive applicator  400  and ultra-violet curing light  410  are mounted on a three-axis stage  420  that is mounted to overhead support member  120 . Three-axis stage  420  is an automated platform that is movable in all three orthogonal directions, in this case, allowing adhesive applicator  400  and ultra-violet curing light  410  to move into area adjacent to device box  132 , optical device  130  and fiber  112 . Adhesive applicator  400  includes an applicator tip  440  connected to an adhesive reservoir  430  containing a ultra-violet cured epoxy  432 . Computer processor  190  controls the movements of three-axis stage  420  and also controls the dispensing of adhesive  432  from the adhesive reservoir  430 . In operation, adhesive applicator  400  and curing light  410  are lowered by stage  420  until applicator tip  440  is proximate to fiber-guide  140  and fiber  112 . Adhesive  432  is injected through applicator tip  440  into fiber-guide  140 , then curing light  410  is turned on for an appropriate period of time to bond fiber  112  to fiber-guide  140 , and to bond fiber-guide  140  to upright  136 . Three-axis stage  420  allows applicator  400  and curing light  410  to be moved to other locations proximate to device box  132  for applying and curing adhesive  432 . For instance, adhesive  432  may also be applied to feed-through tube  137  to prevent water or contaminants from entering device box  132 . In some applications, fiber-guide  140  must have adhesive  432  applied between fiber-guide  140  and upright  136  before fiber  112  is inserted into fiber-guide  140 . In this case, adhesive applicator  400  is lowered into the device box  132 , proximate to upright  136  and dispenses adhesive  432  to upright  136  before the fiber-guide  140  is positioned into device box  132 . 
     Following the application and curing of adhesive  432 , adhesive applicator  400  and curing light  410  are retracted from device box  132 . Fiber-guide holder  142  is also retracted from device box  132 , allowing removal of device box  132  and fiber  112  from system  100 . 
     Though we have described specific embodiments, we do not intend to imply that there are not other ways to implement some of the features of those embodiments. For example, we mentioned using computer processor  190  to move various elements in the system. However, an operator could move those elements manually using the observation cameras  125  and  126 . The exterior shape of the fiber-guide  140  could be something other than cylindrical and, therefore, the fiber-guide clamp could be modified to hold other fiber-guide shapes. We also described manually loading the fiber and the device box into the system, however, one or both of these loading procedures could be automated using an appropriate automated parts handling system. We mentioned ultra-violet cured epoxy as the means by which various elements are attached to each other. However, any appropriate method which affixes one element to another could be used, such as fusing or soldering. We mentioned using UV curable adhesive to create an environmental seal between the fiber and the device feed-through tube, however, any appropriate material (adhesive or solder), or method (thermal cure, soldering or welding), for sealing feed-through could be used. We described the alignment of a fiber to an optical device that is mounted to an upright inside the device box. However, other mounting relationships of the optical device to the device carrier, with or without a device box, could be used with the system. The mounting of one or more of the cameras could be made directly to the base, that is, without the use of the support member. 
     The two cameras  125  and  126  do not necessarily have the same resolution, that is, one camera could have a higher resolution than the other camera, with the higher resolution camera being used to monitor the alignment of the fiber tip to the optical device. Also, the separation distance between the fiber tip and the optical device could be determined using the higher resolution camera, by having the computer processor execute an object recognition algorithm using the signal inputs from the higher resolution camera. We mentioned determining the coordinates of the fiber tip by having the operator roughly establishing the horizontal position of the fiber tip in the focal plane of cameras  125  and  126 , then executing an object recognition algorithm. In some applications, the processor  190  may rotate the fiber with the fiber rotator to cause the fiber tip to come into the focal plane of both cameras  125  and  126  before executing the object recognition algorithm. Furthermore, a third camera (not shown) could be mounted orthogonal to cameras  125  and  126  and used along with cameras  125  and  126  to determine the coordinates of fiber tip  113  with or without rotating fiber  112 . 
     We described the fiber-holder being mounted on a movable fiber-guide carrier, however, the fiber-guide holder could be mounted in a stationary position next to the fiber holder. In this case, the processor would first move the device carrier towards the fiber until the feed-through tube is slid over the fiber, at which point the processor would move the fiber-guide holder into the device box. Then the processor would move the device carrier towards the fiber causing the fiber-guide to be slid over the fiber and bringing the optical device and the fiber-guide next to the fiber tip. 
     We described the device carrier being constructed from a single-axis stage, and having a single-axis of motion, i.e., towards the longitudinal axis of a fiber held by the fiber holder. However, the device carrier could be constructed from a multiple-axis stage that could move towards the fiber in the first axis, and then could move the optical device orthogonally from the longitudinal axis of the fiber and into final alignment with the fiber. In this case, the fiber-guide holder would not be required to move the fiber into final alignment with the optical device. Furthermore, the multiple axis stage could be configured to have other ranges of motion, for instance pitch, roll and yaw movements, and could therefore pitch, roll or yaw the optical device relative to the fiber tip. 
     We described the adhesive applicator as being mounted on a three-axis stage that was attached to the support member. However, the adhesive applicator could be mounted on a one-axis or two-axis stage that is attached to the fiber-guide carrier. In this case, the fiber-guide carrier could move the adhesive applicator in one axis, towards the fiber, and the one-axis or two-axis stage could move the adhesive applicator orthogonally from the longitudinal axis of the fiber, therefore, moving the adhesive applicator near the optical device, the fiber or the feed-through tube. 
     A number of embodiments of the invention have been described. Nevertheless, it will be understood that various modifications may be made without departing from the spirit and scope of the invention. Accordingly, other embodiments are within the scope of the following claims.