Abstract:
The present disclose provides methods and systems for positioning a fiber end of an optical fiber. A block is provided having an opening for receiving the optical fiber. The optical fiber is positioned in the opening to constrain the optical fiber in at least one direction. The optical fiber has a first portion with a free end which is cantilevered or extends from the block. The optical fiber is moved against the at least one direction which is constrained. The movement is provided from a position on a second portion of the optical fiber, which is opposite the first portion relative to the block. This movement causes a lateral displacement of the free end.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to optical fibers, and more particularly, to a system and method for positioning and aligning optical fibers by employing means for pivoting an optical fiber thereby providing accurate positioning of the fiber endface. 
     2. Description of the Related Art 
     Transmitting Optical Subassemblies (TOSA) are hardware components in a fiber optic data link disposed at the transition point from an electrical signal to an optical signal. Near the point where a fiber in the fiber optic data link approaches a laser where the electrical signal is used to create the optical signal, the fiber must be mechanically aligned and held in position. Proper alignment of a fiber&#39;s endface with an optically active portion of the laser is necessary to provide coupling of the laser light into the fiber. 
     Therefore, a need exists for a system and method which accurately holds optical fibers in position and aligns the fiber end for optical signal transfer or other uses. 
     SUMMARY OF THE INVENTION 
     The present disclosure provides methods and systems for positioning a fiber end of an optical fiber. A block is provided having an opening for receiving the optical fiber. The optical fiber is positioned in the opening to constrain the optical fiber in at least one direction. The optical fiber has a first portion with a free end which is cantilevered or extends from the block. The optical fiber is moved against the at least one direction which is constrained. The movement is imposed upon the optical fiber from a position on a second portion of the optical fiber, which is opposite the first portion relative to the block. This movement causes a lateral displacement of the free end. 
     In useful embodiments of the present disclosure, a mechanical means for holding an optical fiber in position using the combination of, for example, a v-groove to constrain the fiber in two directions and a pivot point to force a displacement (in either of two directions) on one side of the pivot point due to a displacement on the other side is disclosed. 
     The pivot v-groove may be located along the fiber in close proximity to the endface of the fiber. The pivot v-groove and the laser may be disposed upon a substrate. An alignment and fixing operation is preferably performed to bring and hold the endface of the fiber into mechanical proximity to the optically active portion of the laser. A system for positioning a fiber end of an optical fiber, in accordance with the present invention, includes a block having an opening for receiving the optical fiber and constraining the optical fiber in at least one direction. A reference is disposed a first distance from the block against which the optical fiber is to be aligned. A positioning system is disposed a second distance from the block on an opposite side of the block relative to the reference, and the positioning system moves the optical fiber laterally relative to the block to cause a lateral displacement of a fiber end on the side of the block where the reference is disposed such that alignment between the fiber end and the reference is achieved. 
     An optical subassembly, in accordance with the present invention includes a block having an opening extending in an axial direction through the block. The opening receives an optical fiber and constrains the optical fiber in at least one direction. A reference is disposed a first distance from the block. A fiber end portion of the optical fiber forms an angle relative to the axial direction of the opening such that a fiber end of the optical fiber is aligned with the reference to provide optical power transfer between the fiber end and the reference. 
     These and other objects, features and advantages of the present invention will become apparent from the following detailed description of illustrative embodiments thereof, which is to be read in connection with the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF DRAWINGS 
     The invention will be described in detail in the following description of preferred embodiments with reference to the following figures wherein: 
     FIG. 1 is a perspective view of a v-groove adapted for use in accordance with the present invention; 
     FIG. 2 is a perspective view of a v-groove block, a laser pedestal and a fiber pedestal disposed on a substrate in accordance with the present invention; 
     FIG. 3 is a perspective view of a v-groove block with a fiber positioned therein, the fiber being held by a holder to provide positioning of the fiber in accordance with the present invention; 
     FIG. 4 is a top view of the v-groove block of FIG. 3 showing a fiber end displaced in a lateral negative x direction to illustrate the pivoting action resulting from a lateral positive x motion of a holder ( 18 ) in accordance with the present invention; 
     FIG. 5 is a perspective view of a substrate with a reference (e.g., laser), a fiber block, and a pad structure for aligning and holding an optical fiber in position, and a holder/stage for positioning the fiber in accordance with the present invention; 
     FIGS. 6A and 6B depict alternate orientations of a v-groove block on a substrate in accordance with the present invention; 
     FIGS. 7A-D depict alternate fiber constraints in accordance with the present invention; 
     FIG. 8 is a perspective view showing an adhesive disposed on a fiber in a region of a v-groove to establish a mechanical link between the fiber and v-groove in accordance with the present invention; 
     FIG. 9 is a side view showing a buffer layer stripped off an optical fiber for use in accordance with one embodiment of the present invention; 
     FIG. 10 is a perspective view of the fiber of FIG. 9 showing an adhesive being applied to the fiber in accordance with the present invention; 
     FIG. 11 is a perspective view of the fiber of FIG. 10 showing the adhesive after being applied to the fiber in accordance with the present invention; 
     FIG. 12 is a perspective view of the fiber of FIG. 11 showing the adhesive being cured in accordance with the present invention; 
     FIG. 13 is a perspective view of an alignment device showing a fiber being aligned to a laser or reference in accordance with the present invention; and 
     FIG. 14 is a perspective view of a portion of an optical subassembly with a fiber aligned in accordance with the present invention. 
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     The present disclosure includes a mechanical device for holding an optical fiber in position using a fiber chuck or holder to constrain the fiber preferably in two directions and provide a pivot point to force a displacement (in either of two directions) on one side of the pivot point due to a displacement on the other side. Rotation about the pivot point may be provided by permitting relative motion with respect to the block holding the fiber. Alternately, a bulbous mass may be formed on the fiber to provide a rocking motion for pivoting a fiber endface. The present invention is also directed to an optical subassembly, which includes an optical fiber aligned to a laser source, etc. in accordance with the methods of the present invention. Referring now in detail to the figures in which like numerals represent the same or similar elements and initially to FIG. 1, a v-groove block  12  is shown for holding and/or constraining an optical fiber. An opening  10  is shown in an “upward” orientation. This orientation will be employed to describe an illustrative embodiment of the present invention. It is to be understood that block  12  may include grooves or other structures etched into a substrate or an other fiber constraining structure. In the illustrative example, opening  10  includes two surfaces oriented at an angle to form a “V,” hence v-groove. The v-groove block is configured to constrain a cylindrically shaped object such as an optical fiber (not shown). The cylindrically shaped fiber rests in the v-groove (a force may be applied to hold the fiber in contact with sidewalls of the v-groove). 
     Edge  11 , for purposes of the present disclosure, is oriented in the axial direction (axial direction of the fiber) and is the axial length of the v-groove  12 . The fiber (not shown) rests in opening  10 . V-groove block  12  is a mechanical element into which opening  10  is formed. Block  12  may have edges  13  broken, e.g., chamfered or radiused to reduce the risk of damage to the fiber. The thickness of block  12  is preferably small. In this way, pivoting of the optical fiber is easily accomplished. The v-groove may be 1) formed from metal, for example, copper or brass, plated with metal, such as gold, or formed from other suitable materials, such as graphite, etc., 2) formed from wire (formed over a slot or v-groove in the substrate), 3) molded into a metal substrate, or 4) etched or otherwise formed into a substrate (silicon, plastic, sintered metal, glass, etc.). The length of the v-groove (the z or axial direction) in one embodiment (the v-grooved formed in copper sheet material) is about 150 microns. A preferred range of v-groove lengths is from about 5 to 250 microns for 125/250 micron diameter fiber. 
     Referring to FIG. 2, in one illustrative application of the present invention, block  12  is disposed upon a substrate  13 . A laser pedestal  14  is mounted on substrate  13 , and a laser  15  is mounted on laser pedestal  14 . A fiber pedestal  16  is a spacer/mechanical feature to which a fiber may attach to provide mechanical strain relief. Fiber pedestal  16  may include a pad or structure for contacting a fiber. (See FIG.  5 ). 
     Referring to FIG. 3, block  12  is shown with a fiber  17  placed within opening  10 . A holder  18  grips fiber  17  and is mounted upon a multi-axis stage  29 . As holder  18  moves in response to displacements made by the multi-axis stage, a controlled portion  19  of fiber  17  moves and bends. An end portion or cantilevered portion  20  of fiber  17  also moves in response to motions of holder  18 . The v-groove of block  12  acts as a pivot point for transverse (X and Y) motions of holder  18 . 
     An endface  21  of the fiber is cantilevered from the v-groove block  12 . The remaining portion of the fiber (in region  19 ), called a controlled portion of the fiber, is mechanically held by a holder  18  which, in turn, is mounted on the multi-axis stage  29 . Moving one of the axis components of the multi-axis stage moves, of course, the controlled portion  19  of the fiber. In turn, cantilevered portion  20  of fiber  17  is moved correspondingly in the opposite direction due to a pivot point created at block  12 . 
     An axial motion (z-direction) of fiber  17 , accomplished by moving a Z axis stage of the multi-axis stage, creates a motion of endface  21  (motion is substantially perpendicular to endface  21  with slight displacement in the x or y directions) of the controlled portion  19  of fiber  17 . The x or y components would be small. A positive Z motion of holder  18  results primarily in a positive Z motion of the endface. A transverse motion of fiber  17 , accomplished by moving an X (or Y) axis stage of the multi-axis stage, creates, primarily, an X (or Y) motion of the endface (motion parallel to endface  21 , nominally) of the controlled portion  19  of the fiber  17 . A positive X (or Y) motion of the holder results in a negative X (or Y) motion of endface  21 . Advantageously, the present invention provides a lateral displacement of fiber  17  which enables appropriate alignment relative to a reference. 
     Referring to FIG. 4, a top down view of v-groove block  12  with fiber  17  disposed in opening  10  is shown. Holder  18  is in a position displaced from rectilinear alignment in the +X direction to illustrate the pivoting action resulting from a lateral positive X motion of holder  18 . Cantilevered portion  20  of fiber  17  is angularly displaced from the center of v-groove opening  10 . A corresponding shift in the negative X direction of endface  21  is also shown. 
     Controlled portion  19  is shown with an arc to illustrate how fiber  17  responds to the illustrated displacement of holder  18 . Fiber  17  is in contact with portions of both sidewall  22  and sidewall  23  of the v-groove. Sidewalls  22  and  23  may be radiused or chamfered to protect fiber  17 . 
     Referring to FIG. 5, a perspective view of substrate  13  with the various components, including fiber  17  in an aligned position is shown. A distance D 1  from the pivot v-groove  12  to holder  18  is much larger than a distance D 2  from the pivot v-groove  12  to a laser, resulting in a mechanical advantage when adjusting fiber  17  to provide appropriate alignment with laser  15 . A relatively crude transverse motion of controlled portion  19  of fiber  17  creates a fine transverse motion of cantilevered or endface portion  20  of fiber  17 . The present invention may provide any range of mechanical advantages, for example, mechanical advantages in the range from 2 to 20 would be particularly useful. 
     V-groove  12  is preferably oriented on a top of substrate  13  such that an open portion of the v-groove is open to or accessible from the top of substrate  13 . The fiber  17  is brought down into the v-groove from the top of the substrate  13 . The fiber is carefully positioned within a V portion of the v-groove such that intimate contact is formed between a left and a right sidewall of the v-groove simultaneously. Holder  18  may be tilted down slightly (e.g., from about 2 to about 5 degrees) toward the v-groove block  12  and the y axis stage lowered to a point where holder  18  forces controlled portion  19  of fiber  17  to form a slight arc  28 , thereby applying force upon the sidewalls of the v-groove  12  by fiber  17 . Subsequent x and y motions of the controlled portion  19  of fiber  17  (introduced by the multi-axis stage) cause the endface to move correspondingly without, over a useful range, driving the fiber from the v-groove. 
     Once positioned fiber  17  can be secured in place with an adhesive or a clamp designed to secure fiber  17  in place. In preferred embodiments, endface  21  of fiber  17  is positioned to transmit or receive optical signals to/from an optical sensor/a laser or light emitting diode. 
     While the embodiment described above implements a v-groove oriented such that an open end of the v-groove is “up,” alternatives to this structure are contemplated. As shown in FIGS. 6A and 6B, the v-groove may be oriented “down” (FIG. 6A) or sideways (FIG.  6 B). Alternatively, the idea of an upward and a downward v-groove may be combined to form a feature having both upward and downward v-grooves, as shown in FIGS. 7A and 7B. Holes  30  may be employed with different shapes as shown in FIGS. 7A-7D. Other configurations may also be employed and are within the scope of the present invention. Portions of a shaped hole  30  can be used as a pivot point, as described above. In many of these alternatives, the fiber is inserted into an opening or hole  30  by moving the fiber axially through the opening  30 . This is not difficult provided means are provided for setting up and observing the endface of the fiber in preparation for entering the opening. 
     Referring to FIG. 8, an alternate embodiment of the present invention is shown. An adhesive  24 , such as an ultraviolet curable adhesive, is applied to fiber  17  to at least partially surround fiber  17 . Adhesive  24  is provided such that regions of the v-groove contact fiber  17  on areas where adhesive is present. For example, adhesive  24  contacts sidewall  22  and sidewall  23  establishing a mechanical link between fiber  17  and v-groove block  12 . Surface tension of a liquid adhesive helps to maintain fiber  17  in contact with surfaces  22  and  23 . 
     Once cured, adhesive  24  locks in the position of fiber  17  relative to a laser beam (not shown), or other reference in which alignment is to be made. 
     In another embodiment, adhesive  24  may be cured on fiber  17  to form a bulbous mass. The bulbous mass may be employed as a contact surface with the v-groove and be used as a rocker mechanism to provide mechanical advantage during the pivoting of fiber  17 . Additional adhesive  24  may be added and cured (e.g., by UV irradiation) to hold the position of the fiber once aligned. 
     Referring to FIGS. 9 and 10, a buffer layer  50  of optical fiber  17  may be removed from a portion of fiber  17  to expose glass  52 . In one example, buffer layer  50  may be removed to, e.g., about 5 mm from end face  21 . 
     A dispenser  54 , which may include a necked down glass rod with a ball ( 53 ) on the end, a syringe or other adhesive dispensing device, is employed to apply adhesive  24  at a position near endface  21  on exposed glass  52  of fiber  17 . In one example, adhesive  24  is applied at a distance of about 1 mm from endface  21 . Fiber  17  may be rotated about its longitudinal axis to provide uniform wetting of glass  52  at the position of application. Adhesive material  24  remains on fiber  17  providing a local coating at the point of application, as shown in FIG.  11 . 
     Referring to FIG. 12, adhesive material  24  is cured to form a bulbous  55  mass on fiber  17 . If a UV curable adhesive is applied, UV light  56  from a UV source  58  is employed to cure adhesive  24 . Since adhesive  24  is preferably a composition which does not readily wet fiber  17 , adhesive  24  “balls up” to form a local, droplet of adhesive (bulbous mass  55 ). 
     Referring to FIG. 13, after mass  55  is formed, fiber  17  is positioned in a v-groove or other constraining structure  60  (see, e.g., FIGS. 6A-B and  7 A-D). Structure  60  may already provide course (or fine) alignment of fiber  17  (e.g., within 50 microns of alignment of a solid state laser  15 ). The surface of droplet or mass  55  rests in a groove of structure  60  and contacts surfaces of the groove to provide a pivoting motion of fiber  17 . By moving a portion of fiber  17  opposite from endface  21  using a positional system  62 , small motions of endface  21  are achieved. These motions provide alignment of endface  21  with a laser beam from laser  15 . Both X and Y motions may be achieved in this fashion. When laser  15  is activated and coupled laser power is monitored at the far end of the fiber (opposite endface  21 ), the alignment of the fiber endface  21  to laser  15  is readily achieved by progressively moving stages of positioning system  62  while observing optical power output. Once the desired level of alignment is achieved (i.e., desired coupled power), an adhesive or other compound can be applied to fiber  17  so that the adhesive flows over mass  55  and wicks into the groove of structure  60 . After checking alignment and adjusting if necessary, the adhesive is then cured (e.g., UV cured adhesive) to hold the position of fiber  17 . It should be noted that the desired coupled power may or may not include the maximum power. Alignment may be to a power of a predetermined value, e.g., compatible with receiver device specifications. In addition, tuning may be performed to achieve the desired power level. 
     Structure  60  may include a material compatible with glass fibers, for example, silicon or glass. Structure  60  may include an etched cavity  61  formed to receive laser  15 . A groove  63  may also be etched into structure  60  to provide some alignment with laser  15 . Other structures are also contemplated. 
     It is to be understood the present invention may be employed for a plurality of fiber optic applications. These applications may include aligning fibers to receiver or transmitter devices, aligning fibers to other fibers, aligning fibers for mechanical connections, etc. In other embodiments, mass  55  may include a split-half (clam shell) mechanical link (e.g., using lead or other materials connected to fiber  17 ) or a ferrule or other device which can be slipped over the fiber end  21  and positioned to provide a pivot point. Structure  60  may also include a block  12 , as described above, to permit a large range of motion for fiber  17 . 
     Referring to FIG. 14, an optical subassembly  100  is shown in accordance with the present invention. Optical subassembly  100  may include, for example, a transmitting optical subassembly (TOSA). A block  12  has an opening  10  extending in an axial direction through the block. The axial direction is indicated by arrow “F”. Opening  10 , e.g., a v-groove, receives an optical fiber  17  and constrains the optical fiber in at least one direction. A reference  15 , which preferably includes a solid state laser, is disposed a first distance from block  12 . A fiber end portion  20  of the optical fiber forms an angle relative to the axial direction of the opening such that a fiber end  21  of the optical fiber  17  is aligned with the reference to provide optical power transfer between the fiber end and the reference. Fiber  17  may be connected to a receiver or other opto-electronic equipment  101 , which are not part of subassembly  100 . The angled fiber placement is a result of the alignment process of fiber  17  in accordance with the present invention. Other portions of optical subassembly  100  may include conventional components. 
     Having described preferred embodiments of a fiber pivot for optical alignment (which are intended to be illustrative and not limiting), it is noted that modifications and variations can be made by persons skilled in the art in light of the above teachings. It is therefore to be understood that changes may be made in the particular embodiments of the invention disclosed which are within the scope and spirit of the invention as outlined by the appended claims. Having thus described the invention with the details and particularity required by the patent laws, what is claimed and desired protected by Letters Patent is set forth in the appended claims.