Patent Publication Number: US-2011075976-A1

Title: Substrates and grippers for optical fiber alignment with optical element(s) and related methods

Description:
BACKGROUND 
     1. Field of the Disclosure 
     The technology of the disclosure relates to the alignment of an optical fiber(s) to an optical element(s) that emits light onto and/or receives light from the optical fiber(s). 
     2. Technical Background 
     Optical systems can include optical elements that transmit light onto and receive light from an optical fiber for light signal transfer. In such systems, alignment of the optical elements with respect to the optical fiber optimizes light signal transfer between the optical elements and the optical fiber. It may be desirable in many photonic applications to have precise alignment of optical fibers to optical elements that emit or receive light. Examples of such optical elements include optical components such as, but not limited to, laser sources, detectors, lens, filters, isolators, or other optical fibers. In this regard, the end of an optical fiber is positioned and aligned over an optical element on a substrate. Active alignment of optical elements may be dependent on operator skill in determining the alignment of the elements and affixing the elements in place. However, active alignment also typically employs expensive equipment to generate and monitor optical signals to assist or confirm proper alignment. 
     An alternative to active alignment is passive alignment. Passive alignment involves aligning optical elements by mechanical means and securing the elements in place. Typical mechanical alignment means include V-grooves, alignment blocks, jigs, and fixtures adapted to align an optical element to a substrate. Passive alignment may be advantageous in terms of cost in that it may not require equipment to generate and monitor optical signals to assist or confirm alignment of the optical elements with optical fiber. However, one possible trade off of passive alignment is a less accurate alignment. Another possible trade off of passive alignment is that it may result in a reduction in light signal transfer due to the absence of equipment to generate and monitor optical signals to assist or confirm proper alignment. 
     SUMMARY OF THE DETAILED DESCRIPTION 
     Embodiments disclosed in the detailed description include apparatuses and methods for the alignment of an optical fiber over an optical element on a substrate. In one embodiment, a substrate having an optical element and at least one gripper element is provided. The at least one gripper element is positioned proximate the optical element along an axial path of an optical fiber, such that when the optical fiber is moved along the axial path until an end of the optical fiber makes contact with the at least one gripper element, the optical fiber is aligned with the active optical element. By positioning the one or more grippers in the axial path of the optical fiber such that an optical fiber may be moved along the axial path until the end of the optical fiber comes in contact with the one or more grippers, the optical fiber may be easily and accurately aligned over an optical element on a substrate. In certain embodiments, the optical fibers may be laser angle-cleaved optical fibers with shaped fiber ends, such as laser angle-cleaved wedge or taper structures. The optical element(s) may be an active optical element(s). 
     Other embodiments include methods of aligning an optical fiber over an optical element on a substrate. One exemplary method comprises providing at least one gripper element proximate the optical element and in an axial path of the optical fiber, and moving the optical fiber along the axial path until the optical path is in contact with the at least one gripper element such that the optical fiber is aligned with the optical element. 
     Additional features and advantages 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 embodiments as described herein, including the detailed description that 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 present embodiments, and are intended to provide an overview or framework for understanding the nature and character of the disclosure. The accompanying drawings are included to provide a further understanding, and are incorporated into and constitute a part of this specification. The drawings illustrate various embodiments, and together with the description serve to explain the principles and operation of the concepts disclosed. 
    
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
         FIG. 1  is a planar view of an exemplary embodiment of grippers on a planar substrate arranged proximate an optical element; 
         FIG. 2  is a planar view showing an exemplary embodiment of an initial insertion of a laser angle-cleaved optical fiber into grippers arranged proximate an optical element on a planar substrate; 
         FIG. 3A  is a side view of an exemplary embodiment of a laser angle-cleaved optical fiber after insertion into the grippers, showing fiber motion as pressure is applied along an axis of the optical fiber; 
         FIG. 3B  is a side view of an exemplary embodiment of a laser angle-cleaved optical fiber after insertion showing contact between a tip of the laser angle-cleaved optical fiber and a gripper positioned in an axial path of a laser angle-cleaved optical fiber; 
         FIG. 4  is a planar view of an exemplary embodiment of a laser angle-cleaved optical fiber held in position by grippers over an optical element; 
         FIG. 5  is a side view of an exemplary embodiment of a laser angle-cleaved optical fiber forced down into contact with an optical element by a gripper sidewall; 
         FIG. 6  is a planar view showing an exemplary embodiment of self-alignment of a laser angle-cleaved optical fiber to an optical element using an alternative angled gripper alignment; 
         FIG. 7  is a planar view showing an exemplary embodiment of self-alignment of a laser angle-cleaved optical fiber to an optical element using an alternative C-shaped gripper embodiment; 
         FIG. 8  is an exemplary embodiment of side tapers on an end of a laser angle-cleaved optical fiber for self-alignment to an optical element; 
         FIG. 9  is a planar view showing an exemplary embodiment of a laser angle-cleaved optical fiber with side tapers being self-aligned to an optical element using a C-shaped gripper; 
         FIG. 10  is a side view of an exemplary embodiment of a tip-removed laser angle-cleaved optical fiber being self-aligned via grippers over an optical element; 
         FIG. 11A  illustrates a standard ultraviolet (UV) exposure process used to fowl polymer grippers, where the direction of the UV exposure is close to the substrate normal direction; 
         FIG. 11B  illustrates a modified UV exposure process used to form polymer grippers with steeper sidewall angles, wherein at least one direction of the UV exposure is at a sharper angle with respect to the substrate normal direction; and 
         FIG. 12  is a side view showing an alternative exemplary embodiment of self-alignment of a laser angle-cleaved optical fiber to an optical element. 
     
    
    
     DETAILED DESCRIPTION 
     Reference will now be made in detail to the embodiments, examples of which are illustrated in the accompanying drawings, in which some, but not all embodiments are shown. Indeed, the concepts may be embodied in many different forms and should not be construed as limiting herein; rather, these embodiments are provided so that this disclosure will satisfy applicable legal requirements. Whenever possible, like reference numbers will be used to refer to like components or parts. 
     Embodiments disclosed in the detailed description include apparatuses and methods for the alignment of an optical fiber over an optical element on a substrate using at least one gripper positioned proximate the optical element and in an axial path of the optical fiber such that the end of the optical fiber is in contact with the at least one gripper. By positioning the at least one gripper in the axial path of the optical fiber such that the end of the optical fiber is in contact with the at least one gripper, the optical fiber can be accurately aligned over an optical element on a substrate. In certain embodiments, the optical fibers may be laser angle-cleaved optical fibers with shaped fiber ends, such as laser angle-cleaved wedge or taper structures. 
     Low-cost passive alignment of optical fiber and fiber arrays to active devices (lasers and detectors) may be addressed using various fiber alignment structures. For example, fibers may be aligned to active devices using silicon V-groove structures or multi-layer ceramic substrates with integrated grooves. Fibers may also be held in place using deformable plastic, metal, or polymeric members that apply downward pressure on fibers to hold them in the groove structure. Such structures are referred to as “grippers” or “restraining members.” 
     The grippers according to one embodiment may be formed in a photosensitive elastic polymeric material that is photolithographically patterned on a planar substrate. The grippers can be created by first spin depositing a relatively thick layer (e.g., 50-200 μm) of polymer material over the entire surface of the substrate. Photolithographic exposure and development processing creates a significant sidewall undercut, with the topside width of the gripper always wider than the bottom width. 
     The grippers may be formed adjacent to regions where optical components are to be held in place. For example, when forming grippers for optical fibers two parallel grippers may be generally positioned on either side of the location where the optical fiber is to be positioned. The gap between the parallel grippers may be set to be less than the diameter of an optical fiber at the top and more than the diameter of an optical fiber at the bottom. When the optical fiber is inserted between the parallel grippers, each gripper deforms slightly. After application of sufficient pressure on the optical fiber, the bottom surface of the optical fiber is in contact with the substrate surface. The gripper sidewalls may generate a compression force to hold the optical fiber in position in both the horizontal and vertical directions. The amount of pressure applied by the grippers can be modified by adjusting the gap between the grippers (via photolithography) or altering the properties of the gripper polymer material. 
     An advantage of using grippers, such as polymer grippers, is that it enables low-cost passive alignment of tapered fibers or fiber arrays to active optical devices. In some embodiments, alignment can be achieved with an accuracy of plus or minus 5 microns. In addition, the polymer gripper layout can be easily modified via photolithographic mask modification to accommodate any type of fiber end treatment (e.g., wedges or tapers). 
     In this regard,  FIG. 1  is a planar view of an exemplary embodiment of grippers on a planar substrate arranged near an active optical element, such as a vertical cavity surface emitting laser (VCSEL), or a photodetector.  FIG. 1  provides an example plan layout of a planar substrate  10  having grippers  12 A,  12 B, and  14  and an optical element  16 . The gripper  12 A has a top surface  12 A-T and a base  12 A-B in this embodiment. The gripper  12 B has a top surface  12 B-T and a base  12 B-B. The grippers  12 A and  12 B may be comprised of laterally spaced flexible strips attached to the surface of the substrate  10 , thereby forming an axial path  17  that has an axis A 1  that runs laterally through the optical element  16  on the substrate  10 . The grippers  12 A and  12 B may be positioned such that that they are parallel to the axis A 1 , and may be referred to as side grippers. 
     The gripper  14  is a structure positioned such that it is along the axis A 1  that runs laterally through the optical element  16  on the substrate  10 . The gripper  14  has a top surface  14 -T and a base  14 -B. The gripper  14  may be positioned proximate the optical element  16  and on the opposite side of the optical element  16  from grippers  12 A and  12 B, and may be referred to as an end gripper. 
     The substrate  10  may include one or more optical elements  16 . Although  FIG. 1  only shows a single optical element  16 , it is to be understood that there may be multiple optical elements  16 . The optical element  16  may be a VCSEL device, a photodetector, or any other optical element, including but not limited to optical fibers, lenses, filters, lensed fibers, optical isolators, and the like. The optical element  16  may be designed to transfer light to and/or from optical fibers or other optical elements. Likewise, although  FIG. 1  shows three grippers  12 A,  12 B, and  14 , any number of grippers or other restraining members may be used to receive and align optical elements. The three grippers  12 A,  12 B, and  14  are photolithographically patterned near the optical element  16 . The grippers  12 A,  12 B, and  14  may be made of a flexible polymer in one embodiment. Further, the grippers  12 A,  12 B, and  14  in one embodiment may be formed using a variety of techniques such as well-known lithographic processes using photopolymerizable compositions and the like. 
     For example, a photopolymerizable composition can be substantially uniformly deposited onto a substrate surface, such as the substrate  10 . The photopolymerizable composition is then imagewise exposed to actinic radiation using a laser and a computer-controlled stage to expose precise areas of the composition with an ultraviolet laser beam, or a collimated ultraviolet (UV) lamp together with a photomask having a pattern of substantially transparent and substantially opaque areas. The nonimaged areas can then be removed with solvent, while leaving the imaged areas in the form of at least one gripping element on the substrate surface. 
     Alternatively, one or more of the grippers  12 A,  12 B, and  14  can be formed by using a soft, flexible embossing tool to pattern the polymerizable composition in the form of at least one gripper element on the substrate  10 . Such soft tooling is commonly made with silicones. The composition is then cured and the tool is removed. The flexibility of the tool must be sufficient so that it can be removed from the cured polymer without damaging the grippers. The polymerizable composition may be cured by various means such as actinic radiation or heat, and should have the viscosity to conform to the raised features of the tool. After removing the tool from the cured composition, at least one gripper will remain on the substrate  10 , depending on the nature of the pattern. The pattern of the tool may include a plurality of gripping elements to provide a substrate for aligning an array of optical fibers and lenses. Suitable polymeric compositions for making the gripping elements are disclosed in commonly assigned U.S. Pat. No. 6,266,472, which is incorporated herein by reference. 
     With continuing reference to  FIG. 1 , the side gripper  12 A has a base  12 A-B attached to a surface of the substrate  10  and a top surface  12 A-T in a plane parallel to the plane of the substrate  10 . The side gripper  12 B has a base  12 B-B attached to a surface of the substrate  10  and a top surface  12 B-T in a plane parallel to the plane of substrate  10 . The end gripper  14  has a base  14 -B attached to a surface of the substrate  10  and a top surface  14 -T in a plane parallel to the plane of the substrate  10 . Each of the side grippers  12 A and  12 B and the end gripper  14  may have a top surface that is wider than its base, such that a footprint of the base of each of the grippers is smaller than the top surface of the grippers. This allows the grippers  12 A,  12 B, and  14  to contact an optical fiber and generate a compression force to hold the optical fiber in position in both the horizontal and vertical directions, while still allowing the optical fiber to move in the axial path  17  along the axis A 1 . This will be shown in more detail in  FIGS. 3A and 3B  and discussed below. 
       FIG. 2  is a planar view that is similar to planar view of  FIG. 1  of grippers on a planar substrate arranged near an active optical element substrate, but  FIG. 2  also shows an exemplary embodiment of an initial insertion of a laser angle-cleaved optical fiber  18  into the grippers  12 A and  12 B on the substrate  10  arranged near the optical element  16 . Note that although  FIG. 2  shows a laser angle-cleaved optical fiber  18  being inserted, the optical fiber  18  does not have to be laser angle-cleaved. Other optical fibers may be used in place of the laser angle-cleaved optical fiber  18 . As one non-limiting example, optical fibers that provide an end, or tip, that is angled via a polishing operation, may be inserted into the grippers  12 A and  12 B on the substrate  10  arranged near the optical element  16 . Referring once again to  FIG. 2 , the laser angle-cleaved optical fiber  18  has a laser angle-cleaved end facet  20  and an internal fiber core  22 . In one embodiment, the laser angled end-facet  20  may comprise a single facet. In other embodiments, the laser angled end-facet  20  may comprise multiple facets, or a large number of facets that approximate a curved facet surface, where the curvature of the curved facet surface may be uniaxial or biaxial. In an example embodiment, the laser angle-cleaved optical fiber  18  is laser cleaved such that the laser angle-cleaved end facet  20  is formed at or near 45 degrees, or at other angles relative to the optical fiber axis that provide improved optical performance (e.g., reduced back reflection, increased bandwidth, etc.). The pointed shapes of the end of the laser angle-cleaved optical fiber  18  facilitate insertion of the laser angle-cleaved optical fiber  18  into channels formed by the grippers  12 A and  12 B on the substrate  10 . When it is desired to align the laser angle-cleaved optical fiber  18  over the optical element  16 , the laser angle-cleaved optical fiber  18  is inserted from the right side of  FIG. 2  into the two right-side grippers  12 A and  12 B. The laser angle-cleaved optical fiber  18  is inserted from the right side of  FIG. 2  and is moved to the left along the axis A 1  by applying pressure along the axis of the laser angle-cleaved optical fiber  18 . This is referred to as moving along an “axial path” of the laser angle-cleaved optical fiber  18 . The grippers  12 A and  12 B are positioned such that they are parallel to the axial path of the laser angle-cleaved optical fiber  18  as the laser angle-cleaved optical fiber  18  is inserted. The gripper  14  is positioned such that it is in the axial path of the laser angle-cleaved optical fiber  18 . Each of the grippers  12 A,  12 B, and  14  has a base portion attached to a surface of the substrate  10 , a top surface which may be substantially parallel with the surface of the substrate  10 , and side walls which provide a groove or channel between the grippers  12 A and  12 B. The sidewalls of each gripper  12 A,  12 B, and  14  may be angled somewhat, but should be sufficiently flat so that each of the grippers  12 A,  12 B, and  14  may contact the laser angle-cleaved optical fiber  18  in at least one point. 
       FIG. 3A  is a side view of an exemplary embodiment of the laser angle-cleaved optical fiber  18  in  FIG. 2  after insertion into the grippers  12 A and  12 B, showing fiber motion to the left as pressure is applied along the axis of the laser angle-cleaved optical fiber  18 . While the grippers  12 A and  12 B (gripper  12 B is not shown in the side view of  FIG. 3A ) hold the laser angle-cleaved optical fiber  18  in close proximity to the substrate  10 , their gripping pressure on the laser angle-cleaved optical fiber  18  can be adjusted to allow the laser angle-cleaved optical fiber  18  to slide further to the left as pressure is applied along the axis of the laser angle-cleaved optical fiber  18 , as shown in  FIG. 3A . 
     As the alignment process continues, the laser angle-cleaved optical fiber  18  is continually moved to the left until contact is made between a tip of the laser angle-cleaved optical fiber  18  and the gripper  14  on the left side of  FIG. 3B . The gripper  14  is positioned in the axial path of the laser angle-cleaved optical fiber  18 , and is positioned such that when the tip of the laser angle-cleaved optical fiber  18  makes contact with the gripper  14 , the laser angle-cleaved optical fiber  18  is positioned over the optical element  16 . In one embodiment, the gripper  14  may be positioned perpendicular to the axis of the laser angle-cleaved optical fiber  18 . 
     The laser angle-cleaved optical fiber  18  is laser angle-cleaved such that an end of the laser angle-cleaved optical fiber  18  is cleaved at an angle α relative to the axis A 1 . In one embodiment, the end of the laser angle-cleaved optical fiber  18  is laser-cleaved such that the angle α is formed at or near 45 degrees. The end gripper  14  is wider at the top than it is at the base. In one embodiment, the end gripper  14  has a sidewall  15  having an angle θ relative to the axis A 1 . It may be desirable to coordinate the sidewall angle θ of the end gripper  14  and the angle α of the end of the laser angle-cleaved optical fiber  18  in order to stop the axial movement of the laser angle-cleaved optical fiber  18  for accurate alignment of the laser angle-cleaved optical fiber  18  with the optical element  16 , while at the same preventing damage to either the end gripper  14  or the end of the laser angle-cleaved optical fiber  18 . The angle α of the end of the laser angle-cleaved optical fiber  18  can be any angle, although in certain embodiments the angle α will be between 30 and 45 degrees with respect to the axis A 1 . 
     The contact between a tip of the laser angle-cleaved optical fiber  18  and the gripper  14  stops the motion of the laser angle-cleaved optical fiber  18  and aligns the laser angle-cleaved end facet  20  with the optical element  16 . The tapered shape of the gripper  14  also ensures that the end of the laser angle-cleaved optical fiber  18  remains in contact with the optical element  16 . As seen in  FIG. 3B , the laser angle-cleaved optical fiber  18  is aligned to the optical element  16  using at least one of the grippers  12 A and  12 B, together with the gripper  14 . The gripper  14  holds the laser angle-cleaved optical fiber  18  down on the substrate  10  and limits the axial travel of the laser angle-cleaved optical fiber  18 . The angled sidewalls of the gripper  14  also engage the angle-cleaved end facet  20  and force the fiber end tip down onto the optical element  16 . 
     As shown in  FIGS. 3A and 3B , the laser angle-cleaved optical fiber  18  is first coarsely aligned and mechanically restrained by grippers  12 A and  12 B that run parallel to the axial path of the laser angle-cleaved optical fiber  18  as the laser angle-cleaved optical fiber  18  is initially inserted into the channel between the grippers  12 A and  12 B. The laser angle-cleaved optical fiber  18  is then more precisely aligned to the optical element  16  by the gripper  14  that is in the axial path of the laser angle-cleaved optical fiber  18  by continually moving the laser angle-cleaved optical fiber  18  to the left until contact is made between a tip of the laser angle-cleaved optical fiber  18  and the gripper  14 . 
     A planar view of the laser angle-cleaved optical fiber  18  held in the grippers  12 A,  12 B, and  14  such that the laser angle-cleaved end facet  20  of the laser angle-cleaved optical fiber  18  is positioned over the optical element  16  is shown in  FIG. 4 . The end gripper  14  has a base  14 -B attached to a surface of the substrate  10  and a top surface  14 -T in a plane parallel to the plane of the substrate  10 . The end gripper  14  may have a top surface that is wider than its base, such that a footprint of the base of the end gripper  14  is smaller than the top surface of the gripper  14 . 
       FIG. 5  is a side view of an exemplary embodiment of the laser angle-cleaved optical fiber  18  forced down into contact with the optical element  16  by a sidewall  15  of the gripper  14 . As can be seen from  FIGS. 4 and 5 , the gripper  14  operates, either alone or in conjunction with one or more of the grippers  12 A and  12 B, to accurately position the laser angle-cleaved end facet  20  of the laser angle-cleaved optical fiber  18  over the optical element  16 . 
     After the laser angle-cleaved optical fiber  18  is aligned to the optical element  16 , the laser angle-cleaved end facet  20  redirects the light from the optical element  16  down the axis of the laser angle-cleaved optical fiber  18  via total internal reflection (TIR), as seen in  FIG. 5 . In  FIG. 5 , light beams  26  from the optical element  16  strike the laser angle-cleaved end facet  20  at the end of the laser angle-cleaved optical fiber  18  and are reflected as light beams  28  which are guided in the internal fiber core  22  of the laser angle-cleaved optical fiber  18 . 
     As discussed above, it may be desirable to coordinate the sidewall angle θ of end gripper  14  and the angle α of the end of the laser angle-cleaved optical fiber  18  in order to stop the axial movement of the laser angle-cleaved optical fiber  18  for accurate alignment of the laser angle-cleaved optical fiber  18  with the optical element  16 , while at the same time ensuring that there is no damage done to either the end gripper  14  or the end of the laser angle-cleaved optical fiber  18 . The sidewall angle of the gripper  14  can be modified by adjusting exposure and development conditions.  FIG. 5  shows a side view of the laser angle-cleaved optical fiber  18  aligned to the gripper  14  with a steeper sidewall angle Φ than the sidewall angle θ of the gripper  14  in  FIGS. 3A and 3B . In the embodiment of  FIG. 5 , the end gripper  14  has a sidewall  15  having an angle Φ relative to the axis A 1 . The sidewall  15  of the gripper  14  having a steeper sidewall angle Φ in  FIG. 5  may be formed by positioning a UV source above the substrate  10 , but not directly overhead, and then rotating the substrate  10 , as discussed in more detail below. The coordination between the sidewall angle Φ of the gripper  14  and the angle α of the end of the laser angle-cleaved optical fiber  18  also ensures that the fiber tip is forced downward into contact with the optical element  16  after assembly. The angle Φ of the sidewall  15  of the gripper  14  may be preferably chosen to be slightly larger than the angle α of the end of the laser angle-cleaved optical fiber  18 . In one embodiment, the angle Φ of the sidewall  15  of the gripper  14  may be preferably chosen to be at least one to two degrees larger than the angle α of the end of the laser angle-cleaved optical fiber  18 . 
       FIG. 6  is a planar view showing an exemplary embodiment of self-alignment of a laser angle-cleaved optical fiber to an active optical element using an alternative angled gripper alignment, where a pair of angled grippers is positioned in an axial path of the laser angle-cleaved optical fiber. In the exemplary embodiment of  FIG. 6 , the arrangement of the gripper  14  near the fiber tip may be modified to self-align the laser angle-cleaved optical fiber  18  with the optical element  16 .  FIG. 6  shows a gripper layout where a pair of grippers  614 A and  614 B are angled and positioned on each side of the tip of the laser angle-cleaved optical fiber  18 . 
     The gripper  614 A has a base  614 A-B attached to a surface of the substrate  10  and a top surface  614 A-T in a plane parallel to the plane of substrate  10 . The gripper  614 B has a base  614 B-B attached to a surface of the substrate  10  and a top surface  614 B-T in a plane parallel to the plane of the substrate  10 . Each of the grippers  614 A and  614 B may have a top surface that is wider than its base, such that the footprint of the base of each of the grippers  614 A and  614 B is smaller than the top surface of the grippers  614 A and  614 B. The gripper  614 A has a longitudinal axis B 1  and is angled with respect to the axis A 1  such that an angle exists between the axis A 1  and the longitudinal axis B 1  of the gripper  614 A. The gripper  614 B has a longitudinal axis B 2  and is angled with respect to axis A 1  such that the angle β 2  exists between the axis A 1  and the longitudinal axis B 2  of the gripper  614 B. In one embodiment, the angles β 1  and β 2  may be between 30 and 45 degrees with respect to the axis A 1 . The longitudinal axis B 1  of the gripper  614 A and the longitudinal axis B 2  of the gripper  614 B intersect at a point along the axis A 1 . The grippers  614 A and  614 B are positioned such that the intersection point of the longitudinal axes B 1  and B 2  of the grippers  614 A and  614 B is in the axial path (i.e., along the axis A 1 ) of the laser angle-cleaved optical fiber  18 . The grippers  614 A and  614 B may physically touch at this intersection point, but it is not necessary that they physically touch at the intersection point. In one embodiment, the grippers  614 A and  614 B do not physically touch at all. The laser angle-cleaved optical fiber  18  is inserted between the grippers  12 A and  12 B in a manner similar to that discussed above with respect to  FIGS. 2-5 . As pressure is applied to the laser angle-cleaved optical fiber  18  from the right in  FIG. 6 , the laser angle-cleaved optical fiber  18  moves left until it comes into contact with the angled grippers  614 A and  614 B. The angled grippers  614 A and  614 B also force the fiber tip downward into contact with the optical element  16 . After the laser angle-cleaved optical fiber  18  is aligned to the optical element  16  via the angled grippers  614 A and  614 B, the laser angle-cleaved end facet  20  redirects the light from the optical element  16  down the axis A 1  of the laser angle-cleaved optical fiber  18  via total internal reflection (TIR), in a manner similar to that illustrated in  FIG. 5 . 
       FIG. 7  is a planar view showing an exemplary embodiment of self-alignment of a laser angle-cleaved optical fiber to an active optical element using a C-shaped gripper embodiment, where a C-shaped gripper is positioned in the axial path of the laser angle-cleaved optical fiber. In  FIG. 7 , a single C-shaped gripper  714  has been patterned to receive the laser angle-cleaved optical fiber  18  and align it to the optical element  16  on the substrate  10 . The gripper  714  has a base  714 -B attached to a surface of the substrate  10  and a top surface  714 -T in a plane parallel to the plane of the substrate  10 . The gripper  714  may have a top surface that is wider than its base, such that the footprint of the base of the gripper  714  is smaller than the top surface of the gripper  714 . 
     The laser angle-cleaved optical fiber  18  is inserted between the grippers  12 A and  12 B in a manner similar to that discussed above with respect to  FIGS. 2-5 . In one embodiment, the C-shaped gripper  714  has a notch  715  cut out of the gripper such that the notch is located in an axial path of the laser angle-cleaved optical fiber  18 . As pressure is applied to the laser angle-cleaved optical fiber  18  from the right in  FIG. 7 , the laser angle-cleaved optical fiber  18  moves left until the end of the laser angle-cleaved optical fiber  18  comes into contact with the C-shaped gripper  714  at points  29 A,  29 B, and  29 C. The C-shaped gripper  714  forces the fiber tip downward into contact with the optical element  16 . After the laser angle-cleaved optical fiber  18  is aligned to the optical element  16  via the C-shaped gripper  714 , the laser angle-cleaved end facet  20  redirects the light from the optical element  16  down the axis A 1  of the laser angle-cleaved optical fiber  18  via total internal reflection (TIR), in a manner similar to that illustrated in  FIG. 5 . 
     The tip of the laser angle-cleaved optical fiber  18  may also be patterned in various ways to enhance the self-alignment approach.  FIG. 8  is an exemplary embodiment of side tapers on an end of the laser angle-cleaved optical fiber  18  for self-alignment to the optical element  16 .  FIG. 8  shows a top view of a fiber end where two additional laser-cut facets  820 A and  820 B are added to the original laser angle-cleaved end facet  20 . The laser-cut facet  820 A is laser-cleaved at an angle λ 1  with respect to the axis A 1 . The laser-cut facet  820 B is laser-cleaved at an angle λ 2  with respect to the axis A 1 . A C-shaped gripper (similar to the one shown in  FIG. 7 ) may be used to self-align the laser angle-cleaved optical fiber  18  to the optical element  16 , as seen in  FIG. 9 . 
       FIG. 9  is a planar view showing an exemplary embodiment of the laser angle-cleaved optical fiber  18  with side tapers  920 A and  920 B being self-aligned to the optical element  16  using a C-shaped gripper  914  positioned in an axial path of the laser angle-cleaved optical fiber  18 . The gripper  914  has a base  914 -B attached to a surface of the substrate  10  and a top surface  914 -T in a plane parallel to the plane of the substrate  10 . Preferably, the C-shaped gripper  914  has a top surface  914 -T that is wider than its base  914 -B, such that the footprint of the base of the C-shaped gripper  914  is smaller than the top surface of the C-shaped gripper  914 . 
     The laser angle-cleaved optical fiber  18  is inserted between the grippers  12 A and  12 B in a manner similar to that discussed above with respect to  FIGS. 2-5 . In one embodiment, the C-shaped gripper  914  has a notch  915  cut out of the gripper such that the notch is located in an axial path of the laser angle-cleaved optical fiber  18 . As pressure is applied to the laser angle-cleaved optical fiber  18  from the right in  FIG. 9 , the laser angle-cleaved optical fiber  18  moves left until the end of the laser angle-cleaved optical fiber  18  comes into contact with the C-shaped gripper  914  at points  30 A,  30 B, and  30 C. The C-shaped gripper  914  forces the fiber tip downward into contact with the optical element  16 . After the laser angle-cleaved optical fiber  18  is aligned to the optical element  16  via the C-shaped gripper  914 , the laser angle-cleaved end facet  20  redirects the light from the optical element  16  down the axis of the laser angle-cleaved optical fiber  18  via total internal reflection (TIR), in a manner similar to that illustrated in  FIG. 5 . 
     Another exemplary embodiment is shown in  FIG. 10 .  FIG. 10  is a side view of an exemplary embodiment of the laser angle-cleaved optical fiber  18  being self-aligned via grippers  12 A,  12 B, and  14  over the optical element  16 . In the embodiment shown in FIG.  10 , the laser angle-cleaved optical fiber  18  has had a tip removed. In this manner, a flat end  32  may be formed at the end of the laser angle-cleaved optical fiber  18  to prevent the pointed fiber tip from damaging the gripper  14  during assembly. The flat end  32  comes in contact with the gripper  14  and limits the travel of the laser angle-cleaved optical fiber  18  during assembly. 
     It is understood that although the details of the grippers  12 A,  12 B, and  14  shown in  FIGS. 1-7 ,  9 , and  10  herein are particularly suitable for gripping elements adapted to secure and passively align cylindrical objects such as optical fibers, grin lenses, and the like, the grippers  12 A,  12 B, and  14  can be sized and configured to secure and passively align a wide variety of other types of non-cylindrical optical elements, for example, including, but not limited to, prisms, lenses, VCSELS, etc. 
     Gripper fabrication according to the embodiments disclosed herein may be based on well-understood photolithographic processing techniques. Moreover, gripper fabrication processes are compatible with planar active device fabrication processes. 
     As discussed above with respect to  FIG. 5 , it may be desirable for more accurate alignment of the laser angle-cleaved optical fiber  18  with the optical element  16  to try to coordinate the angle θ of the sidewall  15  of the end gripper  14  in the axial path of the laser angle-cleaved optical fiber  18  and the angle α of the end of the laser angle-cleaved optical fiber  18  to ensure that the fiber tip is forced downward into contact with the optical element  16  after assembly. The angle θ of the sidewall  15  of the gripper  14  may be chosen to be slightly larger than the angle α of the end of the laser angle-cleaved optical fiber  18 . Alternatively, the angle θ of the sidewall  15  of the gripper  14  may be chosen to be slightly smaller than the angle α of the end of the laser angle-cleaved optical fiber  18 . In one embodiment, the angle θ of the sidewall  15  of the end gripper  14  may be chosen to be at least one to two degrees larger than the angle α of the end of the laser angle-cleaved optical fiber  18 . 
     The gripper sidewall angle is easily modified by adjusting UV exposure and development conditions. For example, steeper sidewall angles may be obtained by exposing the polymer grippers through a mask at an angle, as shown in  FIGS. 11A and 11B . The UV source may also be rotated relative to the device substrate during exposure to increase the sidewall angle further. 
       FIG. 11A  shows the standard gripper exposure process, where the direction of the UV exposure is close to the substrate normal direction. In part  1100  of the process, UV light  1102  is applied to a mask substrate  1104  having a mask pattern  1106  for the desired polymer gripper such that the portions of a polymer gripper substrate  1108  is exposed to the UV light  1102 . The UV light  1102  is applied at an angle θ 1  with respect to the axis A 1 , which is parallel to the polymer gripper substrate  1108 . The portion of the polymer gripper substrate  1108  that is exposed to the UV light  1102  is exposed polymer gripper material  1110  and the portion of the polymer gripper substrate  1108  that is not exposed to the UV light  1102  due to the mask pattern  1106  is unexposed polymer gripper material  1112 . At part  1120  of the process, there is a second UV exposure from a second direction at a second angle, θ 2 , with respect to the axis A 1 . UV light  1122  is applied to the mask substrate  1104  having a mask pattern  1106  such that another portion (labeled  1124 ) of the previously unexposed polymer gripper material  1112  is now exposed to UV light  1122 , leaving only portion  1126  as unexposed polymer gripper material. Then, the removal of all exposed polymer gripper material is performed so that only a polymer gripper  1140  remains. The polymer gripper  1140  has a top surface  1140 -T and a base  1140 -B, where the top surface  1140 -T is preferably wider than the base  1140 -B. The polymer gripper  1140  has a sidewall  1142  having an angle θ 2 , with respect to the axis A 1 . The angular variation in exposure can be provided by positioning the polymer gripper substrate  1108  on a rotating plate, with the source of the UV light positioned above the plate so that the UV light is directed down on the polymer gripper substrate  1108  at a slight angle relative to the substrate normal angle. 
       FIG. 11B  shows a modified gripper exposure process, wherein at least one direction of the UV exposure is at a sharper (i.e. larger) angle with respect to the substrate normal direction in order to obtain a steeper (i.e., more acute, relative to the plane of the substrate) sidewall angle on the formed polymer gripper. In part  1150  of the process, UV light  1152  is applied to a mask substrate  1154  having a mask pattern  1156  for the desired polymer gripper such that the portions of a polymer gripper substrate  1158  is exposed to the UV light  1152 . The UV light  1152  is applied in a direction that is normal to the polymer gripper substrate  1158 . That is, the UV light  1152  is applied at an angle θ 3 , where θ 3  is 90 degrees with respect to the axis A 1 , which is parallel to the polymer gripper substrate  1158 . The portion of the polymer gripper substrate  1158  that is exposed to the UV light  1152  is exposed polymer gripper material  1160  and the portion of the polymer gripper substrate  1158  that is not exposed to the UV light  1152  due to the mask pattern  1156  is unexposed polymer gripper material  1162 . At part  1170  of the process, there is a second UV exposure from a second direction and at a second angle, θ 4 , with respect to the axis A 1 , which is at an angle that is sharper (i.e., larger) with respect to the substrate normal direction as compared to the angle θ 2  of the UV exposures in the normal process of  FIG. 11A . UV light  1172  is applied to the mask substrate  1154  having a mask pattern  1156  such that another portion (labeled  1174 ) of the previously unexposed polymer gripper material  1162  is now exposed to UV light  1172 , leaving only a portion  1176  as unexposed polymer gripper material. Then, the removal of all exposed polymer gripper material is performed so that only polymer gripper  1190  remains. The polymer gripper  1190  has a top surface  1190 -T and a base  1190 -B, where the top surface  1190 -T is preferably wider than the base  1190 -B. The polymer gripper  1190  has a sidewall  1192  having an angle θ 4 , with respect to axis A 1 . Polymer gripper  1190  has a steeper sidewall angle, θ 4 , than the polymer gripper  1140  formed by the normal UV exposure process of  FIG. 11A . The angular variation in exposure can be provided by positioning the polymer gripper substrate  1158  on a rotating plate, with the source of the UV light positioned above the plate so that the UV light is directed down on the polymer gripper substrate  1158  at an angle relative to the substrate normal, or it may be provided via UV illumination of a fixed polymer gripper substrate  1158  from several different angles. 
     According to some embodiments, cement or adhesive may be used to coarsely align and mechanically restrain the optical fibers, in place of the grippers that run parallel to the optical fiber, such as grippers  12 A and  12 B.  FIG. 12  shows such an embodiment. In  FIG. 12 , the laser angle-cleaved optical fiber  18  is coarsely aligned and mechanically restrained by adhesive  34 , which is deposited over the laser angle-cleaved optical fiber  18 . The adhesive  34  thus acts as a restraining member for the laser angle-cleaved optical fiber  18 . The laser angle-cleaved optical fiber  18  is then precisely aligned to the optical element  16  by the gripper  1214 , which is located in the axial path of the laser angle-cleaved optical fiber  18 . The gripper  1214  can be a single gripper like the gripper  14  in  FIGS. 1-6  and  10 , a pair of angled grippers like the grippers  614 A and  614 B in  FIG. 6 , or a C-shaped gripper like the gripper  714  in  FIG. 7 , or the gripper  914  in  FIG. 9 , or a similar gripper structure. The gripper  1214  forces the tip of laser angle-cleaved optical fiber  18  downward into contact with the optical element  16 . After the laser angle-cleaved optical fiber  18  is aligned to the optical element  16  via the gripper  1214 , the laser angle-cleaved end facet  20  redirects the light from the optical element  16  down the axis of the laser angle-cleaved optical fiber  18  via total internal reflection (TIR), in a manner similar to that illustrated in  FIG. 5 . 
     Certain embodiments disclosed herein relate to apparatuses and methods for alignment of various optical elements to substrates. These optical elements may include for example, but are not limited to, optical fibers, lenses, filters, lensed fibers, vertical cavity surface emitting lasers (VCSELs), optical isolators, photonic detectors, and the like. In certain embodiments, an end of an optical fiber, such as a laser angle-cleaved optical fiber, is aligned over an active optical element, such as a VCSEL, on a substrate. The apparatuses and methods may include a substrate that includes alignment features or receiving structures, for example, gripping elements, v-grooves, depressions, recessed regions, keys, trenches, adhesives, or cement, for securing and passively aligning optical modules or modular optical elements. Fiber alignment structures such as grippers may also be used to position fibers normal to the substrate surface, so that fibers pass through a 1-D or 2-D array of apertures in an alignment plate. The grippers may be fowled using deformable mechanical members or by filling a portion of the plate aperture with a polymer gripper material. Fibers in this configuration may be fixed in place using various forms of polymer encapsulation. 
     Fiber gripping structures have also been employed in mechanical splices, where plastic deformable V-grooves may be used to align and restrain one or more mated optical fiber pairs. Fibers can also be held in position using deformable plastic grooves with sidewall barbs that grip the fiber. 
     Certain embodiments disclosed herein include grippers, such as polymer grippers, for passive alignment of components on planar substrates. Although polymer grippers are disclosed herein for passive alignment, other structures, such as restraining members, may also be used to provide alignment and/or mechanical restraint of optical fibers or other optical elements. 
     Grippers can be used to hold optical fibers in place on flat substrates or in V-groove structures formed on silicon substrates. In addition to gripping individual fibers, grippers can be used for positioning arrays of optical fibers, optical components mounted on smaller carrier substrates, fiber lenses, cylindrical lenses and resonator structures, and optical filters. 
     Embodiments described herein include techniques for aligning laser angle-cleaved optical fibers to active devices on a planar substrate (e.g., VCSEL sources and photodetectors) using grippers, such as polymer grippers. Grippers ensure that the tapered or laser angle-cleaved fiber ends are precisely aligned to active components (laser sources or detectors). Grippers can also ensure that the fiber end is held in close proximity to the active device. By positioning the one or more grippers in the axial path of the optical fiber such that an optical fiber may be moved along the axial path until the end of the optical fiber comes in contact with the one or more grippers, the optical fiber may be easily and accurately aligned over an active optical element on a substrate. 
     An advantage of using grippers, such as polymer grippers, is that it enables low-cost passive alignment of tapered fibers or fiber arrays to active optical devices. In addition, the polymer gripper layout can be easily modified via photolithographic mask modification to accommodate any type of fiber end treatment (e.g., wedges or tapers). 
     Certain embodiments disclosed herein provide passive alignment apparatus and methods that are inexpensive and require very few steps to achieve passive alignment of various optical elements. After the elements have been passively aligned, it may be desirable to use cement or adhesive to aid in securing the optical element in place. Alternatively, in other embodiments, no adhesive needs to be used. In the design of optical devices, if the proper positional and angular alignment of the individual optical elements is known, the alignment features on the bases and on the substrate can be designed and properly positioned to achieve passive alignment. 
     According to certain embodiments, a variety of materials and geometric shapes can be used for the gripping elements and the substrate, and a variety of manufacturing procedures may be used to fabricate them. The embodiments disclosed herein allow for low cost passive alignment of optical elements. 
     Further, as used herein, it is intended that terms “fiber optic cables” and/or “optical fibers” include all types of single mode and multi-mode light waveguides, including one or more bare optical fibers, loose-tube optical fibers, tight-buffered optical fibers, ribbonized optical fibers, bend-insensitive optical fibers, or any other expedient of a medium for transmitting light signals. An example of a bend-insensitive optical fiber is ClearCurve® optical fiber, manufactured by Corning Incorporated. 
     Many modifications and other embodiments set forth herein will come to mind to one skilled in the art to which the embodiments pertain having the benefit of the teachings presented in the foregoing descriptions and the associated drawings. Therefore, it is to be understood that the description and claims are not to be limited to the specific embodiments disclosed and that modifications and other embodiments are intended to be included within the scope of the appended claims. It is intended that the embodiments cover the modifications and variations of the embodiments provided they come within the scope of the appended claims and their equivalents. Although specific terms are employed herein, they are used in a generic and descriptive sense only and not for purposes of limitation.