Abstract:
An optical fiber clamp that precisely aligns and clamps multiple optical fibers in multi-channel freespace optical systems, eliminates multiple parts and simplifies assembly. Multiple wafers each having an array of holes passing therethrough, are aligned with respect to each other. Optical fibers are passed through the holes, and at least one of the wafers is moved laterally with respect to the other wafers, so that sidewalls of the holes clamp the optical fibers into a desired location.

Description:
The present application claims priority under 35 U.S.C. §119(e) to U.S. Provisional Application 60/276,337 filed on Mar. 16, 2001, which is hereby incorporated by reference in its entirety for all purposes. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to an apparatus for aligning and clamping multiple optical fibers in an electro-optical device. More particularly, the present invention relates to a method and apparatus for quickly and inexpensively aligning an (M×N) array of optical fibers into a semiconductor wafer. 
     2. Description of the Related Art 
     Multiple channel freespace optical systems require inputs and outputs of optical signals using optical fiber. For systems with small numbers of channels, these fibers can be mechanically routed using v-shaped grooves or other similar mechanisms to hold and align the fibers as a (1×N) array. 
     FIG. 1 is a side view of a conventional one-dimensional optical fiber alignment system  100  having a (1×N) array of optical fibers that are aligned using v-shaped grooves. In this case, a (1×4) array is described. As shown in FIG. 1, a semiconductor wafer  110  has a plurality of v-shaped grooves  113  that each hold a respective one of a plurality of optical fibers  116 . 
     When &lt;100&gt; oriented crystal silicon is used for the semiconductor wafer  110 , v-shaped grooves  113  can be easily formed on a top surface of the wafer  110 . Ends of the optical fibers  116  are placed in these grooves  113  so that they can be properly aligned. Once in these grooves  113 , the optical fibers  116  can be cut and then potted with a glue to be fixed into place. Then a connecting surface, or end face, of the wafer  110  is polished back to provide each of the optical fibers  116  with a clean connective face. The wafer  110  is then aligned as necessary into an optical system. 
     However in optical systems with a large channel count, it is often desirable to have more optical fibers aligned than would be practical in a (1×N) array. Thus, it is necessary in these systems to arrange the fibers into an (M×N) array. The conventional alignment system achieves this by stacking M (1×N) arrays to form an (M×N) array. 
     FIG. 2 is a side view of a conventional multi-dimensional optical fiber alignment system having an (M×N) array of optical fibers that are aligned using v-shaped grooves. In this case, a (4×4) array is described, made by stacking four (1×4) arrays on top of each other. As shown in FIG. 2, the multi-dimensional optical fiber alignment system  200  includes a plurality of stacked semiconductor wafers  210 ,  220 ,  230 , and  240 . The wafers have v-grooves on both sides thereof, or some other structure, to align the stack of wafers to each other. 
     Each of wafers  210 ,  220 ,  230 , and  240  are formed as shown for the (1×N) array in FIG. 1, except for also having the alignment grooves on bottom surfaces thereof. As in the semiconductor wafer  110  of FIG. 1, the first semiconductor wafer  210  includes a plurality of first v-shaped grooves  213  that each hold a respective one of a plurality of first optical fibers  216 . Similarly, the second wafer  220  includes a plurality of second v-shaped grooves  223  that each hold a respective one of a plurality of second optical fibers  226 . The third wafer  230  includes a plurality of third v-shaped grooves  233  that each hold a respective one of a plurality of third optical fibers  236 . Also, the fourth wafer  240  includes a plurality of fourth v-shaped grooves  243  that each hold a respective one of a plurality of fourth optical fibers  246 . Also, wafers  210 ,  220  and  230  are shown as including the v-shaped grooves  238  on respective bottom surfaces thereof, which correspond with respective v-shaped grooves on the upper surfaces of the respective stacked wafers. 
     However, as the (1×N) arrays are stacked on top of each other, alignment errors between individual wafers rapidly compound, resulting in significant alignment errors. Thus, while the fabrication process of the individual wafers  210 ,  220 ,  230 , and  240  provides a very good tolerance in the horizontal direction, the stacking process results in a very poor tolerance as the number of stacked wafers increases. 
     In view of such manufacturing tolerances in the stacking process, special structures and assembly techniques are required to align the array of fibers to the system. However, for multi-channel systems, the use of existing fiber array alignment techniques requires a prohibitively large number of precision alignments per system, as well as numerous fiber holding components to achieve the required level of precision. This can significantly increase fabrication time and cost. 
     It is therefore desirable to have a system and method for quickly and cheaply aligning large arrays of optical fibers. 
     SUMMARY OF THE INVENTION 
     The present invention is therefore directed to multiple fiber chip clamp which substantially overcomes one or more of the problems due to the limitations and disadvantages of the related art. 
     Therefore, a new apparatus and method has been designed that precisely locates and clamps multiple fibers using precision etched silicon wafers or substrates, that eliminates numerous precision alignments, and dramatically reduces the number of components required to clamp the fibers. 
     An optical fiber clamp of the present invention includes a first wafer having a first surface with a plurality of first holes formed therethrough; and a second wafer having a second surface with a plurality of second holes formed therethrough, the second surface of the second wafer facing the first surface of the first wafer. The first and second wafers are laterally movable with respect to each other to a clamping position whereby an optical fiber placed through a respective pair of the first and second holes is held stationary against sidewalls of the first and second holes. 
     For example, the first wafer may be stationary and the second wafer may be laterally movable with respect to the first wafer. As such, the sidewalls of each of the second holes of the second wafer may be covered with a compliant material. The compliant material may comprise one of rubber or plastic. 
     At least one of the first and second holes may be diamond-shaped, triangular-shaped, or rectangular-shaped. 
     The first wafer should be sufficiently thick such that when the second wafer is at the point of farthest movement, or in other words at the clamping position, the optical fibers in the second holes are pressed along the same sidewall of respective second holes. Alternatively, the second wafer may be sufficiently thick such that when the second wafer is at the point of farthest movement, the optical fibers in the first holes are pressed along the same sidewall of respective first holes. 
     In an alternative embodiment, an optical fiber clamp of the present invention includes a plurality of wafers each having a plurality of holes formed therethrough, surfaces of the plurality of wafers through which the holes are formed facing each other so that respective holes of the plurality of wafers are aligned. The plurality of wafers are laterally movable with respect to each other to a clamping position whereby an optical fiber placed through respective aligned holes of each of the plurality of wafers is held stationary against sidewalls of the respective aligned holes. 
     For example, the optical fiber clamp may include three wafers, whereby the middle wafer is laterally movable with respect to the other wafers which are stationary. As such, sidewalls of the holes formed in the middle wafer may be covered with a compliant material. The compliant material may comprise one of rubber or plastic. 
     The holes of the plurality of wafers may be diamond-shaped, triangular-shaped, or rectangular-shaped. 
     Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The present invention will become more fully understood from the detailed description given hereinbelow and the accompanying drawings which are given by way of illustration only, and thus are not limitative of the present invention, and wherein: 
     FIG. 1 is a side view of a conventional one-dimensional optical fiber alignment system having a (1×N) array of optical fibers that are aligned using v-shaped grooves; 
     FIG. 2 is a side view of a conventional multi-dimensional optical fiber alignment system having an (M×N) array of optical fibers that are aligned using v-shaped grooves; 
     FIG. 3 is an overhead view of a multi-dimensional optical fiber alignment system having an (M×N) array of optical fibers according to an embodiment of the present invention, in an optical fiber placement position; 
     FIG. 4 is a side view of the multi-dimensional optical fiber alignment system of FIG. 3, in the optical fiber placement position; 
     FIG. 5 is an overhead view of the multi-dimensional optical fiber alignment system as in FIG. 3, in an optical fiber clamping position; 
     FIG. 6 is a side view of the multi-dimensional optical fiber alignment system of FIG. 5, in the optical fiber clamping position; 
     FIG. 7 is a top view of a wafer of a further embodiment in which the features are triangular-shaped; 
     FIG. 8 is a top view of a wafer of a still further embodiment in which the features are rectangular-shaped; and 
     FIG. 9 is an overhead view of a wafer having a compliant structure bonded to a top surface thereof 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The present invention uses a multiple fiber array clamp design to address the shortcomings of conventional techniques, through the use of lithographically defined features etched into silicon wafers or substrates. These features are large enough to easily receive a plurality of optical fibers, and can be aligned into an (M×N) array of optical fibers with a required level of precision. In this description, M and N are integers than may be the same or different. 
     The features in the silicon wafers may be diamond shaped holes that are etched entirely through the silicon wafer and that have vertical sidewalls. The location of these features is controlled by lithographic precision. Feature size is highly uniform and multiple features may easily be generated to accommodate numerous fibers. 
     In principle, virtually any number of fibers could be accommodated in this arrangement with alignment tolerance on the order of 1 μm. Manufacturing tolerances that limit existing techniques are eliminated and assembly is simplified by the reduction of components used to hold, locate and align the fibers. 
     FIGS. 3 through 6 illustrate a multi-dimensional optical fiber alignment system having an (M×N) array of optical fibers according to an embodiment of the present invention. FIG. 3 is an overhead view of the multi-dimensional optical fiber alignment system in an optical fiber placement position, and FIG. 4 is a side view of the multi-dimensional optical fiber alignment system of FIG. 3 in the optical fiber placement position. It is to be understood that the optical fiber placement position is an initial position prior to a final clamping position. 
     As shown in FIGS. 3 and 4, the system includes an upper wafer  310 , a lower wafer  320 , and a center wafer  330 . Each of the wafers  310 ,  320 , and  330  are etched or processed to include an identical array of diamond-shaped features  340  that pass through the respective wafers  310 ,  320 , and  330 . The diamond-shaped features  340  should have smooth sidewalls. 
     Also, the sidewalls of the diamond-shaped features  340  in center wafer  330  may be coated with a compliant material  360  such as rubber or plastic, for reasons as will be subsequently described. Alternatively, a compliant structure  960  such as rubber or plastic for example, may be bonded on the facing surface of wafer  910 , as shown in FIG.  9 . Opening  970  in compliant structure  960  is aligned to coincide with feature  940  when compliant structure  960  is bonded to the facing surface of wafer  910 . It should be understood that a corresponding optical fiber placed through feature  940  extends out through opening  970  of compliant structure  960 . 
     In operation, the wafers  310 ,  320 , and  330  are placed into an assembly fixture that is used to align the top and bottom wafers, and to move the middle wafer with respect to the top and bottom wafers. The alignment fixture may for example comprise a set of fixed locating pins and a set of movable locating pins, that register the gross alignment features for each wafer. The movable locating pins may for example be controlled by a mechanical micrometer that is mounted onto a precision x-y stage, or by any device that can control the movement of the center wafer  330  to a desired tolerance. 
     In an optical fiber placement position, the wafers  310 ,  320 , and  330  are aligned in the assembly fixture such that the diamond-shaped features  340  on each wafer are in complete alignment. Optical fibers  350  are then inserted through the diamond-shaped features  340  in all three wafers  310 ,  320 , and  330 . 
     Once all of the fibers  350  are inserted through the diamond-shaped features  340 , the center wafer  330  in the stack is moved using the movable locating pins in the assembly fixture to guide the individual fibers  350  into a clamping position. This is accomplished by registering each fiber in the array against the corner of the diamond-shaped features in the top and bottom wafers  310  and  320 . 
     Initially, the fibers will press up against the corner of the center wafer  330  as it moves laterally. But as the lateral movement continues toward the final clamping position, the fibers  350  become wedged between the comers of the diamond-shaped features  340  in the upper and lower wafers  310  and  320 , and the comers of the diamond-shaped features  340  in the center wafer  330 . 
     FIG. 5 is an overhead view of the multi-dimensional optical fiber alignment system of the preferred embodiment, in an optical fiber clamping position, and FIG. 6 is a side view of the multi-dimensional optical fiber alignment system of FIG. 5 in the optical fiber clamping position. It is to be understood that the optical fiber clamping position corresponds to a finally clamped position. 
     As shown in FIGS. 5 and 6, in the clamping position, the center wafer  330  is moved to the side in the direction M, pushing the fibers  350  into place. Once the fibers  350  are pressed between the diamond-shaped features  340  in the upper and lower wafers  310  and  320 , and those of the center wafer  330 , they are all aligned and clamped quickly and accurately. By moving the wafer  330 , the system  300  effectively reduces the overlap size of the diamond-shaped features to one that offers a snug fit for the optical fibers  350 . This makes certain that the fibers  350  will be aligned and clamped to the desired tolerance. 
     Once properly aligned and clamped, the optical fibers  350  can be glued into place with a staking or potting adhesive, solder or other permanent fixing mechanism. Then the fibers can be cut, the end face of the middle wafer can be properly polished, and any other finishing processes can be performed on the aligned bottom wafer. 
     The diamond-shaped features  340  can be formed in the wafers  310 ,  320 , and  330  by any means desired. &lt;110&gt; silicon wafers can be easily etched to form these diamond-shaped features. However, if a Bosch inductively coupled plasma (ICP) dry etch process is used, such features  340  can be formed on any kind of silicon, regardless of its crystalline orientation. 
     The diamond-shaped features  340  may be larger than the diameter of the optical fibers  350 , but are not necessarily limited as being larger. Also the diamond-shaped features may be significantly larger than the diameter of the optical fibers  350 . This allows for easy insertion of optical fibers when the system is in the optical fiber placement position. However, the size of the diamond-shaped features  340  becomes irrelevant with respect to the clamping phase, as the overlap of these features  340  in the various wafers  310 ,  320 , and  330  is reduced to just the diameter of the optical fibers. As a result, it is not necessary to thread a large number of fibers through tiny holes during the initial placement of the optical fibers. 
     The use of a compliant material  360  on the sidewalls of the diamond-shaped features  340  in center wafer  330  as shown in FIG. 5, relieves any undue stress that may be placed on particular ones of the fibers  350  that first contact with the sidewalls of respective ones of the diamond-shaped features  340  of the upper and lower wafers  310  and  320 , for example. Due to imperfect tolerances between the features  340  and the fibers  350 , some of the fibers  350  may contact the sidewalls of respective features  340  before other fibers contact sidewalls of respective features. The compliant material  360  compresses when the fibers  350  come into contact with it, so that when the center wafer  330  is further moved, all of the fibers can ultimately make contact with respective features and the pressure exerted by the wafers may be spread evenly to all of the fibers. Compliant structure  960  of FIG. 9, as bonded to the facing surface of center wafer  330  of FIG. 5 for example, similarly relieves any undue stress that may be placed on the fibers, by compressing upon contact with a fiber along the inner edge of opening  970 . The compliant material  360  and compliant structure  960  are not necessary, but may increase the effectiveness of the clamping process. 
     Although the features  340  have been described as diamond-shaped, the features are not limited in shape. All that is necessary is that the shape of the features is such that when the upper, lower, and center wafers  310 ,  320 , and  330  are shifted with respect to each other, the fibers  350  will each be pressed together to a single point of alignment. For example, the features  340  in the upper and lower wafers  310  and  320  may be triangular, while the features  340  in the center wafer  330  may be square. In the alignment position, the fibers  350  must be pressed into a single position by at least three sidewalls of the various features through which they are placed. 
     FIG. 7 is a top view of a wafer  710  of a multi-dimensional optical fiber alignment system  700  of a further embodiment, in which the features  740  are triangular-shaped. FIG. 8 is a top view of a wafer  810  of a multi-dimensional optical fiber alignment system  800  of a still further embodiment, in which the features  840  are rectangular-shaped. Different shapes in alternate embodiments are also possible, wherein for example the center wafer may have features of a first shape and the upper and lower wafers have respectively different shapes. 
     In addition, although three wafers are described in the above embodiments, any number of wafers may be used. For example, either of the upper wafer  310  or the lower wafer  320  may be eliminated. In such further embodiment, the remaining wafers would necessarily be of sufficient thickness to prevent the fibers from becoming cocked or turned when the wafers are moved into the alignment position. 
     Also, it is not necessary that the center wafer is movable. Although in the above embodiments, the upper and lower wafers  310  and  320  are stationary and the center wafer  330  is movable, such an arrangement of movement may be reversed. The upper and lower wafers  310  and  320  may be movable and the center wafer  330  stationary. Any other arrangement of movement may be applied, as long as features  340  are moved to press the fibers into a single alignment position. It should however be understood that generally, compliant material  360  is coated on sidewalls of the features of wafers that are movable. 
     Through this invention, arrays of virtually any size can be constructed. The current array is provided solely as an example and should not be construed as limiting. Using current processing techniques, it is possible to create identical patterns in wafers  310 ,  320 , and  330  with great precision. As a result, the device has good tolerance in both horizontal and vertical directions. Furthermore, since the features are defined lithographically, scaling of the structure to add additional fiber locations can be easily accommodated and does not affect the alignment precision or process. 
     By this system and method, an array that realizes simple fiber alignment is provided, which eliminates the need to individually align v-grooves formed on wafers. As a result, a greatly improved assembly process is provided. Furthermore, the structure is mechanically strong. By supporting the fibers with a three wafer stack of silicon wafers, rather than a single wafer, improved strength is realized. In addition, by forming all of the fibers in a single array, the structure allows for gang polishing of all of the fiber endfaces and simultaneous optical coating of all fibers in a single fixture. Additionally, uniform angle polishing of fibers may be realized by first staggering the stack of wafers to produce a desired angle, then polishing the fibers, and then realigning the stack to the normal clamp position. 
     The above embodiments have been described whereby silicon wafers are used in the multiple fiber array clamp. However, the wafers are not necessarily limited as being silicon. For example, the wafers may be metal, plastic, glass, ceramic or any suitable material or substrate that may be appropriately etched or processed to create the corresponding holes or features. Also, locating features can be fabricated in various materials using precision etched silicon as a master, from which suitable molds and molded parts may be fabricated with high precision. 
     The invention being thus described, it will be obvious that the same may be varied in many ways. Such variations are not to be regarded as a departure from the spirit and scope of the invention, and all such modifications as would be obvious to one skilled in the art are intended to be included within the scope of the following claims.