Abstract:
A system and method for the alignment of optical elements using an unmounted LED die with a small lens as a beacon for each channel in an optical switch. One LED is mounted next to each optical fiber in an alignment hole in a ceramic form. Each LED has a conductive trace and wire bond for independent electrical control. The LED shines through a pinhole to limit the divergence of the beam. The pinhole is at the focus of a small lens which is positioned adjacent to the form, and creates a real image at its target. Because the LED and fiber are fixed closely together in the form, misalignment due to thermal effects or mechanical drift is negligible.

Description:
RELATED APPLICATION  
       [0001]    This application is a continuation in part of Provisional Application Serial No: 60/273,462 is entitled “Optical Beacon For Aligning Mirror Systems” filed Mar. 5, 2001. 
     
    
     
       FIELD OF THE INVENTION  
         [0002]    The present invention relates generally to optical network systems. More specifically, the present invention pertains to methods of aligning optical network components. The present invention is particularly, though not exclusively, useful for aligning mirrors—including but not limited to those in connection with micro-electromechanical switches (MEMS)—in multi-channel optical switches, using unmounted LED dice with small lenses.  
         BACKGROUND OF THE INVENTION  
         [0003]    Over the past several decades, the use of optical fibers, or fiber optics, to transmit information on a light beam have become increasingly popular. In fact, much of the information which is transmitted today is done over optical fibers. A difficulty of implementing an optical switch having a communication beam and an alignment beam, is that the alignment beam, or beacon, source for optical alignment must be low power, is preferably a different wavelength than the parallel communications beam, detectable with an inexpensive silicon detector, switchable on and off independent of other switches, and produce a nearly diffraction-less beam. Several alternative schemes have been considered. For example, a laser diode array produces a goodly amount of light, but it also produces too much heat because a lasing threshold must be reached. Another option is that a large beacon source can be used, but this does not allow individual channel control. However, a large source can be used with a modulator—for example, a liquid crystal—to make a usable device. Unfortunately, a liquid crystal modulator introduces undesirable features.  
           [0004]    Accordingly, it is an object of the present invention to provide an optical beacon, for aligning optical elements, that meets the above requirements.  
         SUMMARY OF THE PRESENT INVENTION  
         [0005]    To satisfy the above requirements, the present invention utilizes an unmounted LED die with a small lens as a beacon for each channel in an optical switch. One LED is mounted next to each optical fiber which is inside an alignment hole on a rigid ceramic form. Each LED has a conductive trace and wire bond for independent electrical control. The LED shines through a pinhole to limit the divergence of the beam. The pinhole is at the focus of a small lens which is positioned adjacent to the form, and creates a real image at its target. Because the LED and fiber are fixed closely together in the form, misalignment due to thermal effects or mechanical drift is negligible. 
       
    
    
     DESCRIPTION OF THE DRAWINGS  
       [0006]    The novel features of this invention, as well as the invention itself, both as to its structure and its operation, will be best understood from the accompanying drawing, taken in conjunction with the accompanying description, in which like reference characters refer to similar parts, and in which:  
         [0007]    [0007]FIG. 1 is a front view of a first preferred embodiment of the present invention showing a 16-channel array of fibers and LEDs in a ceramic form;  
         [0008]    [0008]FIG. 2 is a front view of the first preferred embodiment of the present invention showing a lens panel superimposed on the array shown in FIG. 1, with the lens panel cutaway to show the array underneath; and  
         [0009]    [0009]FIG. 3 is a cross-sectional view of the first preferred embodiment of the present invention taken along line  3 — 3  of FIG. 2, showing the relative placement and dimensions of the optical fiber, LED, pinhole in mask, and lens panel;  
         [0010]    [0010]FIG. 4 is a cross-sectional view of a second preferred embodiment of the present invention taken along line  3 — 3  of FIG. 2, with the LED in back of the form, and the pinhole in the form. 
     
    
     DETAILED DESCRIPTION  
       [0011]    Referring initially to FIG. 1, a front view of a preferred embodiment of the Optical Beacon for Aligning Mirror Systems (“array”) of the present invention is shown and generally designated  100 . In FIG. 1, array  100  is a 16-channel optical array. More precisely, array  100  is a 4-by-4 two-dimensional array of 16 optical channels  101  in a form  102 . Form  102  is shown in FIG. 1 as a shallow parallelepiped. Alternative shapes for form  102  include but are not limited to prismatoid, pyramidal, tetrahedral, ovoid, lenticular, cylindrical, conic, etc. FIG. 1 shows surface  103  of form  102  as planar. Alternatives for surface  103  include but are not limited to convex, concave, sinusoidal, serrated, etc. Form  102  can be made of ceramic. Alternative materials for form  102  include but are not limited to glass, composite, plastic, etc.  
         [0012]    Each channel  101  comprises a communication beam and a beacon beam. The communication beam comes from an optical element, such as an optical fiber for example, positioned at a known location in form  102 . This location can be, for example, a corner of an alignment hole  104  in form  102 . Please note that fibers  106  are not in themselves part of the present invention. However, fibers  106  are shown in FIG. 1 to illustrate how the present invention can be used to align such fibers with other optical elements. Holes  104  are shown in FIG. 1 as square. Alternative shapes for holes  104  include but are not limited to oval, trapezoidal, triangular, pentagonal, pentagramal, hexagramal, septagramal, etc. Another alternative is that the LEDs or fibers can be mounted on the surface of form  102 , or in recesses in form  102 .  
         [0013]    LED  108  can be mounted on the front of form  102 , and a mask  110  having a pinhole  112  can be placed over LED  108 . In addition, LED  108  can be partially or wholly recessed in form  102 . In any case, pinhole  112  is placed a predetermined distance  117  in a predetermined direction from the location of fiber  106  in hole  104 . Pinhole  112  has a width  113 . Pinhole  112  limits the divergence of light from LED  108 . Pinholes  112  are shown in FIG. 1 as circular. Alternative shapes for pinholes  112  include, but are not limited to oval, trapezoidal, triangular, pentagonal, pentagramal, hexagramal, septagramal, etc.  
         [0014]    Distance  109  and distance  117  are typically on the scale of 0.3 millimeter. This causes any thermal effects and mechanical drift to be common to LED  108 , pinhole  112  and the location of fiber  106  in hole  104 , which reduces misalignment problems to negligible levels.  
         [0015]    Each LED  108  is in common electrical connection with a common conductive path  114  (electrical ground) on form  102 . FIG. 1 shows common conductive path  114  as a conductive trace on form  102 . Alternatively, common conductive path  114  can be wire. Common path  114  is connected to a connector  116  (ground wire). Each LED is uniquely bonded to a unique wire  118  which, in conjunction with common conductive path  114 , provides for the independent switching on and off of each LED  108 . Alternatively, each LED  108  may be provided with two conductive traces on form  102 , one being common conductive path  114 , and the other being a unique conductive path  120  to uniquely switch each LED  108  on and off. Each unique path  120  is uniquely connected to a unique connector  121 .  
         [0016]    [0016]FIG. 2 shows the same front view of the first preferred embodiment of the present invention generally designated  100  as in FIG. 1, except that a lens panel  202  is superimposed on array  100  and partially cut away to show array  100  beneath panel  202 . For each channel  101 , panel  202  contains a beacon lens  204  facing its corresponding pinhole  112 , and a communication lens facing its corresponding fiber  106 .  
         [0017]    [0017]FIG. 3 is a cross-sectional view of the first preferred embodiment of the present invention as taken along line  3 — 3  of FIG. 2.  
         [0018]    Each beacon lens  204  faces its corresponding pinhole  112  at a distance  208  from pinhole  112 , which distance  208  is nearly equal to the focal length of beacon lens  204 , so that beacon light  212  from pinhole  112  is nearly collimated by beacon lens  204  into beacon beam  216 . Each communication lens  206  is similarly placed facing its corresponding fiber  106  at a distance  210  from fiber  106 , which distance  210  is nearly equal to the focal length of communication lens  206 , so that communication light  214  from fiber  106  is collimated by communication lens  206  into communication beam  218 . Beacon beam  216  and communication beam  218  may or may not be parallel, depending on the configuration of their respective targets. Each beam forms a real image at its respective target by and equivalent lens pair on the receiving side.  
         [0019]    In an alternative embodiment as shown in FIG. 3, pinhole  112  has a height  115  greater than its width  113 . This is to limit the divergence of beacon light  212  exiting pinhole  112 . Diameter  113  can be greater than height  115 , but then beacon light  212  would diverge more, and collimating it would require that distance  208  be changed, or that beacon lens  204  be replaced with a lens having a different focal length, or both.  
         [0020]    [0020]FIG. 4 is a cross-sectional view of a second preferred embodiment of the present invention, as taken along line  3 — 3  of FIG. 2. FIG. 4 is similar to FIG. 3 except for the following: LED  108  is now mounted on the back of form  102  instead of on the front; and a pinhole  122  is in form  102  instead of in a mask  110 . Pinhole  122  works similarly to pinhole  112  in FIG. 3, but the height  125  and width  123  of pinhole  122  may or may not be the same as height  115  and width  113 , respectively, of pinhole  112 . In FIG. 4, height  125  coincides with the thickness of form  102 . However, if LED  108  is recessed in or raised above form  102 , height  125  would differ from the thickness of form  102 . Like pinhole  112  in FIG. 3, the width  123  of pinhole  122  is less than its height  125 , so that the divergence of beacon light  212  from pinhole  122  is limited.  
         [0021]    Each beacon lens  204  faces its corresponding pinhole  112  at a distance  208  from pinhole  112 , which distance  208  is equal to the focal length of beacon lens  204 , so that beacon light  212  from pinhole  112  is collimated by beacon lens  204  into beacon beam  216 . Each communication lens  206  is similarly placed facing its corresponding fiber  106  at a distance  210  from fiber  106 , which distance  210  is equal to the focal length of communication lens  206 , so that communication light  214  from fiber  106  is collimated by communication lens  206  into communication beam  218 . Beacon beam  216  and communication beam  218  may or may not be parallel, depending on the configuration of their respective targets. Each beam forms a real image at its respective target.  
         [0022]    While a 16-element array has been discussed herein, it is to be appreciated that the system described may be scalable to virtually any size array, such as a one hundred element array (10 by 10), or a ten thousand element array (100 by 100), for example. Alternatively, the array can be one-dimensional or three-dimensional.  
         [0023]    Although a collimated light beacon has been described in conjunction with the present invention, it is to be appreciated that no limitation on the present invention is intended. Rather, the present invention may be used with virtually any light source, including but not limited to collimated, converging, or diverging light sources.  
         [0024]    While the methods and apparatus for the Optical Beacon for Aligning Mirror Systems of the present invention as herein shown and disclosed in detail is fully capable of obtaining the objects and providing the advantages herein before stated, it is to be understood that it is merely illustrative of preferred embodiments of the invention and that no limitations are intended to the details of the method, construction or design herein shown other than as described in the appended claims.