Abstract:
A method for constructing an optical switch and the switch constructed thereby are described. An optical switch having a pair of chips is assembled with a plurality of optical fibers mounted on the chips such that endfaces of the fibers extend beyond ends of the chips. The optical fibers may be mounted by adhering them to the chips. The endfaces of the fibers and the front surfaces of the chips are then polished to provide coplanar surfaces which are good optical couplers. The chips are then etched with an etchant material which is ineffective at etching the optical fibers. The chips may include a coating which is resistant to the etchant material.

Description:
[0001]    This application claims priority from provisional application serial No. 60/227,461, filed Aug. 24, 2000, the entire disclosure of which is incorporated herein by reference. 
     
    
     
       BACKGROUND  
         [0002]    The present invention generally relates to optical switches, and more particularly to optical switches having fibers with slanted ends and a method for making such optical switches.  
           [0003]    Optical switches having a pair of optical fibers, each having a slanted surface, are known. These conventional switches operate by displacing at least one of the fibers to contact the other fiber (closed position) or to release contact with the other fiber (opened position). In the closed position, input light is transmitted from one optical fiber to the other with little or no transmission loss. In the opened position, input light is reflected at least partially from one of the fibers, leading to complete or partial transmission loss. Complete transmission loss occurs during total internal reflection, when light approaches a dielectric interface at or above a critical angle and is thereby inhibited from being transmitted to the other optical fiber. When the angle is below the critical angle, or the distance between the optical fibers is sufficiently small, some input light may cross the gap between the optical fibers and thereby frustrate the total internal reflection.  
           [0004]    FIGS.  1 - 4  illustrate a conventional optical switch  10  which includes a pair of optical fibers  12  and at least one pair of chips  16 . The chips  16  each have a slanted edge surface  18 , and each of the optical fibers  12  has a slanted face  14 . The slanted nature of the faces  14  of the optical fibers  12  allows for total internal reflection when a pair of faces  14  are separated from one another. As shown in FIGS.  1 - 2 , the slanted faces  14  and the slanted edge surfaces  18  are coplanar, thereby allowing contact between each of the surfaces  18  and each of the faces  14  when the optical switch is in the closed position.  
           [0005]    In the opened position (FIG. 1), input light  22  reaches the face  14 , which acts as a dielectric interface, and is translated into reflected light  24  which is reflected in a direction transverse to the opposing face  14 . In the closed position (FIG. 2), the input light passes through the faces  14  and continues its transmission from one optical fiber  12  to the other optical fiber  12 .  
           [0006]    Conventionally, the faces  14 ,  18  of, respectively, the optical fibers  12  and the chips  16  are formed by polishing. The polishing step is performed to create faces  14  which are coplanar to each other. One observed disadvantage is that during polishing, the optical fibers  12  become abraded at a different rate than the chips  16 . Specifically, the optical fibers  12  abrade at a quicker rate than the chips  16 . Thus, sometimes the polishing process can result in the faces  14  of the optical fibers  12  not being coplanar with the faces  18  of the chips  16 , leading to a greater gap between the fiber end faces  14  than between the chips&#39; edge surfaces  18  (FIG. 3). When the chips  16  contact each other (FIG. 4), a gap  25  remains between the faces  14  of the optical fibers  12 . In such a circumstance, the input light  22  breaks up into a partially reflected portion  26  and a partially transmitted portion  28 . The partially transmitted portion  28  indicates a higher than desired transmission loss.  
         SUMMARY  
         [0007]    The invention provides an optical switch that includes a pair of chips, each with an opposing face, and a pair of optical fibers, each with an opposing endface. Each of the optical fibers is initially mounted on a respective chip such that a portion of each optical fiber extends beyond the face of its respective chip upon final assembly.  
           [0008]    The invention further provides a method for assembling an optical switch. The method includes mounting a pair of optical fibers on a pair of chips, wherein each optical fiber is mounted to overlap its respective chip a given distance, polishing endfaces of the optical fibers, and etching faces of the chips to ensure that each optical fiber overlaps its respective chip a second set distance.  
           [0009]    The foregoing and other advantages and features of the invention will be more readily understood from the following detailed description of the invention, which is provided in connection with the accompanying drawings. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0010]    FIGS.  1 - 4  are cross-sectional views of a conventional optical switch.  
         [0011]    [0011]FIG. 5 is a cross-sectional view of an optical switch constructed in accordance with an embodiment of the invention.  
         [0012]    [0012]FIG. 6 is a cross-sectional view of the optical switch of FIG. 5 after polishing in the open position.  
         [0013]    [0013]FIG. 7 is a cross-sectional view of the optical switch of FIG. 6 in the closed position.  
         [0014]    [0014]FIG. 8 is a cross-sectional view of an optical switch constructed in accordance with another embodiment of the invention.  
         [0015]    [0015]FIG. 9 is a cross-sectional view of the optical switch of FIG. 8 after polishing in the open position.  
         [0016]    [0016]FIG. 10 is a cross-sectional view of the optical switch of FIG. 9 after etching in the open position.  
         [0017]    [0017]FIG. 11 is a flow diagram of steps taken to construct an optical switch in accordance with an embodiment of the invention.  
         [0018]    [0018]FIG. 12 is a cross-sectional view of an optical switch after etching and in the open position constructed in accordance with another embodiment of the invention. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0019]    With reference to FIGS.  5 - 7 , in which like numerals designate like elements, there is shown an optical switch  110  which has a pair of optical fibers  112  and at least one pair of chips  116 . The chips  116  are preferably formed of silicon, while the optical fibers  112  are preferably formed of silica. The optical fibers  112  may be mounted on the chips  116  through the use of an adhering material or mechanism. Any suitable adhering material or mechanism may be used, such as, for example, ultraviolet curable adhesive, solder, aluminum dioxide direct bonding, or Sol-Gel glass. The optical fibers  112  each include an unpolished endface  114  and the chips  116  each have an unpolished edge surface  118 . The optical fibers  112  protrude over the surfaces  118  of the chips  116  a distance  120 . Although a single pair of chips  116  are shown, it is to be understood that two or more pairs of chips  116  may be disposed about the optical fibers  112 . The chips  116  may include grooves into which the optical fibers may be mounted.  
         [0020]    The distance  120  is preferably chosen to at least compensate for the increased rate of abrasion experienced by the optical fibers  112  relative to the chips  116  during the polishing process. After assembly of the optical fibers  112  with the chips  116 , the endfaces  114  and the surfaces  118  of, respectively, the optical fibers  112  and chips  116  are polished. The optical fibers  112 , which are generally formed of a material less resistant to the abrasive characteristics of the polishing process than the chips  116  become more abraded than the chips  116 . With specific reference to FIG. 6, the optical switch  110  is shown in the opened position with the polished endfaces  114 ′ and the polished edge surfaces  118 ′ generally flush with one another. It may be possible, depending upon a variety of factors, such as, for example, the materials used to form the optical fibers and the chips and to form the polishing material and/or the polishing procedure utilized, that the polished endfaces  114 ′ may protrude slightly beyond the polished edge surfaces  118 ′, or the polished edge surfaces  118 ′ may slightly protrude beyond the polished endfaces  114 ′.  
         [0021]    An additional etching step is generally employed next, especially if the polishing step eliminates the protrusion of the optical fibers  112  beyond the chips  116 . Commercially available pre-mixed formulations of potassium hydroxide-based etchants such as, for example, a preferred silicon etchant PSE-200 manufactured by Transene Company, Inc. of Danvers, Mass., serve as a suitable wet chemistry for this purpose provided the selected etchant affords adequate selectivity to both the silica fibers and any adhesive or epoxies present. Additionally, a potassium hydroxide solution mixed from a solid pellet or concentrated liquid form with an appropriate amount of water or isopropyl alcohol as a diluent may be used to etch the chips  116 . Exposing the optical array  110  to the etchant material creates etched edge surfaces  118 ″ on the chips  116  (FIG. 7).  
         [0022]    The optical switch  110  is shown in a closed position in FIG. 7. As shown, the polished endfaces  114 ′ contact one another. Each of the polished endfaces  114 ′ protrude beyond the surfaces  118 ″ a distance  125 . Preferably, the distance  125  is between about 0.4 microns and about three microns. By protruding the optical fibers  116  to a predetermined distance  125  past the surfaces  118 ″ of the chips, the endfaces  114 ′ are allowed to contact one another, thereby allowing the input light  122  to transmit from one of the optical fibers  112  to the other.  
         [0023]    [0023]FIG. 12 shows an alternative embodiment of the invention. An optical switch  410  is illustrated including an optical fiber  12  mounted on a chip  16  such that the endface  14  of the fiber  12  is generally flush with the surface  18  of the chip  16 . In an opposing relationship, there is also illustrated an optical fiber  112  mounted on a chip  116  such that the fiber protrudes beyond the chip. Specifically, as described with relation to FIGS.  5 - 7 , the optical fiber  112  and the chip  116  are polished and etched so as to obtain a polished endface  114 ′ which protrudes a distance  125  beyond an etched edge surface  118 ″. With such an arrangement, the optical switch  410  can move from the open position (as shown in FIG. 12) to the closed position in which the endfaces  14 ,  114 ′ come in contact.  
         [0024]    FIGS.  8 - 10  illustrate another embodiment of the invention, specifically showing an optical array  210  having paired optical fibers  112  with endfaces  114  and paired chips  216 . The chips  216  differ from the chips  116  in that they include a coating  217  on their outer surface. The coating  217  is formed of a material which is resistant to etchant materials, such as, for example, silicon nitride or silicon dioxide. Preferably, the coating  217  is chemical-vapor deposited on the chips  216 . For example, the singulated chips  216  may be placed within a chemical-vapor deposition chamber and conformaily deposited upon with the coating  217 . Alternatively, the chips  216  may be selectively coated by application of the coating  217  on less than all of the surfaces of the chips  216 , or have the coating present only upon the chip edge surface  218  and backside by depositing on the chips while still in wafer form, prior to singulation (dicing).  
         [0025]    As shown in FIG. 8, the edge surfaces  218  are initially coated with the coating  217 . Upon polishing the endfaces  114  and the surfaces  218 , polished endfaces  114 ′ remain which may or may not overlap the polished edge surfaces  218 ′ of the chips  216  (FIG. 9). The polishing step abrades off the coating  217  which was covering the surfaces  218 , leaving exposed the polished surfaces  218 ′. The optical array  210  is then exposed to the etchant material, which does not affect the endfaces  114 ′ of the optical fibers  112 , but etches the surfaces  218 ′ of the chips  216 , leaving etched edge surfaces  218 ″ (FIG. 10). The etchant material does not affect the coating  217 , leaving free standing portions  219  which are extremely fragile as a free standing structure and which may be subsequently removed with ease. By coating the chips  216  with the coating  217 , the chips  216  are protected from the etchant material except at the surfaces  218 .  
         [0026]    [0026]FIG. 11 illustrates various steps used in a method to assemble the optical switch  110 . At step  300 , the optical fibers  112  are assembled with the chips  116 . The assembly includes overlapping the optical fibers  112  with respect to the chips  116  to such an extent as to compensate for the polishing action. The optical fibers  112  then may be mounted upon the chips  116  by adhering the fibers  112  to the chips  116  at step  305 . At step  310 , the endfaces  114  of the optical fibers  112  and the surfaces  118  of the chips  116  are polished, leaving polished endfaces  114 ′ and polished surfaces  118 ′. Finally, at step  315 , an etchant material is used to etch the surfaces  118 ′, leaving etched surfaces  118 ″ which are overlapped by the optical fibers  112 . The etchant material is chosen so as not to etch the optical fibers  112 . Provided the chips are formed of silicon and the optical fibers are formed of silica, the etchant chemistry is chosen to preferentially etch the silicon chips with respect to the silica optical fibers.  
         [0027]    While the invention has been described in detail in connection with the preferred embodiments known at the time, it should be readily understood that the invention is not limited to such disclosed embodiments. Rather, the invention can be modified to incorporate any number of variations, alterations, substitutions or equivalent arrangements not heretofore described, but which are commensurate with the spirit and scope of the invention. For example, although the optical switch  110  has been shown and described with optical fibers having slanted endfaces  114  and slanted surfaces  118 , it should be noted that the invention is not so limited. The endfaces  114  and the surfaces  118  may be parallel to one another. Accordingly, the invention is not to be seen as limited by the foregoing description, but is only limited by the scope of the appended claims.