Abstract:
Provided is a 2×2 optical switch includes a substrate, a first input fiber and a first output fiber, a second input fiber and a second output fiber, a rotating mirror, torsion bars, and an electrostatic force generating part. The first input fiber and a first output fiber are arranged at a predetermined distance from a central point in a first optical path passing through the central point over the substrate. The second input fiber and a second output fiber are arranged at a predetermined distance from the central point in a second optical path that passes through the central point and is orthogonal to the first optical path. The rotating mirror is positioned at around the central point and turns on a turning shaft. The torsion bars support the rotating mirror and the electrostatic force generating part supplies a drive force to the rotating mirror.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    This application claims the priority of Korean Patent Application No. 2003-3667, filed on Jan. 20, 2003, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein in its entirety by reference.  
           [0002]    1. Field of the Invention  
           [0003]    The present invention relates to an optical switch using a micro-electromechanical system (MEMS), and more particularly, to a 2×2 way optical switch.  
           [0004]    2. Description of the Related Art  
           [0005]    U.S. Pat. Nos. 6,303,885, 6,315,462, and 6,229,640 disclose techniques for a 2×2 way optical switch used in various optical applications. Optical switches disclosed in U.S. Pat. Nos. 6,229,640 and 6,315,462 have a structure in which a mirror is driven by an electro-static comb drive and the optical switch disclosed in U.S. Pat. No. 6,303,885 has a structure in which a mirror is driven by spring arms. The structures of the optical switches have a common feature in that the mirror moves in parallel with the plane of a substrate by an actuator.  
           [0006]    [0006]FIG. 1 is a microscopic photo of a conventional 2×2 comb drive optical switch having two inputs and two outputs, and FIG. 2 is a plane view of a portion marked with dotted lines in FIG. 1 to explain the conventional 2×2 comb drive optical switch shown in FIG. 1.  
           [0007]    As shown in FIGS. 1 and 2, first and second optical input fibers  2   a  and  2   b , and first and second optical output fibers  3   a  and  3   b  are arranged at around the central point P at an angle of 90 degrees. A mirror  1  is positioned at the central point P of the first and second optical input and output fibers  2   a ,  2   b ,  3   a , and  3   b.    
           [0008]    As shown in FIG. 3, when the mirror  1  is positioned out of the central point P, optical signals incident through the first and second input fibers  2   a  and  2   b  proceed toward the first and second output fibers  3   a  and  3   b  on the same axes with the first and second input fibers  2   a  and  2   b  without being reflected.  
           [0009]    As can be seen in FIG. 4, when the mirror  1  is positioned at the central point P, an optical signal incident through the first input fiber  2   a  is reflected from one side of the mirror  1  and then proceeds toward the second output fiber  3   b , and an optical signal incident through the second input fiber  2   b  is reflected from the other side of the mirror  1  and then proceeds toward the first output fiber  3   a.    
           [0010]    Here, as shown in FIG. 4, when an optical signal is reflected by a mirror, the optical signal is reflected out of the central point of the mirror. Thus, the reflected optical signal does not proceed toward the central point of a target fiber. This is caused by an offset of an optical path due to the thickness of the mirror.  
           [0011]    The offset causes light loss. The thicker the mirror, the greater the offset, which increases light loss. Accordingly, the thickness of the mirror is required to be reduced as it can be in order to reduce the offset of an optical path changed by the mirror. However, since in the above-described comb drive optical switch, the mirror moves in parallel with the plane of the substrate and a reflective surface of the mirror is perpendicular to the plane of the substrate, there is a limitation in reducing the thickness of the mirror. In particular, when forming a mirror, silicon is vertically etched in a plasma process, and then a metal having a high reflectance is deposited on the surface of the resultant structure. Thus, it is difficult to reduce the thickness of the mirror. Also, since the vertically etched surface is used as a reflective surface, a large amount of light is lost when light is reflected. Furthermore, since a high-priced silicon on insulator (SOI) wafer not a general wafer is used, cost for manufacturing the mirror is high.  
         SUMMARY OF THE INVENTION  
         [0012]    The present invention provides an optical switch capable of reducing an offset of an optical path by reducing the thickness of a mirror.  
           [0013]    The present invention also provides an optical switch which can cause a small amount of light loss and be manufactured at a low cost.  
           [0014]    According to an aspect of the present invention, there is provided an optical switch including a substrate, a first input fiber and a first output fiber, a second input fiber and a second output fiber, a rotating mirror, torsion bars, and an electrostatic force generating part. The first input fiber and a first output fiber are arranged at a predetermined distance from a central point in a first optical path passing through the central point over the substrate. The second input fiber and a second output fiber are arranged at a predetermined distance from the central point in a second optical path that passes through the central point and is orthogonal to the first optical path. The rotating mirror is positioned at around the central point and turns on a turning shaft extending in parallel with the substrate. The torsion bars support the rotating mirror so that the rotating mirror rotates. The electrostatic force generating part supplies a drive force to the rotating mirror.  
           [0015]    In an aspect of the invention, trenches into which the first and second input fibers and the first and second output fibers are inserted are formed in the substrate along the first and second optical paths.  
           [0016]    In an exemplary embodiment of the invention, the rotating mirror has a first position where the rotating mirror is parallel with the substrate and a second position where the rotating mirror is perpendicular to the substrate, and turns from the first position to the second position by the electrostatic force generating part. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0017]    The above and other features and advantages of the present invention will become more apparent by describing in detail exemplary embodiments thereof with reference to the attached drawings in which:  
         [0018]    [0018]FIG. 1 is microscopic photo of a conventional optical switch including a mirror perpendicular to a substrate;  
         [0019]    [0019]FIGS. 2 through 4 are views for illustrating an optical path changed by the conventional optical switch shown in FIG. 1;  
         [0020]    [0020]FIG. 5 is a schematic plane view of an optical switch according to the present invention;  
         [0021]    [0021]FIG. 6 is a perspective view of a mirror and a mirror driving actuator used in the optical switch according to the present invention;  
         [0022]    [0022]FIG. 7 is a schematic cross-sectional view of the mirror driving actuator shown in FIG. 6;  
         [0023]    [0023]FIG. 8 is a cross-sectional view taken along line I-I of in FIG. 5;  
         [0024]    [0024]FIG. 9A is a cross-sectional view of a trench into which an optical fiber is fixed, in the optical switch, according to the present invention, shown in FIG. 5;  
         [0025]    [0025]FIG. 9B is a plan view of a spring formed in an opening of a trench into which an optical fiber is fixed in the optical switch according to an exemplary embodiment of the present invention;  
         [0026]    [0026]FIG. 10 is a schematic cross-sectional view for explaining a process of inserting an optical fiber into a trench in the optical switch according to the present invention;  
         [0027]    [0027]FIGS. 11A and 11B are views for explaining the operation of the optical switch according to the present invention; and  
         [0028]    [0028]FIGS. 12A through 16B are cross-sectional views for explaining a method of manufacturing the optical switch according to the present invention. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0029]    Hereinafter, an optical switch according to an exemplary embodiment of the present invention will be described in detail with reference to the attached drawings.  
         [0030]    As shown in FIG. 5, optical input fibers  20   a  and  20   b , and optical output fibers  30   a  and  30   b  are arranged at around the central point P at an angle of about 90 degrees. A rotating mirror  10  is positioned at the central point P. As in a general optical switch, the optical input fibers  20   a  and  20   b , and the optical output fibers  30   a  and  30   b  are inserted into trenches  41  formed in a substrate  40 . The trenches  41  are arranged at around or at about the central point P at an angle of about 90°. As shown in FIG. 6, the rotating mirror  10  is fixed to posts  42  formed on the substrate  40  and supported by torsion bars  43  that extend from the posts  42  in parallel with the substrate  40 . The torsion bars  43  support the rotating mirror  10  so that the rotating mirror  10  is parallel with the substrate  40 . When the rotating mirror  10  turns due to an electrostatic force, the torsion bars  43  provide a returning force to the rotating mirror  10  so that the rotating mirror  10  returns to the original position. The torsion bars  43  extend toward a turning axis X-X at an angle of approximately 45 degrees with the optical input fibers  20   a  and  20   b  and the optical output fibers  30   a  and  30   b . A well  45  is formed under the rotating mirror  10 . The well  45  has a rectangular shape and a vertical sidewall  44  contacting one side of the rotating mirror  10  when the rotating mirror  10  turns due to an electrostatic force.  
         [0031]    [0031]FIG. 7 shows the cross-section of the well  45  and the rotating mirror  10 . Referring to FIG. 7, a fixed electrode  46 , which is opposite to the rotating mirror  10  when the rotating mirror  10  faces the vertical sidewall  44 , is formed on the vertical sidewall  44 . The fixed electrode  46  extends to the bottom of the well  45 . A dielectric or insulating layer  47 , which serves to prevent the direct contact of the rotating mirror  10  with the fixed electrode  46 , is formed on the fixed electrode  46 . The rotating mirror  10  is formed of a conductive material, e.g., a metal thin film, and has reflective surfaces on either side thereof. Thus, when the rotating mirror  10  is substantially parallel with the substrate  40  as indicated by “A”, the rotating mirror  10  passes a beam so as to optically connect the fibers facing on the same axis, and when the rotating mirror  10  is substantially perpendicular to the substrate  40  as indicated by “B”, the rotating mirror  10  reflects an incident beam so as to change the optical path of the incident beam. According to an exemplary embodiment of the present invention, an anti-electrostatic electrode  48 , which maintains the same potential as the rotating mirror  10 , is formed under the rotating mirror  10  and on an opposite side of the well  45  centering at around the posts  42 . This is to prevent an electrostatic force from being generated between the rotating mirror  10  and the vertical sidewall  44  of the well  45  so that an attractive force is generated only in the well  45  due to the electrostatic force.  
         [0032]    [0032]FIG. 8 is a cross-sectional view taken along line I-I of FIG. 5. Referring to FIG. 8, an insulating layer  49  is formed at around the central area in which the rotating mirror  10  is positioned. A metal layer  50  is formed on the insulating layer  49 . The metal layer  50  is formed from the same material the rotating mirror  10  is formed from, at the same time, and then separated from the rotating mirror  10  during a patterning process of a process of manufacturing the rotating mirror  10 . The insulating layer  49  is a sacrificial layer necessary for forming the rotating mirror  10  and the posts  42 , serves as a layer on which a metal thin film is deposited to form the rotating mirror  10 , and is locally removed after completing the rotating mirror  10 .  
         [0033]    [0033]FIG. 9A is a cross-sectional view showing the internal structure of the trenches to which the optical input fibers  20   a  and  20   b  and the output fibers  30   a  and  30   b  are fixed. Referring to FIG. 9, a portion of the insulating layer  49  and a portion of the substrate  40  are etched to form the trenches  41  into which the optical input fibers  20   a  and  20   b  and the output fibers  30   a  and  30   b  are inserted. Openings of the trenches  41  are narrowed by the metal layer  50 . Here, a spring  51  of the metal layer  50  restrains the optical input fibers  20   a  and  20   b  and the optical output fibers  30   a  and  30   b  from separating from the trenches  41 . Referring to FIG. 9B, the spring  51  may be further flexibly comb-shaped. As shown in FIG. 10, the spring  51  elastically deforms so that the optical input fibers  20   a  and  20   b  and the optical output fibers  30   a  and  30   b  engage the trenches  41 . Channels  41   a  are formed to a width smaller than the diameter of the optical input fibers  20   a  and  20   b  and the optical output fibers  30   a  and  30   b  in the trenches  41  and in the surface of the substrate  40 . The channels  41   a  support the optical input fibers  20   a  and  20   b  and the optical output fibers  30   a  and  30   b  and determine the positions of the optical input fibers  20   a  and  20   b  and the optical output fibers  30   a  and  30   b.    
         [0034]    [0034]FIGS. 11A and 11B are views for explaining an optically switching state by the rotating mirror  10 . FIG. 11A shows that an electrostatic force is not applied to the rotating mirror  10 , i.e., the rotating mirror  10  is parallel with the substrate  40  as indicated by “A” in FIG. 7. In this state, beams incident through the optical input fibers  20   a  and  20   b  proceed toward the optical output fibers  30   a  and  30   b  on the same axes as the optical input fibers  20   a  and  20   b , respectively. FIG. 11B shows that an electrostatic force is applied to the rotating mirror  10 , i.e., the rotating mirror  10  is substantially perpendicular to the substrate  40  as indicated by “B” in FIG. 7. In this state, beams incident through the optical input fibers  20   a  and  20   b  are reflected from the rotating mirror  10  and then proceed toward the optical output fibers  30   b  and  30   a  on the different axes from the optical input fibers  20   a  and  20   b , respectively.  
         [0035]    As described above, an optical switch according to the present invention is a 2×2 optical switch in which a moveable electrostatic actuator and optical fibers are combined. The optical switch has a structure in which a mirror and the fibers are arranged by a trench structure having a spring.  
         [0036]    A process of manufacturing the optical switch of the present invention having the above-described structure will be described in brief with reference to FIGS. 12A through 16B. This process corresponds to a well-known MEMS process, and thus steps of forming detail structures will be briefly explained herein. FIGS. 12A, 13A,  14 A,  15 A, and  16 A are cross-sectional views for showing a mirror and a well thereunder, and FIGS. 12B, 13B,  14 B,  15 B, and  16 B are cross-sectional views for showing trenches.  
         [0037]    [0037]FIGS. 12A and 12B, a well  45  having a vertical sidewall  45   a  and a channel  41   a  constituting a lower part of the trench  41  into which a fiber is inserted are formed in a silicon wafer or a glass substrate  40 . A metal layer is deposited and then patterned to form a fixed electrode  46  and an anti-electrostatic electrode  48 .  
         [0038]    As shown FIGS. 13A and 13B, an insulating layer  47  is formed on the entire surface of the glass substrate  40 .  
         [0039]    As shown in FIGS. 14A and 14B, a film  49  made of an insulator is laminated on the insulating layer  47  on the glass substrate  40 .  
         [0040]    As shown in FIGS. 15A and 15B, a metal layer  50  is deposited on the film  49  and then patterned to form a mirror  10  opposite to the well  45  and a spring  51  that is positioned over the channel  41   a.    
         [0041]    As shown in FIG. 6, structures for supporting the mirror  10  and fibers are completed using a dry etching process.  
         [0042]    As described above, in an optical switch according to the present invention, a mirror can turn at an angle of approximately 90 degrees, which results in adjusting optical paths. In other words, the optical switch according to the present invention can be switched by a moveable actuator having a simple structure without using a comb drive linear actuator having a complicated structure. Here, the thickness of the mirror is determined when depositing a metal layer. In other words, since the metal layer can be deposited to a thickness of hundreds of Å, the thickness of the mirror can be drastically reduced. The reduction in the thickness of the mirror means that the light loss due to an offset in a conventional optical switch can be almost eliminated. Also, since the deposited metal layer is used as the mirror, light loss caused by the roughness of the mirror can greatly be reduced.  
         [0043]    The optical switch according to the present invention can be manufactured using a general wafer unlike existing methods to manufacture switches from an SOI wafer. Thus, the optical switch can be manufactured according to a simple unit process, resulting in a great reduction in cost for manufacturing the optical switch.  
         [0044]    While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it will be understood by those of ordinary skill in the art that various changes in form and details may be made therein without departing from the spirit and scope of the present invention as defined by the following claims.