Abstract:
Novel light switches and attenuators are disclosed. In one form of the invention, a novel 1×2 switch is formed by positioning a moveable cantilever mirror having an opening intermediate three fiberoptic lines. In another form of the invention, a novel n×n switch is formed by positioning a moveable cantilever mirror having n openings intermediate n sets of three fiberoptic lines. In still another form of the invention, a novel variable optical attenuator is formed by incrementally positioning a moveable cantilever mirror having an opening intermediate a set of three fiberoptic lines.

Description:
FIELD OF THE INVENTION  
         [0001]    This invention relates to optical systems in general, and more particularly to switches and attenuators for use in optical systems.  
         BACKGROUND OF THE INVENTION  
         [0002]    In many situations, it is necessary to switch or attenuate an optical signal that is transmitted within an optical system.  
           [0003]    By way of example but not limitation, in a typical optical system, it may be necessary to switch or attenuate an optical signal between a first line (e.g., a fiberoptic or fiber line) and a second line (e.g., a fiberoptic or fiber line).  
           [0004]    Attenuation and switching techniques that exist in the art do not address the problem of fast and accurate switching and attenuation combined with ease of implementation.  
         SUMMARY OF THE INVENTION  
         [0005]    One object of the present invention is to provide novel apparatus for switching a light signal in an optical system.  
           [0006]    Another object of the present invention is to provide novel apparatus for attenuating a light signal in an optical system.  
           [0007]    Still another object of the present invention is to provide a novel method for switching a light signal in an optical system.  
           [0008]    Yet another object of the present invention is to provide a novel method for attenuating a light signal in an optical system.  
           [0009]    These and other objects of the present invention are addressed by the provision and use of novel light switches and attenuators. In one form of the invention, a novel 1×2 switch is formed by positioning a movable mirror having a hole therethrough intermediate three fiberoptic lines. In another form of the invention, an n×n switch is formed by positioning a movable mirror having a plurality of holes therethrough intermediate a plurality of sets of three fiberoptic lines. In still another form of the invention, a novel light attenuator is formed by positioning a movable arm having a hole therethrough intermediate three fiberoptic elements. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0010]    Still other objects and features of the present invention will be more fully disclosed by the following detailed description of the preferred embodiments of the invention, which is to be considered together with the accompanying drawings, wherein like numbers refer to like parts and further wherein:  
         [0011]    [0011]FIG. 1 is a schematic drawing showing the operational use of a switch and variable optical attenuator;  
         [0012]    [0012]FIG. 2 is a schematic top view showing a novel 1×2 switch;  
         [0013]    [0013]FIG. 3 is a top view showing an n×n switch;  
         [0014]    [0014]FIGS. 4 a - 4   d  are cross-sectional side views showing the fabrication of the 1×2 switch of FIG. 2;  
         [0015]    [0015]FIGS. 5 a - 5   b  are cross-sectional side views showing the formation of a hole through the mirror of the 1×2 switch shown in FIG. 2; and  
         [0016]    [0016]FIG. 6 is a schematic diagram showing a method for making the switch of FIG. 2. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0017]    Referring to FIG. 1, there is schematically shown a switch and variable optical attenuator  5  with an input fiber  6 , a first output fiber  7  and a second output fiber  8 . A transmitter device  6   a  is attached to input fiber  6 . Receiver devices  7   a ,  8   a  are attached to output devices  7 ,  8 , respectively. In a preferred embodiment, switch and variable optical attenuator  5  switches a light beam  9 , emitted by transmitter device  6   a  through input fiber  6 , between receiver devices  7   a ,  8   a  coupled with first output fiber  7  and second output fiber  8 , respectively. Additionally, switch and variable optical attenuator  5  may switch light beam  9  traveling from receiver devices  7   a ,  8   a  to transmitter device  6   a . Alternatively, receiver devices  7   a ,  8   a  may comprise a single device with two separate receivers. In another preferred embodiment, switch and variable optical attenuator  5  attenuates light beam  9  as it is switched between first output fiber  7  and second output fiber  8 .  
         [0018]    Looking now at FIG. 2, there is shown a novel 1×2 switch and variable optical attenuator  5  formed in accordance with the present invention. Switch and variable attenuator  5  utilizes a vertical mirror  10  in conjunction with a first fixed optical fiber  15 , a second fixed optical fiber  20 , and a third fixed optical fiber  25 . Input fiber  6 , first output fiber  7  and second output fiber  8  (illustrated in FIG. 1) correspond to first fixed optical fiber  15 , second fixed optical fiber  20  and third fixed optical fiber  25  (illustrated in FIG. 2), respectively. Each of the fibers  15 ,  20  and  25  are contained in v-grooves  166  etched into the structure of switch  5 . V-grooves  166  are positioned at known angles relative to one another. For example, this angle may be 45°. As such, the paths of light beams  45 ,  55 ,  65 , and positioning of mirror  10  relative to these paths, are known.  
         [0019]    Still looking at FIG. 2, mirror  10  contains an opening  30 . Opening  30  may be a physical opening where the light beams constitute visible light. Alternatively, opening  30  may comprise a material that acts as a conduit for particular wavelengths of light while mirror  10  comprises another material that acts as about one end at a point  35 . When mirror  10  is in a first end position  40 , opening  30  is positioned such that light beam  45  emitted by optical fiber  15  is reflected by mirror  10 , adjacent point  50 , toward optical fiber  20  along path  55 . When mirror  10  is in a second end position  60  (as shown in phantom) opening  30  is positioned such that light beam  45 , emitted by optical fiber  15 , passes through mirror  10 , via opening  30 , toward optical fiber  25  along path  65 . Although not shown, light beam  45  can pass through mirror  10  via opening  30  toward optical fiber  25  along path  65 .  
         [0020]    Additionally, mirror  10  may also be positioned between first end position  40  and second end position  60 . This incremental positioning of mirror  10  acts as an attenuator in that a first portion of light beam  45  is reflected by mirror  10  to travel along path  55  while a second portion, which includes all or some of the remainder from the first portion of light beam  45 , is transmitted through mirror opening  30  along path  65 . The first portion of light beam  45  may be configured to increase or decrease in intensity along path  55  toward second optical fiber  20  as mirror  10  is positioned between first end position  40  and second end position  60 . The second portion of light beam  45  may also be configured to increase or decrease in intensity along path  65  toward optical fiber  25  as mirror  10  is positioned between first end position  40  and second end position  60 .  
         [0021]    Furthermore, switch  5  may also selectively transmit light beam  55  and light beam  65  from optical fiber  20  and optical fiber  25 , respectively, to optical fiber  15 . As such, mirror  10  may operate to switch or attenuate light beam  55  and light beam  65 .  
         [0022]    Mirror  10  is actuated in the preferred embodiment by applying a voltage between a first contact pad  70  and a second contact pad  75 . This voltage difference is transferred from the first contact pad  70  and the second contact pad  75  to a first electrode (not shown) and a second electrode (not shown), respectively. Mirror  10  contains the first electrode (not shown). The voltage difference creates an electrostatic force which causes a first end  32  of mirror  10  to deflect from its original position. As shown in FIG. 2, mirror  10  is unactuated at position  40  and is fully actuated at position  60 . It should also be noted that mirror  10  can be partially actuated at any point between position  40  and position  60 . Alternatively, mirror opening  30  can be repositioned such that in the unactuated state light beam  45  is transmitted to third fixed optical mirror  25  and in the fully actuated state light beam  45  is reflected toward second fixed optical fiber  20 .  
         [0023]    In either of the above described configurations, when mirror  10  is in the second end position  60 , it is electrostatically held in place against a shock stop  80 . As such, mirror  10  will not vibrate due to the electrostatic force holding mirror  10  against shock stop  80 . In an alternative embodiment (not shown), another shock stop  80  is also configured opposite to the second end position  60  and adjacent to first end position  40 . In this configuration, mirror  10  will not vibrate if an electrostatic force is applied.  
         [0024]    In end position  40 , without applying an electrostatic force to hold mirror  10  fixedly in place, vibrations may occur in mirror  10 . Opening  30  may be sized larger than the width of light beam  45  to compensate for these vibrations.  
         [0025]    Now referring to FIG. 3, there is shown an n×n switch and variable optical attenuator array  85 . Switch array  85  utilizes a mirror  90  and a first series of fixed optical fibers  95 , a second series of fixed optical fibers  100 , and a third series of fixed optical fibers  105 . Each series of optical fibers  95 ,  100 ,  105  has a number of optical fibers represented by numerals from 1 to n. Further, the number of optical fibers in each series  90 ,  100 ,  105  is typically the same. Mirror  90  contains openings  110   a - 110   n  for allowing light beams  115  to pass, in the manner described below. The number of openings  110  is equal to the number of optical fibers, n, in each series. Generally, each of the optical fibers of first series  95  is associated with one of the mirror openings  110 , with one of the optical fibers of second series  100  and with one of the optical fibers of third series  105 , as illustrated in FIG. 2. That association will be described herein.  
         [0026]    Mirror  90  can be positioned at an angle θ to reflect each light beam  115  emitted by the optical fibers of first series  95  toward the optical fibers of the second series  100  along optical path  116 , as shown in FIG. 3. By changing the angle θ of mirror  90 , each light beam  115 , or a portion thereof, is allowed to pass through its respective opening of openings  110  and toward the optical fibers of the third series  105  along optical path  117 .  
         [0027]    In an alternative embodiment, mirror  90  has nonuniformly configured openings  110 . In such a configuration, openings  110  cause some light beams  115  to be reflected into the optical fibers of the second series  100  while other light beams  115  pass through mirror openings  110  toward the optical fibers of the third series  105 . Each of the openings  110  may be uniquely positioned in mirror  90  to allow varying degrees of intensity of light to be reflected and/or transmitted to the several optical fibers along the second and third series  100 ,  105  while the mirror  90  is at a single position.  
         [0028]    Mirror  90  is actuated in the preferred embodiment by applying a voltage between first contact pad  120  and second contact pad  125 . This voltage difference is transferred from the first contact pad  120  and the second contact pad  125  to a first electrode (not shown) and to a second electrode (not shown), respectively. Mirror  90  contains the first electrode (not shown). The applied voltage difference creates an electrostatic force which causes a first end  128  of mirror  90  to deflect from its original position opposite its base at a second end  130 . A shock stop  135  is positioned adjacent to the first end  128  end of mirror  90 , opposite to its base adjacent to point  130 , at each terminal portion of deflection.  
         [0029]    Now looking at FIGS. 2, 4 a - 4   d ,  5   a - 5   b , and  6 , a method is disclosed for the fabrication of a switch. As seen in FIG. 4 a , a SOI wafer  140  is provided having two Si layers  145   a  and  145   b  with a SiO layer  150  therebetween. Alternatively, the switch may be configured out of two conducting materials separated by an insulating layer therebetween; or two non-conducting layers separated by an insulating layer, provided that electrodes are deposited onto the non-conducting materials, e.g., GaAs/SiO 2 /GaAs. In essence, the wafer may be fabricated out of two etchable materials separated by an etchant stop. Next, top side  155  of the wafer  140  is configured with a pattern (not shown) and on the bottom side  160  of the wafer  140  is also configured with a pattern (not shown). These patterns guide the etching described herein. An etchant is applied to the bottom side  160  to realize an initial portion via-hole  165   b  through  5   i  substrate  145   b  (see FIG. 4 b ). In a preferred embodiment, a wet etchant, such as KOH, is used to realize the initial portion via-hole  165   b  in the bottom side  160  of Si substrate  145   b.    
         [0030]    Now looking at FIGS. 2 and 4 c , an etchant is applied to the top side  155  to realize v-grooves  166  and mirror  10 . In a preferred embodiment, a wet etchant, such as KOH, is used to realize v-grooves  166  (see FIG. 2) and mirror  10  (see FIG. 4 c ) in Si substrate  145   a.    
         [0031]    Looking at FIGS. 5 a  and  5   b , opening  30  is realized in mirror  10  using Deep Reactive Ton Etching (DRIE). In order to begin formation of opening  30 , a thin layer of SiO 2  is grown to protect each V-groove  166  (see FIG. 2) and mirror  10  (see FIG. 4 c ). Any protective film previously applied to wafer  140 , such as during its manufacture, is removed using Deep Reactive Ion Etching (DRIE). Such a protective film may include a silicon nitride film (not shown). For example, one method of forming opening  30  includes applying etchant in two timed steps at portion  170  (see FIG. 5 a ) with opening  30  being realized at the conclusion of the application.  
         [0032]    Now looking at FIGS. 4 c  and  4   d , a via-hole  165   a  is realized to complete a via-hole  165  through wafer  140  (see FIG. 4 d ). First, the SiO 2  layer (not shown) is removed from the surface of mirror  10 . Second, the SiO 2  layer  150  is removed from between the openings  165   a ,  165   b  formed in each of the Si substrate layers  145   a ,  145   b . For example, in a preferred embodiment a buffered oxide etchant is used to remove the SiO 2 .  
         [0033]    In order to finalize switch  5 , looking at FIGS. 2 and 4 d , wafer  140  is oxidized and electrodes are added as described below. One preparation method includes oxidizing wafer  140  with 100 nm of silicon dioxide. Then, a first surface (not shown) and a second surface (not shown) of wafer  140  are each metalized to form a first electrode (not shown) and second electrode (not shown), respectively. In a preferred embodiment, the surface of mirror  10  is one of the electrodes. The surface of this electrode also provides an enhanced reflecting surface. As such, the metalization deposition provides reflectance for the mirror  10  as well as the conductance for the electrode. An example of a metalization deposition involves first covering a surface with chromium for adhesion and then covering the chromium surface with gold to create an electrode. First, contact pad  120  and second contact pad  125  are applied to wafer  140  and are electrically connected to the first electrode and the second electrode, respectively. To complete fabrication of switch  5 , the mirror structure is diced from the wafer and placed onto an optical component package. The preceding sequence of steps illustrated above may be varied, e.g., top side  155  could be etched prior to etching bottom side  160 , etc.  
         [0034]    The silicon wafer  140  is typically composed of a single crystalline structure, referred to as “(100) silicon”. The Miller indicies “(100)” describes the crystalline structure of a unit cube of silicon. The structural configuration of the “100” silicon causes etching to occur at a 45° angle relative to the origin of the unit cube. This is advantageous in that wafer  140  is etched at a known angle, which subsequently allows the precise alignment of optical fibers  15 ,  20  and  25 . Additionally, due to the structural configuration of the silicon wafer, etching permits mirror  10  to be formed with a very flat surface.  
         [0035]    Higher yields and lower costs for production of optical switches are possible due to the simplicity of the fabrication process, described above. Standard starting materials, such as 4-inch and 6-inch wafers, can be used for fabrication. Wet etching of wafer  140 , described above, is usually a multi-wafer process. Deep Reactive Ion Etching (DRIE) of wafer  140 , which is usually a single wafer process, has a low process time. These factors allow high volume production using this fabrication process.  
         [0036]    Additionally, the SiO layer acts as an insulator to reduce the current loss into the silicon wafer. This configuration reduces the power requirements of the unit.