Abstract:
An optical switch comprising an array of voltage-controlled interferometric switching elements. Different configurations and modes of operation are possible, but in each configuration the elements are arranged relative to the input and output fibers, such that a beam of light is incident or outgoing at an angle of 45 degrees to the surface of a corresponding element. This permits each element to be electronically controlled to either transmit or reflect light, such that the output beam exits the switch either parallel to or perpendicular to the input beam.

Description:
TECHNICAL FIELD OF THE INVENTION  
         [0001]    This invention relates to optical communications, and more particularly to an optical cross-connection device using micro-mirror elements.  
         BACKGROUND OF THE INVENTION  
         [0002]    Global communications traffic in the form of voice, data, and video has grown tremendously in the past decade. To meet demand, communications bandwidth capacity and geographic coverage have been substantially expanded. Optical signals sent over optical fiber have been a key factor in enabling these advances.  
           [0003]    A growing number of communications carriers are deploying optical switches, that is, switches that steer light pulses among different fiber spans without converting them into electrical signals at any point. The advantages of all-optical switching are significant. Optical switches promise to relieve bottlenecks, reduce costs, and provide good scalability.  
           [0004]    Researchers are at work on various technologies for optical switching. These include the use of tiny micro-mirrors, liquid crystals, bubbles, holograms, and thermo- and acousto-optics. It may be that different of these technologies are suitable for different applications. For example, some switching fabrics may be better for large scale applications such as optical cross connects, whereas other technologies may be more appropriate for optical add-drop multiplexers or gear used in metro as opposed to long haul networks.  
         SUMMARY OF THE INVENTION  
         [0005]    One aspect of the invention is an optical switch for switching a beam of light from an input fiber to an output fiber, the input fibers being parallel to the output fibers. The switch comprises an array of voltage-controlled interferometric optical switching elements. The elements are arrayed such that the axis of each input fiber and each output fiber is incident on an element at an angle of substantially 45 degrees. The array has two rows of elements such that each input beam and each output beam have an associated pair of elements, one in each row. The array also has an additional pair of elements at one end operable to reflect an input beam from one direction across the second row to the opposite direction across the first row. The array&#39;s configuration permits the elements to be electronically operated such that the output beam is outgoing in a direction parallel to the path of the input beam.  
           [0006]    An advantage of the invention is that it provides for an optical switch for numerous applications, such as for communications, laser displays, projection displays, hologram memory writers, switching between storage networking devices, DWDM signal separation, and others. Applications for optical communications routing are especially promising.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0007]    [0007]FIG. 1 illustrates a typical voltage-controlled interferometric (VCI) optical switch.  
         [0008]    [0008]FIG. 2 illustrates the operation of the switch of FIG. 1.  
         [0009]    [0009]FIG. 3 is a top plan view of a first embodiment of a cross connection switch in accordance with the invention.  
         [0010]    [0010]FIG. 4 is a perspective view of the switch of FIG. 3.  
         [0011]    [0011]FIG. 5 is a top plan view of a second embodiment of the cross connection switch in accordance with the invention.  
         [0012]    [0012]FIG. 6 illustrates how the switch of FIG. 5 may be operated in a one-to-many mode.  
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0013]    The following description is directed to various embodiments of an all-optical switch, suitable for dense wavelength division multiplexing (DWDM). DWDM is a fiber-optic transmission technique that employs light wavelengths to transmit data parallel-by-bit or serial-by-character.  
         [0014]    Various embodiments of the invention are described, each being a high speed optical cross connection comprising a plurality of voltage-controlled interferomeric optical switches.  
         [0015]    Voltage-Controlled Interferometric Optical Switches  
         [0016]    [0016]FIG. 1 illustrates a voltage-controlled interferometric (VCI) optical switch  10 . Switch  10  may be made using semiconductor fabrication techniques, and FIG. 1 is a cross sectional view of the layers of switch  10 .  
         [0017]    A first transparent electrode  12  is fabricated over a substrate  11 . The next layer  13  is a dielectric mirror, which may itself be comprised of multiple layers. An electro-optic polymer layer  14  separates the first mirror layer  13  from a second dielectric mirror layer  15 . The final layer is a second transparent electrode layer  16 .  
         [0018]    The electro-optic polymer layer  14  is made from a material whose optical reflective index varies in response to a change in electric field magnitude. As illustrated schematically by power source circuit  17 , a voltage difference is applied to the two electrode layers  12  and  16 .  
         [0019]    [0019]FIG. 2 illustrates the operation of switch  10 , including circuitry  21  for applying a voltage to operate switch  10 . When an optical length of electro-optical polymer layer  14  is equal to one-half wavelength of incident light, switch  10  is transparent for that wavelength. Therefore, switch  10  operates in response to changing the applied voltage.  
         [0020]    In FIG. 2, the incoming beam of light is incident on switch  10  at an angle. For purposes of this invention, it will be assumed that the angle of incidence is approximately 45 degrees. Because the axis of the incoming beam is not perpendicular to the face of switch  21 , the switching property of switch  10  depends on polarization. Thus, a polarizer  22  is placed in the path of the beam of light reflected from switch  10 . If the incident beam has been polarized, polarization at the output would not be necessary.  
         [0021]    Optical Switching Arrays, Using VCI Elements  
         [0022]    As explained above, a VCI optical switch  10  works as a simple optical switch, having either a reflection or transmission mode for a specific wavelength depending on an applied voltage. As explained below, an arrangement of an array of switches  10 , with a proper tilting angle, can be used as an optical cross connection switch.  
         [0023]    [0023]FIGS. 3 and 4 illustrate a first embodiment of a cross connection switch  30 , comprising an array of VCI switching elements, such as switch  10 . FIG. 3 is a top view, and FIG. 4 is a perspective view of switch  30 .  
         [0024]    The VCI elements  10  are arrayed with a tilting angle of 45 degrees. Input/output optical fibers  32 , which transmit laser beams, are installed parallel to each other and such that their optical axes are adjusted to elements  10 . Elements  10  are configured to operate as being transparent in an “off” state and reflective in an “on” state for a specific wavelength.  
         [0025]    Switch  30  has two rows of elements  10 . Each fiber  32  has an associated element  10  in the first row  30   a  and an associated element in the second row  30   b.    
         [0026]    In operation, an input beam enters switch  30  via an input fiber  32  and is transmitted through the corresponding element  10  in the first row  30   a . The beam is then transmitted across the second row  30   b  by “off” elements  10 , and back up to the first row  30   a  by two “on” end elements  10 . The beam then traverses the first row  30   a , through all appropriate “off” elements  10 , until it reaches the element  10  corresponding to an output fiber  32 . This element  10  is “on” so that the beam is reflected into the output fiber  32 . In this manner, the signal from any input fiber  32  may be routed to an output fiber  32 .  
         [0027]    As indicated in FIG. 3, various optics  33  may be placed in the path of the incoming beam. These optics  33  may include various lenses and prisms, as well as a polarizer. As discussed above, polarization is used because of the angle of incidence of the face of switching elements  10  relative to the incoming beam. Similarly, optics  34  may be placed in the path of the outgoing beam, including a polarizer when the incoming beam is not polarized.  
         [0028]    [0028]FIG. 4 further illustrates switch  30 . Each switching element  10  is installed with an angle of 45 degrees against the optical axis of the input/output fibers  32 . The output beam is transmitted in parallel with the input beam.  
         [0029]    [0029]FIG. 5 illustrates a second embodiment of the invention, a cross connection switch  50  having the beam paths in a perpendicular configuration. Switch  50  has as many rows as output fibers  52 . In the example of FIG. 5, there are four output fibers  52  and thus four rows of switch  50 . An input beam enters switch  50  and is transmitted to the row corresponding to the desired output fiber  52 . It is then reflected at a right angle toward the output fiber  52  and transmitted by intervening elements  10  so that it may enter the output fiber  52 . In this manner, input beams are transmitted perpendicularly towards output fibers  52 .  
         [0030]    [0030]FIG. 6 illustrates how switch  50  may be operated in a one-to-many mode. By adjusting the applied voltage between the “on” state and the “off” state, the beam can be split. Each element  10  in the path of the input beam that corresponds to a desired output fiber  62  is adjusted to this “mid-level” state so as to both transmit and reflect the signal.  
         [0031]    Other Embodiments  
         [0032]    Although the present invention has been described in detail, it should be understood that various changes, substitutions, and alterations can be made hereto without departing from the spirit and scope of the invention as defined by the appended claims.