Abstract:
A one-sided switch for redirecting light between adjacent ports. The switch uses a moveable refractor, in combination with a lens and a stationary reflector, to redirect light from one optical port to another. In a most simple embodiment light is redirected from one output port to another by repositioning the refractor in the optical path of the light and using only a single lens for collimating and focussing the light at the reflector and about the ports, respectively.

Description:
FIELD OF THE INVENTION 
     This invention relates to the switching of light between optical components, and more specifically to an optical switch for providing such switching. 
     BACKGROUND OF THE INVENTION 
     Optical switches of various kinds are well known for selectably switching light from one optical fiber or light-conducting path to another. One such switch is disclosed by Pan in U.S. Pat. No. 5,999,669 issued Dec. 7, 1999, which is incorporated herein by reference. Although this invention appears to adequately perform its intended function, it is believed to be costly to manufacture. For example, Pan&#39;s 1×2 switch requires three collimating lenses to input/output fibers to collimate and focus light received from input fibers and destined for output fibers respectively. Furthermore, Pan provides a two-sided switch wherein optical fibres extend from opposite ends of the switch to allow light to be switched from an input optical fibre on one end with two different output optical fibres at another end. Two-sided switches have proven successful for switching optical signals but remain bulky for packaging into devices requiring such switching. Furthermore two-sided optical switches are more costly to hermetically seal than a single-sided switch. 
     It is therefore an object of the invention to provide a more compact single-sided device providing similar functionality but requiring less space than a two-sided switch. 
     It is an object of the invention to provide a single-sided optical switch that obviates some of the disadvantages associated with two-sided prior art devices. 
     It is an object of this invention to provide an optical switch requiring fewer lenses than ports. 
     SUMMARY OF THE INVENTION 
     In accordance with the invention there is provided, an optical switch, comprising: 
     a plurality of ports for transmitting and receiving a beam of light; 
     a stationary reflector for receiving the beam of light from the at least one of the plurality of ports and for substantially reflecting at least a portion of the beam of light to an other of the plurality of ports; 
     a lens disposed between the plurality of ports and the stationary reflector for substantially collimating the beam of light from at least one of the plurality of ports at the stationary reflector and for substantially focussing the beam of light about the plurality of ports; 
     a moveable refractor selectably positionable between at least one of the plurality of ports and the stationary reflector, for switching the beam of light from one of the plurality of ports to an other of the plurality of ports via the lens and the stationary reflector. 
     An embodiment of the present invention provides one-sided switching through the use of a moveable refractor and a stationary mirror. Switching is effected by repositioning the refractor so as to redirect light from one output port to another. The use of a moveable refracting component is advantageous because the refracting component can be aligned with a relatively high degree of tolerance to small misalignment caused by unwanted vibration, which would affect moveable components more than fixed ones in a switching device. This is opposed to using a moveable mirror as the switching element, which is more sensitive to misalignment than a refracting component. 
     Advantageously, the switch, in accordance with this invention, can be configured to provide a switching device whereby two beams of light transmitted from a first and a second input port are switchable from two output ports to provide controlled feedback, or as a 1×2 switch by allowing a beam of light transmitted from a first port to be switched between output ports. Finally, having the optical fibres enter and leave on the same side makes the device more compact, while having fewer lenses than ports reduces the cost of fabricating and indeed reduces the space required to contain such a device. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Exemplary embodiments of the invention will now be described in conjunction with the drawings in which: 
     FIGS. 1A and 1B are schematic block diagrams depicting a selectable redirection of a beam of light by introducing an internally reflecting device in accordance with the prior art; 
     FIG. 1 is an end view of a fibre sleeve securely holding a plurality of optical fibres; 
     FIGS. 2 a  and  2   c  are illustrations of the invention showing a ray of light directed between optical fibre ports by an optical switch via a spacer, a lens and a reflector; 
     FIGS. 2 b  and  2   d  are schematic block diagrams showing one embodiment of the invention, wherein a ray of light directed between ports is redirected via a spacer, a lens, a reflector and a moveable refractor positionable between the lens and the reflector for selectably redirecting a beam of light between output ports; 
     FIGS. 3 a  and  3   b  are end views of the ports, showing a representation of two modes of operation of the invention; in the first mode of operation two input ports are optically coupled with two output ports prior to switching, while in the second mode there is optical coupling between only one input and one output port; 
     FIG. 4 is a schematic block diagram illustrating the functionality of the switch as described in FIGS. 3 a  and  3   b;    
     FIG. 5 is a schematic representation of another embodiment of the invention with a plurality (two) of movable refractors. 
    
    
     DETAILED DESCRIPTION 
     Turning now to FIGS. 2 a  through  2   d,  an optical switch in accordance with a preferred embodiment of the present invention is shown. An optical fibre sleeve  100  houses a plurality of optical fibre ends in a predetermined spaced relationship, for example as shown in FIG.  1 . The end faces of the fibres serve as ports generally referred to as  102  and more specifically referred to individually as ports  102   a,    102   b,    102   c,  and  102   d.  The ports  102  are optically coupled to a substantially collimating/focussing lens  104 , preferably in the form of a graded index (GRIN) lens, disposed adjacent the ports  102 . The lens  104  is for focussing light at the ports  102  and for collimating light at a distal end of the switch at a reflector  106 , in the form of a stationary reflecting mirror. 
     A moveable refractor  110 , in the form of a light-transmissive wedge, is positionable in or out of the optical path between the lens  104  and the reflector  106 . Alternatively, the refractor  110  comprises a prism or refractive optoelectronic device. An actuator  112  is provided for repositioning refractor  110  such that switching of the beam of light between ports  102  is performed. Optionally, a spacer  108  of light-transmissive material is placed in the optical path between the ports  102  and lens  104  to reduce insertion losses resulting from the air space which exists between the lens  104  and reflector  106 . 
     In a first mode of operation, a beam of light from each of the ports  102   a  and  102   b,  traversing the lens  104  for collimation at the reflector  106 , is reflected to adjacent ports  102   d  and  102   c,  respectively, after being focussed by the same lens  104 . 
     In a second mode of operation, the two beams of light traverse the lens  104  and the refractor  110  for collimation and reflection at the reflector  106 . The beams return by passing through the same refractor  110  and lens  104 , and are directed in such a way that the beam transmitted from port  102   b  is focussed at port  102   d,  while the beam transmitted from port  102   a  is not directed to port  102   c.  As the beam traverses the air-refractor interface its direction changes according to Snell&#39;s Law. 
     Switching between the first and second mode of operation is effected by activating the actuator  112 , which then moves the refractor  110  into or out of the optical path. Alternatively, the refractor  110  is positionable within the path of the beam for redirecting the beam of light. 
     FIG. 2 a  illustrates a beam, represented by a ray directed from port  102   b  to  102   c  in the absence of the refractor  110 . FIG. 2 b  illustrates a beam represented by a ray directed from port  102   b  to  102   d  with the refractor  110  in the path. FIG. 2 c  illustrates a beam, represented by a ray directed from port  102   a  to  102   d  in the absence of the refractor  110 ; and, FIG. 2 d  illustrates the beam represented by a ray directed from port  102   a  shown missing any of the other ports, wherein the light is lost. 
     The first and second modes of operation of the switch as described heretofore are illustrated in FIGS. 3 a  and  3   b.  In the first mode of operation, ports  102   a  and  102   b  are optically coupled with port  102   d  and  102   c,  respectively. In the second mode of operation, port  102   b  is optically coupled with port  102   d  and ports  102   a  and  102   c  have no optical connection. 
     FIG. 4 illustrates the functionality achievable with this embodiment, wherein a first and second mode of operation of the optical switch are indicated by solid and dotted lines, respectively. In the first mode of operation, transmitting port A is optically coupled to receiving port D, while transmitting port B is optically coupled to receiving port C. Following switching to the second mode of operation, port B is optically coupled to port D, and ports A and C are not optically coupled. 
     In a third mode of operation, the port  102   a  is inactive and a beam of light is transmitted from port  102   b  to port  102   c.  Following switching to a fourth mode of operation, light is transmitted from port  102   b  to port  102   d.  Switching between the third and fourth modes thus makes the device effectively a 1×2 switch. 
     Other configurations and modes of operation can be readily adapted, by rearranging the positions and number of input and output fibers, without departing from the scope of the invention. For example, the fibers may be arranged in a single row or a triangular pattern rather than a square array, or more than  4  fibers may be used. Additional prisms may be selectively inserted to achieve 1×3, 1×4, and other modes of operation. 
     FIG. 5 illustrates the latter embodiment. Five ports  102   a - 102   e  are arranged in a linear array, and two refractors  110   a  and  110   b  are arranged to be moved into or out of the optical path. As illustrated in FIG. 5, both refractors are in the optical path and the input beam exits input port  102   a  and is directed to port  102   e.  While FIG. 5 shows also alternative beams directed to ports  102   b,    102   c  and  102   d,  it will be understood that the alternative beams are only created by alternative positions of the refractors  110   a  and  110   b  as per the enclosed table showing the positions of refractors  110   a  and  110   b,  respectively, “out” or “in” the optical path of the optical beam emitted from the port  102   a.  This arrangement therefore represents a 1×4 switch. 
     
       
         
               
               
               
               
             
           
               
                   
                   
               
               
                   
                 110a 
                 102b 
                 output 
               
               
                   
                   
               
             
             
               
                   
                 out 
                 out 
                 102b 
               
               
                   
                 out 
                 in 
                 102c 
               
               
                   
                 in 
                 out 
                 102d 
               
               
                   
                 in 
                 in 
                 102e 
               
               
                   
                   
               
             
          
         
       
     
     Advantageously, the optical switch in accordance with this invention is single-sided and all the fibres exit the switch on the same side, making the switch more compact than a two-sided device. Having one lens also makes the device smaller while reducing the manufacturing cost. Finally, using a moveable light-transmissive wedge as the refractor provides high tolerance to misalignments of light passing therethrough.