Abstract:
The invention discloses an optical deflection switch which uses the output focal plane of a lens more effectively. This is achieved by combining a tapered block of a light-transmissive material having a reflective surface and a second face, wherein the second face includes an input/output port and the reflective surface provides reflection of a beam of light passing through the input/output port into the tapered block with a first block of a light-transmissive material having a first face and a second face, wherein the first face includes an input port thereon for receiving a collimated beam of light and the second face is for providing total internal reflection of the beam of light in a first switching state and for acting as an output/input port for optical communication with the input/output port of the switching block when the total internal reflection is frustrated in a second switching state. The reflective face of the switching block and the second face of the second block have an angle other than zero defined therebetween. The optical deflection switch further includes a rotator for turning the switching block around an axis into one of a plurality of selectable positions, each of the plurality of selectable positions for changing a plane of incidence of the beam of light.

Description:
FIELD OF THE INVENTION 
     This invention relates to optical switches and in particular to an optical switch having a plurality of switching positions. 
     BACKGROUND OF THE INVENTION 
     In optical communication systems it is often necessary to switch an optical signal between different optical paths, be it along an optical waveguide such as an optical fiber, or in free space. Optical switching devices may generally be classified into moving-beam switches and moving-fiber switches. Moving-beam switches redirect the optical signal path between stationary waveguides or in free space. Moving-fiber switches physically change the location of optical fibers to be switched. 
     Different categories of optical switches for switching optical signals include electrical switches, solid-state switches, mechanical switches, and optical switches and combinations therebetween. 
     Electrical switches convert an optical signal to an electrical signal and then switch the electrical signal by conventional switching techniques. Electrical switches then convert the electrical signal back into an optical signal. Electrical switches are faster then existing mechanical switches but are also significantly more expensive. Furthermore, electrical switching of optical signals is bandwidth limited since a converted electrical signal can not carry all the information in an optical signal. This bandwidth limitation of electrical switches severely limits the advantages of using fiber optics. 
     Solid-state optical switches have fast switching speeds and the same bandwidth capacity as fiber optics. However, the cost for solid-state optical switches is 30 to 100 times more than those for existing mechanical switches. Another disadvantage of solid-state optical switches is that they incur insertion losses exceeding 20 times those for existing mechanical optical switches. 
     Mechanical optical switches are typically lower in cost than electrical or solid-state optical switches, provide low insertion loss, and are compatible with the bandwidth of fiber optics 
     The activation mechanism used in the optical deflection switch of the present invention is a moving-beam switch mechanism. 
     An exemplary optical fiber switch that utilizes a moving mirror to perform the switching function is disclosed by Levinson in U.S. Pat. No. 4,580,873 issued Apr. 8, 1986 which is incorporated herein by reference. Although this invention appears to adequately perform its intended function, it is believed too costly and somewhat complex. 
     There have been several designs of optical deflection switches using Frustrated Total Internal Reflection (FTIR) to accomplish switching or modulation of an optical signal. In almost all cases these systems begin with air gap which produces total internal reflection, and then rapidly drives the material to less than one tenth wavelength spacing to produce frustrated total internal reflection. Such systems are disclosed in U.S. Pat. Nos. 4,249,814; 3,649,105; 3,559,101; 3,376,092; 3,338,656; 2,997,922; and 2,565,514. In all of these systems there is a problem in overcoming friction and damage to the glass. 
     Another exemplary moving-beam optical switch that redirects the optical signal path between stationary waveguides is disclosed in U.S. Pat. No. 5,444,801 to Laughlin incorporated herein by reference. The invention described therein teaches an apparatus for switching an optical signal from an input optical fiber to one of a plurality of output optical fibers. This apparatus includes means for changing the angle of the collimated beam with respect to the reference so that the output optical signal is focused on one of the plurality of output optical fibers. Similar mechanical optical switches are disclosed in U.S. Pat. Nos. 5,647,033; 5,875,271; 5,959,756; 5,555,558; 5,841,916; and 5,566,260 to Laughlin incorporated herein by reference. 
     Laughlin teaches switching of optical signals between input fibers and output fibers through shifting of one or more virtual axis of the system by changing the position of a second reflector between multiple positions. This second reflector has a wedge shape to change the angle of the collimated beam by a selected amount to direct the beam to different output locations. However, the output locations are all lying along a diameter in the output focal plane of the GRIN lens as shown in FIG.  1 . 
     It is an object of the invention to provide an optical deflection switch having more switching positions than provided for in Laughlin&#39;s prior art optical switches. This is achieved by using the output focal plane of a lens more effectively. 
     Further, it is an object of the invention to provide an optical deflection switch in which the output beam is more confined to the center of the lens as in comparison to prior art optical switches while still being able to switch an optical signal to a plurality of fibers. 
     SUMMARY OF THE INVENTION 
     In accordance with the invention there is provided an optical deflection switch comprising: a) a tapered block of a light-transmissive material having a reflective surface and a second face, the second face including an input/output port and the reflective surface for providing reflection of a beam of light passing through the input/output port in to the tapered block; b) a first block of a light-transmissive material having a first face and a second face, the first face including an input port thereon for receiving a collimated beam of light and the second face for providing total internal reflection of the beam of light in a first switching state and for acting as an output/input port for optical communication with the input/output port of the switching block when the total internal reflection is frustrated in a second switching state, and an angle defined between the reflective face of the switching block and the second face of the second block being other than zero; and c) a rotator for turning the switching block around an axis into one of a plurality of selectable positions, each of the plurality of selectable positions for changing a plane of incidence of the beam of light. 
     In accordance with the invention there is further provided an optical deflection switch comprising: a first block of a light-transmissive material having an input port and a plurality of output ports at an end face thereof; and a switching block of a light-transmissive material having at least two non-parallel outer faces, said switching block being optically coupled with the first block in at least a first switching mode, and wherein the switching block is relatively rotatable with the first block in the at least first switching mode for reflecting a beam of light to the output ports, said beam of light being received from the input port. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Exemplary embodiments of the invention will now be described in accordance with the drawings in which: 
     FIG. 1 a prior art output focal plane of a lens of a 4×4 cross-bar switch configuration having input and output locations along a diameter of the lens; 
     FIG. 2 depicts a prior art optical switch employing frustrated total internal reflection (FTIR); 
     FIGS. 3A to  3 C the operation of a prior art optical switch; 
     FIG. 3D shows a plurality of output locations for an output focal plane associated with a lens; 
     FIGS. 4A to  4 C show the operation of an optical deflection switch in accordance with the present invention; 
     FIG. 4D shows a plurality of output locations for an output focal plane  470  associated with lens  440 ; 
     FIG. 5 shows an optical deflection switch in accordance with an embodiments of the present invention; and 
     FIG. 6 shows an optical deflection switch in accordance with another embodiment of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     FIG. 1 shows an output focal plane  2  of a lens  4  of a prior art 4×4 cross-bar switch configuration having input and output locations along a diameter of lens  4 . In a preferred embodiment lens  4  is a GRIN lens having a focal plane  2 . Output focal plane  2  of lens  4  includes an output A′ at position  10 , output B′ at position  12 , output C′ at position  14 , and output D′ at position  16 . Each of the output locations A′ to D′ on lens  4  has an optical fiber appropriately coupled to it. To achieve a combination of signals of the prior art cross-bar switch return loops are required. Each of the return loops will route a signal received at the output focal plane  2  back to an input focal plane so that the operation of the cross-bar switch is achieved. FIG. 1 shows a configuration for orientation of the return loops showing input and output locations. The corresponding configuration for the return loops in output focal plane  2  are shown in FIG.  1 . Return loop A is at position  8 , return loop (B) is at position  6 , and return loop (C) is at position  18 . FIG. 1 shows clearly that the output locations are all lying along a diameter in the output focal plane  2  of the GRIN lens  4 . 
     Referring now to FIG. 2 a prior art optical switch, as disclosed in U.S. Pat. No. 5,444,801, utilizing frustrated total internal reflection (FTIR) is shown. This FTIR optical switch  100  includes a lens  176  and another lens  178 . Switch  100  further includes refractor  102 , a right angle prism, positioned between lenses  176  and  178 . Switch  100  also includes a second refractor or switchplate  104  that is used to frustrate the total internal reflection in refractor  102 . Switch  100  also includes actuator  105  for moving switchplate  104  into proximal contact with refractor  102 , such as a piezo-electrical device. Input signals are provided to switch  100  by input fiber  110  located in the focal plane for lens  176 , and output signals are provided to output fibers  112  and  114  located at the focal plane for lens  178 . 
     In the first position of switch  100 , switchplate  104  does not touch refractor  102 . The energy from input fiber  110  is collimated into beam  116  by collimating lens  176  and beam  116  is introduced into refractor  102 . Collimated input beam  116  is reflected at reflecting surface  118  of refractor  102  by total internal reflection and forms a primary collimated output beam  120 . The primary collimated output beam  120  is focused by decollimating output lens  178  and to first output optical fiber  112 . 
     To accomplish switching from input optical fiber  110  to second output optical fiber  114 , switchplate  104  is brought into proximal contact with reflecting surface  118  of refractor  102  by actuator  105 . This frustrates the total internal reflection in refractor  102  resulting in input collimated beam  116  being transmitted into switchplate  104 . Collimated beam  116  is reflected from reflective surface  122  of switchplate  104  by total internal reflection as a secondary collimated output beam  126 . 
     Reflective surface  122  of switchplate  104  is at a bias angle  0   123  to inside surface  124  of switchplate  104 . Secondary collimated output beam  126  leaves refractor  102  at an angle of two times angle  0   123  to that of primary collimated output beam  120 . Secondary collimated output beam  126  is then reimaged by output lens  178  onto second output optical fiber  114 . By this method, an optical signal at input optical fiber  110  can be switched between output optical fibers  112  and  114  by moving switchplate  104  into and out of proximal contact with refractor  102 . When switchplate  104  is not in proximal contact with refractor  102 , the optical signal from input optical fiber  110  is imaged to first output optical fiber  112 . When switchplate  104  is brought into proximal contact with refractor  102 , total internal reflection in refractor  102  is frustrated, thereby causing the optical signal from input optical fiber  110  to be imaged to second output optical fiber  114 . 
     The switchplate  104  in FIG. 2 is depicted as a wedged plate which is put in contact with the refractor/prism  102  to change the beam path. 
     U.S. Pat. No. 5,444,801 to Laughlin uses total internal reflection to deflect a beam into a single GRIN lens that has pickup fibers along a diameter of the GRIN lens. Hence, Laughlin varies the position of a wedge on a transmissive block to deflect a beam at different angles. However, the collimated output beam  126  does not strike the center of the lens  178  and partially misses the GRIN lens when it s deflected. 
     In accordance with an embodiment of the present invention an apparatus and a method are provided that use a lens more efficiently. Further, in accordance with another embodiment of the invention more switching positions are provided than in prior art optical deflection switches, such as the one disclosed by Laughlin. In accordance with an embodiment of the present invention an output beam is directed to the center of the lens while still switching to a plurality of fibers. For example, the output beam is switched to a plurality of output locations on the lens such as to locations having a same distance from an optical axis of the lens, e.g.  10  fibers equidistant from the optical axis. 
     FIGS. 3A to  3 D illustrate the prior art and FIGS. 4A to  4 D illustrate the present invention in a more detailed manner. Turning to FIG. 3A an optical switch  300  is shown including a first refractor  320 , such as a prism, a second refractor  330 , such as a wedge, a lens  340 , and a switch (not shown) for optically coupling the first refractor  320  with the second refractor  330 . In a preferred embodiment lens  340  is a GRIN lens and the first refractor  320  is a 45-90-45 prism. Alternatively, other configurations of the first refractor  320  can be employed without departing from the scope of the present invention. The second refractor  330  of optical switch  300  is used to frustrate the total internal reflection of refractor  320 . The first refractor  320  and the second refractor  330  are made of a light transmissive material having substantially a same refractive index. The second refractor  330  is wedge shaped and adjacent to face  324  of the first refractor  320 . 
     FIG. 3A shows a beam of light  310  being launched into the first refractor  320  at an input location  311 . The beam of light  310  propagates through the first refractor  320  and is reflected at face  322  and face  324  and then exits the first refractor  320  at an output location  331 . 
     Again, FIG. 3B shows a beam of light  310  being launched into the first refractor  320  at an input location  311 . The beam of light  310  propagates through the first refractor  320  and is reflected at face  322 . However, in FIG. 3B the first refractor  320  and the second refractor  330  are optically coupled such that light is allowed to propagate into the second refractor  330  where it is reflected at face  325 . The beam of light  310  exits the first refractor  320  at an output location  332 . Output location  332  is shifted to the right in comparison to output location  331  of FIG.  3 A. 
     FIG. 3C shows a beam of light  310  being launched into the first refractor  320  at an input location  311 . The beam of light  310  propagates through the first refractor  320  and is reflected at face  322 . FIG. 3C shows the second refractor  330  being optically coupled with the first refractor  320  and shifted in the direction of arrow  329 . This shift shortens the path length of the beam while travelling through the second refractor  330 . Hence, the beam of light  310  exits the first refractor  320  at an output location  333 . Output location  333  is located output location  331  and output location  332 . 
     FIG. 3D shows a plurality of output locations for an output focal plane  360  associated with lens  340 . Using an optical switch as shown in FIGS. 3A to  3 C the beam of light  310  is switched to positions  341  to  348 , for example. All switching positions  341  to  348  are located along a diameter of the output focal plane  360  associated with lens  340 . 
     Turning now to FIGS. 4A to  4 D it is understood how the present invention uses an output focal plane of a lens more efficiently and how it provides more switching positions than prior art optical switches, such as optical switch  300  shown in FIGS. 3A to  3 C. 
     Turning to FIG. 4A an optical switch  400  is shown including a first refractor  420 , such as a prism, a second refractor  430 , such as a wedge, a lens  440 , and a switch (not shown) for optically coupling the first refractor  420  with the second refractor  430 . In a preferred embodiment lens  440  is a GRIN lens and the first refractor  420  is a 45-90-45 prism. Alternatively, other configurations of the first refractor  420  can be employed without departing from the scope of the present invention. The second refractor  430  of optical switch  400  is used to frustrate the total internal reflection of refractor  420 . The first refractor  420  and the second refractor  430  are made of a light transmissive material having substantially a same refractive index. The second refractor  430  is wedge shaped and adjacent to face  424  of the first refractor  420 . 
     FIG. 4A shows a beam of light  410  being launched into the first refractor  420  at an input location  411 . The beam of light  410  propagates through the first refractor  420  and is reflected at face  422  and face  424  and then exits the first refractor  420  at an output location  431 . 
     Again, FIG. 4B shows a beam of light  310  being launched into the first refractor  320  at an input location  311 . The beam of light  310  propagates through the first refractor  320  and is reflected at face  322 . However, in FIG. 3B the first refractor  320  and the second refractor  330  are optically coupled such that light is allowed to propagate into the second refractor  330  where it is reflected at face  325 . The beam of light  310  exits the first refractor  320  at an output location  332 . Output location  332  is shifted to the right in comparison to output location  331  of FIG.  3 A. 
     FIG. 4C shows a beam of light  410  being launched into the first refractor  420  at an input location  411 . The beam of light  410  propagates through the first refractor  420  and is reflected at face  422 . FIG. 4C shows the second refractor  430  being optically coupled with the first refractor  420 . However, instead of shifting the second refractor  430  it is rotated around a rotational axis  432 . The rotation around axis  432  alters a plane of incidence of the beam of light  410  when being reflected from face  425 . Thus, for each rotational increment an incident and a reflected ray have a different plane of incidence. As a result the beam of light  410  when exiting refractor  420  and entering lens  440  is more confined to a center of the lens  440  while still being able to switch to a plurality of fibers. 
     FIG. 4D shows a plurality of output locations for an output focal plane  470  associated with lens  440 . Using an optical switch as shown in FIGS. 4A to  4 C the beam of light  410  is switched to positions  441  to  456 , for example. The switching positions  441  to  456  in FIG. 4D are no longer located along a diameter of the output focal plane  470  associated with lens  340  but rather are arranged equidistant from an optical axis  460 . It is appreciated by those skilled in the art that other switching positions having another different distance from the optical axis are obtained, if desired, by appropriate rotation of the second refractor  430 . 
     FIG. 5 shows an optical deflection switch  500  in accordance with an embodiment of the present invention having a third refractor  550 . Refractor  550  is cuboid and made from a light transmissive material and has substantially the same refractive index as the first refractor  520  and the second refractor  530 . If the third refractor  550  is optically coupled with the first refractor  520  such that a beam of light  510  being launched into the first refractor at an input location  511 , is allowed to propagate into the third refractor to frustrate the internal reflection of the beam  510 . If the third refractor  550  is optically coupled with the first refractor  520  twice the number of switching positions result as in comparison to the optical deflection switch  400  shown in FIGS. 4A to  4 D. 
     FIG. 6 shows an optical deflection switch  600  in accordance with another embodiment of the present invention. Refractor  650  is wedge shaped and made from a light transmissive material and has substantially the same refractive index as the first refractor  620  and the second refractor  630 . If the third refractor  650  is optically coupled with the first refractor  620  such that a beam of light  610  being launched into the first refractor at an input location  611 , is allowed to propagate into the third refractor to frustrate the internal reflection of the beam  610 . If the third refractor  650  is optically coupled with the first refractor  620  more than twice the number of switching positions result as in comparison to the optical deflection switch  400  shown in FIGS. 4A to  4 D. 
     Furthermore it is an advantage to switch an input optical signal to a plurality of output locations by means of rotating the second refractor being optically coupled with the first refractor since a rotational movement is more accurate than sliding a wedge shaped refractor. The feedback is tuned more easily for a rotational movement of the second refractor. 
     The above-described embodiments of the invention are intended to be examples of the present invention and numerous modifications, variations, and adaptations may be made to the particular embodiments of the invention without departing from the scope and spirit of the invention, which is defined in the claims.