Abstract:
The present invention relates to an optical switch. The optical switch includes at least two binary control elements movable between a first and second position. The binary control elements include an at least one angle tuning element for adjusting the pathway of an optical signal. With a binary control element in the first position, the angle tuning element is able to adjust the pathway of an optical signal. With the binary control element in a second position, the angle tuning element is not able to adjust the optical pathway of an optical signal. The optical switch of the present invention can also concurrently switch multiple optical signals in parallel.

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates generally to an optical switch, and more specifically to an optical switch for switching between multiple input or output optical pathways. 
   2. Description of the Related Art 
   Optical switches are widely deployed in optical networks to provide functions such as light path routing, protection switching, and system performance monitoring. The switching function is generally achieved by mechanically moving fiber or other bulk optic elements using stepper motors, controlled actuators or electrical relays. 
     FIG. 1  shows a typical prior art 1×2 optical switch configuration. The optical switch  100  is shown in a first position, whereby an input optical signal  102  is directed to a first output optical waveguide  121 .  FIG. 2  shows the prior art 1×2 optical switch of  FIG. 1  in a second position. The optical switch  100  is shown in a second position, whereby the input optical signal  102  is directed to a second output optical waveguide  122 . 
   A 1×N optical switch (with N&gt;2) is usually realized by cascading multiple 1×2 optical switches.  FIG. 3  shows a typical cascaded 1×4 optical switch  300  of the prior art where three 1×2 switch elements are utilized. Within a first optical switch  310 , an input optical signal  302  is directed along either a first optical pathway  314  to a second optical switch  320  or along a second optical pathway  316  to a third optical switch  330 . The second optical switch  320  directs the input optical signal  302  between first and second output optical waveguides  321 ,  322 , while the third optical switch  330  directs the input optical signal  302  between third and fourth output optical waveguides  333 ,  334 . 
   With the typical cascading technique of the prior art, a 1×N optical switch consists of N−1 1×2 individual optical switching elements. As N increases, the number of the 1×2 optical switching elements increases linearly. For example, the 1×4 optical switch of the prior art shown in  FIG. 3  consists of three 1×2 optical switching elements. A 1×8 optical switch of this type would require seven 1×2 optical switching elements, a 1×16 optical switch would require fifteen 1×2 optical switching elements, and so forth. These designs result in increased bulk and complexity, especially as the size of the optical switch increases. Insertion losses also accumulate rapidly as the number of cascading levels increase. As such, cascading 1×2 optical switches are not an optimal solution for high port-count 1×N optical switches. Alternate non-cascading type optical switches of the prior art also require N−1 optical switches or have switching elements that move between more than two switching positions. The number of redundant switching elements adds to the costs of these devices and results in overly complex switching logic. Further, moving between more than two switching positions requires additional time and strict alignment tolerances, making these types of switches unsuitable for low-cost or high-speed applications. 
   Therefore, there is a need for an improved optical switch which overcomes the shortcomings of the prior art described above. 
   SUMMARY OF THE INVENTION 
   Accordingly, the optical switch of the present invention includes a first binary control element having a first angle tuning element that is moveable between a first position and a second position. It also includes a second binary control element, in series with the first binary control element, and having a second angle tuning element that is moveable between a first position and a second position. The first binary control element is configured such that, in the first position, the first angle tuning element is able to adjust a pathway of an optical signal, and in the second position, the first angle tuning element is not able to adjust the pathway of the optical signal. The second binary control element is configured such that, in the first position, the second angle tuning element is able to adjust the pathway of the optical signal and, in the second position, the second angle tuning element is not able to adjust the pathway of the optical signal. 
   According to an alternate embodiment of the optical switch of the present invention, the optical switch comprises a first optical switching stage that includes a first binary control element having a first angle tuning element moveable between a first position and a second position. It also includes a second optical switching stage in series with the first optical switching stage. The second optical switching stages includes a second binary control element having a second angle tuning element moveable between a first position and a second position. The first binary control element is configured such that, in the first position, the first angle tuning element is able to adjust a pathway of an optical signal input and, in the second position, the first angle tuning element is not able to adjust the pathway of the optical signal. The second binary control element is configured such that, in the first position, the second angle tuning element is able to adjust the pathway of the optical signal and, in the second position, the second angle tuning element is not able to adjust the pathway of the optical signal. 
   According to yet another alternate embodiment of the optical switch of the present invention, the optical switch comprises a binary control element moveable between a first position and a second position. The binary control element includes a first angle tuning element and a second angle tuning element. Wherein the first angle tuning element is able to adjust the optical pathway of a first optical signal, and the second angle tuning element is able to adjust the pathway of a second optical signal. 
   Other features and advantages of the present invention are given in the following description and illustrative figures. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  shows a prior art 1×2 optical switch a first position. 
       FIG. 2  shows the prior art 1×2 optical switch of  FIG. 1  in a second position. 
       FIG. 3  shows a prior art cascading 1×4 optical switch. 
       FIG. 4  shows a 1×4 optical switch, according to one embodiment of the present invention. 
       FIG. 5A  shows a vector representation of the 1×4 optical switch shown in  FIG. 4 . 
       FIGS. 5B–D  show the vector representations of an optical switch, according to various alternative embodiments of the present invention. 
       FIG. 6  shows an electrical relay including multiple angle tuning elements. 
       FIG. 7  shows an embodiment of the present invention using multiple prisms mounted on an electrical relay. 
       FIG. 8  shows a 1×8 optical switch, according to one embodiment of the present invention. 
       FIG. 9  shows an integrated 1×8 optical switch, according to one embodiment of the present invention. 
       FIG. 10  shows an optical switch of the present invention including eight 1×2 optical switches. 
       FIG. 11  shows a 1×16 optical switch, according to one embodiment of the present invention. 
   

   DETAILED DESCRIPTION 
     FIG. 4  shows a 1×4 optical switch, according to one embodiment of the present invention. By spatially multiplexing two 1×2 optical switches  435 ,  445  in series within two orthogonal planes, a 1×4 optical switch  400  is created. The 1×4 optical switch  400  includes an input optical assembly  415  having an input optical waveguide  410  and an input collimator  412 , and an output optical assembly  455  having four output optical waveguides  421 ,  422 ,  423 ,  424  and an output collimator  450 . An optical signal  401  is launched from the input optical waveguide  410  selectively into one of the four output optical waveguides  421 ,  422 ,  423 ,  424 . The first 1×optical switch  435  includes a first prism  430  having an angled facet  431  that can adjust the optical pathway  403  of the optical signal  401 . The second 1×2 optical switch  445  includes a second prism  440  having an angled facet  441  that can adjust the optical pathway  403  of the optical signal  401  in a direction orthogonal to that of the first prism  430 . The prisms  430 ,  440  are positioned between the input optical assembly  415  and the output optical assembly  455  such that they may be moved into and out of the optical pathway  403  of the optical signal  401 . To reduce the footprint of the 1×4 optical switch  400 , a four-waveguide collimator is used in this example, however, individual collimators could also be used for each output optical waveguide. 
   As each prism  430 ,  440  provides the functionality of an individual 1×2 optical switch, the two optical switches  435 ,  445  share the same first output optical waveguide  421  when both prisms  430 ,  440  are in a first position out of the optical pathway  403 . When the first prism  430  is moved into a second position within the optical pathway  403 , while the second prism  440  remains in the first position, the optical pathway  403  is adjusted into the second output optical waveguide  422 . Similarly, when the first prism  430  remains in the first position and the second prism  440  is moved into a second position within the optical pathway  403 , the optical pathway  403  is adjusted into the third output optical waveguide  423 . If both prisms  430 ,  440  are moved into the second position within the optical pathway  403 , the optical pathway is adjusted to the fourth output optical waveguide  424 . Thus, this embodiment of the present invention is therefore a 1×4 switch using only 2 binary optical switching elements. The first binary optical switch is provided by the first prism moving from a first position to a second position. The second binary optical switch is provided by the second prism moving from a first position to a second position. As such, the optical pathways in this embodiment of the present invention are spatially multiplexed in a 3-D space along two planes. Similarly, three prisms can be inserted between the input and output collimating lenses to generate a maximum of 8 different optical pathways, and four prisms result in a maximum 16 different pathways, and so forth. 
   To obtain a clear understanding of how the spatial multiplexing works, consider a 3-D coordinate system with the z-axis coincident with the light propagation direction of the initial state of the optical signal. Each of the angle tuning elements used within the optical switch turns or adjusts the light by a small angle relative to the light&#39;s initial optical path. The resulting optical path forms a 2-D characteristic vector when projected onto a X–Y plane.  FIG. 5A  shows a vector representation of the 1×4 optical switch shown in  FIG. 4 . Utilizing two prisms arranged in series, an input optical signal applied to the optical switch of  FIG. 4  will follow one of the four following vectors:
 
0
 
V 1 
 
V 2 
 
V 1 +V 2 (V 3 )
 
   The above four vectors dictate the position of the output optical waveguides  421 ,  422 ,  423 ,  424 . As such, in this configuration the output optical waveguides are arranged in a 2×2 matrix. 
   The maximum number of output optical waveguides (or pathways) is obtained if all of the characteristic vectors and their combinations do not repeat themselves. The optical switch of the present invention can be seen as a series of binary control elements, switchable between first position and second positions. The minimum number of binary control elements required to achieve a 1×N optical switch is the smallest integer equal to or larger than log 2 N. We have
 
 N− 1&gt;┌log 2   N ┐, for  N&gt; 2.
 
That is to say, the most efficient design for a 1×N optical switch is to utilize only ┌log 2 N┐ binary control elements. The binary control elements may be chosen from among electrical relays, linear actuators, comb drives, step motors, and the like. By having a reduced number of optical switching stages, embodiments of the present invention will have a reduced insertion loss relative to optical switches of the prior art.
 
     FIGS. 5B–5D  show vector representations of 1×8, 1×16, and 1×7 optical switches designed in accordance with one or more aspects of the present invention. The vector representation of the 1×8 optical switch  510  shown in  FIG. 5B  forms a 2×4 matrix and is switchable utilizing three prisms in series. The vector representation of the 1×16 switch  520  shown in  FIG. 5C  forms a 4×4 matrix switchable utilizing four prisms in series. In the vector representation of the 1×7 optical switch  530  shown in  FIG. 5D , three prisms are utilized in series, however, only 7 individual output pathways are created by the three vectors because the sum of the three vectors is coincident with the origin (i.e., the initial alignment of the optical pathway). Similar to using a four-waveguide collimator in the 1×4 switch of  FIG. 4 , a multi-waveguide collimator or collimating lens with geometry matching the output optical waveguides of  FIGS. 5B–D  could be used to reduce the size of the optical switches. 
   Another alternate embodiment of the optical switch of the present invention makes use of both sides of a lever arm of an electrical relay. Electrical relays used in optical switching typically have an angle-tuning element attached to a first distal end of the lever arm to achieve the desired movements between a first and second position. However, if a second angle-tuning element is attached to a second distal end of the lever arm, it moves the same as the first angle-tuning element, but in an opposite direction.  FIG. 6  shows an electrical relay including multiple angle tuning elements. The electrical relay  600  includes a body  602 , pivot arm  604 , lever arm  610 , and prisms  620 ,  630  at each distal end of the lever arm  610 . The lever arm  610  moves from a first position to a second position. In the first position, the first prism  620  is out of a first optical pathway  640  (into the page), and the second prism  630  is within a second optical pathway  642  (also into the page). When the lever arm  610  is moved into the second position, the first prism  620  is moved into the first optical pathway  640  and the second prism  630  is removed from the second optical pathway  642 . 
     FIG. 7  shows yet another embodiment of the present invention using multiple prisms mounted on an electrical relay. Two 1×N optical switches are controlled by the same sets of electrical controls. The optical switch  700  includes dual 1×4 switches  702 ,  704 . The dual 1×4 optical switches  702 ,  704  are independent, they switch simultaneously to respective output optical waveguides  760 ,  770 . A first electrical relay  710  includes prisms  714 ,  716  located at opposite distal ends of the lever arm  711 . A second electrical relay  750  includes prisms  754 ,  756  located at opposite distal ends of the lever arm  751 . Similar to the electrical relay shown in  FIG. 6 , the electrical relays  710 ,  750  can move from a first position to a second position, causing alternate prisms to enter and exit the optical pathways  707 ,  709 . When the first electrical relay  710  is in a first position, prism  714  is out of the optical pathway  707  of the first input optical signal  706 , while prism  716  is within the optical pathway  709  of the second input optical signal  708 . As such, the first input optical signal  706  proceeds uninterrupted, while the second optical signal  708  is deflected. Conversely, when the first electrical relay  710  is in position  2 , prism  714  is within the optical pathway  707  of the first input optical signal  706 , while prism  716  is out of the optical pathway  709  of the second input optical signal  708 . Therefore the first optical signal  706  is deflected while the second optical signal  708  proceeds uninterrupted. The second electrical relay  750  functions in a similar fashion to the first electrical relay  710 , moving the prisms  754 ,  756  into and out of the input optical pathways  706 ,  708  respectively. The optical alignment can be also arranged such that prisms  714  and  716  enter or exit the optical path  707  and  709  simultaneously. The same is true for prisms  754  and  756 . 
   A dual optical switch is particularly useful to simplify the complexity of the cascading technique described in the prior art.  FIG. 8  shows a 1×8 optical switch  800 , according to one embodiment of the present invention, that includes a 1×2 optical switch  802  followed by dual 1×4 optical switches  810 ,  820 . The two output optical pathways  804 ,  806  of the 1×2 optical switch  802  respectively couple to the two input optical pathways  812 ,  822  of the dual 1×4 optical switches  810 ,  820 . Although the dual 1×4 optical switches  810 ,  820  are not independently switchable, the 1×8 optical switch  800  functions perfectly well because the switching logic requires only one of the dual 1×4 optical switches  810 ,  820 , together with the 1×2 optical switch  802 , to be set in a desired state at one time. The other 1×4 switch, if not selected, is idle, and thus can be in any state. 
   Yet another alternate embodiment of the present invention uses multiple prisms mounted on an electrical relay and further reduces the complexity of the 1×8 optical switch shown in  FIG. 8 .  FIG. 9  shows an integrated 1×8 optical switch with three binary control elements. This gives a more compact design compared with the cascading 1×N optical switch design described in the prior art. The level of integration is somewhat less than that shown in the optical switch of  FIG. 5 , however, the embodiment of  FIG. 9  reduces the complexity of making high port-count collimators and aligning multiple angle-tuning elements. 
   The 1×8 optical switch  900  includes three binary control elements  910 ,  920 ,  930  moveable between first and second positions. In the first positions, the first binary control element  910  disposes a moveable mirror  912  within an optical pathway  903 , the second binary control element  920  disposes a first prism  922  within an optical pathway  904  and a second prism  924  out of an optical pathway  906 , and the third binary control element  930  disposes a third prism  932  within an optical pathway  905  and a fourth prism  934  out of an optical pathway  907 . In the second positions, the first binary control element  910  disposes the moveable mirror  903  out of the optical pathway  903 , the second binary control element  920  disposes the first prism  922  out of the optical pathway  904  and the second prism  924  within the optical pathway  906 , and the third binary control element  930  disposes the third prism  932  out of the optical pathway  905  and the fourth prism  934  within the optical pathway  907 . 
   An optical signal  901  enters the optical switch  900  along an optical pathway  902 . It is reflected off a first fixed mirror  908  along the optical pathway  903 . The optical signal  901  is then reflected off of the moveable mirror  912  or a second fixed mirror  909 , depending on the position of the first binary control element  910 . The optical signal  901  reflected off of the moveable mirror  912  is directed towards the output optical waveguides  950 , along the optical pathway  904 ,  905 , adjusted by the first and third prisms  922 ,  932  according to the positions of the second and third binary control elements  920 ,  930 . Similarly, the optical signal  901  reflected off of the second fixed mirror  909  is directed towards the output optical waveguides  960 , along the optical pathways  906 ,  907 , adjusted by the second and fourth prisms  924 ,  934  according to the positions of the second and third binary control elements  920 ,  930 . 
   Another alternate embodiment of the present invention using multiple prisms on an electrical relay integrates a series of 1×2 optical switches with one binary control element.  FIG. 10  shows an optical switch  1000  including eight 1×2 optical switches  1010 . Eight angle-tuning elements  1020  are attached on a single bar  1091 . The bar  1091  is controlled by an electrical relay  1090  to move between a first position and a second position such that the eight angle-tuning elements  1020  can be moved into or out of the respective optical pathways  1003  of the input optical signals  1002  traveling between the eight pairs of single input collimating lenses  1030  and dual output collimating lenses  1040 . The bar  1091  preferably moves along the bar direction  1092 , controlled by the electrical relay  1090 , or alternatively a two-position linear actuator. All 1×2 optical switches in the optical switch  1000  switch simultaneously. The embodiment of the present invention illustrated in  FIG. 10  is also suitable for making a 1×16 optical switch with a minimum number of binary controls. 
     FIG. 11  shows a 1×16 optical switch  1100 , according to one embodiment of the present invention. The 1×16 optical switch  1100  is built in four optical switching stages  1110 ,  1120 ,  1130 ,  1140 . Each of the optical switching stages  1110 ,  1120 ,  1130 ,  1140  uses one binary control element  1111 ,  1121 ,  1131 ,  1141  respectively. The three binary control elements  1121 ,  1131 ,  1141 , switch multiple 1×2 optical switches. For efficiency, the optical switch shown in  FIG. 9  could also be used to replace the first three optical switching stages  1110 ,  1120 ,  1130  of  FIG. 11 . 
   One of ordinary skill in the art will recognize that the angle tuning elements used in embodiments of the present invention may be various types of prisms, mirrors, or other appropriate components. Further, the angle tuning elements may be constructed such that they can be disposed within the optical pathway of an optical signal when the binary control element is in both the first and second positions. In this configuration a single angle tuning element could effectively comprise two separate parts, which could be considered two separate angle tuning elements. In a first position, a first part of the angle tuning element would be within the pathway of an optical signal, directing it along a first pathway, while a second part of the angle tuning element would be removed from the pathway of the optical signal. In a second position, the first part of the angle tuning element would be removed from the pathway of the optical signal, while the second part of the angle tuning element would be within the pathway of the optical signal, directing it along a second optical pathway. 
   The binary control elements may be selected from an electrical relay, linear actuator, comb drive, or another binary control element known to one of skill in the art. 
   The angle tuning elements and binary control elements used in the various embodiments of the present invention also need not all be of one type. For example, they could be any combination of those components described previously. Further, the optical switches may be embedded within another optical switch or optical component. They can also function as either a 1×N optical switch, with N output ports, or as a N×1 optical switch with N input ports. 
   While several embodiments according to the present invention have been disclosed, one of ordinary skill in the art will appreciate that these embodiments are illustrative only, and not exhaustive. As such, the scope of the invention should be determined with respect to the appended claims.