Abstract:
Apparatus and methods are disclosed for providing sparing capacity for an optical switch. Apparatus is disclosed comprising: a set of primary mirrors selectively configurable within the optical switch so as to selectively facilitate a plurality of optical connections thereacross; and at least one secondary mirror selectively configurable within the optical switch so as to selectively facilitate at least one spare optical connection thereacross. A method is disclosed for providing sparing capacity for an optical switch, the method comprising: substituting one of at least one spare optical connection selectively facilitated across at least one secondary mirror for one of a plurality of optical connections selectively facilitated across a set of primary mirrors.

Description:
REFERENCE TO RELATED APPLICATION  
       [0001]    This patent application claims benefit of pending prior U.S. Provisional Patent Application Serial No. 60/368,019, filed Mar. 8, 2002 by Robert R. Ward et al. for SPARING METHODS FOR OPTICAL CROSS-CONNECTS AND OPTICAL SWITCHES, which patent application is hereby incorporated herein by reference. 
     
    
     
       FIELD OF THE INVENTION  
         [0002]    This invention relates to optical switches in general, and more particularly to methods and apparatus for providing sparing capacity in optical switches.  
         BACKGROUND OF THE INVENTION  
         [0003]    In their simplest form, optical switches typically include a mirror for selectively directing an input signal supplied at an input port to a desired output port and, in practice, generally comprise an array of such mirrors for selectively directing a plurality of input signals to appropriate output ports.  
           [0004]    The term “optical fabric” is sometimes used to refer to the portion of a switch incorporating the aforementioned mirrors.  
           [0005]    A problem arises when one or more of the mirrors fails to operate, either at the point of manufacture or after it is incorporated into a product. Often, optical fabrics do not fail in their entirety: only individual or grouped portions of the optical fabric will fail. Unfortunately, however, it is frequently impossible to predict where the failure will occur when a fabric is initially manufactured or deployed. Accordingly, a flexible manner for correcting these failures is desired.  
         SUMMARY OF THE INVENTION  
         [0006]    As a result, one object of the present invention is to provide a flexible manner for correcting the aforementioned failures in the optical fabric of a switch.  
           [0007]    Another object of the present invention is to provide additional capacity at the fabric level of the optical switch to account for element failures over time.  
           [0008]    Still another object of the present invention is to provide a method and apparatus for sparing design optimization to solve sparing problems.  
           [0009]    Yet another object of the present invention is to provide a method and apparatus for sparing design optimization comprising internal sparing allocation for improving manufacturing yields.  
           [0010]    And another object of the present invention is to provide a method and apparatus for sparing design optimization comprising external sparing allocation for improving manufacturing yields.  
           [0011]    Still another object of the present invention is to provide a method and apparatus for sparing design optimization comprising spare utilization before failure occurs.  
           [0012]    Yet another object of the present invention is to provide a method and apparatus for sparing design optimization comprising a manual method for re-routing to spares.  
           [0013]    And another object of the present invention is to provide a method and apparatus for sparing design optimization comprising an automatic method for re-routing to spares.  
           [0014]    Still another object of the present invention is to provide a method and apparatus for sparing design optimization to solve sparing problems which involve handling adjacent mirror failures.  
           [0015]    Yet another object of the present invention is to provide a method and apparatus for sparing design optimization comprising a main fabric and a smaller sparing fabric.  
           [0016]    With these and other objects in view, there is provided apparatus for providing sparing capacity for an optical switch, the apparatus comprising: a set of primary mirrors selectively configurable within the optical switch so as to selectively faciliate a plurality of optical connections thereacross; and at least one secondary mirror selectively configurable within the optical switch so as to selectively facilitate at least one spare optical connection thereacross for replacement of at least one of the plurality of optical connections.  
           [0017]    In another aspect of the invention, there is provided a method for providing sparing capacity for an optical switch, the method comprising: substituting one of at least one spare optical connection selectively facilitated across at least one secondary mirror for one of a plurality of optical connections selectively facilitated across a set of primary mirrors so as to provide sparing capacity for the one of the plurality of optical connections selectively facilitated across the set of primary mirrors.  
           [0018]    In another aspect of the invention, there is provided apparatus for allocation of sparing capacity in an optical switch, the apparatus comprising an optical data signal received at an input port of the switch for transmission through the optical switch; a first mirror selectively positionable relative to the optical data signal so as to facilitate an optical connection through the optical switch, a second mirror selectively positionable relative to another optical data signal so as to facilitate an additional optical connection through the optical switch, and a third mirror selectively positionable relative to a spare input port; a first mirror control circuit in electrical connection with the first mirror and receiving feedback related to the optical connection so as to facilitate the optical connection through the optical switch, a second mirror control circuit in electrical connection with the second mirror and receiving feedback related to the additional optical connection so as to facilitate the additional optical connection through the optical switch, and a third mirror control circuit in electrical connection with the third mirror and receiving feedback related to a spare optical connection so as to selectively facilitate the spare optical connection through the optical switch; and re-routing means for reconfiguring the optical data signal from the input port to the spare input port so as to facilitate the spare optical connection through the optical switch using the third mirror.  
           [0019]    In accordance with a further feature of the invention, there is provided a method for allocation of sparing capacity in an optical switch, the method comprising: monitoring an optical data signal being transmitted across a mirror through the optical switch; detecting a failed connection of the optical data signal across the mirror through the optical switch; and re-routing the optical data signal from the failed connection across the mirror to a spare mirror so as to provide a spare connection through the optical switch. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0020]    These and 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:  
         [0021]    FIGS.  1 - 3  are schematic views of an internal fabric sparing allocation system which comprises one embodiment of the present invention;  
         [0022]    FIGS.  4 - 6  are schematic views of an external fabric sparing allocation system which comprises another embodiment of the present invention;  
         [0023]    [0023]FIG. 7 is a schematic view of an external fabric sparing allocation system which comprises another embodiment of the present invention;  
         [0024]    [0024]FIGS. 8 and 9 are schematic views of a flexible optical interconnect which comprises another embodiment of the present invention, with the system being configured to manually route around a failure; and  
         [0025]    FIGS.  10 - 14  are schematic views of an optical switch system which comprises another embodiment of the present invention, with the system being configured to automatically re-route an optical path around a failure that occurs therein. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0026]    Referring to FIGS.  1 - 3 , there is shown an internal fabric sparing allocation system  5  for improving manufacturing yields. More particularly, internal fabric sparing allocation system  5  comprises a switch fabric  10  having a plurality of mirrors  15 A,  15 B,  15 C, etc. These mirrors  15 A,  15 B,  15 C, etc. are designed to receive input signals provided by fibers  20 A,  20 B,  20 C, etc., respectively, and collimated by collimator lenses  25 A,  25 B,  25 C, etc., respectively, and direct those input signals to appropriate output ports as light beams  30 A,  30 B,  30 C, etc., respectively. Mirror control circuits  35 A,  35 B,  35 C, etc. control operation of mirrors  15 A,  15 B,  15 C, etc., respectively.  
         [0027]    With this form of the invention, extra mirrors are provided for use as spares. Electrical control (i.e., appropriate mirror control circuits  35 A,  35 B,  35 C, etc.) is preferably provided for all of the mirrors  15 A,  25 B,  15 C, etc. in fabric  10 , but fiber-collimator connections are allocated only to mirrors that are known to be operational (i.e., only to mirrors that have previously passed a manufacturing test).  
         [0028]    Thus, for example, where the switch fabric  10  comprises a strip of four mirrors  15 A- 15 D, and if the statistical manufacturing data shows that no more than one of the mirrors  15 A- 15 D would be likely to fail within the manufacturing process, then three fibers  20 A- 20 C should be the maximum safe allocation toward each group of four mirrors  15 A- 15 D. The mirrors in fabric  10  would be tested, the operational mirrors noted, and then a fiber-mirror connection map generated to allocate three fibers  20 A- 20 C to an appropriate group of three mirrors in fabric  10 . For example, where mirrors  15 A,  15 B and  15 C are all operating properly, fibers  20 A,  20 B and  20 C might be mapped to mirrors  15 A,  15 B and  15 C, respectively. In this case, mirror control circuits  35 A- 35 C appropriately control mirrors  15 A- 15 C as working mirrors, while mirror control circuit  35 D controls mirror  15 D as an idle mirror (FIG. 1).  
         [0029]    Looking now at FIG. 2, it might occur that one of the working mirrors  15 A- 15 C might fail, or one of the associated mirror control circuits  35 A- 35 C might fail. By way of example, as seen in FIG. 2, mirror  15 B and/or mirror control circuit  35 B might fail.  
         [0030]    In this case, and looking now at FIG. 3, fiber  20 B and collimator lens  25 B could be reassigned to mirror  15 D. This might involve creating a new fiber-mirror connection map to reflect this new assignment of fiber  20 B to mirror  15 D. In other words, fiber  20 B and collimator lens  25 B are re-assigned to mirror  15 D, which is controlled by mirror control circuit  35 D. As a result, the data in fiber  20 B will once again be properly transmitted through switch fabric  10 , despite the failure of mirror  15 B and/or mirror control circuit  35 B.  
         [0031]    Looking now at FIGS.  4 - 6 , there is shown an external fabric sparing allocation system  105  for improving manufacturing yields. More particularly, external fabric sparing allocation system  105  comprises a switch fabric  110  having a plurality of mirrors  115 A,  115 B,  115 C, etc. These mirrors  115 A,  115 B,  115 C, etc. are designed to receive input signals provided by fibers  120 A,  120 B,  120 C, etc., respectively, and collimated by collimator lenses  125 A,  125 B,  125 C, etc., respectively, and direct those input signals to appropriate output ports as light beams  130 A,  130 B,  130 C, etc., respectively. Mirror control circuits  135 A,  135 B,  135 C, etc. control operation of mirrors  115 A,  115 B,  115 C, etc., respectively.  
         [0032]    With this form of the invention, only a subset of the mirrors in switch fabric  110  is used for normal traffic and the remaining (i.e., unused) mirrors of the superset are used for spare traffic. For example, if switch fabric  110  comprises a strip of four mirrors  115 A- 115 D, and if manufacturing data shows that no more than one mirror could fail statistically within the manufacturing process, then only three fibers should be counted on for long-term availability for making connections. Thus, for example, if there are no manufacturing failures for a particular system  105 , the four electrical drivers  135 A- 135 D operate the three mirrors  115 A- 115 C for normal traffic on fibers  120 A- 120 C, respectively, and hold one mirror  115 D as a spare (FIG. 4). If there is a mirror failure, e.g. mirror  115 B (FIG. 5), data is swapped off fiber  120 B and onto fiber  120 D, whereupon the three mirrors  115 A,  115 C and  115 D are used for traffic and the mirror  115 B is idle (FIG. 6). As a result, the data previously transmitted in fiber  120 B will once again be properly transmitted through switch fabric  110 , despite the failure of mirror  115 B.  
         [0033]    Referring now to FIG. 7, there is shown an external fabric sparing allocation system  205 . More particularly, external fabric sparing allocation system  205  comprises a switch fabric  210  having a plurality of mirrors  215 A,  215 B,  215 C, etc. These mirrors  215 A,  215 B,  215 C, etc. are designed to receive input signals provided by fibers  220 A,  220 B,  220 C, etc., respectively, and collimated by collimator lenses  225 A,  225 B,  225 C, etc., respectively, and direct those input signals to appropriate output ports as light beams  230 A,  230 B,  230 C, etc., respectively. Mirror control circuits  235 A,  235 B,  235 C, etc. control operation of mirrors  215 A,  215 B,  215 C, etc., respectively.  
         [0034]    With this form of the invention, if switch fabric  210  comprises a strip of four mirrors  215 A- 215 D, and if statistical data indicates that only one mirror is likely to fail over some target time period, then only three fibers should be counted on for making connections. Thus, for example, the four electrical drivers  235 A- 235 D might operate the three mirrors  215 A- 215 C for normal traffic on fibers  220 A- 220 C, and hold mirror  215 D (and fiber  220 D) as a spare. However, if a failure occurs, the system can be configured to effect complete data re-assignment.  
         [0035]    In other words, suppose mirror  215 B should fail. Rather than swapping only data line ‘ 2 ’ (which is the data in fiber  220 B being directed through mirror  215 B) with data line ‘S’ (which is the data in fiber  220 D being directed through mirror  215 D), such as is the case with the system of FIG. 6, all of the data lines in the system of FIG. 7 may be re-assigned, such that data line ‘S’ is repositioned at the failed mirror  215 B.  
         [0036]    In one embodiment of the present invention, the data lines may be re-assigned by indexing each of the data lines “upward” until the data line ‘S’ is positioned at the failed mirror  215 B, such as is shown in FIG. 7.  
         [0037]    Looking next at FIGS. 8 and 9, there is shown an optical interconnect  305  which may be used to sequentially index the data lines so as to manually route around a failure. Optical interconnect  305  is also sometimes referred to as rotary connector  305  herein. Manual routing around failures is beneficial in that the location of an impending failure may not be known. While optical interconnect  305  may be configured for different numbers of lines, it will herein be discussed in the context of three active data lines and one spare data line.  
         [0038]    More particularly, as seen in FIGS. 8 and 9, fabric  310  has a strip of four mirrors  315 A- 315 D. Optical interconnect  305  includes a first connector body  316  and a second connector body  317 . First connector body  316  and second connector body  317  are rotatably adjustable with respect to one another; preferably first connector body  316  is rotable and second connector body  317  is stationary. First fiber ferrules  318 A- 318 D are disposed within first connector body  316 . Second fiber ferrules  319 A- 319 D are disposed within second connector body  317 . Input fibers  320 A- 320 D have an end in connection with first fiber ferrules  318 A- 318 D, respectively. Output fibers  322 A- 322 D have a first end in connection with second fiber ferrules  319 A- 319 D, respectively, and a second end in connection with collimator lenses  325 A- 325 D, respectively. Light beams  328 A- 328 D are emitted from first fiber ferrules  318 A- 318 D, respectively. Light beams  328 A- 328 D are received by second fiber ferrules  319 A- 319 D, according to the alignment of first fiber ferrules  318 A- 318 D with second fiber ferrules  319 A- 319 D (i.e., according to the angular position of first connector body  316  relative to second connector body  317 ). Light beams  330 A- 330 C (corresponding to three active data lines) are emitted from collimators  325 A- 325 C for connection through mirrors  315 A- 315 C, respectively.  
         [0039]    Still looking at FIGS. 8 and 9, with optical connector  305 , the optical connections N are flexibly allocated to N out of N+M points, with M being the additional sparing capacity of optical fabric  310 . The specific example illustrated in FIGS. 8 and 9 illustrates the case where N=3 and M=1.  
         [0040]    When a failure occurs in the fabric  310 , the number of connections (N=3) must be re-allocated to a minimum of N non-failed elements. This is accomplished by rotating first connector body  316  with respect to second connector body  317  so as to redistribute (i.e., re-arrange) the input connections (N=3) to available “non-failed” elements (N=3). In other words, the connections are redistributed around the failed element. Once this is accomplished, the interconnect mapping, which is also referred to as connection memory, is updated due to the new re-arrangement.  
         [0041]    By way of example, suppose the system is configured in the manner shown FIG. 8, i.e., so that data line ‘ 1 ’, data line ‘ 2 ’ and data line ‘ 3 ’ are directed through mirrors  315 A- 315 C, respectively, and suppose that mirror  315 B should fail. Then first connector body  316  is indexed two positions, so that data line ‘ 1 ’, data line ‘ 2 ’ and data line ‘ 3 ’ are directed through mirrors  315 C,  315 D and  315 A, respectively, in the manner shown in FIG. 9.  
         [0042]    The system shown in FIGS. 8 and 9 is beneficial in that it provides a flexible interconnect which is more compact and “in-service practical” than individual interconnects per fiber, which are hard to manage at a high-density level. This high-density issue is a significant one for large scale cross-connects (such as 256 lines and higher). It can also be a significant issue with small, compact designs with smaller numbers of lines (such as 256 and below).  
         [0043]    Another benefit of using the approach of FIGS. 8 and 9 is that angled ferrules  318 A- 318 D and  319 A- 319 D can still be used for each interconnect point, and still achieve ultra-low return loss. Of course, the ferrule angles must reference the center rotation point of the multi-connector body.  
         [0044]    If redundant switch fabrics  310  are deployed in a system design, the present invention will allow “in-service” repair, such that traffic is supported on another one of the cores during the failure. Once the failure is repaired within the core that had the failure, or routed therearound, switch redundancy is restored.  
         [0045]    Referring now to FIGS.  10 - 14 , there are shown optical switch systems  405 ,  505  to automatically re-route an optical path around a failure that occurs therein. Here, N ports are reallocated across N+M ports. The N+M ports are the direct interconnect points to an optical fabric  410 ,  510 . If one element fails with the N+M capacity, the N ports are automatically routed around the “up to M” failure(s).  
         [0046]    Looking now at FIGS. 10 and 11, that is shown optical switch system  405  which comprises an auto-switch  418  which is in optical connection with input fibers  420 A- 420 D so as to receive signals therefrom. Output fibers  422 A- 422 D each have (1) a first end in optical connection with auto-switch  418  so as to receive signals from input fibers  420 A- 420 D as selectively directed by auto-switch  418 , and (2) a second end in optical connection with collimator lenses  425 A- 425 D, respectively. Light beams  430 A- 430 C are selectively emitted from one of collimator lenses  425 A- 425 D for connection through a corresponding one of mirrors  415 A- 415 D, respectively.  
         [0047]    Optical switch system  405  has the ability to route around a mirror failure. More particularly, suppose the system is initially configured so that data lines ‘ 1 ’, ‘ 2 ’ and ‘ 3 ’ are directed through mirrors  415 A,  415 B and  415 C. Suppose further that mirror  415 B fails. In this case, auto-switch  418  can be reconfigured to direct data ‘ 2 ’ to output fiber  422 D and hence mirror  415 D (FIG. 11).  
         [0048]    Referring next to FIGS.  12 - 14 , there is shown an optical switch system  505  having a first switch fabric  510 A and a second switch fabric  510 B. First switch fabric  510 A includes a first set of mirrors  515 A- 515 C and mirrors  515 A′- 515 C′ that correspond to one another, respectively. Second switch fabric  510 B includes a second set of mirrors  515 D and  515 D′ that correspond to one another. In a preferred embodiment of the present invention, first switch fabric  510 A is sized larger than second switch fabric  510 B. In another preferred embodiment of the present invention (not shown), second switch fabric  510  is sized equal to, or larger than, first switch fabric  510 A. This allows for manual or automatic sparing operations to occur more efficiently and practically by distributing the adjacent failures outside of a single connector, entity, or switch fabric  510 A,  510 B.  
         [0049]    A first auto-switch  518  and a second auto-switch  518 ′ are in optical connection with first external fibers  520 A- 520 D and second external fibers  520 A′- 520 D′, respectively, so as to transmit and/or receive signals therefrom. First internal fibers  522 A- 522 D and second internal fibers  522 A′- 522 D′ each have (1) a first end in optical connection with first auto-switch  518  and second auto-switch  518 ′, respectively, so as to transmit signals to, and/or receive signals from, external fibers  520 A- 520 D and external fibers  520 A′- 520 D′ as selectively directed by first auto-switch  518  and second auto-switch  518 ′, respectively; and (2) a second end in optical connection with collimator lenses  525 A- 525 D and collimator lenses  525 A′- 525 D′, respectively. Light beams  530 A- 530 D and light beams  530 A′- 530 D′ are selectively transmitted through collimators  525 A- 525 D and through collimators  525 A′- 525 D′ so as to form a connection through large fabric  510 A. More particularly, auto-switch  518  and  518 ′, and mirrors  515 A- 515 C and  515 A′- 515 C′, permit data line ‘ 1 ’ to be connected to data line ‘ 5 ’, and data line ‘ 2 ’ to be connected to data line ‘ 6 ’, and data line ‘ 3 ’ to be connected to data line ‘ 7 ’ (FIG. 12).  
         [0050]    However, if, for example, mirror  515 B or mirror  515 B′ should fail, data line ‘ 2 ’ will not be connected to data line ‘ 6 ’ (FIG. 13).  
         [0051]    However, auto-switches  518  and  518 ′, and second switch fabric  510 B, will permit a repair connection to be made. This is done by routing data line ‘ 2 ’ through output fiber  522 D, across mirrors  515 D and  515 D′, out fiber  522 D′, and out data line ‘ 6 ’.  
         [0052]    Significantly, this repair connection can be made using relatively small fabric  510 B compared to the large scale fabric  510 A. For example, in the configuration shown in FIGS.  12 - 14 , the large fabric is sized N×N and the smaller fabric is sized N/3×N/3. In other words, the small fabric is one-third the size of the larger core.  
         [0053]    The preferred embodiments of the present invention as shown and described herein are related to MEM&#39;s based optical switch fabrics. It should, of course, be appreciated that the present invention is by no means limited to the particular constructions and method steps disclosed above and/or shown in the drawings, but also comprises any modifications or equivalents within the scope of the claims, which include, but are not limited to, optical beam steering designs, moving collimator designs, and electrical fabric designs.