Abstract:
An optical switching system and method that provide fault tolerant optical switching without duplicating the entire system. Two optical switches are provided, each of which receives a portion of a transmitted optical signal. Should one switch fail, the other switch is still able to perform the required optical routing of the optical signal to the desired receiving node. The two switches can be the same type of optical switch that have identical switching functionality, or each switch could have a distinct switching functionality. In one example, one switch could be a semiconductor optical amplifier (SOA) switch that has fast switching speed but uses more power, and the other switch could be a micro electro-mechanical systems (MEMS) switch that has slower switching speed but uses less power, thereby combining the benefits of fast switching and low power switching into a single architecture.

Description:
FIELD 
     This disclosure relates to an optical switched interconnect and systems employing optical switching. 
     BACKGROUND 
     The use of optical switching in an optical system is known. The optical switching is used to route an optical signal transmitted by a node to a desired receiving node. When fault tolerance in the system is desired, it is known to duplicate the entire system, with an optical signal being transmitted on different channels, with one optical switch receiving the optical signal on one channel and a second optical switch receiving the optical signal on a second channel. 
     Existing optical switching solutions typically are either fast, for example in the case of semiconductor optical amplifiers or SOAs, or low power, for example in the case of micro electro-mechanical systems or MEMS, but not both fast and low power. 
     SUMMARY 
     Optical switching systems and methods are described that provide fault tolerant optical switching without duplicating the entire system. In addition, in one disclosed example, the benefits of fast switching and low power switching are combined into a single architecture. 
     Two optical switches are provided, each of which receives a portion of a transmitted optical signal. Should one switch fail, the other switch is still able to perform the required optical routing of the optical signal to the desired receiving node. The two switches can be the same type of optical switch that have identical switching functionality. Alternatively, the two switches can be different types of optical switches that have distinct switching functionality from one another. For example, one switch can have a faster switching speed, but use higher power, than the other optical switch which operates more slowly but at lower power. Examples of optical switches that can be used include, but are not limited to, a semiconductor optical amplifier (SOA) switch that has fast switching speed but uses more power, and a micro electro-mechanical systems (MEMS) switch that has slower switching speed but uses less power. 
     In one disclosed embodiment, an optical switching system includes a plurality of transmit nodes, with each transmit node including an optical transmitter capable of transmitting an optical signal. In addition, an optical signal splitter is connected to each optical transmitter, with each optical signal splitter being configured to split an optical signal received from the respective optical transmitter into a first optical signal portion and a second optical signal portion. A first optical switch is provided that includes a plurality of first inputs connected to the optical signal splitters and receiving therefrom the first optical signal portions, and a plurality of first outputs, with each of the first inputs being selectively connectable to each of the first outputs. A second optical switch is also provided that includes a plurality of second inputs connected to the optical signal splitters and receiving therefrom the second optical signal portions, and a plurality of second outputs, with each of the second inputs being selectively connectable to each of the second outputs. A plurality of optical signal combiners are also provided, with each optical signal combiner being connected to one of the first outputs and one of the second outputs. In addition, a plurality of receive nodes are connected to the optical signal combiners, with each receive node including an optical receiver capable of receiving an optical signal. 
     In another disclosed embodiment, an optical switching system includes a plurality of optical transmitters each capable of transmitting an optical signal. A first optical switch is provided that includes a plurality of first inputs connected to the optical transmitters and receiving first optical signal portions, and a plurality of first outputs, where each of the first inputs is selectively connectable to each of the first outputs. A second optical switch is also provided that includes a plurality of second inputs connected to the optical transmitters and receiving second optical signal portions, and a plurality of second outputs, where each of the second inputs is selectively connectable to each of the second outputs. Further, a plurality of optical receivers are connected to the first outputs and the second outputs. In this embodiment, the first optical switch has a faster switching speed than the second optical switch, and the second optical switch uses less power than the first optical switch. 
     A method of providing fault tolerant optical switching includes directing a first portion of a transmitted optical signal to an input of a first optical switch that has a plurality of outputs, directing the first portion of the transmitted optical signal from the input of the first optical switch to a selected one of the outputs of the first optical switch, directing a second portion of the transmitted optical signal to an input of a second optical switch that has a plurality of outputs, and directing the second portion of the transmitted optical signal from the input of the second optical switch to a selected one of the outputs of the second optical switch. 
     If one of the optical switches fails, then the other optical switch can provide optical signal routing. Alternatively, the first optical switch can be disabled (i.e. turned off, shut down, etc.) once the second optical switch has directed the second portion of the transmitted optical signal from the input thereof to the selected one of the outputs thereof, so that only one of the switches remains in operation. This helps to reduce power consumption. 
    
    
     
       DRAWINGS 
         FIG. 1  illustrates an optical switching system as described herein. 
         FIG. 2  illustrates an example of an optical switching system employing an SOA and a MEMS. 
         FIG. 3  illustrates the system of  FIG. 2  showing which connections are optical and which are electrical. 
         FIG. 4  illustrates an exemplary use of the system of  FIG. 2  for directing an optical data packet signal originating from transmit Node  1  to receive Node  3 , with the SOA switch operational. 
         FIG. 5  is similar to  FIG. 4  but shows the MEMS switch operational with the SOA switch disabled. 
     
    
    
     DETAILED DESCRIPTION 
     A fault tolerant optical switching system is described that provides fault tolerant optical switching. In addition to fault tolerance, the system combines the benefits of fast switching and low power switching into a single architecture. 
     With reference to  FIG. 1 , an optical switching system  10  includes a plurality of transmit, single channel nodes  12  (labeled Node  1 , Node  2 , Node  3  and Node  4 ) each of which includes an optical transmitter  14  capable of transmitting an optical signal  16  on a single channel. Optical signal splitters  18  receive the transmitted optical signals and split the transmitted signal  16  into two half-power signal portions  16   a ,  16   b.    
     A first optical switch  20  and a second optical switch  22  are provided to receive the signal portions  16   a ,  16   b . The first and second optical switch  20 ,  22  can be any optical switches that can receive an optical signal and route the received optical signal to a desired output of the optical switch. The two switches  20 ,  22  can be the same type of optical switch that have identical switching functionality. For example, each switch  20 ,  22  could be, for example, a SOA, MEMS, or other type of optical switch. 
     Alternatively, the two switches  20 ,  22  can be different types of optical switches that have distinct switching functionality from one another, which is discussed further below with respect to  FIGS. 2-5 . For example, the switch  20  can have a faster switching speed, but use higher power, for example a SOA, than the other optical switch  22  which operates more slowly but at lower power, for example a MEMS. 
     The switch  20  includes a plurality of optical inputs  30  connected to the optical signal splitters  18  and receiving the first optical signal portions  16   a . The switch  20  also includes a plurality of optical outputs  32 . Each input  30  is selectively connectable to any one of the outputs  32  so that the signal portion  16   a  received by an input  30  can be routed to any one of the outputs  32 . As would be understood by a person of ordinary skill in the art, the switching of the switch  20  (and of the switch  22 ) would be controlled by suitable control logic based on the intended destination of the signal  16 . 
     Likewise, the second optical switch  22  includes a plurality of optical inputs  34  connected to the optical signal splitters  18  and receiving therefrom the second optical signal portions  16   b . The switch  22  also includes a plurality of optical outputs  36 . Each input  34  is selectively connectable to each of the outputs  36  so that the signal portion  16   b  received by an input  34  can be routed to any one of the outputs  36 . 
     Downstream of the switches  20 ,  22  are a plurality of receive nodes  40  (labeled Node  1 , Node  2 , Node  3  and Node  4 ). Each receive node  40  includes an optical signal receiver  42  capable of receiving an optical signal. Optical signal combiners  44  are connected to the receivers  42  and to one of the outputs  32  of the switch  20  and one of the outputs  36  of the switch  22 . The optical signal combiners  44  can receive both signal portions  16   a ,  16   b  and combine them back into the transmitted signal  16  which is then input into the respective receiver  42  of the receive node  40 . 
     In the system  10 , if one of the switches  20 ,  22  fails, the system is still able to route the optical signal to the appropriate receive node  40 . However, the receive node would receive only half of the originally transmitted signal  16 , i.e. either signal portion  16   a  or  16   b  depending upon which switch fails. The sensitivity of the receivers  42  is such as to allow receipt of the combined signal portions  16   a ,  16   b  or just an individual signal portion  16   a ,  16   b.    
     Although four transmit nodes and four receive nodes are illustrated, the system  10  could be implemented with a larger or smaller number of transmit and receive nodes. In addition, although the transmit nodes are described as having transmitters  14  and the receive nodes as having receivers  42 , transceivers could be used in place of the transmitters and/or the receivers to allow the transmit nodes and the receive nodes to transmit and receive. 
     Turning to  FIGS. 2-5 , a fault tolerant optical switching system  50  is illustrated that utilizes different types of optical switches  52 ,  54  that have distinct switching functionality from one another. The system  50  includes a plurality of transmit, single channel nodes  60  (labeled Node  1 , Node  2 , Node  3  and Node  4 ) each of which includes an optical transmitter  62  capable of transmitting an optical signal  64  on a single channel. Optical signal splitters  66  receive the transmitted optical signals and split the transmitted signal  64  into two half-power signal portions  68   a ,  68   b.    
     The first optical switch  52  and the second optical switch  54  receive the signal portions  68   a ,  68   b . In the illustrated example, the first optical switch  52  is a SOA switch while the second optical switch  54  is a MEMS switch. Thus, the switch  52  has faster switching speed, but uses higher power, compared to the MEMS switch  54 , while the MEMS switch operates more slowly but at lower power. 
     The switch  52  includes a plurality of optical inputs  70  connected to the optical signal splitters  66  and receiving the first optical signal portions  68   a . The switch  52  also includes a plurality of optical outputs  72 . Each input  70  is selectively connectable to each of the outputs  72  so that the signal portion  68   a  received by an input  70  can be routed to any one of the outputs  72 . 
     Likewise, the switch  54  includes a plurality of optical inputs  74  connected to the optical signal splitters  66  and receiving therefrom the second optical signal portions  68   b . The switch  54  also includes a plurality of optical outputs  76 . Each input  74  is selectively connectable to each of the outputs  76  so that the signal portion  68   b  received by an input  74  can be routed to any one of the outputs  76 . 
     A plurality of receive nodes  80  (labeled Node  1 , Node  2 , Node  3  and Node  4 ) are downstream of the switches  52 ,  54 . Each receive node  80  includes an optical signal receiver  82  capable of receiving an optical signal. Optical signal combiners  84  are connected to the receivers  82  and to one of the outputs  72  of the switch  52  and one of the outputs  76  of the switch  54 . The optical signal combiners  84  can receive both si portions  68   a ,  68   b  and combine them back into the transmitted signal  64  which is then input into the respective receiver  82  of the receive node  80 . 
     The system  50  also includes a plurality of optical-to-electrical receivers  90 , each of which is connected between an associated one of the optical transmitters  62  and the corresponding optical signal splitter  66 . The receivers  90  receive the optical signals  64  from the transmitters  62 , convert the optical signals to electrical signals, and send the electrical signals to decoders  92 . The decoders  92  decode the electrical signals, which carry instructions indicating which nodes the switches  52 ,  54  should route the optical signals  64  to.  FIG. 3  illustrates the connections that are optical connections (shown in heavy line) and the connections that are electrical connections (shown in lighter line). 
     Control logic is connected to each decoder  92  and to the switches  52 ,  54  for controlling the switches based on the decoded instructions. The control logic can be located at any suitable location to allow the control logic to perform the control functions on the switches  52 ,  54 . For example, as illustrated in  FIGS. 2-5 , the control logic can be provided in a controller  94  that is separate from the decoders  92  and the switches  52 ,  54 . The controller  94  receives inputs from all of the decoders  92  for appropriate control of the switches  52 ,  54 . Alternatively, the control logic can be embedded in each decoder  92 , or the control logic can be embedded in one of the decoder  92 , with the rest of the decoders being connected to the decoder containing the control logic. 
     With reference to  FIGS. 4 and 5 , an exemplary operation of the system  50  is shown. The transmitter  62  of Node  1  transmits an optical signal intended for receive Node  3 . The signal is received by the O/E receiver  90  which converts the optical signal to an electrical signal, and sends the electrical signal to the decoder  92 . The decoder decodes the electrical signal to determine which receive node the transmitted optical signal is to be routed to. The transmitted optical signal is also split by the splitter  66  into the first and second signal portions. The control logic in controller  94  receives a signal from the decoder  92 , and controls the switches  52 ,  54  to begin routing the optical signal to receive Node  3 . 
     As indicated in  FIG. 4 , because the SOA switch  52  has fast switching speed, it switches first so as to route the signal portion  68   a  from the Node  1  input  70  to the Node  3  output  72  of the switch  52 . The signal portion  68   a  is then passed through the combiner  84  and is received by the receiver  82  of receive Node  3 . 
     At the same time that the SOA switch  52  switches, the MEMS switch  54  is switching. Since the MEMS switch  54  is slower, it takes longer to complete the switch. Ultimately, as shown in  FIG. 5 , the MEMS switch  54  will complete its switch so as to route the signal portion  68   b  from the Node  1  input  74  to the Node  3  output  76  of the switch  54 . The signal portion  68   b  is then passed through the combiner  84  and is received by the receiver  82  of receive Node  3 . 
     Although not illustrated, there will be a brief period of time where both the SOA switch  52  and the MEMS switch  54  will route the respective signal portions  68   a ,  68   b  to receive Node  3 , in which case the combiner  84  will combine the signal portions  68   a ,  68   b  into a single signal. However, once the MEMS switch  54  has completed the switch, the SOA switch  52  can be instructed by the control logic to turn off to conserve power. The configuration shown in  FIG. 5  is thus achieved where only the signal portion  68   b  is passed to receive Node  3 . The sensitivity of the receiver  82  is such that it is still able to detect the half-power signal portion  68   b.    
     In the event that either one of the switches  52 ,  54  fails, the remaining switch is able to take-over the switching duties for the entire system  50 . Therefore, the system  50  is fault tolerant so that failure of one of the switches does not take down the entire system. 
     Although four transmit nodes and four receive nodes are illustrated, the system  50  could be implemented with a larger or smaller number of transmit and receive nodes, In addition, although the transmit nodes are described as having transmitters and the receive nodes as having receivers, transceivers could be used in place of the transmitters and/or the receivers to allow the transmit nodes and the receive nodes to transmit and receive. 
     The examples disclosed in this application are to be considered in all respects as illustrative and not limitative. The scope of the invention is indicated by the appended claims rather than by the foregoing description; and all changes which come within the meaning and range of equivalency of the claims are intended to be embraced therein.