Fast optical switch
View Patent ↗A last optical switch is needed to realize an economical and scaleable optical-core network. In the disclosed optical switch, switching is effected by rapid wavelength conversion. Either channel switching, Time Division Multiplex (TDM) switching or both may be provided by the fast optical switch. The operation of the fast optical switch is enabled by a fast scheduler. The throughput of the optical switch may be increased through a process of bimodal pipelined connection-packing. An in-band exchange of control signals with external nodes may serve to minimize the control overhead. Such control signals may include time-locking signals and connection-requests. A modular structure may be configured to comprise several fast optical switches to yield a high-speed, high-capacity, fully-connected optical switch.
1. A method of switching in an optical switch, the optical switch comprising a plurality of output ports each associated with a respective wavelength band from among a plurality of wavelength bands, input ports each having a spectral translator for translating an input optical signal to any wavelength band in said plurality of wavelength bands, and a controller connecting to a selected output port associated with a control wavelength band and a selected input port, the method of switching comprising:
transmitting from a first output port an output optical signal instructing a first edge node having a first time counter to send a first optical signal containing continuous readings of said first time counter;
receiving at a first input port said first optical signal;
instructing said first input port to translate said first optical signal during a designated time slot to a translated optical signal within said control wavelength band;
receiving said translated optical signal at said controller;
comparing at said controller a time indicator determined from said translated optical signal with a reading of a master time counter of said controller; and
transmitting from said first output port a signal instructing said first edge node to adjust said first time counter according to said comparing,
wherein said time indicator is a reading of said first time counter and said continuous readings comprise successive readings of said first time counter each of said successive readings occupying less than half said designated time slot.
2. The method of claim 1 wherein said designated time slot is specific to said first input port.
3. The method of claim 1 wherein said designated time slot is a time slot in a repetitive slotted time frame.
4. The method of claim 1 comprising a further step of instructing said first edge node to transmit regular control signals during said designated time slot, each of said regular control signals including readings of said first time counter and requests for specific connections, each request specifying a destination output port, from among said plurality of output ports, and a corresponding connection capacity.
5. The method of claim 4 comprising further steps of:
determining accepted connections from among said specific connections;
determining a schedule for said accepted connections said schedule designating at least one time slot in a repetitive slotted time frame for each of said accepted connections; and
transmitting said schedule to said first edge node.
6. The method of claim 5 further comprising instructing said first input port to translate each optical signal received during each of said at least one time slot to a wavelength band corresponding to a destination output port corresponding to said each of said accepted connections.
7. The method of claim 1 wherein said first output port is any of said plurality of output ports excluding said selected output port, said first edge node is any edge node in a plurality of edge nodes connecting to said optical switch, and said input port is any of a plurality of input ports excluding said selected input port.
8. The method of claim 1 further comprising:
specifying a time duration of each of said continuous readings of said first time counter.
9. The method of claim 1 further comprising:
associating a second designated time slot with a second input port for receiving control signals from said second input port.
10. A controller connecting to a selected input port from among a plurality of input ports of an optical switch, where each input port steers an input optical signal to a selected output port from among a plurality of output ports of said optical switch by spectral translation of said input optical signal to a control wavelength band corresponding to said selected output port, where said controller:
transmits from a first output port an output optical signal instructing a first edge node having a first time counter to transmit continuous readings of said first time counter;
receives at a first input port said input optical signal containing said continuous readings;
instructs said first input port to translate said input optical signal during a first designated time slot to said control wavelength band;
ascertains a time indicator from said input optical signal and compares said time indicator with a reading of a master time counter of said controller; and
sends from said first output port a signal instructing said first edge node to adjust said first time counter,
wherein said time indicator is a reading of said first time counter and said continuous readings comprise successive readings of said first time counter each of said successive readings occupying less than half said designated time slot.
11. The controller of claim 10 further operative to specify a time duration of each of said continuous readings of said first time counter.
12. The controller of claim 10 further operative to associate said first designated time slot with any time slot in a repetitive slotted time frame.
13. The controller of claim 10 further operative to associate a second designated time slot with a second input port from among said plurality of input ports for receiving control signals from said second input port.
14. The controller of claim 10 further operative to instruct said first edge node to transmit regular control signals during said first designated time slot, each of said regular control signals including readings of said first time counter and a number of connection requests, where each of said connection request specifies a destination output port, from among said plurality of output ports, and a corresponding connection capacity.
15. The controller of claim 14 further operable to:
determine, where said number of connection requests exceed zero, acceptable connections from among said number of connections, and where there is at least one acceptable connection;
determine a schedule for said at least one acceptable connection; and
send said schedule to said first edge node, said schedule designating at least one time slot in a time-slotted frame for each of said at least one acceptable connection.
16. The controller of claim 15 further operable to instruct said first input port to translate each optical signal received during each of said at least one time slot to a wavelength band corresponding to a destination output port associated with said each of said at least one acceptable connection.
17. The controller of claim 10 wherein said first output port is any output port in said plurality of output ports excluding said selected output port and said first input port is any of said plurality of input ports excluding said selected input port.
18. The controller of claim 10 , wherein said first designated time slot is specific to said first input port.