Optical switch with connection verification

• US 20020012143A1
• Filed: 05/18/2001
• Published: 01/31/2002
• Est. Priority Date: 05/30/2000
• Status: Active Grant

• Current Assignee: RPX Clearinghouse LLC (RPX Corporation)
• Original Assignee: Nortel Networks Limited (Nortel Networks Corporation)
• Inventors: Bryant, Adrew J., Graves, Alan F., Gruber, John G.
• Granted Patent: US 6,871,021 B2
• Time in Patent Office: Days
• US Class Current: 398/87
• CPC Class Codes: H04Q 11/0005 Switch and router aspects
• CPC Class Codes: H04Q 2011/0015 using splitting combining
• CPC Class Codes: H04Q 2011/0043 Fault tolerance
• CPC Class Codes: H04Q 2011/0083 Testing; Monitoring
• CPC Class Codes: H04Q 2011/0084 Quality of service aspects

Abstract

An optical switch is equipped with a set of optical intensity controllers at its input, each intensity controller being driven to vary a corresponding WDM input traffic signal with a low power test signal. The switch is also equipped with optical splitters at its output and a path integrity analyzer connected to the splitters and to the intensity controllers. The path integrity analyzer generates or controls generation of the test signals applied by the intensity controllers. The path integrity analyzer also receives the tapped portions of the WDM output signals and separates them into their single-carrier components in order to recover a set of switched single-carrier optical signals. The path integrity analyzer is further provided with test signal detectors used to detect the presence of a test signal in each recovered switched single-carrier optical signal. The path integrity analyzer thus ascertains the integrity of the connection involving each switched single-carrier optical signal by comparing detected test signals to expected test signals that are derived from a connection map.

Claims

1. A switch for optical signals, comprising:

a plurality of wavelength division demultiplexers (WDDs), each having an input port and a plurality of output ports;

a plurality of wavelength division multiplexers (WDMs), each having an output port and a plurality of input ports;

an optical switching core having a plurality of input ports at which optical signals enter said core and a plurality of output ports at which optical signals exit said core, a subset of the input ports of said core being connected to the output ports of said WDDs and a subset of the output ports of said core being connected to the input ports of said WDMs, said core being capable of establishing photonic connections between said subset of its input ports and said subset of its output ports in response to an indication of desired connections;

a plurality of optical intensity controllers, each connected to the input port of a corresponding one of said WDDs and adapted to vary the intensity of an input multi-carrier optical signal entering the input port of said corresponding one of said WDDs;

a plurality of optical splitters, each connected to the output port of a corresponding one of said WDMs and adapted to tap a fraction of the intensity of an output multi-carrier optical signal exiting the output port of said corresponding one of said WDMs; and

a connection verification unit connected to said optical intensity controllers and to said optical splitters, said connection verification unit being operable to;

(a) control said optical intensity controllers so as to cause a test signal to be applied to at least one of the input multi-carrier optical signals;

(b) determine, on the basis of at least one of the desired connections and for at least one of the signals exiting said subset of the output ports of said core, which test signal is expected to appear in said at least one of the signals exiting said subset of the output ports of said core;

(c) process the output multi-carrier optical signals tapped by said optical splitters in order to detect which test signal, if any, appears in said at least one of the signals exiting said subset of the output ports of said core; and

(d) compare the detected and expected test signals, thereby determining whether said at least one of the desired connections has been correctly established by said core.

2. A switch as claimed in claim 1, wherein the connection verification unit comprises:

a first stage, for separating the output multi-carrier optical signals tapped by said optical splitters into single-carrier component signals corresponding to said at least one of the signals exiting said subset of the output ports of said core;

a second stage connected to the first stage, for detecting test signals appearing in said single-carrier component signals; and

a third stage connected to the second stage, for comparing the test signals detected in said single-carrier component signals to the test signals expected to appear in the corresponding signals exiting said subset of the output ports of said core.

3. A switch as claimed in claim 2, wherein the second stage is further operable to convert each single-carrier component signal into an electrical signal prior to detecting the test signals appearing in said single-carrier component signals.

4. A switch as claimed in claim 3, wherein each electrical signal has a data bandwidth narrower than that of the single-carrier component signal from which it is obtained.

5. A switch as claimed in claim 2, wherein said first stage comprises a plurality of second WDDs, each having a respective plurality of output ports and having a respective input port connected to a respective one of the optical splitters.

6. A switch as claimed in claim 5, wherein the second stage comprises:

a plurality of optical receivers, each receiver having an output port and having an input port connected to a corresponding one of the output ports of one of the second WDDs; and

a plurality of test signal detectors, each test signal detector having an output port and having an input port connected to a respective one of the optical receivers.

7. A switch as claimed in claim 2, wherein said first stage comprises a plurality of tunable optical filters, each having an output port and having an input port connected to a respective one of the optical splitters, each tunable optical filter being adapted to admit an optical signal in a selected optical frequency range through to said second stage.

8. A switch as claimed in claim 7, wherein the connection verification unit comprises a controller for controlling application of the test signals by the intensity controllers and for selecting the optical frequency range admitted by at least one tunable optical filter.

9. A switch as claimed in claim 7, wherein the second stage comprises:

a plurality of optical receivers, each receiver having an output port and having an input port connected to the output port of a corresponding one of the tunable optical filters; and

a plurality of test signal detectors, each test signal detector having an output port and having an input port connected to a respective one of the optical receivers.

10. A switch as claimed in claim 2, wherein the first stage comprises:

an optical switching element having an output port and having a plurality of input ports respectively connected to the optical splitters, said optical switching element being arranged to admit an optical signal appearing on a selected one of its input ports through to its output port; and

a second WDD having a plurality of output ports and having an input port connected to the output port of said optical switching element.

11. A switch as claimed in claim 10, wherein the connection verification unit comprises a controller for controlling application of the test signals by the intensity controllers and for selecting the input port of the optical switching element on which appears the optical signal admitted to the output port of the optical switching element.

12. A switch as claimed in claim 10, wherein the second stage comprises:

a plurality of optical receivers, each having an output port and having an input port connected to a corresponding one of the output ports of said second WDD; and

a plurality of test signal detectors, each having an output port and having an input port connected to a corresponding one of said optical receivers.

13. A switch as claimed in claim 2, wherein the first stage comprises:

a first optical switching element having an output port and having a plurality of input ports respectively connected to the optical splitters, said optical switching element being adapted to pass an optical signal appearing on a selected one of its input ports through to its output port; and

a second WDD having a plurality of output ports and having an input port connected to the output port of said first optical switching element; and

at least one second optical switching element connected to the output ports of said second WDD, each said at least one second optical switching element having an output port, said at least one second optical switching element having an aggregate number of input ports sufficient to accommodate the output ports of said WDD, each said second optical switching element being adapted to pass an optical signal appearing on a selected one of its input ports through to its output port.

14. A switch as claimed in claim 13, wherein the connection verification unit comprises a controller for controlling application of the test signals by the intensity controllers and for selecting the input port of the optical switching element on which appears the optical signal admitted to the output port of each first and second optical switching element.

15. A switch as claimed in claim 13, wherein the second stage comprises:

at least one optical receiver, each having an output port and having an input port connected to a corresponding one of said at least one second optical switching element; and

at least one test signal detector, each having an output port and having an input port connected to a corresponding one of said at least one optical receiver.

16. A switch as claimed in claim 2, wherein the first stage comprises:

an optical switching element having an output port and having a plurality of input ports respectively connected to the optical splitters, said optical switching element being arranged to admit an optical signal appearing on a selected one of its input ports through to its output port; and

a tunable optical filter connected to the output port of said optical switching element, said tunable optical filter being adapted to admit an optical signal in a selected optical frequency range through to said second stage.

17. A switch as claimed in claim 16, wherein the connection verification unit comprises a controller for controlling application of the test signals by the intensity controllers and for selecting the optical frequency range admitted by said tunable optical filter.

18. A switch as claimed in claim 16, wherein the second stage comprises:

an optical receiver having an ouptut and having an input connected to said tunable optical filter; and

a test signal detector connected to said optical receiver.

19. A switch as claimed in claim 2, said core comprising a plurality of optical switching elements, each said optical switching element having a plurality of input ports and a plurality of output ports and operable to establish photonic connections therebetween, wherein a subset of the input ports of said optical switching elements represents said subset of the input ports of the core and wherein a subset of the output ports of said optical switching elements represents said subset of the output ports of the core.

20. A switch as claimed in claim 19, further comprising a wavelength converting switch, said wavelength converting switch having a plurality of input ports and a plurality of output ports and operable to establish non-photonic connections therebetween, wherein the input ports of the wavelength converting switch are connected to output ports of the core which are not members of said subset of the output ports of the core and wherein the output ports of the wavelength converting switch are connected to input ports of the core which are not members of said subset of the input ports of the core.

21. A switch as claimed in claim 20, further comprising a plurality of second optical splitters connected to the output ports of the core which are not members of said subset of the output ports of the core.

22. A switch as claimed in claim 21, wherein the first stage comprises:

a plurality of second WDMs, each having an output port and having a plurality of input ports connected to the second optical splitters;

an optical switching element having an output port and having a plurality of input ports each connected to a corresponding one of the first optical splitters or to a corresponding one of the output ports of one of the second WDMS, said optical switching element being arranged to admit an optical signal appearing on a selected one of its input ports through to its output port; and

a second WDD having a plurality of output ports and having an input port connected to the output port of said optical switching element.

23. A switch as claimed in claim 22, wherein the first stage further comprises:

at least one second optical switching element connected to the output ports of said second WDD, each said at least one second optical switching element having an output port, said at least one second optical switching element having an aggregate number of input ports sufficient to accommodate the output ports of said WDD, each said second optical switching element being adapted to pass an optical signal appearing on a selected one of its input ports through to its output port.

24. A switch as claimed in claim 23, wherein the second stage comprises:

a plurality of first optical receivers, each having an output port and having an input port connected either to a corresponding one of the second optical splitters or to a corresponding one of the output ports of one of the second WDDs;

a plurality of first test signal detectors, each first test signal detector having an output port and having an input port connected to a respective one of the optical receivers;

at least one second optical receiver, each having an output port and having an input port connected to the output port of a corresponding one of said at least one second optical switching element in the first stage; and

a second test signal detector having an output port and having an input port connected to the output of the second optical receiver.

25. A switch as claimed in claim 21, wherein the first stage comprises:

a plurality of second WDMs, each having an output port and having a plurality of input ports connected to the second optical splitters;

an optical switching element having an output port and having a plurality of input ports each connected to a corresponding one of the first optical splitters or to a corresponding one of the output ports of one of the second WDMs, said optical switching element being arranged to admit an optical signal appearing on a selected one of its input ports through to its output port; and

a tunable optical filter connected to the output port of said optical switching element, said tunable optical filter being adapted to admit an optical signal in a selected optical frequency range through to said second stage.

26. A switch as claimed in claim 25, wherein the second stage comprises:

an optical receiver having an output port and having an input port connected to the output port of the tunable optical filter; and

a test signal detector having an output port and having an input port connected to a the optical receiver.

27. A switch as claimed in claim 2, further comprising a power spectrum equalization unit connected to said first stage and utilizing said single-carrier component signals corresponding to said at least one of the signals exiting said subset of the output ports of said core.

28. A switch as claimed in claim 1, wherein test signals applied to different ones of the input multi-carrier optical signals have mutually distinct amplitudes or frequency content or encode mutually distinct digital messages.

29. A switch as claimed in claim 1, further comprising a test signal cancellation unit for removing at least one test signal from at least one of optical signals exiting said subset of the output ports of the core.

30. A switch as claimed in claim 29, wherein said at least one test signal is a frequency tone and wherein said test signal cancellation unit comprises an anti-phase modulator.

31. A switch as claimed in claim 30, wherein said anti-phase modulator is adapted to derive anti-phase modulation by tapping said at least one test signal from said connection verification unit and passing the at least one tapped signal through an inverting amplifier.

32. A switch as claimed in claim 2, wherein the test signals applied to at least two different input multi-carrier optical signals are mutually non-interfering.

33. A system for use with a switch for optical signals, the switch having a plurality of wavelength division demultiplexers (WDDs), each having an input port and a plurality of output ports;

a plurality of wavelength division multiplexers (WDMs), each having an output port and a plurality of input ports; and

an optical switching core having a plurality of input ports at which optical signals enter the core and a plurality of output ports at which optical signals exit the core, wherein a subset of the input ports of the core is connected to the output ports of the WDDs and wherein a subset of the output ports of the core is connected to the input ports of the WDMs, the core being capable of establishing photonic connections between the subset of its input ports and the subset of its output ports in response to an indication of desired connections, the system comprising;

a plurality of optical intensity controllers, each connectable to the input port of a corresponding one of the WDDs and adapted to vary the intensity of an input multi-carrier optical signal entering the input port of the corresponding one of the WDDs;

a plurality of optical splitters, each connectable to the output port of a corresponding one of the WDMs and adapted to tap a fraction of the optical intensity of an output multi-carrier optical signal exiting the output port of the corresponding one of the WDMs; and

a connection verification unit connected to said optical intensity controllers and to said optical splitters and being operable to;

(a) control said optical intensity controllers so as to cause a test signal to be applied to at least one of the input multi-carrier optical signals;

(b) determine, on the basis of at least one of the desired connections and for at least one of the signals exiting said subset of the output ports of said core, which test signal is expected to appear in said at least one of the signals exiting said subset of the output ports of said core;

(c) process the output multi-carrier optical signals tapped by said optical splitters in order to detect which test signal, if any, appears in said at least one of the signals exiting said subset of the output ports of said core; and

(d) compare the detected and expected test signals, thereby determining whether said at least one of the desired connections has been correctly established by said core.

34. A connection verification unit for use with an optical switch having a switching core capable of establishing photonic connections between a plurality of input ports and a plurality of output ports in response to an indication of desired connections, wherein optical signals entering a subset of the input ports originate from a plurality of input multi-carrier optical signals and wherein optical signals exiting a subset of the output ports are recombined into a plurality of output multi-carrier optical signals, a method of determining whether at least one of the desired connections has been established by the core, comprising:

a controller for controlling application of test signals to the input multi-carrier optical signals;

a first stage, for separating the output multi-carrier optical signals into single-carrier component signals corresponding to the at least one of the signals exiting the subset of the output ports of the core;

a second stage connected to the first stage, for detecting test signals appearing in the single-carrier component signals; and

a third stage connected to the second stage, for comparing the test signals detected in the single-carrier component signals to the test signals expected to appear in the corresponding signals exiting the subset of the output ports of the core.

35. A connection verification unit for use with an optical switch having a switching core capable of establishing photonic connections between a plurality of input ports and a plurality of output ports in response to an indication of desired connections, wherein optical signals entering a subset of the input ports originate from a plurality of input multi-carrier optical signals and wherein optical signals exiting a subset of the output ports are recombined into a plurality of output multi-carrier optical signals, a method of determining whether at least one of the desired connections has been established by the core, comprising:

(a) means for causing a test signal to be applied to at least one of the input multi-carrier optical signals;

(b) means for determining, on the basis of at least one of the desired connections and for at least one of the optical signals exiting the subset of the output ports, which test signal is expected to appear in said at least one of the optical signals exiting the subset of the output ports;

(c) means for processing the output multi-carrier optical signals in order to detect which test signal, if any, appears in said at least one of the signals exiting the subset of the output ports; and

(d) means for comparing the detected and expected test signals.

36. In an optical switch having a switching core capable of establishing photonic connections between a plurality of input ports and a plurality of output ports in response to an indication of desired connections, wherein optical signals entering a subset of the input ports originate from a plurality of input multi-carrier optical signals and wherein optical signals exiting a subset of the output ports are recombined into a plurality of output multi-carrier optical signals, a method of determining whether at least one of the desired connections has been established by the core, comprising:

(a) causing a test signal to be applied to at least one of the input multi-carrier optical signals;

(b) determining, on the basis of at least one of the desired connections and for at least one of the optical signals exiting the subset of the output ports, which test signal is expected to appear in said at least one of the optical signals exiting the subset of the output ports;

(c) processing the output multi-carrier optical signals in order to detect which test signal, if any, appears in said at least one of the signals exiting the subset of the output ports; and

(d) comparing the detected and expected test signals.

37. A method as claimed in claim 36, wherein determining the test signal expected to appear in the signal exiting a particular one of the output ports of the core comprises determining the test signal applied to the input multi-carrier optical signal from which originates the optical signal that enters the input port of the core which is defined by one of the desired connections as being connected to said particular one of the output ports of the core.

38. A method as claimed in claim 37, further comprising:

if the test signal expected to appear in the signal exiting a particular one of the output ports of the core does not match the test signal, if any, appearing in the signal exiting said particular one of the output ports of the core, declaring a mis-connection and entering a diagnostic mode to localize the source of the mis-connection.

39. A method as claimed in claim 36, further comprising:

removing at least one test signal from at least one of the optical signals exiting said subset of the output ports of the core.

40. A method as claimed in claim 39, wherein at least one test signal is a frequency tones, the method further comprising:

introducing anti-phase modulation of the tone in order to effect substantial removal of said at least one test signal from said at least one of the optical signals exiting said subset of the output ports of the core.