Signal identification in optical communications networks
Signals in an optical communications network, such as optical channels in an optical WDM network for example, are each identified by at least two low frequency dither tones with which the signal is modulated. The dither tones alternate with a predetermined periodicity to produce a cyclically repeated sequence of dither tones. A network parameter, such as a channel identifier for example, is obtained by the detection of the particular combination of dither tones in the sequence. To detect a number of network parameters a signal is modulated with a number of cyclically repeated sequences of dither tones each uniquely identifying a respective network parameter. In some implementations each dither tone in a cyclically repeated sequence of dither tones is repeated with substantially the same phase and coherent averaging is performed over a number of periods to detect dither tones on low power signals.
1. A method of identifying a signal in an optical communications network comprising the steps of:
(a) modulating an optical signal with a cyclically repeated sequence of low frequency dither tones, the cyclically repeated sequence having a predetermined periodicity;
(b) performing a sequence of discrete transform operations on the optical signal to produce respective frequency analysis results; and
(c) performing coherent averaging of the frequency analysis results over the discrete transform operations to detect the low frequency dither tones.
2. The method according to claim 1 , wherein the step of modulating comprises allocating one or more dither tones for identifying a network parameter of the optical communications network.
3. The method according to claim 2 , wherein the network parameter is identified by two or more low frequency dither tones modulated simultaneously, the method further comprising identifying network parameter by detecting at least one of the low frequency dither tones modulated simultaneously.
4. A method according to claim 1 , wherein the optical signal is modulated with at least one other cyclically repeated sequence of low frequency dither tones, the other cyclically repeated sequence having a respective predetermined periodicity, the method further comprising:
for each other cyclically repeated sequence of low frequency dither tones:
detecting the low frequency dither tones by coherently averaging the respective frequency analysis results produced by the discrete transform operations, and
identifying a respective network parameter from the detected low frequency dither tones.
5. A method according to claim 4 wherein each cyclically repeated sequence of low frequency dither tones uniquely identifies said respective network parameter.
6. A method according to claim 4 wherein each network parameter comprises one of a channel ID (IDentifier), a link ID, an optical fiber ID, a fiber section ID, an optical band ID, a source node ID, a destination node ID, and a bundle ID.
7. A method according to claim 4 , wherein the cyclically repeated sequences of low frequency dither tones are modulated in one of the following ways: (a) simultaneously; (b) consecutively; and (c) using a combination of (a) and (b).
8. A method according to claim 1 , wherein each low frequency dither tone in the cyclically repeated sequence of low frequency dither tones is repeated with substantially the same phase at said predetermined periodicity.
9. A method according to claim 1 , wherein at least one of the low frequency dither tones is modulated at least twice within the sequence.
10. A method according to claim 1 , wherein the cyclically repeated sequence of low frequency dither tones comprises a plurality of sets of at least one low frequency dither tone modulated simultaneously, at least two of the plurality of sets having different numbers of low frequency dither tones.
11. A detection arrangement for an optical communications network comprising:
a detector for detecting an optical signal modulated with a cyclically repeated sequence of low frequency dither tones, the cyclically repeated sequence having a predetermined periodicity; and
a processor for performing a sequence of discrete transform operations on the optical signal to produce respective frequency analysis results and for coherently averaging the frequency analysis results over the discrete transform operations to detect the low frequency dither tones.
12. An arrangement according to claim 11 wherein the processor comprises means for identifying a network parameter from the detection of the low frequency dither tones.
13. An arrangement according to claim 12 wherein each network parameter comprises one of a channel ID (IDentifier), a link ID, an optical fiber ID, a fiber section ID, an optical band ID, a source node ID, a destination node ID, and a bundle ID.
14. An arrangement according to claim 11 wherein the cyclically repeated sequence of low frequency dither tones comprises at least one set of low frequency dither tones modulated simultaneously, the processor comprising means for identifying a network parameter by detecting at least one of the low frequency dither tones modulated simultaneously from each set.
15. An arrangement according to claim 11 wherein the optical signal is modulated with at least one other cyclically repeated sequence of low frequency dither tones, said at least one other cyclically repeated sequence having a respective predetermined periodicity, processor comprising:
means for coherently averaging the frequency analysis results over the discrete transform operations to detect the low frequency dither tones for each said at least one other cyclically repeated sequence; and
means for identifying a respective network parameter from the detected low frequency dither tones.
16. An arrangement according to claim 15 wherein each cyclically repeated sequence of low frequency dither tones uniquely identifies said respective network parameter.
17. An arrangement according to claim 15 , wherein the cyclically repeated sequences of low frequency dither tones are modulated in one of the following ways: (a) simultaneously; (b) consecutively; and (c) using a combination of (a) and (b).
18. An arrangement according to claim 11 wherein each low frequency dither tone in the cyclically repeated sequence of low frequency dither tones is repeated with substantially the same phase at said predetermined periodicity.
19. The combination according to claim 18 , wherein the modulating arrangement comprises means for producing at least one other cyclically repeated sequence of low frequency dither tones, the sequence having a predetermined periodicity, the modulator comprising means for modulating the optical signal with the at least one other cyclically repeated sequence of low frequency dither tones.
20. The combination according to claim 18 , wherein the means for producing a cyclically repeated sequence of low frequency dither tones comprises at least one programmable frequency source for generating the low frequency dither tones.
21. The combination according to claim 18 , wherein the means for producing a cyclically repeated sequence of low frequency dither tones comprises at least two programmable frequency sources for generating the low frequency dither tones and at least one selector for alternately selecting the low frequency dither tones.
22. The combination according to claim 18 , wherein the means for producing a cyclically repeated sequence of low frequency dither tones comprises a DAC (Digital to Analog Converter) for generating the low frequency dither tones.
23. In combination, a detection arrangement of claim 11 , and a modulating arrangement for modulating an optical signal, the modulating arrangement comprising:
means for producing a cyclically repeated sequence of low frequency dither tones, the sequence having a predetermined periodicity; and
a modulator for modulating the optical signal with the cyclically repeated sequence of low frequency dither tones.
24. The combination according to claim 23 , wherein the cyclically repeated sequence of low frequency dither tones comprises at least one set of low frequency dither tones modulated simultaneously.
25. An optical system, comprising:
a modulating arrangement for generating a cyclically repeated sequence of low frequency dither tones, the sequence having a predetermined periodicity, and for modulating an optical signal with the cyclically repeated sequence of low frequency dither tones; and
a detection arrangement for:
detecting the optical signal;
performing a sequence of discrete transform operations on the optical signal to produce respective frequency analysis results; and
detecting the low frequency dither tones by coherently averaging the frequency analysis results over the discrete transform operations.
26. The system according to claim 25 , comprising a global clock for synchronizing time intervals for modulating the optical signal with the low frequency dithers tones at the modulating arrangements and time intervals for detecting the low frequency dither tones at the detection arrangement.
27. The system according to claim 26 , wherein the time intervals of modulating and detecting respective dither tones have same duration and start at an instant of switching dither tone frequencies.