Switching status and performance monitoring technology for wavelength selective switch and optical networks

• US 7,254,327 B1
• Filed: 02/02/2004
• Issued: 08/07/2007
• Est. Priority Date: 01/31/2003
• Status: Active Grant

• Current Assignee: Ciena Corporation
• Original Assignee: Ciena Corporation
• Inventors: Zhong, Shan, Archambault, Jean-Luc, Pelekhaty, Vladimir
• Primary Examiner(s): Pascal; Leslie
• Application Number:
  US10/768,020
• Time in Patent Office: 1,282 Days
• Field of Search: 398 30- 33, 709/224
• US Class Current: 398/33
• CPC Class Codes: H04B 10/0775 Performance monitoring and measurement of transmission parameters
• CPC Class Codes: H04L 43/50 Testing arrangements
• CPC Class Codes: H04Q 11/0005 Switch and router aspects
• CPC Class Codes: H04Q 2011/0009 using wavelength filters
• 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

Abstract

A universal in-service monitoring scheme to monitor performances of optical networks, including elements that make up the optical network, is proposed. The elements may be a wavelength selective switch or an optical cross connect. In this scheme, a small tunable probe signal is injected into the optical network via an input of the network. An output signal is received at the output and processed to determine if the probe signal is contained within the output signal. The scheme is such that probe signal injection and detection devices need not be physically co-located. Thus, the scheme is useful to test even optical network that spans thousands of miles. The probe signal is non-interfering with the network traffic so the network can be providing service while its performance is monitored. As examples of the probe signal detection mechanisms include lock-in amplification and coherent detection.

Claims

1. An apparatus to monitor performance of an optical network, comprising:

at least one probe signal generator configured to generate a probe signal, wherein said at least one probe signal generator is a tunable laser such that a frequency of the probe signal is tunable;

at least one modulation signal generator optically or electrically connected to said at least one probe signal generator, said at least one modulation signal generator configured generate a modulation signal at a predetermined modulation frequency, wherein the probe signal generated by said probe signal generator is modulated based on the modulation signal;

an ingress switch including at least one input and a plurality of outputs, wherein said at least one input of said ingress switch is optically connected to said at least one probe signal generator and said plurality of outputs are optically connected to a plurality of inputs of the optical network, said ingress switch being configured to selectively direct the probe signal to at least one of the plurality of inputs of the optical network;

an egress switch including a plurality of inputs and at least one output, wherein said plurality of inputs of said egress switch are optically connected to a plurality of outputs of the optical network, said egress switch being configured to selectively direct an output signal from at least one of said plurality of outputs of said optical network to said at least one output of said egress switch; and

at least one probe signal detector optically connected to said at least one output of said egress switch, said at least one probe signal detector configured to detect a presence of the probe signal in the output signal,

wherein said at least one probe signal detector comprises a resonant photo detector configured to receive the output signal and to detect the probe signal within the output signal and a lock-in amplifier optically or electrically connected to said at least one modulation signal generator, said lock-in amplifier configured to amplify the probe signal detected by said at least one resonant photo detector based on the modulation signal.

2. The apparatus of claim 1, wherein the probe signal generated by said at least one probe signal generator is non-interfering with network traffic on the optical network.

3. The apparatus of claim 2, wherein a strength of said probe signal is substantially at least −

30 dB below a single wavelength division multiplexed (WDM) channel.

4. The apparatus of claim 2, wherein the optical network is a wavelength selective switch (WSS) or an optical cross connect (OXC).

5. The apparatus of claim 4, wherein:

a plurality of probe signal generators are optically connected to a corresponding input of a plurality, of inputs of said ingress switch, each of said plurality of probe signal generators connected to a corresponding one of a plurality of modulation signal generator generating a corresponding predetermined modulation frequency, and

a plurality of probe signal detectors are optically connected to a corresponding output of a plurality of outputs of said egress switch, each of said plurality of probe signal detectors being configured to detect a presence of a corresponding probe signal from a corresponding output signal from said WSS or OXC.

6. The apparatus of claim 5, wherein at least one of the following is true:

said plurality of probe signal generators are capable of sending the plurality of probe signals substantially simultaneously; and

said plurality of probe detectors are capable of detecting the presence of the plurality of probe signals substantially simultaneously.

7. The apparatus of claim 2, wherein said at least one probe signal generator is not geographically co-located with said at least one probe signal detector.

8. The apparatus of claim 7, wherein said at least one probe signal generator is a tunable laser such that a frequency of the probe signal is tunable, the apparatus further comprising at least one input modulation signal generator optically or electrically connected to said at least one probe signal generator, said at least one input modulation signal generator configured generate an input modulation signal at a predetermined input modulation frequency, wherein the probe signal generated by said at least one probe signal generator is modulated based on the input modulation signal.

9. The apparatus of claim 8, further comprising at least one output modulation signal generator optically or electrically connected to said at least one probe signal detector, said at least one output modulation signal generator configured to generate a reference output modulation signal at a reference output frequency, wherein the at least one probe signal detector modulates the output signal based on the reference output reference signal.

10. The apparatus of claim 9, wherein said at least one probe signal detector is configured to modulate the output signal using a range of modulation frequencies, wherein the reference output modulation frequency is included in the range of the modulation frequencies.

11. The apparatus of claim 10, wherein the reference output modulation frequency is substantially equal to the input modulation frequency.

12. The apparatus of claim 10, wherein said at least one probe signal detector comprises:

a resonant photo detector configured to receive the output signal and to detect the probe signal within the output signal; and

a lock-in amplifier configured to amplify the probe signal detected by said at least one resonant photo detector based on the output modulation frequency.

13. The apparatus of claim 1, wherein said at least one probe signal detector further comprises a tunable filter configured to receive the output signal from said at least one output of said egress switch, to substantially filter out noise contributions from other wavelength division multiplexed (WDM) channels to the output signal, and to send the filtered output signal to said resonant photo detector.

14. The apparatus of claim 1, wherein said lock-in amplifier is a digital signal processing (DSP) lock-in amplifier.

15. The apparatus of claim 1, further comprising:

at least one phase modulator optically connected to said at least one probe signal generator, said at least one phase modulator configured to generate a substantially constant modulated signal based on the probe signal; and

at least one polarization scrambler optically connected to receive the substantially constant modulated signal from said at least one phase modulator, at least one polarization scrambler configured to reduce fluctuations caused by polarization change in the substantially constant modulated signal,

wherein said at least one probe signal detector is optically connected to said at least one polarization scrambler, said at least one probe signal detector further configured to detect the presence of the probe signal in the output signal based on a signal from said at least one polarization scrambler.

16. The apparatus of claim 1, wherein said resonant photo detector comprises:

a photo detector configured to receive the output signal; and

a resonant amplification circuit configured to substantially filter out data signal and noise outside of a resonant band from the output signal.

17. The apparatus of claim 16, wherein said resonant amplification circuit is configured to resonate at frequency substantially equal to the modulation frequency of the modulation signal generated by said modulation signal generator.

18. A method to monitor performance of an optical network, the method comprising:

generating a probe signal, wherein said step of generating said probe signal comprises tuning a frequency of the probe signal, wherein said step of generating the probe signal further comprises generating a modulation signal of a predetermined modulation frequency and modulating the probe signal based on the modulation signal;

selectively sending the probe signal to at least one of a plurality of inputs of the optical network;

selectively receiving an output signal from at least one of a plurality of outputs of said optical network; and

detecting a presence of the probe signal in the output signal,

wherein said step of detecting the probe signal comprises lock-in amplifying the probe signal based on the modulation signal.

19. The method of claim 18, wherein the probe signal generated is non-interfering with network traffic on the optical network.

20. The method of claim 19, wherein a strength of said probe signal is substantially at least −

30 dB below a single wavelength division multiplexed (WDM) channel.

21. The method of claim 19, wherein the optical network is a wavelength selective switch (WSS) or an optical cross connect (OXC).

22. The method of claim 21, further comprising at least one of:

substantially simultaneously sending a plurality of probe signals to the plurality of inputs of the WSS or OXC; and

substantially simultaneously detecting corresponding presence of the plurality of probe signals from the corresponding plurality of outputs from the WSS or OXC.

23. The method of claim 19, wherein:

said step of generating the probe signal further comprises modulating the probe signal at an input modulation frequency, and

said step of detecting the presence of the probe signal further comprises modulating the output signal based on a reference output modulation frequency.

24. The method of claim 23, wherein said step of detecting the presence of the probe signal based on the reference output modulation frequency comprises modulating the output signal using a range of modulation frequencies, wherein the reference output modulation frequency is included in the range of the modulation frequencies.

25. The apparatus of claim 24, wherein the reference output modulation frequency is substantially equal to the input modulation frequency.

26. The method of claim 24, wherein said step of detecting the presence of the probe signal further comprises amplifying the probe signal based on the output modulation frequency.

27. The method of claim 18, wherein said step of detecting the probe signal further comprises filtering out data signal and noise outside of a resonant band from the output signal prior to performing said lock-in amplifying step.

28. The method of claim 18, wherein said step of detecting at least one probe signal detector further comprises substantially filtering out noise contributions from other wavelength division multiplexed (WDM) channels to the output signal prior to performing said lock-in amplifying step.

29. The method of claim 18, wherein said step of lock-in amplifying comprises lock-in amplifying with digital signal processing (DSP).

30. The method of claim 18, further comprising:

generating a substantially constant modulated signal based on the probe signal; and

reducing fluctuations of the substantially constant modulated signal caused by polarization change to generate a resulting signal,

wherein said step of detecting the presence of the probe signal further comprises detecting the probe signal in the output signal based on the resulting signal.

31. The apparatus of claim 30, wherein said step of detecting the presence of the probe signal utilizes a coherent detection scheme.