Systems and methods for wavelength scanning of in-service wavelength division multiplexing systems

1. A module comprising:

a first light source configured to emit a first light signal to one or more empty channels of an in-service Wavelength Division Multiplexing (“WDM”) system;

a tunable second light source configured to emit a second light signal to the one or more empty channels to test the one or more empty channels; and

a first switch module configured to:

receive from the first light source and output to the one or more empty channels, the first light signal during a first time interval; and

receive from the second light source and output to the one or more empty channels, the second light signal during a second time interval, the second time interval being a duration wherein a channel power monitoring function of the in-service WDM system is not triggered; and

a testing output module configured to receive and analyze an output test signal, comprising:

a splitter configured to receive and output the output test signal;

a clock recovery module configured to receive the output test signal from the splitter and output a clock pulse indicative of a output time interval during which the output test signal is received;

a second switch module configured to, in response to receiving the clock pulse from the clock recovery module:

receive the output test signal from the splitter; and

output the output test signal during the output time interval; and

a signal analyzer configured to analyze the output test signal.

2. The module of claim 1 , wherein the first light signal is configured with a power wherein the one or more empty channels become or are maintained in an unblocked status in response to receiving the first light signal.

3. The module of claim 1 , wherein the duration of the second time interval is less than a duration of the first time interval.

4. The module of claim 1 , further comprising a control module configured to control the first switch module to output the first light signal and the second light signal during the first time interval and the second time interval, respectively.

5. The module of claim 4 , further comprising a second switch module configured to receive from the second light source, the second light signal, and to be controlled by the control module to output to the first switch module, the second light signal during a third time interval.

6. The module of claim 5 , wherein a duration of the third time interval is less than the duration of the second time interval.

7. The module of claim 1 , wherein the first time interval and the second time interval are non-overlapping time intervals.

8. The module of claim 1 , wherein the first light source is selected from a group consisting of a fixed wavelength light source, a multi-wavelength light source and a tunable light source.

9. A system comprising:

an in-service WDM system configured to receive one or more first light signals and one or more input test signals and to output an output test signal;

a testing input module configured to:

output to one or more empty channels of the in-service WDM system, the one or more first light signals, the one or more first light signals being output from a first switch module during a first time interval;

output to the one or more empty channels of the in-service WDM system, the one or more input test signals, the one or more input test signals being output from the first switch module during a second time interval to test the one or more empty channels of the in-service WDM system, the second time interval being a duration wherein a channel power monitoring function of the in-service WDM system is not triggered; and

a testing output module configured to receive and analyze the output test signal, comprising:

a splitter configured to receive and output the output test signal;

a clock recovery module configured to receive the output test signal from the splitter and output a clock pulse indicative of a output time interval during which the output test signal is received;

a second switch module configured to, in response to receiving the clock pulse from the clock recovery module:

receive the output test signal from the splitter; and

output the output test signal during the output time interval; and

a signal analyzer configured to analyze the output test signal.

10. The system of claim 9 , wherein a power of the first light signal causes the one or more empty channels to become or to be maintained in an unblocked status in response to receiving the first light signal.

11. The system of claim 9 , wherein the in-service WDM system simultaneously receives at, at least two of the one or more empty channels of the in-service WDM system, at least two of the one or more first light signals and at least two of the one or more input test signals, the first light signals being generated by a multi-wavelength first light source, and

wherein the output test signal is a signal indicative of a combined two or more input test signals after transmission through the in-service WDM system.

12. The system of claim 9 , wherein the in-service WDM system

receives at a first of the one or more empty channels of the in-service WDM system, one of the one or more first light signals and one of the one or more input test signals, the one of the one or more first light signals being generated by a tunable first light source,

and wherein the in-service WDM system receives at a second of the one or more empty channels of the in-service WDM system, another one of the one or more first light signals and another one of the one or more input test signals, the other one of the one or more first light signals being generated by the tunable first light source, and

wherein the output test signal is a signal indicative of the one of the one or more input test signals or the other one of the one or more input test signals after transmission through the in-service WDM system.

13. The system of claim 9 , wherein the signal analyzer is configured to analyze the output test signal to measure at least one of: a polarization mode dispersion, pass band shape, optical signal-to-noise radio or latency of one or more of the one or more empty channels of the in-service WDM system.

14. The system of claim 9 , wherein the output time interval is greater than the third time interval and less than the first time interval and the duration of the second time interval.

15. A method comprising:

generating a first light signal;

generating a second light signal;

powering on one or more switching mechanisms configured to output to one or more empty channels, a first light signal and the second light signal;

receiving by the one or more empty channels, the first light signal;

receiving by the one or more empty channels, the second light signal for testing the one or more empty channels wherein the second light signal is received during a time interval of a duration configured to prevent triggering of a channel power monitoring function of an in-service WDM system;

receiving and outputting, at a splitter, an output test signal;

receiving, at a clock recovery module, the outputted test signal from the splitter and output a clock pulse indicative of a output time interval during which the output test signal is received;

receiving, at a second switch module, the output test signal from the splitter in response to receiving the clock pulse from the clock recovery module;

outputting the output test signal during the output time interval; and

analyzing, at a signal analyzer, the output test signal.

16. The method of claim 15 , wherein the first light signal is received during a first time interval, the second light signal is received during a second time interval, the first time interval and the second time interval being non-overlapping time intervals, and the second time interval being a duration wherein a channel power monitoring function of the one or more empty channels is not triggered.

17. The method of claim 15 , further comprising:

recovering a clock associated with the output test signal, wherein the output test signal is a modified version of the second light signal having a substantially same information content of the second light signal and the outputting of the output test signal is performed in response to information indicative of the recovered clock; and

measuring one or more parameters of the one or more empty channels.

18. The method of claim 17 , wherein the one or more parameters of the one or more empty channels is at least one of: polarization mode dispersion, pass band shape, optical signal-to-noise radio or latency.

19. The method of claim 15 , further comprising the one or more empty channels having an unblocked status in response to receiving the first light signal.