Feedback Controlled Locking of Optical Channel Signals in Optical Receivers in Wavelength Division Multiplexed (WDM) Communication Systems

1 . A method for optical wavelength division multiplexed (WDM) communications, comprising:

using a tunable optical WDM demultiplexer to separate different optical WDM channels in a received WDM signal into different optical WDM channel signals;

converting each optical WDM channel signal into an electronic WDM channel signal;

processing each electronic WDM channel signal to measure a digital error count; and

using the measured digital error counts from the electronic WDM channel signals as a feedback to control the tunable optical WDM demultiplexer to shift center frequencies of the WDM channels to minimize or reduce the measured digital error count in each electronic WDM channel signal.

2 . The method as in claim 1 , comprising:

applying a forward error correction (FEC) processing to each electronic WDM channel signal to measure the digital error count in each electronic WDM channel signal.

3 . The method as in claim 1 , comprising:

using a plurality of millimeter or microwave carriers to modulate a single CW laser beam to produce the different optical WDM channels; and

controlling phase values of the millimeter or microwave carriers to achieve an optical orthogonal frequency division multiplexing condition in the different optical WDM channels.

4 . The method as in claim 1 , comprising:

using different lasers to produce the different optical WDM channels; and

using a common wavelength locker to lock the frequencies of the different lasers.

5 . A method for optical wavelength division multiplexed (WDM) communications, comprising:

using a tunable optical WDM demultiplexer to separate different optical WDM channels in a received WDM signal into different optical WDM channel signals;

converting each optical WDM channel signal into an electronic WDM channel signal;

processing each electronic WDM channel signal to measure a signal quality; and

using the measured signal quality from the electronic WDM channel signals as a feedback to control the tunable optical WDM demultiplexer to shift center frequencies of the WDM channels to increase the measured signal quality in each electronic WDM channel signal.

6 . The method as in claim 5 , comprising:

applying a forward error correction (FEC) processing to each electronic WDM channel signal to measure the digital error count in each electronic WDM channel signal.

7 . The method as in claim 5 , comprising:

using a plurality of millimeter or microwave carriers to modulate a single CW laser beam to produce the different optical WDM channels; and

controlling phase values of the millimeter or microwave carriers to achieve an optical orthogonal frequency division multiplexing condition in the different optical WDM channels.

8 . The method as in claim 5 , comprising:

using different lasers to produce the different optical WDM channels; and

using a common wavelength locker to lock the frequencies of the different lasers.

9 . A method for optical wavelength division multiplexed (WDM) communications, comprising:

separating a received WDM signal having different optical WDM channels into different optical signals along different optical paths, each carrying all the different optical WDM channels;

using a tunable optical filter in each optical path to filter a respective optical signal to produce an optical WDM channel signal at a respective WDM optical frequency while rejecting light at other WDM optical frequencies;

converting the optical WDM channel signal in each optical path into an electronic WDM channel signal;

processing each electronic WDM channel signal to measure a digital error count; and

using the measured digital error count from the electronic WDM channel signal as a feedback to control the tunable optical filter in each optical path to shift the center frequency of the tunable optical filter to minimize or reduce the measured digital error count in each electronic WDM channel signal.

10 . The method as in claim 9 , comprising:

applying a forward error correction (FEC) processing to each electronic WDM channel signal to measure the digital error count in each electronic WDM channel signal.

11 . The method as in claim 9 , comprising:

using a plurality of millimeter or microwave carriers to modulate a single CW laser beam to produce the different optical WDM channels; and

controlling phase values of the millimeter or microwave carriers to achieve an optical orthogonal frequency division multiplexing condition in the different optical WDM channels.

12 . The method as in claim 9 , comprising:

using different lasers to produce the different optical WDM channels; and

using a common wavelength locker to lock the frequencies of the different lasers.

13 . A method for optical wavelength division multiplexed (WDM) communications, comprising:

separating a received WDM signal having different optical WDM channels into different optical signals along different optical paths, each carrying all the different optical WDM channels;

using a tunable optical filter in each optical path to filter each optical signal to produce an optical WDM channel signal at a respective WDM optical frequency while rejecting light at other WDM optical frequencies;

converting the optical WDM channel signal into an electronic WDM channel signal;

processing each electronic WDM channel signal to measure a signal quality; and

using the measured signal quality from the electronic WDM channel signal as a feedback to control the tunable optical filter in each optical path to shift the center frequency of the tunable optical filter to increase the measured signal quality in each electronic WDM channel signal.

14 . The method as in claim 13 , comprising:

applying a forward error correction (FEC) processing to each electronic WDM channel signal to measure the digital error count in each electronic WDM channel signal.

15 . The method as in claim 13 , comprising:

using a plurality of millimeter or microwave carriers to modulate a single CW laser beam to produce the different optical WDM channels; and

controlling phase values of the millimeter or microwave carriers to achieve an optical orthogonal frequency division multiplexing condition in the different optical WDM channels.

16 . The method as in claim 13 , comprising:

using different lasers to produce the different optical WDM channels; and

using a common wavelength locker to lock the frequencies of the different lasers.

17 . An optical device for optical wavelength division multiplexed (WDM) communications, comprising:

an optical element that receives a WDM signal comprising different optical WDM channels at different optical wavelengths into different optical signals along different optical paths, each carrying all the different optical WDM channels; and

a plurality of receivers in the different optical paths, respectively, each receiver separating a respective optical WDM channel from other optical WDM channels and detecting the respective optical WDM channel,

wherein each receiver comprises:

a tunable optical filter in a respective optical path to filter a respective optical signal to produce an optical WDM channel signal at a respective optical wavelength while rejecting light at other optical wavelengths;

an optical detector downstream from the tunable optical filter to convert the respective optical WDM channel signal into a respective electronic WDM channel signal;

a processing circuit to receive and process the respective electronic WDM channel signal to measure a signal quality; and

a feedback control circuit that produces a feedback control signal based on the measured signal quality to control the tunable optical filter in each optical path to shift the center frequency of the tunable optical filter to increase the measured signal quality in each electronic WDM channel signal.

18 . The device as in claim 17 , wherein:

the signal quality is measured by a digital error count in the respective electronic WDM channel signal.

19 . The device as in claim 17 , wherein:

the signal quality is measured by a degree of an eye opening of an eye diagram for the respective electronic WDM channel signal.

20 . The device as in claim 17 , wherein:

the processing circuit applies a forward error correction (FEC) processing to the respective electronic WDM channel signal to measure a digital error count to represent the signal quality of the respective electronic WDM channel signal.

21 . The device as in claim 17 , comprising a transmitter module which comprises:

a single laser that produce a single CW laser beam;

an optical modulator that receives a plurality of millimeter or microwave carriers and modulates the single CW laser beam by using the millimeter or microwave carriers to produce different output optical WDM channels; and

an optical combiner that combines the different output optical WDM channels to produce an output WDM signal for transmission.

22 . The device as in claim 21 , wherein:

the transmitter module controls phase values of the millimeter or microwave carriers to achieve an optical orthogonal frequency division multiplexing condition in the different output optical WDM channels.

23 . The device as in claim 17 , comprising a transmitter module which comprises:

different lasers to produce different output optical WDM channels;

an optical combiner that combines the different output optical WDM channels to produce an output WDM signal for transmission;

an optical tap downstream from the optical combiner to split optical power of the output WDM signal to produce an optical monitor signal comprising light of the different output optical WDM channels; and

a common wavelength locker to receive the optical monitor signal, detect errors in frequencies of the different output optical WDM channels and to control frequencies of the different lasers to reduce the errors.

24 . An optical device for optical wavelength division multiplexed (WDM) communications, comprising:

a tunable optical WDM demultiplexer that receives a WDM signal comprising different optical WDM channels at different optical wavelengths and separates the received WDM signal into different optical WDM channels along different optical paths, the tunable optical WDM demultiplexer operable to tune a frequency of each optical WDM channel; and

a plurality of optical detectors in the different optical paths, respectively, each optical detector detecting a respective optical WDM channel to produce a respective electronic WDM channel signal,

a plurality of receiver circuits downstream from the optical detectors, respectively, wherein each receiver circuit operable to process a respective electronic WDM channel signal to measure a signal quality of the respective electronic WDM channel signal; and

a feedback control circuit that produces a feedback control signal based on the measured signal quality of the electronic WDM channel signals from the receiver circuits to control the tunable optical WDM demultiplexer to shift a frequency of a respective optical WDM channel in each optical path to increase the measured signal quality in the respective electronic WDM channel signal.

25 . The device as in claim 24 , wherein:

the signal quality is measured by a digital error count in the respective electronic WDM channel signal.

26 . The device as in claim 24 , wherein:

the signal quality is measured by a degree of an eye opening of an eye diagram for the respective electronic WDM channel signal.

27 . The device as in claim 24 , wherein:

the processing circuit applies a forward error correction (FEC) processing to the respective electronic WDM channel signal to measure a digital error count to represent the signal quality of the respective electronic WDM channel signal.

28 . The device as in claim 24 , comprising a transmitter module which comprises:

a single laser that produce a single CW laser beam;

an optical modulator that receives a plurality of millimeter or microwave carriers and modulates the single CW laser beam by using the millimeter or microwave carriers to produce different output optical WDM channels; and

an optical combiner that combines the different output optical WDM channels to produce an output WDM signal for transmission.

29 . The device as in claim 28 , wherein:

the transmitter module controls phase values of the millimeter or microwave carriers to achieve an optical orthogonal frequency division multiplexing condition in the different output optical WDM channels.

30 . The device as in claim 24 , comprising a transmitter module which comprises:

different lasers to produce different output optical WDM channels;

an optical combiner that combines the different output optical WDM channels to produce an output WDM signal for transmission;

an optical tap downstream from the optical combiner to split optical power of the output WDM signal to produce an optical monitor signal comprising light of the different output optical WDM channels; and

a common wavelength locker to receive the optical monitor signal, detect errors in frequencies of the different output optical WDM channels and to control frequencies of the different lasers to reduce the errors.