Monitoring polarization-mode dispersion and signal-to-noise ratio in optical signals based on polarization analysis

1. A device for monitoring a polarization mode dispersion (PMD) effect in an optical signal, comprising:

an optical coupler to split an input optical signal into a first optical signal having a polarization of the input optical polarization in a first optical path and a second optical signal having the polarization of the input optical polarization in a second, separate optical path;

a first optical filter in the first optical path to filter the first optical signal to have a first optical bandwidth that is less than an input optical bandwidth of the input optical signal and is different from a second optical bandwidth of the second optical signal;

a first optical detector coupled to the first optical path to measure a degree of polarization of the first optical signal after being filtered by the first optical filter;

a second optical detector in the second optical path to measure a degree of polarization of the second optical signal; and

a processing unit in communication with the first and second optical detectors to receive outputs of the first and second optical detectors, the processing unit processing the measured degree of polarization of the first optical signal and the measured degree of polarization of the second optical signal to determine a depolarization factor of the input optical signal to reflect the PMD effect in the input optical signal and to determine an optical to signal noise ratio of the input optical signal.

2. The device as in claim 1 , comprising:

a second optical filter in the second optical path to filter the second optical signal to have the second optical bandwidth that is different from the first optical bandwidth of the first optical signal after being filtered by the first optical filter.

3. The device as in claim 1 , comprising:

an input optical filter placed in the optical path of the input optical signal upstream to the optical coupler to filter the input optical signal to allow transmission of spectral components in a transmission band of the input optical filter while rejecting other spectral components in the input optical signal.

4. The device as in claim 3 , wherein:

the input optical filter is a bandpass filter centered at a wavelength division multiplexed (WDM) wavelength grid under a WDM standard by the International Telecommunications Union (ITU) to select one WDM channel in the input optical signal while rejecting other WDM channels.

5. The device as in claim 4 , wherein:

the input optical filter is a tunable bandpass filter to select one WDM channel to measure the depolarization factor and the optical to signal noise ratio of the selected WDM channel at first and subsequently select another WDM channel to measure the depolarization factor and the optical to signal noise ratio of the subsequently selected another WDM channel.

6. The device as in claim 5 , wherein:

the first optical filter is a Fabry-Perot filter that has transmission resonance peaks that coincide with ITU WDM frequencies.