Device, system and method for processing an optical signal

1. A device for processing a signal, the device comprising:

a polarization module configured to:

receive a multi-wavelength optical input signal comprising a plurality of wavelengths; and

for each wavelength, convert a component of each wavelength having a first polarization mode into a converted component having a second, different, polarization mode; and

processing circuitry configured to:

combine the converted component of each wavelength with a direct component of each wavelength received with the second polarization mode; and

generate a multi-wavelength optical output signal solely having the second polarization mode;

wherein the processing circuitry comprises:

a first optical phase shift module configured to apply a first phase shift to each wavelength of the converted component and/or direct component received from the polarization module; and

a first optical coupler configured to receive the converted component and direct component, at least one of the converted component and direct component being phase shifted by the first phase shift; and

wherein the first optical phase shift module is configured to apply the first phase shift such that the first optical coupler outputs a first and second optical signal of substantially equal power.

2. The device of claim 1 , wherein the device is configured to receive the multi-wavelength optical input signal in which each wavelength has substantially the same state of polarization.

3. The device of claim 1 :

wherein the processing circuitry comprises:

a second optical phase shift module configured to apply a second phase shift to each wavelength of the first and/or second optical signal received from the first optical coupler; and

a second optical coupler configured to receive the first and/or second optical signal, at least one of the first and/or second optical signal being phase shifted by the second phase shift; and

wherein the second optical phase shift module is configured to apply the phase shift such that the coupler outputs a combined multi-wavelength optical signal solely having the second polarization mode.

4. The device of claim 3 , wherein the first and/or second optical phase shift modules are controlled to vary the respective first and/or second phase shift.

5. The device of claim 4 , wherein the device comprises a measurement unit configured to detect an optical power within the device, and control the first and/or second phase shift modules based on the detected optical power.

6. An optical communication system, comprising:

a transmitter configured to transmit a multi-wavelength optical signal comprising a plurality of wavelengths along an optical fiber;

a receiver comprising a device for processing a signal, the device comprising:

a polarization module configured to:

receive the multi-wavelength optical signal comprising the plurality of wavelengths; and

for each wavelength, convert a component of each wavelength having a first polarization mode into a converted component having a second, different, polarization mode; and

processing circuitry configured to:

combine the converted component of each wavelength with a direct component of each wavelength received with the second polarization mode; and

generate a multi-wavelength optical output signal solely having the second polarization mode;

wherein the transmitter is configured to transmit wavelengths which are selected to be within a determined bandwidth; and

wherein the bandwidth is determined such that the polarization modes of the wavelengths within the bandwidth have a variation which is substantially uniform among the wavelengths.

7. The system of claim 6 , wherein the transmitter comprises:

a generator unit configured to generate the plurality of wavelengths; and

a multiplexer unit configured to multiplex the plurality of wavelengths;

wherein the multiplexer unit is configured to maintain a polarization of each wavelength.

8. The system of claim 6 , wherein the determined bandwidth is based on an average differential group delay of the optical fiber, and/or based on a phase modulation dispersion coefficient of the optical fiber and a length of the fiber.

9. The system of claim 6 , wherein the determined bandwidth is defined by:

Δλ=1/<Δ T>

where Δλ is the determined bandwidth in units of nanometers, and <Δ T > is the average differential group delay in units of picoseconds.

10. The system of claim 9 , wherein

<Δ T >=PMD coeff.×L½

where PMD coeff. is a coefficient indicating the phase modulation dispersion of the fiber in units of ps/km½, and L is the length of the fiber between the transmitter and receiver in units of kilometers.

11. A method for processing a signal, the method comprising:

receiving a multi-wavelength optical input signal comprising a plurality of wavelengths;

for each wavelength, converting a component of each wavelength having a first polarization mode into a converted component having a second, different, polarization mode; and

combining the converted component of each wavelength with a direct component of each wavelength received with the second polarization mode; and

generating a multi-wavelength optical output signal solely having the second polarization mode;

applying a first phase shift to each wavelength of the converted component and/or direct component received from the polarization module; and

coupling the received the converted component and direct component, at least one of the converted component and direct component being phase shifted by the first phase shift;

wherein the first phase shift applied is such that the coupling outputs a first and second optical signal of substantially equal power.

12. The method of claim 11 , further comprising receiving the multi-wavelength optical input signal in which each wavelength has substantially the same state of polarization.

13. The method of claim 11 , further comprising controlling the first phase shift.

14. An optical communication method, comprising:

transmitting a multi-wavelength optical signal comprising a plurality of wavelengths along an optical fiber; and

receiving the multi-wavelength optical signal comprising the plurality of wavelengths;

for each wavelength, converting a component of each wavelength having a first polarization mode into a converted component having a second, different, polarization mode; and

combining the converted component of each wavelength with a direct component of each wavelength received with the second polarization mode; and

generating a multi-wavelength optical output signal solely having the second polarization mode;

wherein the transmitting comprises transmitting wavelengths which are selected to be within a determined bandwidth; and

wherein the bandwidth is determined such that the polarization modes of the wavelengths within the bandwidth have a variation which is substantially uniform among the wavelengths.

15. The method of claim 14 , wherein the transmitting comprises:

generating the plurality of wavelengths; and

multiplexing the plurality of wavelengths, wherein the multiplexing comprises maintaining a polarization of each wavelength.

16. The method of claim 14 , wherein the determined bandwidth is based on an average differential group delay of the optical fiber, and/or based on a phase modulation dispersion coefficient of the optical fiber and a length of the fiber.