OPTICAL ORTHOGONAL FREQUENCY DIVISION MULTIPLEXED COMMUNICATIONS WITH COHERENT DETECTION

• US 20080159758A1
• Filed: 03/11/2008
• Published: 07/03/2008
• Est. Priority Date: 09/22/2003
• Status: Active Grant

• Current Assignee: CeLight, Inc.
• Original Assignee: CeLight, Inc.
• Inventors: Shpantzer, Isaac, Khurgin, Jacob, Meiman, Yehouda, Genusov, Alexander
• Granted Patent: US 8,064,767 B2
• Time in Patent Office: Days
• US Class Current: 398/214
• CPC Class Codes: G02B 2006/12147 Coupler
• CPC Class Codes: G02B 6/126 using polarisation effects G02B6/1226 takes precedence
• CPC Class Codes: H04B 10/2575 Radio-over-fibre, e.g. radio frequency signal modulated onto an optical carrier
• CPC Class Codes: H04B 10/61 Coherent receivers
• CPC Class Codes: H04B 10/614 comprising one or more polarization beam splitters, e.g. polarization multiplexed [PolMux] X-PSK coherent receivers, polarization diversity heterodyne coherent receivers H04J14/06 takes precedence
• CPC Class Codes: H04B 10/65 Intradyne, i.e. coherent receivers with a free running local oscillator having a frequency close but not phase-locked to the carrier signal
• CPC Class Codes: H04J 14/06 Polarisation multiplex systems

Abstract

The present invention provides a system and method of optical communications that utilize coherent detection technique and optical orthogonal frequency division multiplexing for phase encoded data transmission. In particular the invention addresses a device and method for digital polarization compensation of optical signals with up to 100 Gb/s transmission rate received via an optical link. The polarization compensation operates in two modes: acquisition mode and tracking mode. The polarization recovery is performed at the receiver side using the received digital signal conversion into frequency domain and separate reconstruction of the polarization state in each spectral component.

Claims

1. An optical receiver, comprising:

a polarization beam splitter for receiving an optical beam with data and splitting it into a first and a second beam;

a first optical hybrid for receiving the first beam and a first local oscillator beam;

a first set of photodetectors receiving output beams from the first optical hybrid and producing electrical signals;

a digital signal processing unit receiving the electrical signals, converting them into digital signals, transforming the digital signals into frequency domain, forming a set of spectral signals each having its own digital frequency, recovering the polarization state of each spectral signal, demodulating the data encoded in each spectral signal, and outputting an information encoded in the optical beam with data.

2. The receiver of claim 1, wherein the first optical hybrid is a 90-degrees optical hybrid.

3. The receiver of claim 2, the first optical hybrid comprising:

a first coupler coupled to a first input and producing at least a first and second output;

a second coupler coupled to a second input and producing at least a first and second output;

a third coupler coupled to the first output of the first coupler and to the first output of the second coupler;

a fourth coupler coupled to the second output of the first coupler and to the second output of the second coupler;

first and second crossing waveguides with an angle selected to minimize crosstalk and losses between the first and second cross waveguides, the first crossing waveguide connecting one of the first or second outputs from the first coupler with an input of the fourth coupler, the second crossing waveguide connecting one of the first or second outputs from the second coupler with an input of the third coupler;

a first phase shifter coupled to the first and second waveguides, the first and second waveguides connecting one of the outputs of the first or second coupler and one of the inputs of the third or fourth couplers.

4. The receiver of claim 1, wherein the optical hybrid is a 120-degrees optical hybrid.

5. The receiver of claim 4, the optical hybrid comprising:

a coupler having three inputs and three outputs.

6. The receiver of claim 1, wherein the data is encoded using at least one of phase shift keying format, amplitude shift keying format, and frequency shift keying format.

7. The receiver of claim 1, wherein

the optical hybrid is an integrated device made of an electro-optical material or thermo-optical material or a combination of thereof.

8. The receiver of claim 1, wherein

the optical hybrid is formed as part of a single planar chip made of a semiconductor material or a ferroelectric material or a combination of thereof.

9. The receiver of claim 1, wherein

the coherent optical receiver is adapted for operation with the optical signal of two polarization states.

10. The receiver of claim 1, further comprising

a second optical hybrid for receiving the second beam and a second local oscillator beam;

a second set of photodetectors receiving output beams from the second optical hybrid and producing electrical signals; and

the digital signal processing unit receiving the electrical signals from the second optical hybrid, converting them into digital signals, transforming the digital signals into frequency domain, forming a set of spectral signals each having its own digital frequency, recovering the polarization state of each spectral signal, demodulating the data encoded in each spectral signal, and outputting an information encoded in the optical beam with data.

11. The receiver of claim 1, wherein

recovering the polarization of each spectral signal operates in two modes:

an acquisition mode being performed before the link starts to operate and a tracking mode being performed periodically during the receiver exploitation.

12. The receiver of claim 11, wherein

the acquisition mode comprises an estimation of the Jones Matrix for each sub-carrier frequency.

13. The receiver of claim 12, wherein

the estimation of the Jones Matrix is based on a correlation analysis of a preamble transmission.

14. The receiver of claim 11, wherein

the acquisition mode is also performed periodically during the receiver operation with a period P1.

15. The receiver of claim 14, wherein

the period P1 is from 10 ms to 1 s.

16. The receiver of claim 11, wherein

the tracking mode is performed periodically during the receiver operation with a period P2 from the range 1-50 ns.

17. The receiver of claim 11, wherein

the tracking mode is based on multiplying the Jones Matrix by an error correction signal to adjust the Jones Matrix to changed transmission characteristics.

18. A system for a data transmission via an optical communication link, comprising:

a light source generating an optical beam, the optical beam being split into a first and a second beam having two different polarization states, the first beam being encoded in a first modulator driven by a first encoding signal from an optical frequency division multiplexed encoder, the encoding signal comprising a set of digital spectral signals, each with different embedded data;

the encoded beam being transmitted via the optical link;

a polarization beam splitter receiving the encoded beam and splitting it into a first and a second received beams having different polarization states;

a coherent receiver receiving the first received beam, the receiver mixing the first received beam with a first local oscillator beam coming from a local oscillator;

the receiver producing a set of output electrical signals;

a digital signal processing unit receiving the electrical signals, converting them into digital signals, transforming the digital signals into frequency domain, forming the set of spectral signals each having its own digital frequency, recovering the polarization of each spectral signal, demodulating the data encoded in each spectral signal, and outputting an information encoded in the optical beam;

wherein the coherent receiver is based on an optical hybrid.

19. The system of claim 18,

wherein the optical hybrid is a 90-degrees optical hybrid.

20. The system of claim 18,

wherein the optical hybrid is a 120-degrees optical hybrid.

21. The system of claim 18,

wherein the modulator modulates the optical beam using a phase shift keying format.

22. The system of claim 18, wherein the optical link is a fiber or a free space link.

23. The system of claim 18, wherein

recovering the polarization of each spectral signal operates in two modes:

an acquisition mode being performed before the link starts to operate and a tracking mode being performed periodically during the receiver exploitation.

24. A method of optical communication, comprising:

forming a first encoding signal in an optical frequency division multiplexed encoder, the encoding signal comprising a set of digital spectral signals, each with different embedded data;

applying the encoding signal to an optical beam in a modulator;

transmitting the modulated optical signal to a coherent receiver via an optical link;

receiving the encoded signal;

splitting the received signal by a polarization beam splitter into a first received beam and a second received beam having different polarization states;

mixing the first received signal with a first local oscillator signal in an optical hybrid;

converting output signals from the optical hybrid into electrical signals, digitizing the electrical signals, transforming the digital signals into frequency domain, forming the set of spectral signals each having its own digital frequency, recovering the polarization of each spectral signal, demodulating the data encoded in each spectral signal, and outputting an information encoded in the optical beam.