PMD insensitive direct-detection optical OFDM systems using self-polarization diversity
View Patent ↗A self-polarization diversity technique to combat PMD in a direct-detection optical OFDM system. This technique does not require any dynamic polarization control, and can simultaneous compensate PMD in a WDM system with one device. Simulation results show that this technique virtually completely eliminates the PMD impairments in direct-detection optical OFDM systems.
1. A method of receiving an optical signal, the method comprising:
splitting an orthogonal frequency division multiplexed (OFDM) optical signal into a first portion and a second portion;
directing the first portion to a first direct-detection OFDM receiver;
directing the second portion to a circulator;
rotating one of a carrier or sub-carriers portion of the second portion such that states of polarization of the one of the carrier or sub-carriers portion as measured before and after the circulator are orthogonal while states of polarization for the other of the carrier or sub-carriers portion of the second portion remain the same before and after the circulator;
directing output of the circulator to a second direct-detection OFDM receiver;
combining outputs of the first and second direct-detection OFDM receivers; and
directing the combined outputs to a demodulator for demodulation of data.
2. The method of claim 1 wherein said splitting exhibits <5 dB loss.
3. The method of claim 2 wherein said splitting is performed by an asymmetric splitter.
4. The method of claim 2 wherein said splitting is performed by a symmetric 50/50 splitter.
5. The method of claim 1 wherein said rotating of the one of the carrier or sub-carriers portion is provided by an effect of an optical filter terminated with a Faraday rotator mirror.
6. The method of claim 5 wherein said optical filter is a fiber Bragg grating (FBG) filter.
7. The method of claim 1 further comprising:
demodulating the combined outputs.
8. The method of claim 1 wherein said receiving of the optical signal occurs at a receiver.
9. An apparatus for receiving an optical signal, the apparatus comprising:
a splitter for splitting an orthogonal frequency division multiplexed (OFDM) optical signal into a first portion and a second portion;
a first direct-detection OFDM receiver for detecting the first portion;
a circulator for rotating one of a carrier or sub-carriers portion of the second portion such that states of polarization of the one of the carrier or sub-carriers portion as measured before and after the circulator are orthogonal while states of polarization for the other of the carrier or the sub-carriers portion of the second portion remain the same before and after the circulator;
a second direct-detection OFDM receiver for detecting output of the circulator; and
a combiner for producing a combined output based on output of the first direct-detection OFDM receiver and second direct-detection OFDM receiver.
10. The apparatus of claim 9 wherein said splitter exhibits <5 dB loss.
11. The apparatus of claim 10 wherein said splitter is an asymmetric splitter.
12. The apparatus of claim 10 wherein said splitter is a symmetric 50/50 splitter.
13. The apparatus of claim 9 wherein said circulator includes an optical filter and a Faraday rotator mirror.
14. The apparatus of claim 13 wherein said optical filter is a fiber Bragg grating (FBG) filter.
15. The apparatus of claim 9 further comprising a demodulator for demodulating data based on the combined output.
16. An apparatus for receiving an optical signal, the apparatus comprising:
a splitter for splitting an orthogonal frequency division multiplexed (OFDM) optical signal into a first portion and a second portion;
a first direct-detection OFDM receiver for detecting the first portion;
a circulator for rotating a carrier portion of the second portion such that states of polarization of the carrier portion as measured before and after the circulator are orthogonal while states of polarization for a sub-carriers portion of the second portion remain the same before and after the circulator;
a second direct-detection OFDM receiver for detecting output of the circulator; and
a combiner for producing a combined output based on output of the first direct-detection OFDM receiver and second direct-detection OFDM receiver.
17. The apparatus of claim 16 wherein said splitter is an asymmetric splitter.
18. The apparatus of claim 16 wherein said splitter is a symmetric 50/50 splitter.
19. The apparatus of claim 16 wherein said circulator includes an optical filter and a Faraday rotator mirror.
20. The apparatus of claim 19 wherein said optical filter is a fiber Bragg grating (FBG) filter.
21. The apparatus of claim 16 further comprising a demodulator for demodulating data based on the combined output.