Polarisation mode dispersion mitigation in coherent optical orthogonal frequency division multiplexed systems

Introduction: Recently we have proposed a multi-carrier format called coherent optical orthogonal frequency division multiplexing (CO-OFDM) to combat fibre chromatic dispersion, and have shown that a CO-OFDM signal can traverse 3000 km of standard singlemode fibre without dispersion compensation [1]. In this Letter, we show another critical feature for the CO-OFDM system, namely, its extreme resilience to polarisation mode dispersion (PMD). We find that a CO-OFDM signal at 10 Gbit=s experiences no penalty through firstorder PMD fibre with a differential group delay (DGD) of 700 ps, and all-order PMD fibre with a mean PMD of 150 ps. This finding is significant because it shows that the CO-OFDM system could provide a feasible solution to the mitigation of PMD in existing installed fibre links. Furthermore, the PMD mitigation with CO-OFDM is intrinsically embedded in the receiver signal processing for data demodulation, which does not require any additional complicated hardware, such as polarisation controllers and birefringence elements. We also note that incoherent optical OFDM (IO-OFDM) provides similar chromatic dispersion tolerance with a simpler detection scheme [2], but it does not provide a PMD mitigation capability.