We present real-time transmission of 50-Gbaud polarization-division-multiplexed (PDM) return-to-zero differential quadrature phase-shift keying (4 bit/symbol) over five fiber spans, 430 km in total. The two PDM channels are demultiplexed using a beam splitter and automatic optical polarization control with interference detection. For the first time, PDM signal tracking speeds of up to 40 krad/s are demonstrated.

An endless polarization tracker detects and minimizes interchannel interference, enabling automatic optical polarization demultiplex and consecutive direct detection of a 20-Gb/s polarization division multiplex RZ-DPSK signal at polarization scrambling speeds up to 40 krad/s. Transmission over 430 km of fiber is error-free.

We present in numerical simulations the robustness of subcarrier index modulation (SIM) OFDM to combat laser phase noise. The ability of using DFB lasers with SIM-OFDM in 16-QAM CO-OFDM system with 1024-point FFT has been verified. Although SIM-OFDM has lower spectral efficiency compared to the conventional CO-OFDM system, it is a good candidate for 16-QAM CO-OFDM system with 1024-point FFT which uses a DFB laser of 1 MHz linewidth. In addition, we show the tolerance of SIM-OFDM for mitigation of fiber nonlinearities in long-haul CO-OFDM system. The simulation results show a significant penalty reduction, essentially that due to SPM.

In coherent optical orthogonal frequency division multiplexing (CO-OFDM) systems, phase noise has an important impact on the system performance. They are highly sensitive to phase noise induced by transmitter laser and local oscillator laser. We explain different kinds of phase noise effects on the OFDM signals and analyze the phase noise effect induced by transmitter laser and local oscillator. We analyze the standard RF-pilot (RFP) phase noise compensation method and explain its drawbacks. We provide two extended RFP schemes that overcome the drawbacks of the standard RFP scheme and enhance the performance of CO-OFDM systems. Furthermore, the phase noise effects for various laser linewidths and the effect of the received optical power (ROP) on the system performance are quantified. A CO-OFDM transmission system with 16-QAM is simulated with VPItransmissionMaker™ V8.5.

In coherent optical orthogonal frequency division multiplexing (CO-OFDM) systems, phase noise of transmitter and local oscillator lasers has an important impact on system performance. In this letter, a partial pilot filling compensation scheme is analyzed and compared to conventional common phase error compensation and RF-pilot-based phase noise compensation. The effects of phase noise for various laser linewidths and of received optical power on system performance are evaluated. A CO-OFDM transmission system with 4-QAM is simulated with VPI transmissionMaker V8.7.

(40-Word Limit): We present the robustness of subcarrier-index modulation OFDM to combat laser phase noise. Simulation results show the ability of using DFB lasers with SIM-OFDM in 16-QAM CO-OFDM system with 1024-point FFT.