The optical orthogonal frequency division multiplexing （OFDM） signal is affected by impairments intro- duced by electrical filters and optical chromatic dispersion. An enhanced fourth-power algorithm for phase estimation with frequency separation is used to estimate and compensate the phase rotation of OFDM subcarriers. The performance of the proposed phase estimation algorithm is evaluated on a 4-Gb/s OFDM signal at different frequencies. Experimental results using the proposed algorithm show a 1.8-dB received power sensitivity improvement at a bit error rate of 1 × 10^-4 after a 100-kin standard single-mode fiber transmission, compared with the conventional technique.
We demonstrate a digital optical communication system based on minimum shift keying （MSK） signal transmission with coherent detection. 5-Gb/s MSK signal can transmit over a 160-km standard single mode fiber （SSMF） without phase compensation. At the receiver, we use data-aided channel estimation and frequency domain equalization （FDE） techniques in the digital signal processing （DSP） algorithm, then analyze its performance characteristics compared with quadrature phase shift keying （QPSK） format. The simulation results show that the MSK format will be a potential candidate for next-generation access network.
