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Multi-Tap Equalization for Performance Improvement in Optical Fast OFDM Systems

We show that multi-tap equalization can significantly enhance the tolerance to laser frequency instability and phase noise in optical fast orthogonal frequency division multiplexing (OFDM) systems. We demonstrate the transmission of a 38-Gb/s 16 quadrature amplitude modulation coherent optical fast OFDM signal over 1000-km single-mode fiber using different types of lasers. It is shown that with this technique, the receiver sensitivity can be greatly improved and overhead for carrier frequency offset estimation to track the wavelength can be reduced for commercial lasers. This verifies the benefits of the technique in a continuous-mode optical communication system. We also show that the performance of multi-tap equalization in optical fast OFDM can be better than that in conventional OFDM, and an experiment using lasers with frequency modulation to emulate frequency oscillating effect during wavelength transition shows that optical fast OFDM can be a more potential multicarrier solution for wavelength-selective optical packet networks.