Experimental Demonstration of CO-OFDM Systems Using Superimposed Pilot

We investigate the superimposed pilot (SP)-based channel estimation (CE) for long-haul coherent optical orthogonal frequency division multiplexing (CO-OFDM) systems. With specifically designed SP, we demonstrate the impacts that both SP and phase noise have on the performance of CE, from which we obtain the optimal signal-to-pilot power ratio. To enhance the estimation quality of the SP-aided scheme, we exploit an iterative decision feedback algorithm, and in turn, improve the system performance. Experimental results show that the SP-aided CE behaves robust to the phase noise when lasers with moderate linewidth (<;100 KHz), and can offer similar performance as the conventional preamble based methods without scarifying bandwidth efficiency. A CO-OFDM transmission over 5000 km of standard single mode fiber is successfully demonstrated using the SP-aided CE scheme, which shows a spectral efficiency gain of ~10%.