Digital interpolation-based SFO compensation in OCT precoding-enabled NHS-OFDM transmission systems

Abstract The non-Hermitian symmetric optical orthogonal frequency division multiplexing (NHS-OFDM) system exhibits lower hardware implementation complexity and power consumption as maintaining the same bandwidth granularity, compared to the conventional Hermitian symmetric optical OFDM (HS-OFDM) system. Also, NHS-OFDM can obtain a similar peak-to-average power ratio as well as bit error rate (BER) performance. It is expected to be a new candidate for the next-generation passive optical network. In the asynchronous NHS-OFDM system, the sampling clocks for the analog to digital converter in the receiver and the digital to analog converter in the transmitter generated from different sources and their frequencies always have a certain degree of deviation, i.e., sampling frequency offset (SFO). It may significantly deteriorate the receiver performance. Besides, the imperfect frequency response of the optical/electrical devices is another factor for the degraded BER performance. In this work, we experimentally investigate the digital interpolation (DI)-based SFO compensation in a short-reach NHS-OFDM transmission system. The orthogonal circulant matrix transform (OCT) precoding technique is employed to equalize the signal-to-noise ratio over data-carrying subcarriers and then improve the BER performance. The experimental results indicate that, with the help of the 4-th order DI, the SFO up to 200 ppm can be well compensated without power penalties in comparison with the SFO-free case. Furthermore, the receiver sensitivity of the NHS-OFDM enabled by OCT precoding can be improved by more than 2 dB at the BER of 1e-3 after 20 km standard single-mode fiber transmission.