Joint signal-to-signal beat interference mitigation for the field recovery of symmetric carrier-assisted differential detection with low carrier-to-signal power ratio.

As a combination of direct detection and coherent detection technologies, self-coherent detection has the advantages of low cost and optical field recovery ability. However, most of the self-coherent detection techniques are limited to single sideband (SSB) signals. Recently, carrier-assisted differential detection (CADD) has been proposed to realize complex-valued double sideband (DSB) signals, but it requires a high carrier-to-signal power ratio (CSPR) to mitigate the signal-to-signal beat interference (SSBI). Later, a more cost-effective symmetric CADD (S-CADD) has been proposed while the required CSPR is still high. In order to alleviate the high requirements of CSPR, we propose a scheme based on the joint of digital pre-distortion (DPD) at transmitter and clipping at receiver to further improve the S-CADD system performance. This joint processing can not only solve the problem of non-uniform distribution of subcarrier signal-to-noise ratio (SNR) caused by non-ideal transfer function, but also the error propagation problem caused by enhanced SSBI under low CSPR. After the validation of the 64 Gbaud 16-ary quadrature amplitude modulation (16-QAM) orthogonal frequency division multiplexing (OFDM) signal transmitted over 80 km standard single mode fiber (SSMF), the CSPR required by the proposed scheme to reach the 20% soft decision-forward error correction (SD-FEC) and 7% hard decision-forward error correction (HD-FEC) can be reduced by 1.3 dB and 2.8 dB, respectively, with a comparison of the conventional S-CADD. The results show the potential of the proposed scheme in the short-reach optical transmissions.