Theoretical and Experimental Investigations of Interleaved Carrier-Assisted Differential Detection

Self-coherent detection is a promising solution for extending the transmission reach for direct detection system. For these schemes, high carrier-to-signal power ratio (CSPR) is usually required to mitigate the inherent signal-signal beat interference (SSBI) induced from direct detection. Recently, carrier-assisted differential detection (CADD) receiver has been proposed to recover the optical field of complex-valued double sideband (DSB) signals via direct detection. Aiming at relaxing the high CSPR requirement for self-coherent detection systems, we propose an interleaved subcarrier loading scheme for double-sideband signals. At transmitter, only odd subcarriers are loaded with data while even subcarriers are left unused. By utilizing the CADD receiver, signal can be retrieved without the degradation of SSBI, which enables optical field recovery at low CSPRs. In this article, we first show by theory and simulation that the proposed scheme can work under lower CSPRs than the previous SSB self-coherent systems. Meanwhile, the electrical spectral efficiency of the proposed interleaved CADD is almost the same as SSB self-coherent systems. We also illustrate the process of parameter optimization for interleaved CADD, including optical delay, CSPR, and frequency gap. We successfully transmit 100-Gbps 16-QAM OFDM signals over 160-km uncompensated standard single mode fiber (SSMF) at 3.5-dB CSPR.