Linear optical field recovery based on time-slot-assisted self-coherent direct detection for high-speed optical access networks.

Optical field recovery in direct detection systems is a critical enabler for improving the capacity and performance of next-generation optical access networks, yet existing single-photodiode (PD) self-coherent schemes often impose prohibitive computational complexity or stringent carrier-to-signal power ratio (CSPR) requirements. This paper proposes a time-slot-assisted self-coherent direct detection (TA-DD) scheme that achieves linear optical field reconstruction with minimal DSP. By leveraging single-PD detection and a time-diversity mechanism, this scheme allows for the theoretical cancellation of signal-signal beat interference (SSBI) at the receiver using simple multiplication-free time-domain subtraction operations. The proposed approach eliminates the need for high CSPR, complex nonlinear operations, and iterative algorithms, and by enabling coherent signal superposition over dual slots, it significantly enhances receiver sensitivity while maintaining low-complexity optical field recovery. Numerical simulations of a single-wavelength 100 Gb/s passive optical network (PON) link demonstrate that the TA-DD scheme provides a 3.4 dB sensitivity improvement over conventional PAM4 intensity modulation/direct-detection (IM/DD) and supports up to 60 km point-to-multipoint (PtMP) transmission with a 1:32 split ratio. Furthermore, the system exhibits high tolerance to laser linewidth variations up to 10 MHz and limited receiver bandwidths, validating its suitability for cost-effective optical access networks.