Spectral-diversity receiver for dispersion-induced power-fading mitigation in C-band IM-DD systems.

With the ongoing expansion of artificial intelligence data centers and the increasing demand for high-speed data transmission, cost-effective optical communication systems have become critical. Intensity modulation with direct detection (IM-DD) systems are widely used due to their simplicity and low cost. However, these systems suffer from serious performance degradation caused by chromatic dispersion (CD)-induced power fading, which limits their bandwidth and transmission distance. In this work, we propose a spectral-diversity receiver (SDR) designed to compensate for CD-induced distortions in IM-DD systems. The proposed SDR scheme introduces a high-frequency band replica of the transmitted signal to provide complementary CD information, facilitating the reconstruction of the dispersion-degraded signal. The effectiveness of the SDR is demonstrated through both theoretical analysis and experimental validation using a 25-GBaud probabilistic-shaped 64-ary quadrature amplitude modulation (PS-QAM-64) signal over various transmission distances, ranging from back-to-back (BTB) to 75-km standard single-mode fiber (SSMF). The results indicate that the SDR significantly enhances the normalized generalized mutual information (NGMI). Specifically, the proposed scheme achieves average NGMI improvements of 0.214, 0.277, and 0.285 for the 25-/50-/75-km transmission, respectively. The SDR achieves a net data rate of 113.9 Gb/s after 75-km SSMF transmission based on a 2 × 1 feed-forward equalizer (FFE). The adaptability of the scheme is further highlighted by the flexible adjustment of the guard band and subcarrier multiplexing strategy, which optimizes the system performance without using additional optical/electrical components. Despite the trade-off of utilizing half the available bandwidth, the proposed SDR offers a cost-effective and efficient solution for combating CD in high-speed optical communication systems.