Analog Mobile Fronthaul Transmissions Based on FBG-Enabled Phase Modulation and Direct Detection

Owing to its high cost-effectiveness and operational simplicity, IMDD is favored in MFH transmissions. However, a DC bias is still needed at the transmitter to ensure optimal transmission performance, and high received optical power is required to achieve high link gain. To address these challenges, we have proposed the use of MZI to break the phase balance of phase-modulated signals, which, although excellent in enhancing the link RF gain, also leads to the amplification of nonlinear distortions and also suffers from power cyclic fading due to dispersion and square-law detection. In this paper, we utilize FBG to break the amplitude balance of phase-modulated signals, which not only eliminates the need for bias point control but also improves the link gain for MFH transmissions while overcoming power cyclic fading. The FBG-enabled PMDD-based MFH transmission links are first introduced through theoretical analysis, and then extensive numerical exploration of their performance are conducted. The simulation results show that CSPR and FBG SLSR play important roles in determining the transmission performance. More importantly, the simulation results also show that FBG-enabled PMDD improves the receiver sensitivity by about 3.1 dB due to its inherently high link gain compared to IMDD.