SNR-enhanced and high-order frequency multiplied 64-QAM millimeter-wave signal generation enabled by MZM-based angle modulation

We propose and experimentally demonstrate a novel scheme to generate ultrahigh-order frequency multiplied millimeter-wave (mm-wave) signals with high fidelity enabled by angle modulation (ANG-M). The constant envelope (CE) characteristic of the ANG-M signal makes it possible to avoid nonlinear distortion induced by photonic frequency multiplication. In addition, the theoretical formula and the simulation results prove that the modulation index (MI) of the ANG-M signal increases along with frequency multiplication, so as to improve the signal-to-noise ratio (SNR) of the frequency-multiplied signal. In the experiment, we confirm the SNR of the 4-fold signal is enhanced by 2.1 dB approximately for the increased MI compared to the 2-fold signal. Finally, a 6-Gb/s 64-QAM signal with a carrier frequency of 30 GHz is generated and transmitted over 25-km standard single-mode fiber (SSMF) using only a 3-GHz radio frequency signal and 10-GHz bandwidth Mach-Zehnder modulator. To the best of our knowledge, it is the first time that a 10-fold frequency-multiplied 64-QAM signal with high fidelity is generated. The results prove that the proposed method will be a potential solution for low-cost mm-wave signal generation in future 6G communication.