The 18-tupling frequency 16QAM millimeter-wave generation scheme based on polarization division multiplexing

To better utilize the optical fiber bandwidth and enhance the communication capability of the RoF system, this paper combines photonic vector modulation and optical millimeter-wave generation techniques, proposing an 18-fold frequency 16 quadrature amplitude modulation (QAM) millimeter-wave generation scheme based on polarization division multiplexing (PDM). The system consists of two parallel modules: frequency doubling and vector modulation. In the frequency doubling module, two dual-parallel Mach-Zehnder modulators (DP-MZM) and an optical phase shifter are used to generate the ±6th-order optical sidebands. After passing through a semiconductor optical amplifier (SOA), four-wave mixing effects are induced, and the 18th-order sidebands are obtained through filtering. In the vector modulation module, eight 10 Gbit/s binary NRZ signals drive the DP-MZM, and polarization multiplexing technology is applied to implement 16QAM optical domain modulation on two orthogonal polarization directions. The PDM-16QAM signal is coupled with the 18th-order optical sidebands and, after photodetection, an 18-fold frequency PDM-16QAM signal is generated. Simulation analysis shows that when the photodetector's received power is −25 dBm, the signal-to-noise ratio (SNR) of the system is greater than 20.5 dB, and after 30 km transmission through single-mode optical fiber, the system performance remains good. Even when there are fluctuations in the SOA injection current and laser linewidth within a certain range, the bit error rate (BER) of the system remains below 3.8×10⁻³.