Multidimensional Optimization of a Radio-Over-Fiber Link

Nonlinear distortion and chromatic dispersion are two long-standing limiting factors of radio-over-fiber (ROF) links. Here, we proposed an ROF link with both the two problems mitigated simultaneously. Furthermore, a tunable optical carrier-to-sideband ratio (CSR) can also be implemented in this simple system to improve the gain and the noise figure (NF) of the link. All these three factors are optimized in a simple ROF link which shows increased performance of the system. The scheme is based on a single dual-polarization Mach-Zehnder modulator (DPol-MZM). One bias voltage of the Dpol-MZM is employed to mitigate the nonlinear distortion. The polarization direction and the phase relationship of the modulated polarization multiplexed signal are used to adjust the CSR and suppress the dispersion, respectively, by adjusting a polarization controller (PC). In the experiment, 3-30-GHz RF signal is transmitted without power fading. A two-tone signal with the frequencies of 12.5 and 12.505 GHz is employed to verify the optimization of three main parameters of the ROF link [link gain, NF, and spurious-free dynamic range (SFDR)] where the link gain, NF, and SFDR are improved by 11.9, 5.8, and 14.5 dB, respectively, compared with conventional quadrature biased link based on one Mach-Zehnder modulator for 50-km single-mode fiber (SMF) transmission. Meanwhile, 100-Mbaud 16 quadrature amplitude modulation (QAM) signals centered at 12.5 and 14.7 GHz are used to verify the transmission performance. After dispersion compensation, nonlinear optimization, and CSR optimization, error vector magnitude (EVM) is improved from 17.03% to 2.97%.