Filterless frequency 32-tupling millimeter ROF system without bit walk-off effect by Mach-Zehnder modulators

A novel scheme to generate a frequency 32-tripling millimeter wave (MMW) and transmit it over fiber without the bit walk-off effect is proposed. The operation principle and feasibility of our proposed scheme are theoretically analyzed and verified with simulation experiments. The main part of our designed scheme is a ± 16th order sidebands generator (SG) which is constructed by eight Mach-Zehnder modulators (MZM) in parallel. In the back-to-back transmission case, by properly adjusting the voltage and initial phase of the radio frequency (RF) drive signals loaded on the MZMs, ± 16th order sidebands are generated by the SG. In the data transmission case, the data signal is split into two paths first, one of which modulates the RF drive signal with an electrical phase modulator (PM), and the other is amplified by an electrical gainer (EG), and then the two paths signal are combined into one which is used as the RF drive signal to the MZMs. By adjusting the modulation index of the PM and the gain of the EG, the data signal can be modulated only to the + 16th order sideband of the output of the SG. The output signal of the SG is transmitted to the remote base station via optical fiber and injected into the photodetector to generate the 32-tripling frequency MMW with data. The influence on the bit error rate (BER) by the key parameters in the system is also analyzed. Our designed scheme can effectively overcome the bit walk-off effect caused by optical fiber chromatic dispersion, greatly increase the optical fiber transmission distance, and has important application prospects in radio over fiber (ROF).