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

A novel frequency 32-tupling millimeter wave (MMW) radio over fiber(ROF) system without bit walk-off effect by Mach-Zehnder modulator (MZM) is proposed. Our proposed scheme's operation principle and feasibility are theoretically analyzed and verified with simulation experiments. The main part of our designed scheme is a +/- 16th order sidebands generator (SG) constructed by eight parallel Mach-Zehnder modulators (MZM). 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, one is modulated by the RF drive signal with an electrical phase modulator (PM), the other is amplified by an electrical gainer (EG), and then the two paths signal are combined into one which is used as the composite 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 from SG is transported to the base station via optical fiber and beat in the photodetector to generate the frequency 32-tupling MMW with data. The influences on the bit error rate by the key parameters in the system are also analyzed. Our designed scheme can effectively reduce the bit walk-off effect caused by optical fiber chromatic dispersion, significantly increase the transmission distance of fiber, and has important application prospects in MMW ROF.