Research On Photonic Generation Of Microwave Or Millimeter-Wave In ROF System

The technologies of broadband network and wireless communication are the most important technologies in the field of information and communication technology nowadays. The combination of them is the future direction of the communication industry. Ro F techniques based on photonic technologies are able to generate, transport, and radiate in a straightforward manner microwave and millimeter-wave signals, and has attracted wide attention in recent years. Optical millimeter-wave signal generation are considered as a potential costeffective solution in ROF system, this paper mainly studies optical mm-wave signal generation scheme based on external modulation.First, this paper analyzes the research background, principle and prospects of ROF system, and summarizes several proposals for optical millimeter-wave signal generation, including direct modulation technology, optical heterodyne method, optic-electronic oscillator and external modulation techniques. And the scheme based on external modulation to achieve photonic triangular wave generation is briefly described.Secondly, the models of the major optic-electronic devices in ROF system, including Li Nb O3 Mach-Zehnder modulator(LN-MZM) and photodiode are analyzed, focusing on the structure and principle of dual-electrode Mach-Zehnder modulator(DE-MZM) and dualparallel Mach-Zehnder modulator(DP-MZM), and the theory of fiber dispersion and fourwave-mixing(FWM) effect are described.Then, based on the scheme of the cascading MZM and DP-MZM to achieve photonic frequency sextupling, a novel frequency 18-tupling scheme based on external modulation assisted with FWM effect is presented. This paper respectively describes theoretical analysis of the frequency sextupling scheme and the frequency 18-tupling scheme, followed by simulation and experimental validation. In the frequency sextupling scheme, MZM and one of the sub-modulator of DP-MZM are driven by the same RF local oscillator signal. By setting the bias voltage of MZM and DP-MZM, each modulator works at the appropriate operating point. Experiment results show that the OSSR and RFSSR of the frequency sextupling scheme can both reach 20 d B, the OSSR and RFSSR of the frequency 18-tupling scheme can reach 8d B and 16 d B respectively.Finally, another novel scheme based on DE-MZM and fiber dispersion is proposed to achieve photonic triangular wave generation. The optical carrier is modulated by the RF signals with only one arm of the modulator. Simulation results show that the generated triangular wave signal has the same pulse repetition rate as reference RF signal frequency. This proposed scheme is simple in structure and cost-effective.