Research On Microwave Photonic Link Based On Phase Modulation

With the rapid development of optoelectronic devices and microwave communications technology,optical science and electrical science interact each other to form an interdisciplinary science,namely microwave photonics.Microwave photonics has the advantages of high bandwidth,light weight,anti-electromagnetic interference and low loss,and has great advantages in the occurrence,transmission and processing of microwave signals,and is widely used in communication and military aspects.The microwave photonic link is the core technology of microwave photonics.In this paper,the performance parameters of microwave photonic links are analyzed.In order to solve the performance defects caused by nonlinear distortion,a linearization scheme based on phase modulation is proposed.Firstly,several key performance parameters of microwave photonic link are analyzed by theoretical derivation,namely,gain,noise,bandwidth,nonlinear distortion and so on.And external modulation technology and phase modulation technology from the point of the theory are analyzed.The analysis provides the theoretical basis for the scheme.Secondly,two schemes for converting phase modulation to intensity modulation are proposed,namely,dispersion method and filter method.Based on the filtering method,the conversion technology is applied to the optical down conversion technology.This technique mainly uses the local oscillator to convert the microwave signal to the low frequency and intermediate frequency signal in the way of secondary modulation of the optical radio frequency signal,so as to facilitate the demodulation and processing of the microwave signal for the reception.Finally,a microwave photonic link with large dynamic range based on phase modulation is proposed.The scheme uses two polarization axes of the phase modulator to divide the modulated optical carrier frequency signal into two paths,then phase modulation is converted to intensity modulation by filtering mothod,and then the two signals are combined.By controlling the two optical carrier input power ratio,the third-order nonlinear distortion of the link can be suppressed,thereby the dynamic range of the link is increased.Also,the filtered single sideband signal can make the link unaffected by dispersion.