Research On Photonic-assisted Radio Frequcency Filter Based On Coherent Light Source

The current radio frequency(RF)microwave system is developing in the direction of broadband and multi-functional integration.Traditional electric RF filters are subject by electronic bottlenecks,and are severely limited in terms of tunability and reconfigurability.Therefore,it is difficult to support the need for filter tuning and reconfiguration in traditional electric RF filters.Microwave photonic filters(MPF)process microwave signals in the optical domain with photonic methods,which can achieve high bandwidth,anti-electromagnetic interference,fast tunability and reconfigurability performance.MPFs have broad research prospects and application value,and have become one of the hot research topics in recent years.In recent years,researchers have conducted a lot of research on the wide bandwidth and tunability of microwave photonic filters,but there is still a large room for improvement in the resolution and arbitrary reconfigurability of MPFs.In particular,high-resolution microwave photonic filters have become the focus of researchers.This thesis conducts a research on microwave photonic filters based on coherent light,focusing on the high-resolution and arbitrary reconfigurable characteristics of the filter.The main work is as follows:1)We theoretically analyzed the process of generating a flat optical frequency comb(OFC)using the cascaded modulator method,including investigating the input RF signal power,the number of cascaded phase modulators,and the selection of intensity modulation bias points.Finally,one intensity modulator and five phase modulators are cascaded to generate a flat OFC with free spectrum range(FSR)of 11.2 GHz and more than 100 teeth,providing a coherent light source for a high-resolution microwave photonic filter.2)A high-resolution reconfigurable finite impulse response(FIR)MPF based on an OFC was proposed,and the formula derivation and simulation verification were carried out.It is shown that a flat OFC with a large number of teeth can be used as a light source to increase the number of taps,thereby realizing high-resolution filters.The programmable optical filter is used to complete the independent and flexible configuration of the tap coefficients,and the coherent detection technology is used to realize the positive and negative taps of the filter,so that the filter shape can be reconfigured arbitrarily.It is verified by simulation that the filter has a high resolution of 93 MHz and can realize arbitrary shape filtering.3)Aiming at the limitation of operating frequency range of FIR MPF based on coherent OFC,a high-resolution reconfigurable photon-assisted RF filter scheme that can realize arbitrary filter shape with wide bandwidth and interference suppression is proposed.Operating frequency range extension of the MPF can be achieved by single-sideband modulation.In addition,interferences in the MPF are also suppressed by pre-introducing dispersion.The simulation results show that the surface spurious suppression reaches above 40 dB MPF can realize low-pass,band-pass,high-pass,and band-stop filters with different center frequencies,and arbitrary filter shapes such as rectangle,Gaussian,and Sinc shape.Finally,this paper gives a complete design process of high-resolution broadband MPF.