Research On Tunable Microwave Photonic Filter Based On Phase Modulation

Microwave photonic filter as an significant research of microwave photonics,compared with the traditional digital filter,has the dominant positions of low loss,high bandwidth and anti-electromagnetic interference.The bandpass or notch center frequency can be continuously tuned.Microwave photonic filter is becoming one of the hotspots of many scholars at home and abroad.In this dissertation,we mainly study the tunable microwave photonic filter based on phase modulation.The main contents are as follows:Firstly,the system structure and application of the microwave photonic filter are introduced,and the microwave photonic filters are classified according to different characteristics.The research status of tunable microwave photonic filters is summarized.Second,the basic principle of microwave photonic filter is described.The bandpass filter and the notch filter based on the phase modulation are analyzed in detail.The main performance parameters of the microwave photonic filter are analyzed.The theoretical basis for the tunable microwave photonic filter introduced in the following chapter is presented.Third,a tunable microwave photonic filter based on four wave mixing is proposed.Based on the four wave mixing effect,the multi-wavelength optical signal is used as the light source of the microwave photonic filter,and the structure of band pass and notch filter system is proposed.In the bandpass filter system structure,the wavelength spacing of the two single wavelength tunable lasers can be continuously tuned,so that the wavelength spacing of the multi-wavelength light source change continuously and the center frequency of the bandpass microwave photonic filter tune continuously.In the notch microwave photonic filter system structure,the notch spectrum response can be realized by controlling the amplitude and phase of the phase modulation signal through Fourier-domain optical processor,and the center frequency of notch filter can be continuously tuned by introducing additional phase shift through Fourier-domain optical processor.Fourth,a tunable microwave photonic filter based on multi wavelength fiber laser is proposed.The multi-wavelength optical signals based on the nonlinear polarization rotation effect as the light source of microwave photonic filter,the bandwidth of bandpass or notch filter can be reduced by increasing the number of wavelengths.In the system structure,by introducing the Fourier-domain optical processor to control the sideband of the phase modulation signal,the phase modulation to the single sideband intensity modulation is realized.The bandpass filter to switch notch filter can be realized by controlling the amplitude and phase of the phase modulation signal through Fourier-domain optical processor.Finally,the center frequency of bandpass and notch filter can be continuously tuned by introducing additional phase shift through Fourier-domain optical processor,and the shape of frequency response keeps unchanged when the phase is tuned.