Research On Continuously Tunable Complex-Coefficient Microwave Photonic Filter

Microwave photonics mainly includes optoelectronic devices and microwave signal control processing units.As an important part of the microwave signal processing unit,microwave photonic filter(MPF)combines the theory of microwave and optical fiber communication,and realizes modulation and transmission of microwave signals by using optical devices and technologies.It plays an important role in the field of microwave communication.In this paper,the continuously tunable complex coefficient microwave photonic filter is studied.The main research contents are as follows:Firstly,the application,classification,performance parameters of MPF and the development and research status of complex coefficient MPF are analyzed.Secondly,the definition and implementation of different tap coefficients of MPF are studied systematically.The theory of continuously tunable complex coefficient microwave photonic filters and continuously tunable complex coefficient flat notch microwave photonic filters are analyzed.The research on how to realize the complex coefficient MPF is studied,and the tunable performance of MPF is analyzed.It provides theoretical preparation for the third chapter and the fourth chapter.Thirdly,a continuously tunable complex coefficient microwave photonic filter based on broadband optical source is proposed.In this structure,a programmable optical processor(waveshaper)is used to cut and shape the broadband optical source to achieve a stable,controllable multi-wavelength optical source.Through programming the waveshaper to control the tap distribution of the multi-wavelength optical source,positive coefficient MPF,negative coefficient MPF and bandpass notch switchable MPF can be realized at the same time.Free spectral range and 3dB bandwidth tuning of bandpass and notch MPF can be achieved by controlling the wavelength spacing and number of taps of the multi-wavelength optical source,respectively.The Fourier domain optical processor(FD-OP)is used to induce additional phase shift,and the complex coefficient microwave photonic filter is realized.By changing the phase shift,continuous tuning of bandpass and notch MPF center frequency is realized and the shape is unchanged.Fourthly,a continuously tunable complex coefficient flat notch microwave photonic filter is proposed.The multi-wavelength optical source of this structure is composed of a tunable laser and a broadband optical source,which are respectively referred to as a first tap and secondary taps.The tap distribution is designed to achieve a flat notch microwave photonic filter with a passband ripple of less than 0.65 dB,when the power of the first tap is equal to the sum of the secondary taps' powers.Free spectral ranges and 3dB bandwidth tuning can be achieved by changing the delay time and the number of taps respectively.The notch depth of MPF can be adjusted by adjusting the amplitude of the first tap.The additionalphase shift is induced by FD-OP to realize the complex coefficient flat notch microwave photonic filter.And by changing the phase shift,the center of the flat notch MPF is continuously tuned,and the spectrum shape is unchanged.