Research On Microwave Photonic Filter Based On Delay Dispersion Unit

Nowadays,with the development of microwave technology and information technology,the requirements of communication capacity is increasing.The microwave communication is developing towards higher frequency signal communication,but there are several problems.Firstly,the limited bandwidth of microwave signals is limited,which restricts the further development of microwave communication.Secondly,high frequency signals suffer from serious loss after long-distance transmission.Because of bandwidth and sampling frequency of traditional electrical filters are limited,so it can only filter low frequency signals,and it easily causes electromagnetic interference.And it is necessary to re-design the whole filter circuit when the frequency of microwave signal is changed.Microwave photonic filter(MPF)consists of microwave and photonic devices,and it can achieve the processing of high frequency microwave signals in optical domain.The drawbacks of microwave communication are overcome and high bandwidth,low loss,anti-electromagnetic interference are provided.In addition,the realization tunability and reconfigurability improves flexibility and frequency selection characteristics of MPF.In this paper,the MPF based on delayed dispersion unit is studied.The main research contents are as follows:Firstly,a multi-passband MPF based on delayed dispersion fiber is proposed.In the structure,the multi-wavelength optical sources with different wavelength spacings are implemented by using a waveshaper,and the radio frequency(RF)signals to be modulated to form modulated signals.The modulated signals that passes through the section of single mode fiber(SMF1)and transmitted at the coupler,the section of SMF1 is kept unchanged and the section of SMF2 in the lower branch is changed.The MPFs of 2?8 passbands are respectively realized.Secondly,a negative and complex coefficients MPF based on delayed dispersion fiber is proposed.In the structure,multi-wavelength optical sources with different wavelength spacings can be achieved by waveshaper,and carrier modulation on microwave signals and optical sources can be realized by polarization modulator(Po IM),the baseband response caused by the phase modulator(PM)and SMF response can be eliminated.By adjusting the polarization state of the input light into Po IM,the MPF with negative coefficient characteristic is realized.The SMF is usedas the delay dispersion unit,the Fourier domain optical processor(FD-OP)is introduced additional phase shift and the size is changed to achieve complex coefficient characteristic and continuously tunable characteristic,the spectrum shape is unchanged.The continuously tunable range is 0GHz ? 34.97 GHz.Thirdly,a tunable and reconfigurable MPF based on delayed dispersion fiber and cascade fiber rings is proposed.In the structure,multi-wavelength optical sources with different numbers of tap are realized using a waveshaper.For the delay unit,the reconfigurable characteristic of MPF is realized by cascading SMF with two fiber rings.The 3d B bandwidth is 0.019 GHz,the Q factor is 470.895,and the main sidelobe suppression ratio(MSSR)is 59.356 d B.The FD-OP is used to introduce additional phase shift and the size is changed to achieve the tunable characteristic of MPF.The tuning range is 4.47 GHz ?13.41 GHz.