Research On Microwave Photonic Filter Based On Phase Control

With the increasing of information density in modern society,communication technology needs to keep developing rapidly to meet the explosive growth of information.In the continuous expansion of communication frequency bands to higher frequency bands,due to the limitations of traditional electronic devices,significant challenges are encountered in the transmitting and processing of high frequency microwave signals.For the electronic devices,the bandwidth and sampling rate for processing high frequency signals are limited.The transmission loss of high frequency microwave signals is rather high in atmosphere and coaxial cables.Optical communication technology exhibits advantages such as extremely low transmission loss,large bandwidth and immunity to electromagnetic interference.Therefore,microwave photonics,in which photonic technology is used to generate,transmit and process microwave signals,became one of the most promising method to overcome these problems.As a key device in signal processing,the microwave photonic filter(MPF)is an important branch of microwave photonics.Compared with the traditional electronic filter,the MPF not only inherits the advantages of photonic technology with large bandwidth and immunity to electromagnetic interference,but also possesses the characteristics of small size,light weight and high flexibility.This thesis is focused on the specific problems encountered in the development of MPF.The main content can be summarized as follows:(1)Based on a dual-drive Mach-Zehnder modulator(DDMZM)and a broadband optical source which is sliced by a delay interferometer,a tunable single-passband MPF that overcomes the amplitude attenuation caused by dispersion is realized.The central frequency of the MPF can be tuned by adjusting the free spectrum range of the delay interferometer.In the proposed MPF,only one electrode in the DDMZM is driven by the microwave signal.By adjusting the direct current bias of the DDMZM to change the phase shift between the two arms,the amplitude attenuation caused by dispersion at any passband can be fully compensated.In the proposed MPF,the center frequency of the passband can be tuned from 0 to 30 GHz,and the passband amplitude of the MPF remains constant during the tuning process.(2)Based on a monolithically integrated cascaded microring resonator(MRR)and a photodetector on silicon-on-insulator foundry,an MPF with a flat-top passband and adjustable bandwidth is proposed.An optical filter with a full width at half maximum(FWHM)of 21.6 GHz can be obtained by the implemented 10 th order MRR.The power ripple of the passband of the MPF is less than 0.3 dB and the rejection ratio is 32 dB.By optically filtering the phase-modulated signal,a band-pass MPF can be obtained after the photodetector.When the offset wavelength between the carrier wavelength and the center wavelength of the optical bandpass filter is adjusted,the FWHM bandwidth of MPF can be tuned from 5.3 to 19.5 GHz while the rejection ratio remains more than 30 dB during the tuning process.(3)Based on the method of self-compensation of loss,the possibility of implementing an all-pass filter(APF)are theoretically demonstrated.A general method of implementing a first-order APF with common coupling structure is summarized.Based on the analysis,a structure based on Mach-Zehnder interferometer assisted MRR to implement the APF is designed and fabricated on a silicon-on-insulator chip.The experimental results can verify that the amplitude of the optical all-pass filter in the range of 10 nm remains almost constant while the phase changes periodically.Based on the optical APF,a microwave photonic allpass fitler is realized and the amplitude of the MPF is constant in the range of 0?40 GHz while the phase changes by 1.8 ?.Based on the optical APF,a microwave photonic notch filter and a microwave phononic bandpass filter are implemented.The center frequencies of the two MPFs can be adjusted from 0 to 40 GHz and the rejection ratio are more than 50 dB and 30 dB,respectively.Based on the APF,a microwave photonic phase shifter is realized and the phase shift can be tuned from 0 to 1.7 ? while the change of the power of the signal is less than ±0.8 dB during the tuning of the phase shift.A microwave photonic time delay based on the APF is also realized.When the time delay changes in the range of 0?200 ps,the power change of the signal is less than ±0.4 dB.