Research On Tunable Microwave Photonic Bandpass Filter Based On Micro Ring Resonator

The microwave photonic filter(MPF)is one of the most important devices for microwave photonic signal processing system,and it has broad applications in communication fileds.Until now,many MPFs based on discrete fiber components have been proposed.However,these MPFs have shortcomings of big footprint and slow tuning rate,which restrict their applications.Recently,the integrated MPFs have aroused researcher's attention,but the filter's performances including out of band radio frequency(RF)suppression ratio and so on still need to be improved.In addition,there are few researches that can achieve frequency tuning and bandwidth reconfiguration simultaneously.In this thesis,the microwave photonic bandpass filters based on the tunable micro-ring resonator(MRR)were studied theoretically and experimentally,using phase modulation and intensity modulation respectively.The performances of the proposed MPFs were improved,and large tuning ranges of frequency and bandwidth were achieved.In order to achieve MPFs with high frequency resolution,the MRRs based on dual-strip Si₃N₄ waveguide with low transmission loss were used to achieve high quality factor,and the spectra reconfigurations were realized using thermos-optic effect.Photoelectric coupling of the Si₃N₄ MRR chip was achieved and an automatic driving and measurement software of the MRR were bulit based on Labview,which was used to obtain the tuning performances of the Si₃N₄MRR.In general,microwave photonic bandpass filters based on the all-pass MRR can be implemented using the principle of phase modulation to intensity modulation conversation.However,the filter's out of band RF rejection ratio and shape factor are limited due to the MRR's residual phase,which can seriously degrade the filter's performance.The microwave photonic bandpass filter using dual optical carriers was proposed.The residual phase induced by the ring resonator at radio frequencies falling outside the region of the notch stopband was reduced by using dual optical carriers,thus the out-of-band RF rejection ratio and shape factor of the MPF were greatly improved.The proposed MPF was both verified theoretically and experimentally.Compared with single optical carrier method,the out-of-band RF rejection ratio of the filter was enhanced from 17.7d B to 31.5d B,and the filter's shape factor was improved from 3.05 to 1.78.Besides,the filter's frequency and bandwidth were tuned by varying the wavelengths of the two optical carriers,the ring resonator's coupling coefficients and resonance wavelengths.Finally,a tunable microwave photonic bandpass filter with frequency tuning range of 2?14GHz,3d B bandwidth tuning range of 0.673?2.798GHz was demonstrated.In addition,larger bandwidth tuning range can be achieved by increasing the number of optical carriers through theoretical analysis.On the other hand,a reconfigurable microwave photonic bandpass filter based on the add-drop Si₃N₄MRR was achieved using optical single sideband modulation and optical carrier separation,which maps the optical bandpass response to the radio frequency domain.The theoretical model of the bandpass MPF was constructed.And the feasibility of the proposed filter was experimentally verified.The measured bandwidth and out-of-band RF rejection ratio of the proposed MPF were 726MHz and 37d B,respectively.By tuning the optical carrier's wavelength,a filter with frequency tuning range of 1.64?23.41GHz was achieved.In addition,by changing the coupling coefficient of the MRR,the bandwidth can be reconfigured in the range of 0.683?2.246GHz with out-of-band RF rejection ratio more than 26d B.