The Study Of Wideband Tunable Optoelectronic Oscillator Based On A Microwave Photonic Filter

Microwave photonics(MWP),which combines the worlds of microwave engineering and optoelectronics,is an interdisciplinary area.Compared with the traditional microwave engineering,MWP enables the generation,transmission and processing of microwave signals in the optical domain.In this way,MWP cannot only solve the problem of electronic bottleneck,but also takes the advantages of photonic technology.Optical generation of microwave signals is one key applications.The development of communication systems is inseparable from high-quality microwave signals,and different systems have different requirements for microwave frequency bands.With the development of military forces in various countries,the battlefield environments are becoming more and more complex.To improve battlefield survivability,the integration of multiple systems such as radar,communications,and electronic warfare,is significantly demanded.The fusion of multiple systems places an urgent need on high-quality tunable microwave signals.Optoelectronic oscillator(OEO)can meet the needs well.Different from the traditional microwave oscillators,OEO uses the ultra-low transmission loss of optical fibers to store energy in the optical domain.Based on the opto-electronic hybrid positive feedback loop,in OEOs the optical energy is directly converted to the microwave signal,which overcomes the disadvantage that the phase noise of traditional electronic oscillators is significantly deteriorated with the increase of the oscillating frequency.However,it is difficult for OEO to have the advantages of low phase noise,large side mode suppression ratio(SMSR)and ultra-wide tunable range at the same time.A widely tunable microwave photonics bandpass filter(MPBF)with an ultra-narrow passband is used in the OEO for mode selection,which can meet the free switching of the oscillating frequency in a wide spectral range while mataining low phase noise and large SMSR.Wideband tunable OEO is an ideal microwave signal generator,which can be widely applied to wireless communication,radar,electronic warfare,optical sensing,electronic measurement and clinical medicine,etc.This thesis focuses on improving the frequency tunability of OEO,improving phase noise performance,suppressing mode competition,improving the SMSR and miniaturization and integration of OEO.The main contributions and innovations of this thesis are as follows:(1)Based on the stimulated Brillouin scattering(SBS)in high nonlinear fiber(HNLF),a narrowband MPBF is proposed.We analyze the operation principle of SBS-based MPF(SBS-MPF)to optimize the performance of the SBS-MPF.By optimizing the pump power,the HNLF length and the polarization states of the pump and signal waves,the amplitude suppression ratio between the passbands generated by SBS gain and loss is increased.Therefore,the limitation that maximum tuning range of the previously reported SBS-MPFs is limited within two folds of the Brillouin frequency shift,is successfully broken.In the experiment,the central frequency of the single passband MPF can be tuned from 0 to 40 GHz,the rejection ratio can reach above 50 d B and the full width at half-maximum(FWHM)bandwidth is 16 MHz.(2)Based on cascaded MPFs,an ultra-narrow bandpass MPF with wideband tunability is proposed and experimentally demonstrated.By analyzing the operation principle and operation conditions of the cascaded filters,the ultra-narrow passband is realized by cascading the SBS-MPF and an infinite impulse response MPF(IIR-MPF)based on an active fiber recirculating delay loop.The measured FWHM bandwidth of the cascaded MPFs is 150 k Hz.To the best of my knowledge,this is the first time realizing such a narrow passband in single-passband MPF.Owing to the widely tunability of SBS-MPF,the frequency tunability of the cascade MPFs also reaches 40 GHz.Using the cascaded MPFs to replace the electronic bandpass filter in the OEO for mode selection,a widely tunable low phase noise OEO is achieved.The obtained OEO can maintain low phase noise,wideband tunability,and large SMSR simultaneously.(3)A miniaturized OEO is proposed based on high-Q silicon microring resonator(MRR).The design,fabrication and testing of on-chip high-Q microcavities are introduced.An MRR based on silicon-on-insulator is fabricated and a single passband MPF with narrow bandwidth is achieved.Then the miniaturized OEO is conducted and demonstrated,which lays the foundation for monolithically integrated OEO.