Research On Characteristics And Application Of Tunable Optoelectronic Oscillator Based On Integrated Optical Filter

Optoelectronic oscillators can generate high-quality microwave signals with high spectral purity and low phase noise,which are very desired in the fields of radar and communications,and have been extensively investigated in the past 30 years.Benefitting from their high-quality hybrid optoelectronic signal characteristics,optoelectronic oscillators have also been used in arbitrary waveform generation,sensing and measurement,computing and signal processing.Until now,some key technologies such as phase noise optimization,high-frequency signal generation,side-mode rejection ratio enhancement,frequency broadband tunability and stability have been studied.However,in some application scenarios,the integration and miniaturization of optoelectronic oscillators are needed.In the process of optoelectronic oscillator miniaturization,the above-mentioned key technologies are also needed to be developed.In this thesis,a tunable optoelectronic oscillator based on a high-Q silicon nitride microdisk resonator was proposed and its phase noise optimization,side-mode rejection ratio improvement,frequency broadband tunability and related applications were investigated.The main contents of the thesis are shown below:(1)Based on the low loss double-stripe silicon nitride waveguide,a high-Q microdisk resonator optical filter was designed and fabricated,whose 3 d B bandwidth,extinction ratio and quality factor are about 300 MHz,18 d B and 6.5×10~5,respectively.Combining the microdisk resonator filter with phase modulation link,a microwave photonic band-pass filter with 3 d B bandwidth of about 300 MHz and frequency tuning range of 1 GHz～24 GHz was realized based on the phase-intensity conversion principle.By controlling the polarization state of the optical signal input into the microdisk resonator,the spectral response of the microwave photonic filter was optimized and the out-of-band rejection ratio was improved from 20 d B to 30.7 d B in the experiment.(2)By using the tunable microwave photonic filter based on silicon nitride microdisk,combined with the mode selection mechanism of parity-time symmetry breaking,a parity-time symmetric tunable optoelectronic oscillator with double loop structure was proposed.Relative large side-mode rejection ratio(31 d B),wide-band tuning range(3 GHz～20 GHz),and low phase noise(-120 d Bc/Hz@10k Hz)were achieved in experiment.Considering that parity-time symmetry condition could be destroyed when the environmental sensitive double loop structure was involved,a single loop parity time symmetric tunable optoelectronic oscillator structure based on dual optical carriers and cascaded phase shift Bragg gratings was also proposed.The experimental results show that the side-mode rejection ratio is 37 d B,the frequency tuning range is 1 GHz～22 GHz,and the phase noise can reach-130 d Bc/Hz@10k Hz.(3)By introducing an active mode-locking mechanism into a silicon nitride microdisk-based tunable optoelectronic oscillator,its potential oscillation modes were phase locked to generate microwave frequency comb with tunable center frequency Experiments are carried out on the comb spacing and number of comb teeth,fundamental frequency mode locking and harmonic mode locking,phase noise,and stability of the proposed microwave frequency comb.The results show that when the loop length of the optoelectronic oscillator is 2 km,the number of comb teeth reaches50 within 5 MHz bandwidth through fundamental frequency mode locking.In addition,the third and sixth harmonic mode locking were also achieved and microwave frequency combs with different mode spacings were obtained.Furthermore,the phase noise of the signal reaches-110d Bc/Hz@10 k Hz,and the frequency tuning range is 1～22 GHz.(4)Based on the main oscillation power amplification effect of an optoelectronic oscillator when working at the gain threshold state,a frequency measurement system based on a microdisk resonator tunable optoelectronic oscillator was proposed.Experiments show that in the range of 1GHz～20 GHz,the gain dynamic range reaches 75 d B,the maximum gain is 61.7 d B,the detection sensitivity is about-105 d Bm,and the frequency measurement error is±375 MHz.