The Optimization Of Phase Noise And Spurious Mode Of Optoelectronic Oscillators

High-quality oscillators are an important part of modern electronic systems.They have extremely wide application in many fields,such as measurement and control,radar,communications,navigation,electronic countermeasures,astronomy and modern physics experiments.With the rapid development of high-frequency electronic systems and modern wireless communications,these electronic and communications systems offer increasingly high requirements on the frequency range,frequency stability and phase noise of signals generated by oscillators.Crystal oscillator with high frequency stability is conveniently used as a standard signal generator.Although the crystal oscillator having low phase noise,its frequency is generally lower than 100 MHz.The generation of high-frequency signals through frequency multiplication is based on the sacrifice of phase noise,and it is difficult to meet the requirements of high-frequency systems.The voltage-controlled oscillator can generate signals of several GHz,but the phase noise performance is poor.With the rapid development of microwave photonics,optoelectronic oscillators have emerged as new types of oscillators that convert the light energy of lasers into microwave signal energy.They can generate low phase noise signals of several GHz and even hundreds of GHz.This dissertation focuses on the optimization of the performance of optoelectronic oscillators.The main innovations of the thesis are as follows:1.The basic principle of optoelectronic oscillators is analyzed.The quasi-linear dynamic oscillation model of optoelectronic oscillator and phase noise model in the Laplace domain are discussed.Secondly,the noise source of the optoelectronic oscillator is considered comprehensively.The influence of the relative intensity noise of the laser,the thermal noise,the shot noise,the flicker noise of the microwave amplifier on the phase noise of the optoelectronic oscillator is also theoretically analyzed.2.For the sake of improving the long-term frequency stability of the optoelectronic oscillator and ensuring reliable repeatable measured phase noise at the determined offset frequency,the frequency stability principle and phase noise model of the optoelectronic oscillator based on the phase-locked loop are analyzed.A phase-locked optoelectronic oscillator system was constructed.Within the average measurement time of 1024 seconds,the Allan variance reached 1.43 × 10-12,which was an improvement of 5 orders of magnitude compared to the Allan variance of the free-running optoelectronic oscillator.The long-term frequency stability of the optoelectronic oscillator is improved.At the same time,the phase-locked optoelectronic oscillator improves the phase noise at near-carrier frequencies while preserving the low phase noise at high offset frequency.3.In order to optimize the phase noise performance of optoelectronic oscillator,the impact of the laser linewidth,relative intensity noise,the incident optical power of the photodetector,the Rayleigh scattering in the fiber link,the noise of the microwave amplifier and the band-pass filter on the phase noise of optoelectronic oscillator were analyzed.Using the method of control variables,the optoelectronic oscillator phase noise optimization methods are summarized:selecting appropriate linewidth and low relative intensity noise laser,finding the optimal optical detector's incident optical power point,laser current modulation and using low phase noise or low noise microwave amplifiers to compensate for link gains.The optoelectronic oscillator with phase noise below-140dBc/Hz@ 10 kHz is obtained.4.Based on the structure of a single-loop optoelectronic oscillator,an optoelectronic hybrid filter loop is proposed.Based on this filter,a narrow-band,high-Q filter of a millimeter-wave optoelectronic oscillator is implemented,effectively suppressing the optoelectronic oscillator's spurious mode.By controlling the closed-loop gain of the optoelectronic hybrid filter loop,a high-Q millimeter-wave filter with center frequency of 29.99 GHz and 3 dB bandwidth of 1 MHz was obtained.Combining this filter,millimeter-wave optoelectronic oscillators produce low-phase-noise,low-spurious millimeter-wave signals which single-sideband phase noise and spur suppression ratios are respectively-113 dBc/Hz @ 10 kHz and 83 dBc.5.Based on the structure of the coupled optoelectronic oscillator,a mutual injection locking scheme is proposed to suppress its super-mode noise.A coupled optoelectronic oscillator acts as a main oscillator,and the microwave feedback path is closed in the electrical domain to form a slave oscillator circuit.Since the closed-loop feedback is a single-mode oscillation signal,the supermodes can be effectively suppressed.The spurious suppression ratio is as high as-120 dBc,and the single-sideband phase noise of the generated 9.99 GHz microwave signal is approximately-117 dBc/Hz@ 10 kHz.