Research On Tunable Optoelectronic Oscillator With Hybrid Filtering Structure

With the continuous development and progress of communication technology,people's demand for high-quality microwave signals is increasingly urgent.Microwave photonics is an interdisciplinary subject based on electronics and optics.Its main research direction is the generation,transmission and corresponding processing of microwave signals.In recent years,microwave photonics has developed rapidly,realizing many functions that cannot be achieved by conventional electrical methods.Microwave signals with high purity,low phase noise,and large tuning range often play an important role in radar systems,communication systems,and radio frequency over optical systems.How to obtain high-quality microwave signals has become a hot research topic.The microwave signal is generated by traditional electronic means,and then the high-frequency microwave signal can be obtained through the process of frequency doubling.However,during this process,the phase noise of the microwave signal will continue to deteriorate with the frequency doubling process.It is often difficult to achieve large-scale tuning of microwave signals,which is the so-called "electronic bottleneck".Based on microwave photonic technology,a series of methods for generating high-frequency microwaves have been derived by taking advantage of the advantages of low transmission loss and large transmission bandwidth in optical fibers.Among them,the use of photoelectric oscillators to generate high-frequency microwave signals has obvious advantages.At present,the microwave signal generated by the photoelectric oscillator method has been widely used in wireless communication,frequency measurement,optical fiber sensing,radar and other systems.This paper first introduces the background of microwave photonics and its unique advantages,then introduces various methods for generating high-frequency signals based on microwave photonics,analyzes and compares the advantages and disadvantages of each method,and then focuses on the introduction.A method for generating high-frequency microwave signals by photoelectric oscillators.Using an optoelectronic oscillator as a signal generator can achieve many advantages of high spectral purity of the output signal,low phase noise,and a wide tuning range,and the optoelectronic oscillator has two output modes of optical signal and electrical signal,which can be used in various systems.There are broad prospects in the application.In this paper,an optoelectronic oscillator based on stimulated Brillouin scattering effect and Mach-Zehnder interferometer filtering is proposed.The stimulated Brillouin scattering effect and the principle of Mach-Zehnder interferometer are analyzed,and the principle of a microwave photonic filter based on the MachZehnder interferometer and stimulated Brillouin scattering effect is analyzed,and the filter transfer function is given,Simulation experiments are carried out in Matlab and Optisystem systems.The simulation results show that the structure can realize the filtering function and can generate notches on both sides of the gain spectrum of the SBS,which can be used in the design of optoelectronic oscillators.The side-mode suppression ratio,stability,resolution,tuning range and phase noise of the broadband tunable optoelectronic oscillator based on Mach-Zehnder interferometer and stimulated Brillouin scattering effect were tested.The oscillator generates a stable single-mode oscillation signal at 9.4GHz,the side-mode rejection ratio reaches 42 d B,and the phase noise is-84.05 d Bc/Hz at the offset of 10 k Hz.Within 420 s,the frequency drift of the system is lower than 50 k Hz.,a tuning range of280 MHz from 9.25 to 9.53 GHz is obtained by adjusting the wavelength of the tunable laser,and broadband tuning from 9.4 to 24.9GHz is achieved by introducing an independent pump source.The optoelectronic oscillator is filtered by introducing a Mach-Zehnder interferometer to synergize with the stimulated Brillouin scattering effect,so that the system can achieve stable single-mode oscillation.The microwave signal output by the system has a high-purity spectrum,ultra-low phase noise,frequency It has the advantages of high stability and wide tuning range.And the system has great advantages in integration,and has great potential in the process of commercializing optoelectronic oscillators in the future.Finally,the current development of optoelectronic oscillators is summarized,and the difficulties that need to be solved urgently in this direction are pointed out.At the same time,the development direction and research hotspots of optoelectronic oscillators in the future are also expounded.