Research On Tunable Optoelectronic Oscillator And Its Applications

Microwave photonics is a new subject of the fusion of microwave and photonics,it mainly studies the photonics generation,processing,and transmission of microwave signals.Microwave photonics can achieve many functions in microwave systems that are too complicated or cannot be achieved by conventional electronic methods.Microwave/millimeter-wave signal sources with high spectral purity and low phase noise play a very important role in systems,such as wireless communications,radio over optical transmission(RoF),and radar.Therefore,research on methods for generating high-quality microwave signals has become research hotspots recently.Traditional electrical methods of generating microwave signals have many limitations on the electronic bottleneck effect and tuning bandwidth of electrical devices.The use of photonic technology has the advantages of high processing speed,low loss in optical fiber transmission,and large bandwidth.Thus,the use of photonics in combination with existing electrical methods and theories to generate microwave and millimeter-wave signals has become one of the research hotspots.People use microwave photonic technology to generate microwave signals,which play an important role in applications,such as communications,high-speed signal processing,navigation,radar,and measurement systems.An optoelectronic oscillator(OEO)is one of the methods for generating microwave signals using microwave photonics technology.It can produce microwave signals with low phase noise by storing microwave energy in an optical delay line.This paper summarizes several common microwave signal generation methods,analyzes and compares the advantages and disadvantages of different microwave signal generation methods,then focuses on the method of using OEOs to generate microwave signals.OEOs have remarkable low-noise characteristics and very high stability,as well as functional characteristics which electronic oscillators cannot achieve.Usually,OEOs use electrical and optical components that have high efficiency,high speed,and low dispersion in microwave communication systems.Due to the output of an OEO can directly obtain microwave signals and optical modulation signals,an OEO can also be regarded as a hybrid oscillator,which is very important for applications involving optical components,devices,or systems.The first design idea of this paper is to demonstrate a high-frequency tunable OEO using the stimulated Brillouin scattering(SBS)effect.Then an optical true delay line based on the on-chip subwavelength grating is proposed,then a tunable multi-cavity OEO based on the on-chip optical true delay line is demonstrated,which has the potential to realize the integration of OEOs.Finally,using the SBS effect and the characteristics of the OEOs,a frequency converter based on the OEO is designed.The specific design ideas and research innovations are as follows:1.A tunable frequency-decuple optoelectronic oscillator based on optical frequency comb and SBS is proposed to realize the high-frequency of the OEO.In this structure,the Mach-Zehnder modulator and the dual-parallel Mach-Zehnder modulator are cascaded to generate an optical frequency comb,which can be used as multiple pumps instead of a single pump.Using the principle of Brillouin gain loss compensation and carrier phase-shift double-sideband modulation,a microwave signal with an output decuple frequency of the Brillouin frequency shift is realized.Utilizing the wavelength dependence of the Brillouin frequency shift,a tunable frequency-decuple OEO is obtained by tuning the wavelength of the tunable laser source.The system has great potential in high-frequency microwave signals and radar communication systems.2.In order to satisfy that the frequency and phase of the output microwave signal can be adjusted in practical applications,this paper proposes a triple-frequency OEO with frequency-and phase-tunable based on SBS effect and carrier phase-shift single-sideband modulation.The carrier phase-shifted single-sideband modulation signal in this structure is composed of a dual-parallel Mach-Zehnder modulator and a tunable band-pass filter.Adjusting the wavelength of the pump light can make the frequency of the output microwave signal tunable,and the phase of the output microwave signal can be changed by controlling the DC bias voltage of the dual-parallel Mach-Zehnder modulator.3.An index-variable optical true time delay line(OTTDL)based on an array of 40 subwavelength grating(SWG)waveguides in silicon-on-insulator(SOI)is experimentally demonstrated.The serpentine arrangement structure of the subwavelength grating waveguide is used to increase the length while maintaining a compact size;the chip area occupied by the array is about 6.5 mm×8.7 mm=56.55mm~2.Using the measured data and numerical simulations,we determine the oscillation spectra,phase noise,and frequency tuning of the multi-cavity OEOs.The design of the on-chip optical true delay line brings the proposed OEOs closer to the development of integration.4.An all-optical microwave photonic frequency up/down converter based on stimulated Brillouin scattering is proposed and experimentally verified.The key technologies of this scheme are selective amplification and frequency shift of the SBS effect.The narrow gain spectrum generated by the stimulated Brillouin scattering effect can produce Stokes light whose frequency is shifted down.After filtering by a tunable optical bandpass filter,the input signal can be up-converted or down-converted through the same system.Since there is only one laser,the structure is simple,there is a certain tolerance for the dispersion introduced by the fiber.In addition,due to the all-optical microwave photonic frequency converter does not contain electronic components,it can break through the electronic bottleneck effect and solve the problem of limited bandwidth.Utilizing the characteristics of the OEOs,e.g.,the pure spectrum of the microwave signal,and the phase noise does not degrade greatly when increasing oscillation frequency,a microwave photonic frequency converter based on the SBS effect and the OEO.The frequency converter uses a modulator and an optical filter to generate two pump lights.The system uses only one laser source to avoid system instability caused by two laser sources.The proposed up-conversion system based on the OEO can achieve a wide tuning range of 22.4?61.4 GHz.