Research On The Key Technologies Of Photonic Generation Of Microwave Signals Based On Optoelectronic Oscillator

Optoelectronic oscillator is one of the technologies of photonic generation of microwave.It has some very prominent advantages,such as high frequency,low phase noise and so on.Besides,it can overcome the difficulties faced by the electrical generation of microwave.OEO has been widely used in areas such as RoF,satellite communication,radar system and so on.In this paper,we mainly focus on the key technologies of the photonic generation of microwave based on OEO.A structure of double frequency OEO based on stimulated Brillouin scattering and a structure of the generation of microwave waveform based on OEO are proposed in detail.The main work in this work includes:1.The main mechanism of the frequency drift of OEO was discussed.On the basis of theoretical analysis of OEO,the factors which influence the frequency stability of OEO was investigated deeply.We firstly introduced the basic situation of FBG.Then we analyzed the reflection spectrum of FBG,and the length of FBG and modulation depth of refractive index are discussed on the purpose of how they influence the reflection spectrum of FBG.Then a measurement on the refractive index of optical fiber changing with strain was proposed,and this scheme was based on FBG.The principle of the scheme was demonstrated in detail.The experiment was built according to the scheme and the results were analyzed.The experimental results show that the refractive index of the fiber decreases linearly with the increase of the longitudinal strain.The scheme shows that the refractive index is changed by the stress sensitivity of the optical fiber,which leads to the drift of the output frequency of the optoelectronic oscillator.Therefore,in addition to overcoming the influence of temperature,the influence of stress on the whole OEO system also needs to be considered.Finally,the experiment of the photonic generating of microwave based on OEO was set up,and a 2.327 GHz microwave signal was successfully generated.2.An OEO scheme based on stimulated Brillouin scattering was proposed.Firstly,the concept of SBS,the generation process of SBS,Brillouin gain spectrum and Brillouin threshold were discussed in detail.After a certain theoretical basis,the SBS-based OEO scheme is demonstrated.The principle of scheme was introduced deeply.Then the modulation mode of the DPMZM used in the scheme was described.Then,the whole OEO system is simulated by using the quadrature modulation of DPMZM.Finally,a microwave signal with a frequency of 73.59 GHz was generated and the frequency tunable range is 70.42GHz~75.55 GHz.Besides,a microwave signal with quadruple Brillouin frequency shift and a phase tunable range of 0~360 is also generated.In addition,the phase noise of the generated signal was simulated,and the theoretical simulation value of the phase noise is-111.8 dBc /Hz@10kHz.3.A scheme of the generation of microwave waveform based on OEO was proposed in detail.By adjusting the modulation index of the modulator,the phase shift of the phase shifter,the delay time of the electrical delay line,square waveform,triangular waveform,sawtooth wave and the reversed-sawtooth waveform can be successfully generated.Firstly,we analyzed the principle of the generation of microwave waveform.After that,the scheme was simulated and the 10 GHz square,triangular,sawtooth and reversedsawtooth waveforms are obtained.In addition,the influence of extinction ratio on the whole system was also discussed.The results obtained from the simulation can be known that the generated waveform will not be affected by the extinction ratio of the modulator.