The Study Of The Coherent Spectral Analysis Based On Brillouin Scattering In Optical Fiber

With the development of photonics devices,the fine spectral response of analytical optical frequency combs in absolute distance measurement,laser wavelength calibration,and material analysis requires the resolution of the spectrometer to reach the order of fm;to identify the high-quality optical microcavity in the nanoparticle,the interaction change in the detection process requires the use of fm-level resolution spectral analysis methods;the analysis of channel aliasing in high-speed communications in optical multiplexing technology also requires the use of a high-resolution spectrometer.However,the current resolution of commonly used spectrometers is only on the order of pm,and it is impossible to analyze the fine spectral response of the fm order obtained by the abovementioned photonic devices,and more useful information contained therein cannot be effectively extracted.Aiming at the above problems,this paper proposes a coherent spectrum analysis technique based on fiber Brillouin scattering,from the construction and application of the Brillouin equivalent optical filter,the coherent process analysis of the double-beam Brillouin signal,and the wavelength in the measurement process.Carry out research on the calibration of these three aspects,and design experiments for verification.The main research contents of this paper are as follows:1.Study fiber Brillouin scattering to construct equivalent optical filters and design application methods.To make up for the defects of the coherence principle,starting from the generation mechanism of fiber Brillouin scattering,the optical power evolution model of fiber Brillouin scattering is used to construct an equivalent optical filter to obtain the Brillouin local oscillator required for subsequent coherence.And Brillouin to be inspected.The relationship between the center frequency of the equivalent optical filter and the temperature and strain is studied to provide a measurement method for the beat frequency results of the double-beam Brillouin signal.The method of adjusting the center frequency of the equivalent optical filter is designed with temperature as an independent variable,and the temperature coefficient of the Brillouin frequency shift in the time-delay fiber used in the subject is measured experimentally to precisely adjust the center frequency of the equivalent optical filter.2.Study the coherent process of the dual-beam Brillouin signal and establish a mathematical model.Aiming at the mirror image problem existing in the classical coherence principle,the time domain model of the Brillouin local oscillator and the Brillouin light to be detected is constructed through the linear function of Brillouin scattering,and the beat of the double-beam Brillouin signal is established on this basis.Frequency model.In the time domain and frequency domain,the model is numerically analyzed,and the processing method of the beat signal in the frequency domain is studied:the intensity information of the signal to be detected is extracted by band-pass filtering,and the center frequency offset error and bandwidth error are analyzed;use the principle of detection to extract the envelope of the light intensity information to be detected,and the single-peak response obtained shows that the spectral analysis method proposed in this topic does not have the problem of mirroring and that the resolution achieved by this method is theoretically equivalent to the band The bandwidth of the pass filter.3.Study the wavelength calibration method and design the overall system.In view of the low accuracy of the existing wavelength calibration methods and the inability to accurately describe the wavelength position in the measurement process,based on the research of the fiber ring resonator and the HCN gas cell,a calibration method to improve the wavelength accuracy is designed,and the corresponding calibration process is analyzed.On the basis of studying the equivalent optical filter and coherence theory,the overall design of the spectral analysis method proposed in this topic is carried out,and the working flow chart of the system is given,and the function and work engineering of each module of the system are analyzed in detail.4.Build the spectrum analysis system and perform performance testing.First,set up a wavelength calibration experiment to measure the wavelength accuracy of the spectrum analysis system designed in this article;then,build a complete system on this basis to verify the principle of the system designed in this topic,and then expand the measurement of the system’s spectral resolution and dynamic range Experiments and experiments show that the coherent spectrum analysis method based on fiber Brillouin scattering can achieve16 fm spectral resolution,40 d B dynamic range and 0.16 pm wavelength accuracy;finally,the optical frequency comb light source and a special broadband light source involved in the background of the subject are used as the light to be inspected,and a commercial spectrometer and the spectrum analysis system designed in this subject are used for detection and comparison to verify the reliability of the system.At the same time,it shows that the spectroscopic analysis system designed in this subject can meet the measurement requirements of photonics devices such as optical frequency combs and optical microcavities.