Research On The Key Technologies Of Brillouin Spectrum Manipulating In Frequency And Space Domain

Since the discovery of stimulated Brillouin scattering(SBS)phenomenon,the basic scientific researches and commercial applications around the SBS effect have attracted much attentions and became an important branch and research hotspot in nonlinear optics.SBS has successfully applied in various research fields and achieved a series of remarkable results.For instance,phase conjugate mirror,gyroscope,distributed fiber sensors,adjustable slow light,microwave photonic filter,all-optical dynamic grating,laser amplification,nonlinear optics microscopic imaging,and highdimensional orbital angular momentum(OAM)photon-phonon conversion and so on.However,the measuring speed of weak Brillouin spectroscopy signals in the background of strong noise is an important factor limiting the development of applications based on the SBS.Therefore,this thesis takes the fast measurement of Brillouin scattering spectrum signal and the controllable separation of signal and noise of high gain amplification as the entry point.Aiming at the needs of different researches and applications,two new methods of frequency domain staring pumpprobe technique for Brillouin spectroscopy fast measurement are put forward.For the problem of OAM spatial mode division filtering technology which is used for the separation of signal and noise in Brillouin spectroscopy.A flat gain technology over arbitrary OAM spitial modes is proposed.A signal-to-noise controllable separation technique for targeted light field manipulation and amplification in space domain is proposed.In addition,for the mentioned above,theoretical analysis and experimental verifications are carried out.First,based on the SBS coupled-wave equations,the theoretical model of frequency domain staring pump-probe Brillouin spectrum technology is established.The theoretical model of stimulated Brillouin amplification(SBA)involving OAM spatial mode is established.The accurate mathematical description of the OAM mode beams generation and propagation evolution is derived.Researches show,in OAM spatial mode division filtering technology,the gain decreasing with the orders is ascribed to a poor overlap of interaction modes.Based on the the theoretical model of frequency domain staring pump-probe Brillouin spectrum technology,the feasibility of this technology to achieve fast measurement of Brillouin spectrum has been proved by theoretical analysis.This scheme has a high SNR characteristic based on SBA principle without time-consuming sweeping and measuring power spectrum.For multi-phonon modes media,an adaptive phase matching probe-injection technique for Brillouin gain spectrum(BGS)fast measurement is proposed.Based on the low polarization seeding light unit consists of an amplified spontaneous emission source and fiber bandwidth band-pass filter,the rules of energy transfer efficiency and dual-BGSs as the media properties changing are investigated.The main stage BGS maximum gain is approximate 15 dB.A scanningfree measurement of mutil-BGSs is presented and demonstrated experimentally.Taking two-dimension Brillouin microscopy as the research background,the technology of Brillouin spectroscopy chirp modulation probing is proposed.The distributed feedback laser is directly modulated by periodic triangular wave electrical signals,and the flat top with bandwidth controllable output light is used as Stokes and anti-Stokes seeding light to realize BGS and Brillouin loss spectrum(BLS)scanningfree measurements,respectively.Researches show,in the heterodyne detection,the polarization filtering methods can increase the BGS-SNR by approximate 21 dB and obtain the BLS with a SNR of approximate 23 dB.A scanning-free measurement of BGS and BLS is realized experimentally.Combined the theoretical model of SBA process involving OAM spatial mode,for the gain limitation of OAM mode division filtering with high order modes in SBA process,a flat gain technology over arbitrary OAM spitial modes is proposed.By imaging the order independent wave sources of propagation of OAM modes in nonlinear medium,the dependence of the poor overlap on the order is eliminated,thereby the amplification gain of the high order OAM signal beams can be improved.Under the experimental system conditions,for Stokes beam with OAM mode of ?=10,the energy transfer efficiency of large signal can be increased by approximate 12.4%,and the gain of small signal can be increased by approximate 27.5dB.Furthermore,this technique provides a practicable way to relatively uniform and selective amplification of OAM modes including high dimensional superposition of multiple OAM modes and realizes OAM mode filters in mode-division multiplexing system,and can also be applied in other optical amplifications or nonlinear interactions involving OAM mode overlap.Finally,aiming at the shortcomings of the existing Brillouin spectroscopy signal-tonoise separation method,a signal-to-noise controllable separation technique for targeted light field manipulation and amplification is proposed.For the first time,the Hilbert transform for spatial spectrum operation is introduced into the third-order nonlinearity.In the field of optics,the research work on the Brillouin spectral signalto-noise separation technology is first carried out in the spatial frequency domain.The basic principle of targeted light field manipulation is analyzed theoretically and experimentally.The noise source and solution are discussed.The experimental results show that the technique can realize the controllable separation of signal and noise in Brillouin spectroscopy.