Enhancement Of Brillouin Scattering Signal Using Flat-top Broaden-spectrum Injection Seeding

Brillouin scattering has been widely used in many research fields such as fiber laser, distributed fiber sensing, optical fiber gyroscope, optics storage and slow light generation. More and more attentions have been paid to the methods of generation and enhancement of Brillouin scattering signal(BSS). The pulse-pump and pump-probe technique based on stimulated Brillouin scattering(SBS) have been used to enhance the BSS. However, the experimental arrangements of these methods are usually more complicated and higher cost. Some other available methods have been put forward, such as heterodyne-detection method, pump-probe multiplexing, balance detection, pulse coding and improving the special optical fiber coupling method. However, these methods cannot largely improve the signal to noise ratio(SNR) of the Brillouin gain spectrum(BGS). To solve the problems above, we propose the BSS enhancement method using flat-top broaden-spectrum injection seeding. And the theoretical analysis and experimental verification of the enhancement character have been given in this thesis.At first, based on Brillouin scattering principle and signal enhancement theoretical model, the flat-top broaden spectra injection seeding with different bandwidths are simulated to select the seed light bandwidth using commercial available mathematical software, i.e., Fortran. We obtain the simulation results of seed light with different powers, which turn out to be effective to enhance the BSS. Combined with the distributed feedback(DFB) laser direct-modulation theory and the formula of frequency shift, the output seeding of DFB laser with periodic triangle signal modulation are analyzed theoretically by utilizing Matlab simulation. The results show the dependence of the quality of output spectrum and bandwidth on the frequency, duty and amplitude of modulation signal.And then, an experimental setup of generating seeding light by DFB laser with modulation signal is built with a frequency of 2.8MHz, the duty of 38% and the amplitude of 28 mVpp. The BSS enhancement using flat-top broaden-spectrum injection seeding by amplifier spontaneous emission(ASE) source and DFB laser are investigated experimentally, respectively. The experiment results show that the seeding light with bandwidth of ~2.58 GHz produced by ASE and band-pass filter can effectively enhance the BSS and that the BGS-SNR increases by ~15dB. A seeding light with a bandwidth of ~300MHz can be generated with DFB laser internal-modulation, the BGS-SNR is increased by ~11.46 dB under the beat polarization matching detection, and ~24dB under the beat polarization mismatching detection.