Characteristics Of Stimulated Brillouin Scattering And Amplification In Liquid-core Optical Fibers

Stimulated Brillouin scattering (SBS) has great application value in some areas such as optical phase conjugate, narrow-band filtering, laser combining, distributed fiber sensing, optical storage, and so on. SBS usually takes place in liquid media or fibers. However, conventional focusing geometry easily cause optical breakdown, which results in low SBS reflectivity and stability. The SBS pulses and transmitted pulses of single-mode or multimode quartz fibers display serious modulations, which lead to bad fidelity. To overcome above problems, this dissertation presents a scheme of producing the SBS with high reflectivity, high pulse-shape (PS) and phase-conjugation (PC) fidelities using liquid-core optical fiber (LOCF) filled with CS2, and a new design to generate and amplify hollow beam simultaneously using LCOF. The characteristics of SBS and amplification in LCOF contained CS2are theoretically and experimentally investigated.Firstly, based on the theoretical model of transient SBS, we numerically simulate the dependences of the SBS reflectivity of LCOFs with different lengths and core diameters as well as the SBS pulse shape on pump energy. Secondly, the experimental system of SBS in LOCFs is set up. A frequency-doubled Nd:YAG pulse laser with a pulse duration of10ns is used, and CS2is chosen as core-liquid medium. Experimental verifications are performed. Moreover, the dependences of SBS PC fidelity and SBS depolarization factor on pump energy are experimentally investigated. Research results show that the SBS energy reflectivity of over90%is obtained in LCOFs. The SBS waveforms are all single peaks, and no pulse modulations are observed, and as a result, high PS fidelity is achieved. The transmitted pump pulse without a surplus peak has a good flat top, and hence clearly optical limiting. High PS and PC fidelities of over90%as well as SBS depolarization of3%are obtained. The bending of the LCOF has little influence on the SBS energy reflectivity. Finally, Brillioun amplification in LCOF is experimentally investigated. According to the characteristics of noise in LCOF amplifier, we design a non-collinear Brillioun amplification system to generate and amplify hollow beam simultaneously. The spatial distributions of amplified signal beam and noise are studied experimentally, and the performance parameters of amplifier such as signal amplification factor (SAF) and signal-to-noise ratio (SNR) are measured. A SAF of106and SNR of about102are obtained.