Basic Research On Raman Effect Of Chalcogenide Glass Fiber Lasers

Raman fiber lasers(RFLs) is one of the most significant applications of stimulated Raman scattering(SRS) in optical fibers. Using fibers as their gain medium thanks to the SRS, RFLs can generate longer wavelength Stokes radiation with pump sources of different wavelength. Theoretically, the output wavelength of this kind of lasers can be extended to arbitrary wavelength with a considerable tunable range. Besides, compared to other conventional solid-state or chemical lasers, RFLs have a number of merits such as great beam quality, compact size, high conversion efficiency and favorable heat dissipation effect. Due to the output wavelength of silica-fiber-based Raman lasers are restricted to under 2μm, researchers expect to find new approaches to generate mid-infrared(MIR) RFLs operating at lager than 2μm, because MIR RFLs of this wavelength range can be widely applied in the field of national defense, medical, materials processing and optical communications. Compared with traditional silica fiber, chalcogenide glass fibers possess higher nonlinear coefficients, low phonon energy and excellent MIR transmittances, which makes them become a research hotspot.In this dissertation, theoretical simulation and experiment with respect to the Raman properties of MIR chalcogenide-fiber-based Raman lasers have been conducted and analyzed, which can be divided into the following three sections:Firstly, the classification of fiber lasers, applications of MIR lasers, characteristics, the research history and actualities of RFLs are introduced systematically. The principle of SRS, the Raman gain coefficient and the Raman threshold are also given. The elementary structure and operating principle of typical linear first-order and second order RFLs are elaborated with three essential elements of RFLs: pump source, Raman fiber and resonant cavity.Secondly, based on the theoretical model of first order and second order Raman lasers based on As-Se fiber, numerical simulations are constructed using MATLAB. For the first order one, the simulations are based on fourth order Runge-Kutta method; and for the second order one, the calculations are based on not only fourth order Runge-Kutta, but also multidimensional parallel shooting method in order to look for initial value. After obtaining the power distribution of pump light and Stokes waves in the resonant cavity, the parameters with respect to the pump light, the fiber length, the output and input coupling reflectivity of stokes waves and the loss of fiber are best-optimized and analyzed in both first order and second order Raman structures. At last, the availability of achieving mid-infrared Stokes waves using chalcogenide-fiber based Raman lasers has been proved.Finally, by choosing appropriate As-S fiber as the Raman fiber, using a 1981 nm Tm3+-doped fiber laser as the pump source, the experiment system for RFLs is set up. This experiment system setup is appropriately adjusted and the experimental results are well analyzed. Based on the numerical simulation model, the best-optimized experiment scheme is provided.