Theory Research On Gain Characteristics Of Tm³⁺-doped Chalcogenide Glass Photonic Crystal Fibers

Rare-earth doped fiber lasers and amplifiers have broad application prospects in spaceexploration, infrared remote sensing, military and civilian fields. Howerer, quartz basedconventional single mode fibers are mostly used which limit their applications in mid and far-infrared filed. Moreover, the traditional optical fiber cores are very thin, easily to bring nonlinearand thermal side-effects in high power operation situations, which may cause fiber end-facedamage and even burn out the fiber. So it is not conducive to the generation and transmission ofhigh-quality laser beam.In this thesis, in order to improve the performance of fiber lasers and amplifiers from hostmaterial and fiber structure, the gain characteristics of Tm3+-doped chalcogenide PCF amplifierswere theoretically studied on the basis of previous researches. The GeS2-Ga2S3-CsI glass systemis chosen as host material. A series of work such as sample preparation, spectroscopy testing,optical parameters calculation, performance of amplifier model, structure design of photoniccrystal fiber and numerical simulation were accomplished, which provided related theoretical basisfor the design and implementation of chalcogenide glass-based high power PCF lasers andamplifiers operating on near and middle infrared bands.In Chapter One, the application and generation of mid-infrared light sources were brieflyintroduced. This part mainly focused on the development of mid-infrared emission in rare-earthions especially Tm3+ion doped chalcogenide glasses. Then the basic theory and developmentprocess of chalcogenide photonic crystal fibers were concluded and research status of rare-earthions doped chalcogenide PCF amplifiers were analyzed. Finally, the content, purpose andsignificance of this thesis were presented.In Chapter Two, basic theoretical knowledge used in this paper was outlined from threeaspects. First, calculation of spectrum parameter in rare-doped chalcogenide glasses was presented,including Judd-Ofelt theory, McCumber theory and Futchbauer-Ladenurg theory. Second, thetheoretical basis of fiber amplifier was introduced, such as the principle of amplifier, four energylevel system, the energy transfer process and simulation method. Third, the theoretical analysismethods for photonic crystal fiber were mentioned. In Chapter Three, the preparation process of glass sample and measurement methods ofsample properties were introduced such as thermal stability, absorption spectrum, emissionspectrum and so on.In Chapter Four, the gain characteristics around3.73μm of Tm3+-doped GeS2-Ga2S3-CsIchalcogenide conventional single-mode fiber were studied. The optical parameters were calculatedand four-level fiber amplifier modeling was analyzed on the basis of a comprehensive variety ofenergy level transition. Then broadband amplification characteristics under different pump powerswere discussed. Simulation results showed that the Tm3+-doped chalcohalide glass fiber exhibited ahigher signal gain and broad mid-infrared gain spectrum. Meanwhile, there existed the mostsuitable pump power and fiber length while the amplifier had the maximum signal gain.In Chapter Five, structure parameters and mode field distribution of the photonic crystal fiberwere studied and the gain properties of PCF amplifier were demonstrated compared with theconventional single-mode fiber under the same parameters. Then the effect of the signal gain withdifferent pump power, signal power and fiber length were analyzed. The results exhibited amaximum signal gain close to33dB and a spectral width wider than200nm. So the PCF amplifierpresented in this work was suitable for Mid-IR multi-band amplification applications.In Chapter Six, the amplification characteristics of Tm3+-doped GGSI photonic crystal fiberoperating on the1.8μm band were studied. The absorption and emission cross sections werecalculated around1.8μm and the output signal gain was discussed by employing the rate-propagation equations. Simulation results showed that the maximum gain reached39dB andoptimal fiber length was about0.6m.In the end, all the results of the present work were outlined, and some shortages which shouldbe improved in the future were pointed out.