Study On ALL Fiber Acousto-Optic Tunable Filter And Tunable Dual-wavelength Fiber Laser

In the field of optical fiber communication networks and fiber sensing systems,all fiber lasers are essentially important,which have numerous advantages such as small volume,light weight,higher power,lower noise,high frequency modulation with no chirp effect,good beam quality,wide tunable wavelength range and so on.Flexibly tunable all fiber lasers are of great significance,especially in the wavelength-division multiplexing technology.In the lasers,tunable filter are the key components,which have been developed based on fiber grating,polarization controller,acousto-optic effect in fiber and so on.All-fiber acousto-optic tunable filter gains much faster response time than others with simple driving structure and high channel isolation.Moreover,compared with nonlinear frequency shift,the acousto-optic frequency shift in the structure is typical of higher stability,lower threshold and easier controlling.In this dissertation,the basic principle of all-fiber acousto-optic tunable filter(AOTF)was introduced and an In-fiber acousto-optic tunable Mach-Zehnder interferometer(MZI)was constructed.Subsequently,with its comb filter characteristic,we proposed a dual-wavelength laser configuration with suitable radio-frequency driving signal applied to the MZI.Besides,we also studied acousto-optic tunable filter structure in polarization maintaining fiber(PMF)based on coupled-mode theory to clarify its characters as acousto-optic filters.The thesis includes four chapters,whose content are presented as follows:In Chapter one,the significance and up-to-date progress of tunable filters and the fiber lasers based on it are introduced.In Chapter two,based on all-fiber acousto-optic tunable filter,we present a novel In-fiber acousto-optic tunable Mach-Zehnder interferometer with comb filter characteristic,which acts as the tunable component in dual-wavelength laser to modify the wavelength.In the experiment,the spectral spacing between the two output wavelengths could be tuned from ~0 nm to 2.65 nm,and the further analysis based on calculation showed that spectral spacing of 10 nm or more could be achieved.The center wavelength could cover the range from 1545 nm to 1582 nm,which was within the range of the spontaneous gain of erbium-doped fiber amplifier.This configuration has advantages of high efficiency,easily control and wavelength spacing tunability and so on.In Chapter three,the acousto-optic interaction in optical polarization maintaining fiber was analyzed by the mode coupling theory and the birefringence character of PMF was also presented.The coupling theory of the acousto-optic grating in fiber was similar to that of the long-period fiber grating,which led to the coupling between the core mode and cladding mode.Besides,simulation in PMF with acoustic-optic tunable filter concluded the spacing of two center beams could be up to 31.5 nm,where wavelengths were around 1537.9 nm and 1569.4 nm,respectively.The simulation was consistent with the experimental results.Finally in Chapter four,we made a brief summary of this paper and gave a prospect of the future research,and put forward solutions to the future works.