| Gain-guided and index-antiguided fiber(GG-IAG)was proposed in 2003,which has potential application in high power laser.Due to the larger mode area,single mode,and easy fabrication,GG-IAG has been extensively studied by many research groups.In this work,the laser threshold performance of the GG-IAG fiber is simulated by theoretical analysis based on its operating principle.Two new kinds of fibers of ‘gain-guided and index crossover-guided' and ‘index-guided and index alternative-guided' are proposed,and the corresponding theoretical models are established and some useful results are obtained.Nd-doped phosphate glass gain-guided and index-(anti)guided fibers are fabricated and its laser performance is demonstrated.Firstly,the traditional theory of the fiber laser rate equations is improved and applied in the GG-IAG LMA fiber,then the threshold characteristics of Nd-doped phosphate GG-IAG fiber laser are obtained through the analytical method under the conditions of one-end pumped and sideuniform-pumped schemes.The relationship between the threshold characteristics and fiber parameters are obtained and used as an optimization scheme to decrease the laser threshold.Secondly,aiming at the problem of low efficiency of GG-IAG fiber under end pumped scheme,an improved gain-guided and index-crossover guided fiber structure model is established.The threshold characteristics of gain-guided and index-crossover guided fiber laser under bi-directional pumped condition are derived by means of analytical method for the first time.The results show that the threshold value of the gain-guided and index-crossover guided fiber laser is lower than that of the GG-IAG fiber,so the output characteristics of the fiber laser are improved.Thirdly,a new structure of gain-guided and index-alternate guided large mode area fiber structure is proposed for the first time in this paper,and the corresponding theoretical model is established with boundary conditions.Through the design of the optical fiber parameters,the fiber can be operated with large mode area and single mode characteristics.The pump light and signal light propagation characteristics and output laser characteristics are researched under the conditions of forward-pumped,backward-pumped and bi-directional pumped schemes.The results show that the laser threshold is greatly reduced,and laser output efficiency is greatly improved,so it can be used to solve the low efficiency of GG-IAG fiber.3-dimensional temperature distribution function is also constructed,and the distribution characteristics of 3-D temperature field of the fiber in steady state are analysed systematically.The results provide a solution for the heat dissipation of the fiber laser.Finally,the fiber core and cladding materials are designed and fabricated.The influence of the doping concentration on the spectral properties of the laser glass is studied.By means of J-O theory and McCumber theory,the spectral parameters were calculated and characterized,and the core glass material with excellent spectral performance was obtained.By adjusting the formulation of the glass,the higher and lower refractive index materials are both designed as the claddings of the fiber,then the optical properties,temperature performance and mechanical properties of the the fiber core and cladding material are in accordance effectively.The gain-guided and index(anti)guided large mode area fiber performs are prepared by the method of rod in tube,and the fibers are successfully drawed with the diameter from 230?m to 790?m.Unfortunately,due to the high loss of the fiber,Fresnel reflection loss of optical fiber end and diffraction loss in the cavity,the laser threshold is high,in addition,the efficiency of pump is low,the laser signal is not obtained.But fortunately,the laser signal amplification is obtained.The signal amplification efficiency of the gain-guided and index(anti)guided fiber reaches are 10.2% / cm(9.67% / cm),respectively,when the average pump power is 0.65 mW with pulse work mode. |
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