Theoretical And Experimental Study On Nd³⁺-doped Gain-guided Index-crossover Guided Fiber

GG-IAG fiber is a new type of large-mode field fiber structure which proposed in recent years.Based on the fundamental principle of GG-IAG fiber,this paper presents a theoretical model of GG-ICG fiber,and the power distribution and threshold characteristics are researched through theoretical design and simulation.The temperature distribution of GG-ICG fiber is obtained and the influence of each parameter is studied.The Nd3+-doped phosphate glass of GG-ICG fiber is designed and fabricated.The refractive index distribution is adopted a series of studies.Firstly,the theoretical model of GG-ICG fiber is established,and the rate equations of Nd3+ GG-ICG fiber laser under end-pumped conditions are obtained.The power distribution in fiber is numerically solved and analysed.Secondly,the threshold formula of the fiber laser is solved by analytic method.The influence of the optical fiber parameters on the threshold characteristics of the GG-ICG fiber laser is investigated.The results show that the optimal doping concentration is N = 1 × 1020 cm-3,and the best core radius is a = 45 ?m,which make the threshold pump power the lowest.When the retro-cavity reflectivity of signal light power R2 s = 0.85,the fiber length L = 1 cm,the threshold pump power achieve a minimum of 2.95 W.The GG-ICG fiber lasers are optimized according to the above results.Thirdly,the heat transfer equations of the fiber under the three-dimensional coordinates are established.The heat conduction equation of the Nd3+GG-ICG fiber laser is obtained.The temperature characteristics of the GG-ICG fiber with the one-end and dual-end pumped method are studied.The influence of the parameters such as cladding radius and the refractive index on the thermal effect is discussed.A theoretical reference for optimizing GG-ICG fiber lasers is provided.Finally,the fiber core and cladding materials are designed and fabricated.The preparation process of the phosphate glass was discussed.The relationship between the individual components and the refractive index is researched.The fiber core and cladding glass which meet the demand of core and cladding refractive index is obtained.The performances of the glass are studied.The possibility of drawing GG-ICG fibe is discussed and the optical characteristics are studied,providing experimental basis for the subsequent production of the optical fiber.