3?m Dy³⁺-doped Mid-infrared Continuous And Pulsed Fiber Laser

The 3?m mid-infrared fiber laser has important and widespread applications in remote sensing,medicine and defense.The rare-earth ion-doped fiber laser has compact structure,good beam quality,high output power and excellent heat dissipation performance,which has been favored by researchers.This thesis mainly studies the continuous Dy3+ZBLAN fiber laser and gain-switched Dy3+ZBLAN fiber laser pumped by 1100 nm lasser.The specific research work is as follows.1.Based on Dy3+ZBLAN fiber,we established the theoretical model of Dy3+ion in ZBLAN fiber.Combining the energy level rate equation and power transfer equation,the model is solved.In addition,we optimized the length of the fiber and the reflectivity of the output cavity mirror.When the fiber length is 1.05 m and the output cavity mirror reflectance is 70%,the threshold and slope efficiency of the laser are 348.1 mW and 16.9%,respectively.When the reflectivity of the output cavity mirror is 20%-85%,the output power can maintain a high level.On the basis of simulation,we built continuous Dy3+ZBLAN fiber laser pumped by 1100 nm laser and tuned the wavelength by a planar blazed grating.The wavelength tuning range is 2815.3?3012.8 nm.2.In order to obtain gain-switched Dy3+ZBLAN fiber laser based on 1100 nm square wave pulse pump,firstly we built a 1086 nm high repetition frequency square wave pulse source.The high-repetition frequency square wave pulse source is based on nonlinear polarization rotation(NPR)structure and Lyot filter.Then we get 1086 nm square wave pulse laser with repetition frequency of 1.881 MHz.The maximum output power is 15.03 mW.The pulse duration is 14.5 ns and the maximum pulse energy is 7.99 nJ.Since the output power of square wave pulse is low,which can not provide enough energy for pumping Dy3+ZBLAN fiber.So the ring cavity based on the NPR structure is used as a seed source.Then the power is amplified to 5W through a MOPA structure.The pulse duration is 14.7 ns and the pulse energy is 2.65 ?J.After which,the Dy3+ZBLAN fiber is pumped by the amplified square wave pulse to get a gain-switched fiber laser.3.We use the obtained square wave pulse of 1.881 MHz and 1086 nm as a pump source to pump the Dy3+ZBLAN fiber.A phenomenon similar to relaxation oscillation is observed in the simulation results.It indicates that gain-switched pulse can't generate under high pump repetition frequency,such as 1.881 MHz.At the same time,we establish a theoretical model.In the model,we use 1100 nm square wave pulse to pump the Dy3+ZBLAN fiber.We carry out the numerical simulations at low pump repetition frequency and high pump repetition frequency.Among the low pump repetition frequency,We get stable gain-switched pulse and study the influence of pump pulse width,peak power and repetition frequency on the gain-switched pulse,Which is similar to other gain-switched fiber lasers.But when the pump repetition frequency is above the 575 kHz,The laser system will not be able to get stable gain-switched pulse.