Theoretical and Experimental Study on the Key Techniques of Main Amplifier in High Power Master-Oscillator Power-Amplifier Fiber Laser Source
|School||National University of Defense Science and Technology|
|Keywords||High power fiber laser systems Master oscillator to enlarge Main amplifier Large mode area fiber Multimode fiber Mode control Double-clad fiber amplifier|
Compared with the traditional linear cavity fiber laser, high-power master oscillator power amplifier (MOPA) fiber laser technology has a simple structure, flexible design advantages can further improve the output characteristics of the fiber laser systems have higher academic value. In recent years, research has focused on how to suppress the nonlinear effect in the system of the main amplifier stage, thereby further improving the output power, and the design characteristics of the gain medium optical fiber having a larger mode field area and a higher order mode suppression. The papers around the high power MOPA fiber laser systems main amplifier stage several key technologies to expand the experimental and theoretical studies, aimed at exploring the design, build and optimization methods. The main contents include: starting from the the classic fiber amplifiers physical model and the steady-state rate equation, through the analysis of the signal laser along the fiber amplifier, power amplifier mode signal and pump laser transfer equation; introduction of power to fill factor, fiber cross-sectional mode field distribution function and the mode coupling coefficients of the physical mechanism of the core mode competition analyzes the space characteristics of the excitation of the laser beam on the fiber end face, and gives the optical output beam quality and mode characteristics of the exit end relations, the establishment of a cladding-pumped large mode area fiber amplifier theoretical model. Cladding pump according to the established large mode area fiber amplifier theoretical model, in the case of taking into account the mode between the gain, loss, and mutually coupled, the theoretical simulation of the output characteristics of the optical fiber amplifier of the multi-mode operation, and studied different face excitation conditions, the impact of the structural parameters of the fiber length, pump configuration, pump power and coupling coefficient of the output laser characteristics. The results show that: the multimode operation of the fiber amplifier, the mode between competitive, resulting in the decline in the quality of the output laser beam; reduced coupling coefficient and reduce the fiber length, and optimization of the end surface excitation conditions can effectively improve the quality of the output beam. Thus, the use of large core diameter multimode core ideas of double-clad fiber build the main amplifier through its mode control, suppress high-order mode, you can improve the quality characteristics of the output laser beam. 3. Analysis of the demand for high power MOPA fiber laser systems main amplifier stage fiber gain medium, large mode area gain fiber structure parameters on the performance of optical fiber. From the fiber mode field theory and the establishment of large mode area fiber amplifier theoretical model given arbitrary refractive index distribution and dopant distribution of the gain medium, the optical fiber effective mode area, and the method of calculation of the higher order mode suppression characteristics, and analysis of the bending of the introduction of mode field distortion of the gain medium, the influence of the fiber characteristics, the design of the optical fiber of the complex refractive index than other refractive index distribution fiber to exhibit strong anti-bending characteristics, and has a large mode area, the core diameter of several tens of microns large mode area fiber, more practical, the rare earth ions in the fiber is concentrated to the center of the core, the higher order mode can be suppressed, thereby improving the system output beam quality. Thus, the mode field area 1000μm gain medium fiber optimized design. Numerical Simulation of large mode area fiber amplifier analysis of system structure parameters of the amplifier output characteristics, and end-pumped doped Yb 3 sup> important part of the double-clad fiber amplifier and key technologies. Rejection problem for the ASE and the phenomenon of self-excited amplifier system, and its optical characteristics of double-clad fiber end face polishing theoretical and experimental research, and explore the double-clad fiber end face polishing technology. Finally, the proposed high-power fiber amplifier system design, optimization and construction methods. Build a high power cladding-pumped fiber amplifier platform single-frequency, continuous wave laser and ns-level pulse laser amplification experiments. 2.3W of 1083nm single frequency laser output; repetition frequency 7kHz average power of 73mW, pulse width lt; through the amplifier pulse with a 1 ns, average output power of 832mW peak power of about 120W. On this basis, the fiber amplifier system the bending mode selection method of multi-mode operation, the experimental study, design and build of the test system of the beam quality, gain by measuring the output of the laser beam quality of the fiber in different winding radius, found that the optical fiber is wound can effectively to improve amplifier output beam quality, and results have good agreement of experimental results with theoretical calculations.