Study Of Fiber Coupling For 974nm Semiconductor Laser Diode

Since the semiconductor laser has many advantages, such as long life, small size, high photoelectric conversion efficiency and high reliability, it is widely used in medical, military and materials processing, and so on. As the seed source of fiber laser, the coupling of semiconductor laser and single mode fiber can provide the high quality seeds light for optical amplifier, which need meet high demands of coupling efficiency. In this thesis, based on the mode field distribution characteristics of semiconductor laser and single mode fiber, the coupling of the two are studied in accordance with mode coupling theory, the factors affecting the coupling efficiency and the method improving coupling efficiency are found, and then coupling model is designed to research semiconductor laser and single mode fiber in theory and practice in detail. The main research results are listed as follows:1. The main factors affecting the coupling efficiency is the mismatch of mode field and phase between the semiconductor laser and single mode fiber. Based on the mode coupling theory, a new method of processing into wedge micro lens from optical fiber end face is put forward, the special wedge surface is designed to compress the fast axis of semiconductor laser and realize the mode field matching, and the cylindrical micro lens of the top of the wedge angle can effectively reduce the phase mismatch, which will improve the coupling efficiency.2. Through designing the coupling model of semiconductor laser and wedge lens fiber, a new method which can optimize multivariate parameters by genetic algorithm is put forward. Genetic algorithm is adopted to optimize micro lens parameters of wedge type fiber, the result is that the coupling efficiency achieves optimum with cylinder lens radius 3.44μm and wedge-angle 88°and coupling distance 6.13μm.3. According to the optimization data of genetic algorithm, the coupling model is established and ray traced by ZEMAX optical simulation software, the spot image of end fiber is observed, the result is that the coupling efficiency is 88.9%.4. In view of optimizing the laser welding sequence and parameters, the ANSYS workbench finite element simulation method is used to get the temperature distribution of the weldment and fiber migration after welding. The result show that fiber migration after welding achieves minimum using the sequence of first welding before two points and after welding behind two points; Using triangle curve to welding saddle frame and fiber casing, fiber migration achieves minimum,the migration is 0.818μm.5. The micro lens parameters of wedge fiber are used in the experiment and the coupling of semiconductor laser and single mode is researched, the maximum coupling efficiency is up to 81.48% after laser spot welding and the high and low temperature environment test. The experimental results are similar with the simulation results, the output coupling power can satisfy the demands of seed source power for fiber laser.