Technique Research On Wavefront Combination On Fiber Laser Array Using Optically Addressed LC-SLM

Because of the inevitable issues of high power damage, nonlinear effect, gain saturation, output power is limited on the practical unit laser system. Thereby, the technique of laser combination becomes one of the hot research interests on the area of high power laser. Based on the property of phase retardation on the device of optical addressed liquid crystal spatial light modulator(LC-SLM), an improved wave front combination method on fiber laser array is presented to demonstrate a result of coherent beam combination. It includes the method of fine phase control using blue light and the mechanism of maintaining wave front.In this thesis, based on the optically addressed LC-SLM, the physical model of fiber laser array coherent beam combination is built so as to be numerical simulated. According to the specific research project, the work of the fiber laser array coherent beam combination is shown as follows:(1)The technique solution of fiber laser array coherent beam combination is proposed based on the optically addressed LC-SLM, and the optical diffraction problems are analyzed in coherent beam combination. Then the physic model of 1064 nm infrared light fiber laser array is established, according to the technology solution.(2)The addressing mode principles of LC-SLM are analyzed, including optically addressing and electrically addressing. The solving processes of the liquid crystal director are researched based on the photoelectric properties and the theory of LC continuous elastomer. In the case of different driving voltages, the liquid crystal directors are simulated using the differential iterative method and finite element method. According to the phase modulation characteristic of optically addressed LC-SLM, the relationship is analyzed between the optical power density of 450 nm blue light and phase modulation.(3)The fiber basic parameters with the fiber laser array are studied, and the mode characteristics and the limiting condition of single-mode and multimode are analyzed. In the physic model, the cut-off condition of 1064 nm infrared light single mode transmission and the mode numbers of 450 nm blue light are researched by calculating the fiber basic parameters and simulating every mode optical field distribution. The phase modulation distribution of infrared light is gotten according to the blue light optical field distribution and the voltage divider of BSO.(4)The effecting factors of fiber laser array coherent beam combination are analyzed, including the beam numbers of fiber laser array, the infrared light power density, arrangement of fiber laser array, fiber geometry parameters. Through the numerical simulation of the physic model and the analysis of the results, a good coherent beam combination condition is given with an optimization fiber arrangement and appropriate beam numbers, infrared light power density, fiber diameter and distance of fiber core.