Analysis And Experimental Research Of Partially Coherent Beam Based On Phase Modulation

The atmospheric effect on coherent beam makes it degenerate to partially coherent beam in the transmission process. At the same time, the transmission characteristics of partially coherent light can effectively suppress the intensity turbulence and phase fluctuation effect, which are produced by turbulence. The new system composite imaging radar, which is one of the recent radar research hotspots, uses the partially coherent laser coherent optical properties as the emitting source. Therefore, the study on a method of producing partially coherent beam is essential. Using the dynamic speckle that is formed by laser irradiated to the rotating frosted glass as partially coherent source, is the most commonly used methods, which has the high feasibility and low system cost, but the frosted glass will greatly reduce the output power of the laser power modulation; The system based on laser inside-resonator modulate to generates partially coherent beam is more complex, and has a higher cost; The partially coherent light scheme based on liquid crystal spatial light modulator is limited by the output power, modulation rate and other factors. So the research on producing high power output, controllable and can be quickly preset coherence of light field of partially coherent beam generating system, has an important academic significance and application value.The theory of array beam synthesis and the theory of partially coherent beam are introduced firstly. Then the paper verifies the method that optical fiber array generates partially coherent light through experiment. Based on the interference principle of the light waves, the coherent theory of light is elicited. Then the author states the temporal coherence of, spatial coherence as well as partial coherence of light sequentially. The paper introduces the mathematical model of partially coherent light and describes the coherence of its light filed from the perspective of correlation which briefly describes the high-order correlation theory of the light field, and proposes the correlation function of light intensity to build theory foundation to test coherent length of coherent light. According to the beam combing theory, the author studies the light field distribution model and numerical simulation of different model, different spacing, different additional random phases under jitter variance, which offers theory basis on improving the experimental system and experimental test.By using the lithium niobate phase modulator, the planar waveguide(PLC) fiber optic splitter and the fiber array substate(FA) in the laboratory, the partially coherent beam plan designed in lab is improved. The phase modulator driving circuit which is developed on FPGA by the lab can provide the maximum of 10 MHz, ±5V analog voltage output for the phase modulator. Fiber array is used to generate partially coherent beam system. And through the system, an experiment on partially coherent synthesis of light intensity distribution and spatial coherence is tested. It means that through the driving system, the author loads uniform random voltage of different ranges and from the receiving screen which is 1m away from the light source, the intensity correlation coefficient can be controlled at the range of 1-1.48. That compared the experimental results test to the theoretical simulation, the feasibility of the program checks.