Study On The Propagation And Transformation Properties Of Semiconductor Laser Beams

Owing to the advantage of quick, wide-angle scanning but requiring low drive voltage and small size, optical waveguide array electro-optic scanner is expected to be widely used in the fields of laser radar, laser fuse and laser guidance. Because the optical source of the scanner system is semiconductor laser currently, it is necessary to design a coupler which can couple the wide-angle beams of semiconductor laser into the scanner for the purpose of increasing the utilization efficiency of light energy and improving the working performance of scanner.In this paper, using the study of coupling technique of scanner as a point of departure, the propagation and transformation properties of semiconductor laser beams are studied. The main study contents in this paper are summed up as following:1. Based on the nonparaxial vector Rayleigh-Sommerfeld far-field diffraction integral formula, a vector expression for describing the far field of a semiconductor laser is proposed. Through the analysis of the error yielded by the scalar approximation to the properties of laser diode beams, it is found that the error is only correlative with propagation distance and the coordinate perpendicular to the junction plane and there is a certain relationship between the error and a space angle.2. By means of expanding the source distribution function into Gaussian function's polynomial, an analytical propagation expression of laser diode beams is proposed based on the nonparaxial vectorial Rayleigh-Sommerfeld diffraction integral formula. Thought comparing those two expressions, the variation of discrepancy between them with respect to spatial location and beams parameters is investigated, and some significant conclusions are obtained.3. The analytical expression of collimation field of semiconductor laser nonparaxial beams is derived by the method of stationary phase. According to the expression, it is found that the sizes of collimation beams in two directions are not correlative with transmission distance and is direct proportion to the focal length of lens. On-axis intensity is inversely proportional to the square of the focal length and is relative to the beams parameters of semiconductor laser. The phase distribution of collimation field varies with transmission distance. These results are important to engineering application.4. A novel unitary optical mode converter is proposed, which can transform Hermite-Gaussian beams with the same Rayleigh range and waist position into Laguerre-Gaussian beams. Being unitary and having only two reflecting faces, the mode converter is easily adjusted and had very small reflecting lost. In view of the Hermite-Gaussian beams with different Rayleigh range and waist position, a waist adjuster is proposed. Such Hermite-Gaussian beams can also be transformed into Laguerre-Gaussian beams combining the adjuster and the converter.5. A coupler which can couple efficiently the beams of semiconductor laser into the scanner is designed. Thought contracting the beams in the direction perpendicular to the junction and collimating that normal to the junction, the beams shape of semiconductor laser can match that of end face of scanner, which let the electrical optical effect in scanner be used fully and the light energy of semiconductor laser be utilized effectively, then the working performance of scanner can be improved. Experimental research shows that the coupler meet basically the coupling require of scanner.