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Experimental and Theoretical Study on Improvement of the Beam Quality of High Power Diode Laser Array

Author: DingPeng
Tutor: ZuoTieZuo；WangZhiYong
School: Beijing University of Technology
Course: Optical Engineering
Keywords: Semiconductor laser array Coherent coupling Fiber external cavity Volume holographic grating Polarization Coupling
CLC: TN248
Type: PhD thesis
Year: 2009
Downloads: 494
Quote: 4
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Abstract

To promote the direct application of high-power semiconductor lasers in material processing, for the main object of study in order to improve the high-power semiconductor laser array beam quality for high-power semiconductor laser array of light-emitting unit number between direct optical contact array overall poor beam quality, the use of fiber coherent coupling external cavity volume holographic grating external cavity laser beam polarization coupling of these three methods to improve the beam quality of the semiconductor laser array. Theoretical and experimental analysis of the various methods, and discuss its feasibility in practical applications. The high-power semiconductor laser array of light-emitting unit is optically isolated, coherent coupling and incoherent coupling are two ways to improve the beam quality. Lock-in technique of the outer chamber, through the external mirror or grating added to outside of the semiconductor laser has a certain reflectance, the phase-conjugate mirror, etc. to form the outer chamber, the use of optical radiation outside the diffraction effect in the cavity propagation effect of phase-locked . Optical radiation feedback from the external cavity mirror reflected back into the active region of the semiconductor laser, due to diffraction is fed back to the other units in order to achieve a mutual coupling between the array light emitting unit. Existing external cavity phase-locked coherent coupling technology can only ensure the coupling between adjacent light-emitting unit, and can not form a strong coupling between the light-emitting unit. In this paper, the introduction of fiber optic shaper external cavity phase-locked semiconductor laser array, fiber-coupled semiconductor laser external cavity lock. In the external cavity of the semiconductor laser array, the use of the flexibility of the optical fiber bundle, low loss characteristics, so that the light emitting unit was a two-dimensional arrangement. Thus, an increase in number of adjacent cells to participate in the phase-locked in the external cavity, and because the end face of the optical fiber bundling do not have to consider the heat problem, the optical fiber can be closely arranged to increase the fill factor of the light-emitting unit, favor the formation of the coupled in parallel, to improve the degree of coherent outer chamber . The method of the external cavity of the optical fiber coupler of the semiconductor laser array between the light emitting unit of the PLL output, the phase-locked the forefront array spectral width of 2.6nm, PLL after spectral width of 0.23nm, to improve the array the overall coherence of the output beam light intensity can be improved. Fiber-coupled external cavity array as a whole is running at a unified supermodel. This paper to determine the coupling coefficient matrix analysis the array order Supermodel of modal gain, the distribution of near-field and far-field distribution. Analysis of the optical fiber outer chamber forward and reverse power transmission case, the coupling efficiency are obtained. According to the cause of the loss of the main power improvement program. The outer chamber of the volume holographic grating does not change the arrangement of the array of light emitting unit, the coupling between the light emitting unit is weak, but the structure is simple, the energy loss is small. Meanwhile, the outer chamber has a good wavelength stability. In this paper, the volume holographic grating external cavity to improve the spectral characteristics of the semiconductor laser array and its theoretical analysis and software simulation to determine the optimal length of the external cavity. The spectral linewidth of the experiment will be narrowed to about 0.22nm 0.01nm / ° C., a wavelength shift with temperature is reduced to. Coherent coupling through external cavity feedback light field between the unit are coupled to each other, in order to reduce the external optical feedback self-coupling coefficient, the experiment with a plano-concave cylindrical lens as a mirror of the external cavity, the cavity length is set to half-a total of coke chamber, and theoretical analysis, through the outer chamber experiments, array spectral width narrowed from 2.5nm to 0.5nm, to some extent, improve the coherence properties of a semiconductor laser array. On this basis, the volume holographic grating and a plano-concave cylindrical lens constitute a double of the outer chamber, and the output of the dual wavelength is obtained in the experiments, the linewidth reached 0.2nm, varies with temperature, the wavelength interval is always stable at 1.8nm. Polarization couplers are non-coherent coupling, and the coherence properties of the semiconductor laser array can not be changed, but can increase the brightness of the output laser beam. With wavelength coupling space coupled with the use of the brightness of the laser beam can be improved greatly. Article, the use of two semiconductor laser stack, using polarization coupling method, developed a direct application of high-power semiconductor lasers, the maximum output power of 1kW. In the operating current is 130A, the electro-optical conversion efficiency of about 43%. Use UFF100 laser beam quality diagnostic measurements, focal spot rectangular distribution of the focal spot area of ??0.55 × 5.0mm2, stable and fast axis optical parametric plot Kf = 26.1mm · mrad, the laser system. With the rail surface hardening, aluminum alloy welding test. Improve the beam quality of high-power semiconductor laser arrays has important practical significance. High beam quality can be generated high focusing power density, meet the deep penetration welding, the need to require high power density applications. Herein, the output laser beam light intensity and brightness by increasing the semiconductor laser array to thereby obtain a higher power density. Array of output spectrum narrowed, more application-pumped solid-state lasers require narrow linewidth occasions. The same time, the external cavity coupled parallel coupled mode theory analysis of the array or planar array has a guiding role.

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