| Semiconductor Laser is a kind of early matured and fast developed laser. Owing to its such advantages as light weight, high efficiency, stabilization, etc., the Laser Diode (LD) has been becoming the most extensively applied laser among the energy-type-laser family. Even with the distinct superiority within application spectrum, both the six to one quality difference between the light beams in the horizontal and vertical directions and the astigmation (the Waist location is inconsistent) all together increase the LD's difficulty in application. To make the LD be more widely used, the beam quality must be evaluated correctly. And based on this, the poor quality of beam and the low watt density should be resolved by shaping method. After meeting the requirements of the receiving devices (such as optical fiber and laser crystal) in spot size, angle of divergence and even the light intensity distribution, the LD works effectively.A variety of evaluating methods for beam quality were introduced in this thesis, attached with the respective ranges of application and limitations of these methods. The result of analysis and comparison based on this made us to believe that it was an effective way to evaluate the quality of beam by the expense when beam was collimated under a certain coupling efficiency (90%). The collimation expense was visually described by the parameters, L,θ_y and As of the LD its own. And the difficulty level was then further reflected by the collimation expense.Based on the introduction of the necessity of beam shaping technology and the development condition at home and abroad, two kinds of nonspherical microlens without spherical aberration, elliptical microlens and hyperbolical microlens, were designed with the help of geometric optics method. The beam was shaped and the beam quality was improved. The main work and the feature of this thesis was listed as below.1. The development history of LD, the fundamental principles and the composition of the system were introduced. Compared with some other usual lasers such as optical fiber and gas laser, the LD was supposed to have such characteristics as light weight, high efficiency, stabilization and so on. Some main application of LD in various fields was introduced, too.2. The main character of LD's beam was introduced. And the necessity of the beam quality evaluating and the beam shaping was discussed. LD is usually a kind of laser diodes array (LDA) which is arrayed by a number of LED units (emiter) along the horizontal direction at a certain order cycle. As the special mode of operation, there exists a six to one quality difference for the laser stimulated by this LDA between the light beams in the horizontal and vertical directions. And the astigmatic (Waist location inconsistency) happens. Usually the direction perpendicular to the p-n junction is known as fast-axis direction, and the direction parallel to the p-n junction as the slow-axis orientation. It is because of the disequilibrium in these two directions that makes it difficult to apply LD. Further more, the beam with such a large quality difference in fast- and slow-direction can't be directly improved to reach a high power density output by common optic systems. The LD meets its increased application difficulty because of its inner defect, even with the superiority in application domain compared with other light source. As a result, to reach a broader application, the beam quality must be evaluated exactly. Based on the evaluation, after the poor beam quality and the low power density are resolved by beam shaping method to meet the requirement of receiving devices( such as optic fiber and laser crystal) in spot size, divergence angle, and even the distribution of light intensity, the LD could work effectively.3. Some traditional beam quality evaluation methods were introduced, such as the focal spot size, far-field divergence angle, diffraction limit multiplier p value, Strehl ratio, encircled energy and the M2 factor, etc.. On the basis of this analysis and comparison, the traditional beam quality evaluation methods all have their own obvious defects which can only be applied under their specific beam conditions. We suggested that, under the premise of certain coupling efficiency (90%), using the beam collimating expense (the product of collimation degree and numerical aperture) to evaluate the beam quality, and using the laser diode's own parameters L,θyand As to directly describe the collimation expense which reflects the Difficulty Level of beam collimation, was an effective way to evaluate the quality of beam.4. To reach a broader application of LD, we suggested that the beam shaping method must be adopted to resolve the poor beam quality and the low power density. Unfortunately, the LD was beyond the traditional optical systems for beam transformation. Firstly, as the waist location inconsistency between the fast- and slow-axis-beam of LD array, it was impossible to use the rotational symmetric spheric lens system to achieve effective transformation in both these two directions. Secondly, almost all the applications were requested the focal spot size and the numerical aperture as small as possible to maintain the highest possible power density and brightness. Namely, the optical parameter product of focal spot (or the receive components) should be very small, always between the optical parameter products of fast- and slow-axis. According to the theory that the optical parameter product of ideal lens system keeps invariable, the spot in the direction of slow-axis would not be able to meet the parameters of plot-matching requirements. If it is coupled with the receive components (for example, optic fiber) by traditional optic systems, that will cause the loss of energy. The spot parameter product in the fast-axis direction is commonly far more less than the receive components'. Although there's no energy loss, the brightness of LD is brought down. As a result, the traditional optical design theory will not be able to meet the design requirements of the LD array's beam transformation system. Thirdly, there exists a dead space for one of the LD array's cycle memories. Take the common used LD Bar for example, within a 400μm cycle, the size of the luminescence element in the slow-axis direction is 150μm, while the dead space is 250μm. To sum up, without specific beam shaping system, it is impossible to focus this kind of array type line sources (which have such serious imbalance between fast- and slow-axis) to bright spot (bright line) with limited numerical aperture.5. Based on the reports of various shaping methods at home and abroad, using the geometric optics design method, two kinds of nonspherical microlens without spherical aberration, elliptical microlens and hyperbolical microlens, were designed. The simulation results were given with the help of optics software. The result indicated that the semiconductor laser beam could be collimated effectively in the fast- and slow-axis directions by cylindrical microlens and cylindrical microlens group.The study results in this thesis have important practical significance to promote the broadly application of laser diode in engineering aspect. |
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