| Summary: | 碩士 === 國立中央大學 === 光電科學研究所碩士在職專班 === 95 === The low efficiency of traditional pickup head is limited by the difference of vertical divergent angle and horizontal divergent angle. The vertical divergent angle is much larger than the horizontal one. To get the circular laser beam, the collimating lens is designed with the divergent angle which intensity is in the horizontal direction. Therefore there is a lot of energy wasted. This thesis uses the cylindrical afocal system and the prismatic system to expand the beam separately in the horizontal direction. The expander makes the beam size which intensity is in the horizontal direction as large as the beam size which intensity is in the vertical direction. Then the highly efficient collimating lens is designed with the divergent angle in the vertical direction.
First, this thesis designs traditional Blu-ray Disc pickup head. It covers the design of its objective lens, the design of its collimating lens, tolerance analysis and the focusing error signal, and then simulates the total efficiency. This thesis introduces the concept of beam expanded in the horizontal direction to improve the total efficiency. This thesis designs the cylindrical expander and prismatic expander. It also covers the design of the collimating lens, tolerance analysis and the focusing error signal, and then simulates the total efficiency. At last summarize all of the new designs which are proposed by the thesis.
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