| Summary: | 碩士 === 國立成功大學 === 機械工程學系 === 105 === This thesis studies the design and optical performance of collimating lenses for modulating the UV lights from an ultraviolet light emitting diode (UV LED). The lens design is based on freeform surfaces and total internal reflection (TIR) surfaces for collimating the UV light which might have a relatively large diverging angle when emitting from the LED. The advantages of this kind of lens design are higher optical efficiency, lower fabrication cost, and compact lens size. A systematic approach for the lens design is developed based on geometrical optics by assuming a point source for the LED. However, since LEDs are finite area light sources in reality, the optical performance and characteristics of the obtained lens profile along with its corresponding UV LED are simulated and analyzed by a commercial ray tracing software (Zemax).
The designed lens/LED units are used for two different applications: (1) to illuminate a fly’s eyes homogenizer system and therefore project the UV light into an area with uniform intensity distribution; and (2) to collectively form an array of UV light sources for UV exposure. For the first purpose and when working with a high power (13.4 Watt) UV-LED with a 3×3 mm2 emitting area size and a divergent angle of 120°, a freeform/TIR collimating lens can achieve a high optical efficiency of 67.6 % and a collimation angle of ±4.5°. For the second applications, a conventional double convex lens with both aspheric surfaces is designed for two kinds of UV-LEDs of 60o and 120o divergent angles, and the optical efficiency is 42.62 % and 30.70 %, respectively, with and collimation angle of ±3.94° and ±2.55°, respectively. Finally, to further improve the optical performance, a freeform/TIR collimating lens is designed for a low power UV-LED with a 1.25×1.25 mm2 emitting area size and a divergent angle of 120°. The optical efficiency is 45.8 % with the collimation angle of ±2°. Experimental measurements have been carried out on the conventional double convex lens along with two UV LEDs, and the measured data are analyzed and compared with their theoretical counterparts.
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