||Design and Simulation of Freeform Lens for Engineering Applications of Ultra-Violet Light Emitting Diodes (UV-LED’s)
||Department of Mechanical Engineering
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.
Table of Contents IV
List of Tables VII
List of Figures VIII
Chapter 1 Introduction 1
1.1 Background 1
1.2 Problem statement 2
1.2.1 A collimating lens for high power UV-LED and for fly’s eye homogenizer. 3
1.2.1 A collimating lens for Planner UV-LED UV-exposure system for Lithography 4
1.3 Literature review on freeform collimating lens 6
1.3.1 Collimation using freeform collimator TIR lens. 6
1.3.2 LED collimating element based on freeform and parabolic TIR surface. 7
1.3.3 Collimating lens using parabolic TIR and freeform surface. 9
1.3.4 Collimating lens using freeform and ellipsoidal TIR surface. 10
1.4 Research motivation and objectives 12
Chapter 2 Methodology 15
2-1 Freeform Lens Design for Collimating UV Light form a LED 15
2.1.1 Construction of ellipsoidal TIR Surface. 15
2.1.2 Construction of first freeform surface CD 21
2.1.3 Construction of second freeform surface 26
2.1.4 Construction of third freeform surface 29
2.1.5 Construction of Spherical refractive surface 33
Chapter 3 Design and Simulation 35
3.1. Fly’s eyes Homogenizer 35
3.1.1 Construction of freeform collimator lens for fly’s eyes homogenizer 37
3.1.2 Ray tracing Simulation and Results. 43
3.2 Planner UV-LED UV-exposure system for Lithography. 51
3.2.1 Photolithography process 51
3.3 Construction of double convex lens. 53
3.3.1 Design of double convex lens. 53
3.3.2 Ray tracing Simulation and results using 60° LG (3535) series UV-LED. 55
3.3.3 Simulation using 120° (CUN66A1B) UV-LED 60
3.4 Construction of freeform collimating lens for Planner UV light UV-exposure system for Lithography. 66
3.4.1 Design of freeform collimator lens. 66
3.4.2 Ray tracing Simulation and Results. 69
Chapter 4 Experiment and Measurement 74
4.1 Experimental Setup 75
4.1.1 Intensity measurement 76
4.1.2 Collimation half angle measurement 78
4.2 Measurement Results 79
4.2.1 Measurement using 60° LG (3535) series UV-LED. 79
4.2.2 Measurement using CUN66A1B 120° UV-LED. 82
4.3 Compression of simulation data with measured data. 85
Chapter 5 Conclusion 89
5.1 Summary 89
5.2 Future work 90
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17. Zemax fly’s eye homogenizer. http://www.zemax.com/os/resources/learn/knowledgebase/flys-eye-arrays-for-uniform-illumination-in-digita.
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19. Data sheet for the UV-LED used for the LG 60° 3535 series 365 nm UV-LED. https://www.lasercomponents.com/de/?embedded=1&file=fileadmin/user_upload/home/Datasheets/lg/lg_uv_led_overview.pdf&no_cache=1.
20. Data sheet for the UV-LED used for the printed circuit board exposure system CUN66A1B.http://www.neumueller.com/datenblatt/seoulviosys/CUN66A1B_R10.pdf.
21. Data sheet for the UV-LED used for fly’s eye homogenizer application. http://www.luminus.com/products/Luminus_CBT90UV_Datasheet.pdf
22. Data sheet for power meter used to measure the light intensity and collimation angle. http://www.ophiropt.com/laser--measurement/sites/default/files/IS-1_3A-IS_3A-IS-IRG_1.pdf.
23. Pinhole mounted on the power meter.www.edmundoptics.com/optomechanics/irises-apertures/pinholes-slits/100mum-aperture-diameter-mounted-precision-pinhole/.
24. Power meter reader used to measure the light intensity and collimation angle. . http://www.ophiropt.com/laser--measurement/laser-power-energy-meters/products/smart-displays/nova2?r=drp
25. Sigma Koki stage. http://www.global-optosigma.com/en_jp/Catalogs/gno/? from=page&pnoname=SGSP20%28XY%29&ccode=W9012&dcode=&gnoname=SGSP20-85%28XY%29.
26. UV- LED application. http://www.ledsmagazine.com/articles/print/volume-12/issue-11/features/strategically-speaking/emerging-applications-for-uv-leds-drive-broad-interest.html.