- 學位論文
繞射光學元件設計應用於雷射照明系統
Design of Diffractive Optical Elements for Laser Lighting System
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摘要
雷射二極體光源於顯示與照明系統的應用擁有廣色域、高輸出功率密度，並且於高輸入功率密度時有高轉換效率與低能量損耗等優點。雷射激發遠程螢光 (laser activated remote phosphor, LARP) 為有效提供高亮度的雷射照明系統機制，以雷射光束激發螢光材料，並藉由調變螢光材料基板、厚度、濃度、鍍膜等方式達到特定應用領域的光色、輻射功率、發光效率、使用壽命等需求。 由於雷射光束於激發螢光時光點上的高溫容易促使螢光片材料毀損，因此雷射光束集中造成熱光點的現象為影響光學系統表現的關鍵議題。本研究提出一避免雷射激發螢光片時之光場分佈過於集中之方法，以演算法設計繞射光學元件 (diffractive optical element, DOE) ，使雷射光束通過該元件結構後產生繞射，而在螢光片入射面達到欲設計的光場分佈。在雷射激發遠程螢光系統中加入繞射式勻化片後，可使螢光材料於光束功率為2.5瓦特之雷射照射2分鐘後，正向接收面之照度衰減由53.8%降低為16.4%。然而由於繞射光學元件之製程誤差會使得光束之部分能量在通過元件結構後無法受到理想調變，而在後焦面與光軸交點處產生一強度較高之光點，稱為零階效應。本研究亦提出一針對零階效應優化之演算法，在結構深度誤差率為0.1時，可使繞射光場之零階效應降低24.7%，使繞射光學元件結構擁有高製程容忍度，降低零階效應產生光點集中的現象。 在不同光學機構下，螢光片隨著基板厚度與螢光材料濃度配比的不同，其受雷射激發之色彩、光轉換效率、溫度變化與系統照射時間的關係亦有所不同。可藉由選用適當的螢光材料配合繞射光學元件與光學系統的設計，達到雷射照明對於光學特性、系統壽命及穩定性的需求。
並列摘要
There are many advantages in employing laser diode as the light source for display and lighting optical systems, such as having wide color gamut, high output power density, high conversion efficiency at high input power density, and so on. Laser activated remote phosphor (LARP) is an effective approach of laser lighting system for producing a high intensity light source capable of satisfying the following requirements on properties such as color, illumination power, efficiency, and lifetime, by adjusting the phosphor material concentration, thickness, or the film coated on the phosphor plate for certain applications. However, one particular issue to note is the issue of hot spots, which is critical for the performance of laser phosphor lighting systems, caused by the high energy concentration of laser beam focusing, which will easily damage the phosphor plate. In this study, we present a novel algorithm to design a diffractive optical element (DOE), which diffracts the laser beam to shape it into a desired intensity distribution, when illuminating the phosphor plate. After employing a diffractive diffuser for laser beam shaping, the illuminance attenuation of LARP with laser optical power of 2.5 watts is reduced from 53.8% to 16.4% for 2 minutes illumination. However, due to the fabricating error, a part of the laser beam will not be modulated exactly according to the ideal calculated state by the resulting DOE, and it creates a strong spot at the point of intersection of the back focal plane and the optical axis, resulting in what is called the zero-order effect. This proposed algorithm in the study also place a strong focus in the suppressing of the zero-order effect, which can be suppressed by 24.7% with depth error rate of 0.1 after employing the algorithm. It makes the designed DOE structures to possess a better acceptable tolerance during fabrication, and increase the suppression of the zero-order diffraction. With varying thicknesses and phosphor material concentrations, the phosphor plate exhibits different emission spectra, conversion efficiencies, and device temperatures while being illuminated by the same laser beam. By using an appropriate combination of suitable phosphor materials, DOE and optical system designs, a desired property of the laser lighting system can be achieved.
參考文獻
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