近年來，許多文獻中關於 LED 光強度增加改善之技術屢見不鮮，包括在LED背面鍍上反射鏡、表面粗化、覆晶結構、微結構陣列……等。在本文中，我們利用布拉格反射鏡(DBR)搭配高反射率的銀鏡與鋁鏡作為氮化鎵發光二極體的背反射鏡來提升氮化鎵藍光LED的光輸出強度。此外，布拉格反射鏡(DBR)對小角度入射的光的增強效果特別明顯。依此特點，我們可以製作出具有方向性的LED，增強光纖耦合的光量，進而應用在短距離的塑膠光纖(POF)通訊.
實驗首先從模擬DBR、Ag搭配DBR 、Al搭配DBR在藍光波段(460nm)的反射率，確認在藍光波段有高反射率，再來是將反射鏡鍍在玻璃上。經由量測6對DBR的反射率為93%，Al+2.5對DBR的反射率為95.04%，Ag+3對DBR的反射率為97.71%，最後將反射鏡實際鍍在元件的背面來分析光特性。在注入電流為50mA下，以6對DBR作為背反射鏡可增強光強度(output power)約38.7%，以Al+2.5對DBR作為背反射鏡可增強光輸出強度(output power)約36%，以Ag+3對DBR作為背反射鏡可增強光輸出強度(output power)約34.1%。發散角部分，注入電流為50mA下，REF LED 的水平與垂直發散角度分別為151.6°、144.6°，以6對DBR作為背反射鏡的水平與垂直發散角分別為123.6°、112.4°，以Al+2.5對DBR作為背反射鏡的水平與垂直發散角分別為125.9°、 119.1°，以Ag+3對DBR作為背反射鏡的水平與垂直發散角分別為127.3°、 119.2°。由此可發現，有背反射鏡的LED發散角度都可縮小25~32°。

In recent years, some methods or techniques that enhance light output power of LEDs have been published from many researches, including backside reflector 、surface roughness、flip chip、micro-structure array, and so on. In this thesis, we used DBR 、Al +DBR and Ag+DBR as backside reflector of GaN-based LEDs to enhance light output power. In addition, DBR can enhance the small-angle incident light particularly evident. Based on the characteristic, we can fabricate highly directional LEDs and increased the coupling light into a fiber. It can be applied to plastic optical fiber (POF) communication.
In our experiment ,we simulated the reflectivity of DBR、Al+DBR、Ag+DBR in blue region (460nm) first, check the high reflectivity in blue region, and then deposited these reflectors on glass. By measuring, the reflectivity of 6pairs DBR is 93%、Al+2.5pairs DBR is 95.04% and Ag+3pairs DBR is 97.71%, finally we deposited these reflectors on backside of device and analysis optical properties. LEDs with 6 pairs DBR on backside can enhance light output power about 38.7% at 50mA, LEDs with Al+2.5pairs DBR on backside can enhance light output power about 36% at 50mA, LEDs with Ag+3pairs DBR on backside can enhance light output power about 34.1% at 50mA. In the divergence angle measurement, the horizontal and vertical divergence angle of REF LED is 151.6°、144.6° respectively at 50mA, the horizontal and vertical divergence angle of LED with 6 pairs DBR is 123.6°、112.4° respectively at 50mA, the horizontal and vertical divergence angle of LED with Al+2.5pairs DBR is 125.9°、 119.1° respectively at 50mA, the horizontal and vertical divergence angle of LED with Ag+3pairs DBR is 127.3°、 119.2° respectively at 50mA. It was found that the LEDs with backside reflectors can reduce the divergence angle 25~32°.

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