GaN藍光二極體雷射之特性量測

Abstract

本論文主要是研究 GaN 藍光雷射二極體的發光特性、頻率穩定性以及穩頻之後的結果。用於此研究中的雷射有兩種功率：一是 5 mW低功率的雷射(NLHV 500A)，一是 30 mW高功率的雷射(NLHV 3000E)。低功率雷射的臨界電流及中心波長分別是 48 mA、407 nm，高功率的則是 39 mA、400 nm。其T0 分別為 213.8 K 和 141.4 K，這代表GaN藍光雷射二極體不易受溫度影響。由電流對輸出功率的關係，可得到量子效率分別為 38 % 和 31 %。波長對電流的變化量則是 0.00267 nm/mA，相當於 5 GHz/mA，而波長對溫度的變化量則是 0.016 nm/oC，相當於 30 GHz/oC。其橫向模態是TEM00。由 Fabry-Perot 干涉儀所量到的線寬是 5 MHz。除此之外，我們亦利用低功率的雷射架設外腔以觀察其波長的調變範圍，得到約 2 nm的調變範圍。最後，我們用一個光回授系統來量測高功率雷射的頻率穩定性，並加以穩頻。目前在 1000 秒的時間內所得到的穩定度是 1E-9，比雷射自由飄移的頻率穩定性提高了 2 個數量級。

In this thesis, we investigated the commercially available GaN blue lasers including the emission characteristics and the frequency stability of the lasers. We used two types of GaN lasers. One is 5 mW (NLHV 500A), and the other is 30 mW (NLHV 3000E). Threshold current and center wavelength of low-power type are 48 mA and 407 nm. Those of high-power type are 39 mA and 400 nm. The temperature dependence of L-I curve showed a characteristic temperature T0 is 213.8 K and 141.4 K for low power and high power laser respectively. From current versus the output power, we get quantum efficiency of around 38 % for low power device and 31 % for high power device. The wavelength shift of current and temperature variation are 0.00267 nm/mA which corresponding to 5 GHz/mA, and 0.016 nm/oC = 30 GHz/oC. The transverse mode is TEM00 and the linewidth measured by a scanning Fabry-Perot interferometer is about 5 MHz. These data indicate the GaN laser is relatively insensitive to thermal effect. Besides these, we setup an external cavity using the low power laser, and obtained a tuning range about 2 nm. We also used an optical feedback system to stabilize the high power laser and measured stability about 1E-9 for a 1000 sec period, which is two orders better than the free-running laser.