摻雜氧化鎂鈮酸鋰之帶狀波導綠光雷射晶片之研製

Abstract

本論文之目的在研究波長532nm的綠光雷射，採用的方法是在摻雜氧化鎂鈮酸鋰晶片上製作出第一階倍頻準一維週期性反轉結構帶狀波導，再以1064nm基頻光耦合至光波導，並量測其輸出之綠光功率。實驗結果發現透過波導對光場之侷限性，可提高綠光倍頻之轉換效率。 本論文所使用的波導有鋅鎳共同擴散波導及鎵擴散波導兩種。 在波導製程方面，鋅鎳共同擴散波導寬度為160μm，可單導TM模態，量測結果符合極化與製程相依之特性；鎵擴散波導寬度亦為160μm，可單導TM模態，量測結果亦符合前人所作之結果。 在綠光量測方面係以8mW的 1064nm基頻光耦合至光波導。鋅鎳波導和鎵波導的外部轉換效率分別為22%和18%。入射波導最大功率可由6mW提升至8mW。這顯示利用摻雜氧化鎂之鈮酸鋰有助於光損害閥值的提升，即有助於提升入射光強度的峰值。 附錄為利用氧化鎵擴散製造脊形結構的新方法，其優點是可簡化製造過程。

First order quasi one-dimensional (1-D) periodically-poled magnesium-doped lithium niobate (PPMgO: LN) optical strip waveguides are presented. Green laser of wavelength 532nm is obtained when launched with an incident laser of wavelength 1064nm. Experimental results show the conservation efficiencies are increased owing to the waveguide structures. For comparison, two special waveguides of the same width 160μm are fabricated by zinc-and-nickel co-diffusion and gallium diffusion, respectively. The zinc-and-nickel co-diffusion waveguides are verified to have process-dependent polarizations. However, only transverse magnetic (TM) mode waveguides are used because of larger diffusion depth for easy coupling. Similarly, only TM modes are supported in the gallium diffusion waveguides, which agrees quite well with those reported previously. When an incident laser of 8mW is coupled to the waveguides, the measured green laser conversion efficiencies are 22% and 18% for zinc-and-nickel and gallium diffusion waveguides, respectively. Comparing to those without waveguide structures on lithium niobate substrate, the allowable maximum input power is increased from 6mW to 8mW. That’s because the optical damage threshold of magnesium-doped lithium niobate is increased. Finally, in the appendix, a simple method for the fabrication of ridge structure by using gallium diffusion is proposed.