多週期極化反轉鈮酸鋰帶狀波導綠光雷射晶片之研製

Abstract

本論文探討在Z切鈮酸鋰基板製作具有帶狀波導之多週期極化反轉結構。入射基頻光波長為1064nm，經由準相位匹配倍頻產生532nm的綠光。 所使用之帶狀波導有鋅鎳共同擴散式與鎵擴散式等兩種，線寬均為160μm。其中鋅鎳共同擴散式波導可導TM和TE兩種模態光，而鎵擴散式波導僅可導TM模態光。 量測結果顯示具有鋅鎳共同擴散式波導溫度頻寬為45℃，倍頻轉換效率為15% ; 而具有鎵擴散式波導則溫度頻寬為50℃，倍頻轉換效率為13.3%。相較於單一週期波導晶片顯示多週期晶片在鋅鎳共同擴散式波導上之溫度頻寬增加9倍，而轉換效率卻僅下降1.47倍 ; 在鎵波導上之溫度頻寬增加了7倍，而轉換效率卻僅下降1.33倍。因此週期性極化反轉結構上加光波導，可增加光場侷限，有助於倍頻轉換效率的提升。

Segment-chirped grating structure is used for the fabrication of multi-periodically poled lithium niobate (PPLN) for second harmonic generation (SHG) of green laser. To enhance the optical confinement, some metal diffused waveguides are fabricated on the structure. Green laser of wavelength 532nm is obtained by the quasi-phase matching second harmonic generation (QPM-SHG), when launched with an incident laser of wavelength 1064nm. Zinc-and-nickel co-diffusion and gallium diffusion waveguides of the same linewidth 160 μm are fabricated. TM and TE modes are supported in the zinc-and-nickel co-diffusion waveguide, but only TM modes are supported in the gallium diffusion waveguide. PPLN with the zinc-and-nickel co-diffusion waveguide has a temperature bandwidth of 45˚C and a green laser conversion efficiency of 15%. PPLN with the gallium diffusion waveguide has a temperature bandwidth of 50˚C and a green laser conversion efficiency of 13.3%. As compared with single period waveguide PPLN, the temperature bandwidth of segment-chirped grating ZnNi:PPLN is broadened by a factor of 9, whereas the conversion efficiency is reduced only by a factor of 1.47. As for the Ga:PPLN, the temperature broadening factor 7 and the conversion efficiency reduction factor is 1.33. That shows waveguides provide significant optical confinement to compensate for the decrease in conversion efficiencies of PPLN.