摻鈦藍寶石寬頻晶體光纖光源之製備與檢測

Abstract

使用雷射加熱基座長晶法長出摻鈦藍寶石單晶光纖，並取得最佳製程。單晶光纖可藉由雷射退火和高溫環境爐退火，解決鈦離子氧化問題，並提升晶體品質，以高溫環境爐使用5%氫氣95%氬氣在最高溫1550 oC持溫三小時有最佳的退火成效。 針對雷射加熱基座長晶法成功生長出來的單纖衣摻鈦藍寶石晶體光纖與雙纖衣摻鈦藍寶石晶體光纖，使用雷射掃描量測折射率法藉由端面反射強度得出晶纖端面個別折射率值，再經電子微探儀加以確認離子濃度分布與取得高倍率(5000 X)晶纖端面照，確認雙纖衣摻鈦藍寶石晶體光纖的內纖衣層成份是由氧化鋁與石英玻璃混合而成，但由於氧化鋁與石英玻璃互熔效果不佳，在內纖衣層存在有許多微米等級大小的氧化鋁微顆粒，並在纖芯與內纖衣層界面造成嚴重的表面散射，量測單纖衣與雙纖衣晶纖的波導結構傳輸損耗分別為0.2 dB/cm和3 dB/cm，故單纖衣晶纖為目前適合的波導結構。 以532-nm綠光雷射幫浦單纖衣摻鈦藍寶石晶纖，可得到寬頻輸出功率15.6 mW，斜線效率0.74%，使用446-nm藍光二極體雷射幫浦，得到2.45 mW輸出功率，斜線效率0.62%，其輸出光譜中心波長760 nm，半高寬為181 nm，應用於光學同調斷層掃描術具有1.5 μm的縱向解析度，又因光譜接近完美高斯分布，干涉訊號旁瓣極小，縱向畫素間cross talk值非常低。

We fabricated the Ti3+:Al2O3 single crystal fibers by means of laser heated pedestal growth method and achieved the best growth parameters. Two annealing methods, including laser annealing and furnace annealing were used for recovering the Ti3+ ion concentration which reduces the infrared residual absorption and effectively improving the optical efficiency. The furnace annealing method with a 1550 oC annealing temperature for 3 hours showed the highest fluorescence intensity. By means of laser heated pedestal growth method, we also successfully fabricated the Ti3+:Al2O3 single-clad crystal fiber and double-clad crystal fiber. Laser scanning measurement method was used for measured crystal fiber refractive index profiles from the reflection intensities of the crystal fiber endfaces. The ions concentration distributions and micro structures on the crystal fiber interfaces were further measured by the electron probe micro-analyzer. The compositions of the inner cladding layer of the double-clad crystal fiber include Al2O3 and fused silica. There are many Al2O3 micro-particles of the micrometer scale in the inner cladding layer due to incomplete mixing of the Al2O3 and fused silica. Serious surface scattering was induced at the core and inner cladding interface. The measured fiber propagation losses of the Ti3+:Al2O3 single-clad crystal fiber and double-clad crystal fiber at 850 nm were 0.2 dB/cm and 3.2 dB/cm, respectively. Therefore the single-clad crystal fiber was a superior waveguide structure now. The Ti3+:Al2O3 single-clad crystal fiber generated broadband 15.6 mW amplified spontaneous emission power pumped by the 532-nm laser with a slope efficiency of 0.74%. We also demonstrated 2.45 mW output power by using a 446-nm diode laser as the pump source and the slope efficiency was 0.62% for the same crystal fiber. The broadband fluorescence spectrum centered at 760 nm with 180 nm bandwidth was measured. Using the broadband fluorescence as a light source for optical coherence tomography, we measured low axial cross talk factor with a 1.5-μm-axial resolution.