非破壞性高折射率差光纖直徑量測

Abstract

高折射率差光纖，包含了新型半導體纖芯光纖等研究，近年來引起了越來越多的科學家的興趣與關注。但由於這些半導體光纖纖芯與披覆層的折射率差異相當大以及纖芯的折射率帶有虛數項的關係，其纖芯的光學直徑量測一直是一個高挑戰性的課題。於此，我們展示了一個簡單，新穎和非破壞性的方法可以同時測量高折射率差光纖（Δn> 0.06）纖芯與披覆層的直徑。這種方法在未來有可能發展成即時直徑量測系統的可能性。在測量結果上，目前使用這種方法測量纖芯與披覆層的直徑的準確度在折射率油光纖（Δn= 0.36）時可以達到97％，以及在矽核光纖（Δn= 2.97 + 0.88i）時可以達到96％。在矽核光纖時，披覆層直徑目前可以測量自30微米至15微米。當對應的光纖批覆層直徑為15微米時，其有效纖芯直徑的測量範圍可以從6.3微米測量至9.3微米。根據模擬此量測方法未來有潛力可以量測披覆層直徑自126微米至15微米的矽核光纖。此光學量測方法比用光學顯微鏡方法測量纖芯直徑更好是因為根據斯涅爾定律的結果，纖芯直徑在光學顯微鏡圖像上的量測結果是不可靠且不準確的。這種測量方法目前可適用於矽核光纖（Δn= 2.97 + 0.88i）和折射率差範圍從1.52至1.82的高折射率差光纖。但根據模擬，此光學量測方法應能量測折射率差範圍從1.52至4.15的高折射率差光纖，只可惜目前沒有市售的從1.82至4.15折射率範圍的折射率油來做實驗驗證。此外由於矽核光纖的纖芯複數折射率太大的關係，會導致光傳播過不同類型纖芯的矽核光纖的時候，其散射條紋完全一致。因此此量測方法可以同時應用在量測不同類型的矽核光纖(例如amorphous 矽核光纖以及single crystalline的矽核光纖)。

The research of high refractive index contrast fibers, including novel semiconductor-core fibers has interested more and more scientists recently. But the diameter optical measurement of these fibers is a difficult challenge due to its high refractive index contrast and imaginary terms of core refractive index. We demonstrate a simple, novel and non-destructive method to measure both core and cladding diameters of high refractive contrast fibers (Δn>0.06) simultaneously which has not been reported. This method has potential to be a real-time measurement in the future. As the result of measurement, the accuracy of diameter measurement using this method can reach 97% for index-oil-cored-fibers (Δn=0.36) and 96% for silicon cored fibers (Δn=2.97+0.88i) currently. For silicon cored fibers, the effective core diameter measurement range can be from 6.3μm to 9.3μm when the corresponding cladding diameter is 15μm. According to the simulation, this method may suitable to measure cladding diameter ranging from 126 to 15μm for Si-cored fiber. It’s better than Optical microscope (OM) examination since core diameter in the OM picture is inaccurate due to Snell’s law. This measurement method is suitable for silicon cored fibers (Δn=2.97+0.88i) and high refractive contrast fibers with core refractive indices ranging from 1.52 to 1.82 due to the availability of refractive liquid oil ranging from 1.82 to 4.15. Besides, this method can be used in measuring diameters of different types of silicon cored fiber in the same database.