| Summary: | 碩士 === 逢甲大學 === 光電學系 === 106 === Since bands of optical communication is often in 1.5-µm wave length region, to build a reference frequency which is accurate and easy to use in this band is a very important job. To achieve this goal, we demonstrate an all-fiber system based on optical nanofiber (ONF) to probe the saturation absorption of the P(9) line of the acetylene ν1+ν3 band, which is the strongest line of ν1+ν3band at room temperature. The diameter and length of the nanofiber waist are 600 nm and 3.65 mm, respectively, which allows most of the light energy to leak out of the surface of the fiber and interact with the gas molecules. Since the optical backscattering reflection(OBR) of the ONF interferes with the probe beam, the saturation absorption signal is deteriorated and is hard to be observed. To reduce the interference between the OBR and probe beam, we introduce a large optical path difference. In addition, we observed that, for the ONF with 85% transmittance, an incident light of 6.66 mW would result in 591 μW of OBR. Finally, the saturated absorption spectrum becomes more apparent by using frequency derivative spectroscopy.
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