近年來由於稠密波長分割多工(Dense Wavelength Division Multiplexing，DWDM )在光通訊上的廣泛使用，因此在光通訊頻段附近，簡單可靠的頻率標準的建立成為一項重要的課題。過去幾年中，在這方面的研究大部分都集中在 C-band (1550 nm)上的研究，在較短波長範圍如 1530 nm頻段的研究比較缺乏 ; 有鑑於此，本實驗室計畫建立一套利用分子躍遷譜線中心穩頻的雷射系統。配合光纖光頻梳，來測量分子躍遷的絕對頻率，並協助建立其他光通訊頻段的頻率標準。

本論文的重點在於探討利用多光程吸收室偵測乙炔在 1530 nm頻段飽和凹陷的可行性，並依此建立一套穩頻雷射，預備未來的精密頻率測量，建立起1530 nm頻段的頻率標準。本實驗所使用的光源為一台商用外腔式二極體雷射經摻鉺光纖擴大器放大。為了偵測飽和凹陷，將雷射光送入一個充入低氣壓乙炔的多光程吸收室中，光程約為 4 m，並將雷射光沿原光路反射。在本實驗中，乙炔譜線的飽和凹陷已被成功的偵測到，線寬約為 3 MHz，訊噪比約為 200 Hz-1/2 ; 並利用三次諧波的波長調制技術，可成功地將雷射頻率穩定在乙炔的飽和凹陷中心，穩定度約為 120 kHz。

The frequency references in the band of optical communication receive great attentions as Dense Wavelength Division Multiplexing (DWDM) is widely adopted in recent years. Most research is focused in 1550 nm region because of lowest loss in fiber and only a few researches which are studied in shorter wavelength like 1530 nm. In this thesis, our lab plan to build up an accurate laser system which is stabilized on molecular transition, and use the fiber comb system to get the absolute frequency of molecular transition. By this technique, the frequency standard in 1530 nm region can be built up and become a reference frequency for measuring other molecular transition.

The main point of this study is to find the capability of detecting the saturation dip of acetylene molecule in 1530 nm with multi-pass cell, and then try to stabilize the laser frequency in order to measure its absolute frequency in 1530 nm region. In this study, the laser source is a commercial External Cavity Diode Laser which is amplified by Erbium- Doped Fiber Amplifier. In order to detect the saturation dip, two laser beams with opposite propagating directions pass through a multi-pass cell (White cell) filled up with the low pressure acetylene molecule, and the effective optical path in cell is 4 meter. The Lamb dip of 12C2H2 can be observed successfully, and the linewidth of dip is closed to 3 MHz, and SNR is 200 Hz-1/2. Finally, by 3-order demodulation technique, we can succeed to stabilize the laser frequency at the center of saturation dip. The stability of frequency is about 120 kHz.

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