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Research on Fiber-Optic Vibration Sensor and SHG Laser System with High Frequency Stability Based on Laser Frequency Locking Technology

Author: ZhangLe
Tutor: ShenYongXing
School: Zhejiang University
Course: Optical Engineering
Keywords: laser frequency locking technology fiber-optic sensing fiber Bragg gratin PHD PPLN crystal second harmonic generation(SHG) the saturated absorption spectroscopy thesis
CLC: TP212.14
Type: Master's thesis
Year: 2012
Downloads: 119
Quote: 0
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Abstract


Laser has been widely used in the fields of communication, measurement, and other medical and biological researches, because of its high directivity, monochromaticity, coherence, intensity resistance and tunable characteristics. In many application fields of laser, the frequency stability is an extremely important parameter, and characterizes the degree of frequency stability. Over years, a variety of frequency locking technologies have been developed, and the frequency stability of laser has been improved. Now, this technology has expanded into other research areas, such as the field of optical fiber sensing. In this thesis, the main work is on the development and application of laser frequency locking technology, including:fiber-optic vibration sensor based on the Pound-Drever-Hall(PHD) frequency locking technique; 780nm fiber laser based on the saturated absorption spectroscopy technique and PPLN crystal.A highly sensitive fiber-optic vibration sensor was developed based on the PDH frequency locking scheme. The system mainly consists of a single frequency DFB laser, phase modulation, photon detector, a fiber bragg FP cavity, and circuits for signal transfer and control. It measured the vibration signal by the electric signal transferred and amplified from the phase change of the fiber bragg FP cavity. By testing, the sensor system was proved having a nice sensing capability to the vibration signals within a frequency range from 1 kHz to 5 kHz. It obtained a more than 50dB signal to noise ratio. The analysis of the sensor, taking into account the parameters of elements used in the system and many environment factors, shows it may reach a resolution as high as 11.7picostrain/(?), which is much better than traditional fiber sensing systems.The 780nm fiber laser system based on the saturated absorption spectroscopy frequency locking technique and PPLN crystal includes three parts:fiber laser based on MOPA system; second harmonic generation (SHG) based on PPLN crystal; saturated absorption spectroscopy frequency locking. In thesis, characteristics of PPLN crystal have been theoretically analyzed based on the QPM theory, the factors affecting the result of SHG were discussed here. And the theoretical tolerance tuning curves of PPLN crystals, including polar inversion grating period, temperature and fundamental wavelength etc, have been simulated. In this experiment, we seeded the 1560nm DFB laser into EYDFA and amplified it for frequency doubling by using PPLN crystal. Now, we have completed the first two steps, and can observe the 780nm out-put laser. In the next step, we will improve the SHG efficiency and then lock the 1560nm DFB laser on Rb absorption spectroscopy.

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CLC: > Industrial Technology > Automation technology,computer technology > Automation technology and equipment > Automation components,parts > Transmitter ( converter),the sensor > Physical sensors > Light sensor
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