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Abstract
Optical wavelength sensing interrogator based on hydrogen cyanide (HCN) gas absorption cell and tunable fiber laser are researched, besides, high performance simultaneous sampling card is used in the system to acquire sensing signals of six channels simultaneously. The absorption wavelengths of HCN spectrum are identified followed by the recognizing two absorption wavelengths with maximum spacing, thus high-resolution and real-time calibration of sweep-wavelength can be achieved, which can eliminate the fiber Fabry-Pérot tunable filter (FFP-TFs) disadvantages such as non linearity and poor repeatability. Experimental results show that the resolution of the system is 1.6 pm and the long-term repeatability is 3.4 pm for fiber Bragg grating measurement, which means that high resolution wavelength demodulation can be achieved with the scheme.
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The effect of the end reflectivity of reflective fiber on the quality of fiber F-P sensor's output signal was discussed. A method that can improve the intensity and contrast of F-P sensor's output signal was proposed, which was by increase the end reflectivity of reflective fiber. In order to gain the best quality of the output signal within F-P sensor's working cavity length range, the optimal end reflectivity was worked out through the LMSE (Least Mean Square Error) method. It is demonstrated through simulation that the quality of F-P sensor's output signal using optical end reflectivity is better than those using non-optical end reflectivity.
Based on the theory of Fabry-Perot, the influence of light source on optical fiber F-P strain sensor system has been analyzed. The stress was put on the optical spectrum of light source, and the periodical jumping phenomenon of the output of the system was observed. The computational simulation and the experiment were comparatively done on this phenomenon, and the results were coincident well to each other.
A broadband tunable ring erbium-doped fiber laser is presented. The laser is characterized by simple structure, broad tunable wavelength range, narrow line width and flattened output power covering both C and L bands. A narrow bandwidth fiber Fabry-Perot tunable filter with a free spectrum range of 116 nm is used for wavelength selection. By decreasing the intra-cavity losses, optimizing the length of the erbium-doped fiber and the injected power of the pump laser, the widest tuning range of 103 nm (1511-1614 nm) and the peak output power of -1.4 dB with a line width of less than 0.03 nm have been achieved. And furthermore, the output peak power fluctuation of less than 0.2 dB in 97 nm range (1515-1612 nm) and the side mode suppression ratio of more than 52 dB have also been obtained.
The white light interferometry for the measurement of low-finesse extrinsic Fabry-Perot interferometer (EFPI) is reported. A broadband light is injected into EFPI, and the reflected light is scanned by another high-finesse tunable Fabry-Perot filter, the periodic spectra of EFPI can be obtained. To measure the cavity length, the spectra are fast Fourier transformed, the absolute length of cavity can be calculated by using the periodic spectra. The measuring accuracy is limited by the length of cavity. The longer cavity has higher measuring accuracy. When the length of cavity are 200 μm, 400 μm, and 600 μm respectively, the measured results are agree with the actual length of the cavity.
Physical mechanism of using nonlinear polarization rotation as saturable absorber to obtain pulse is analyzed theoretically. Experimental study of improved femtosecond fiber ring laser is reported. A fiber ring laser with highly Er3+-doped fiber as gain medium is demonstrated, 976 nm laser diode (LD) laser is used as pump source, and in the fiber ring cavity, nonlinear polarization rotation mode-locking is realized by adopting single polarization controller. By tuning polarization controller, stable mode-locked pulses centered at 1535.9 nm with 23.5 nm bandwidth at 3 dB, 131 fs duration and an average output power as high as 5.91 mW are successfully obtained at the repetition rate of 11.20 MHz.
