| Summary: | 碩士 === 國立臺北科技大學 === 光電工程系研究所 === 98 === This thesis proposed a novel polarization interferometer for measuring wavelength shifts. It possesses the characteristics of full fiber design, common-path, and non-equal optical path length, so it is with the preformance of compact optical setup, high measurement sensitivity, and high measurement stability. The interferometer comprises a reference and measurement pathes. The lightwave of the reference path passes through a rotating optical chopper to generate a reference signal on directly, and it is received by an optical sensor and became reference signal. Whereas the beam of the measurement path travels through a fiber linear polarizer, fiber polarization controller, polarization maintaining fiber, fiber quarter-wave plate, and an analyzer coaxially mounted on the chopper, this beam is then incident on an optical sensor to generate a measurement signal. By comparing the measurement and reference signals, the wavelength shift of the lightbeam can be obtained.
The optical path difference of measurement path comes from the birefringent effect of the polarization maintaining fiber. In this research, there were polarization maintaining fibers of 5m and 10m. They made interferometer be with sensitivities of 297.87 °/nm and 598.53 °/nm, and stabilities of 4.73×10-3 nm and 6.77×10-3 nm, respectively.
In application, the interferometer was adopted to detect dynamic and static strains on fiber-optic Bragg gratings (FBGs). In the static detection, a FBG and strain gage were attached onto the opposite sides of a four-point bending beam loaded by a static force. The wavelength shift of the wave reflected from the FBG was examined by the interferometer, and the measured shift was transferred into the strain of the beam, which is consistent with that measured by the gage. In the dynamic measurement, a FBG was affixed onto a structure driven by a PZT, the interferometer performed the ability to examine the strain of the structure while it was loaded periodically by PZT.
Finally, the proposed interferometer is conducted to inspect the strains of FBGs in a TDM and WDM systems, the experiment results demonstrate the applicability of the interferometer.
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