In this paper, a Sagnac interferometer with polarization maintaining fiber (PMF) for vector transversal loading measurement has been proposed and experimentally demonstrated. The light propagated in different axes of the PMF has different velocity because of fiber birefringence, which results in phase difference, and thus interferometer pattern is produced. When the birefringence parameters are affected by transversal loading, the phase difference of the light propagating in different axes will change, and as a result of the interferometer pattern of the Sagnac loop shifts. When transversal loading with the opposite direction is applied on the sensing fiber, the interferometer pattern also shifts, but oppositely to longer or shorter wavelength, by monitoring which vector transversal loading measurement can be achieved. The sensing characteristics when transversal loading is applied in different angles have also been studied. The proposed measurement method has a simple structure, and is easy to implement, which shows a good application prospects in the sensing field.
We have proposed and experimentally demonstrated a fiber-optic temperature sensing system based on an optoelectronic oscillator (OEO). A part of the fiber in the oscillator loop is used as the sensing fiber. As the free spectrum range (FSR) of the OEO is determined by the length of the oscillator loop, when the temperature of the sensing fiber is changed, the refractive index of the fiber varies; thus, the optical path length changes as well as the FSR of the OEO. By tracking one peak of the OEO harmonics, the temperature variation can be monitored. Therefore, the temperature variation can be converted to the frequency shift of the radio frequency signals. In the experiment, we have measured the spectra of the OEO with different temperatures, which show good sensing linearity. We have also measured the relationship between the sensing responsivity and the tracked frequency (1.0, 1.5, 2.0, and 3.0 GHz) in the experiment, which shows that the harmonics at a higher frequency produce a higher sensing responsivity. The proposed temperature sensing system exhibits good tunability, stability, linearity tailorable sensing responsivity, and ease of implementation, thus it shows good application potential in remote fiber-optical temperature sensing and monitoring.
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