The curvature condition of power cables is monitored by a fiber sensor based on anti-resonant reflecting guidance mechanism in hollow core optical fibers. The sensor head is simple, which only consists of a section of hollow core fiber fusion spliced between single mode fibers. Multiple transmission dips are observed in the transmission spectrum, which arise from the anti-resonant reflecting effect in the silica ring cladding. The curvature of a power wire can be detected by attaching the fiber sensor to the cable. The transmitted intensity at resonant wavelengths rises as curvature applied on the power cable increases, and a sensitivity of 3.414 dB/m-1 is achieved. The temperature response of the sensor is also investigated, and the results indicate that such a sensor has low temperature cross-sensitivity of 0.002m(-1)/degrees C.

We propose and verify a fiber optic temperature sensor whose demodulation method is measuring the spectra contrast, which is quantified by the amplitude of the fast Fourier transform (FFT) of interference fringes within a certain small wavelength range. A section of polarization-maintaining fiber (PMF) is spliced in the sensing arm of the Mach-Zehnder interferometer (MZI). Due to the birefringence of the PMF, a visible envelope is formed in the interference fringes. Within a certain range of optical frequency (i.e. wavelength), the change of birefringence caused by external temperature will drive the envelope drift, and the amplitude of interference fringe after fast Fourier transform will also change correspondingly. By measuring the change of amplitude, the purpose of demodulating external temperature can be realized. Experimental results show high sensitivity better than 2.1 dB/degrees Cwith a high accuracy of 0.00048 degrees C, comparing with the envelope drift measuring results 1.62 nm/degrees C with resolution of 0.012 degrees C. The resolution of this scheme is increased by two orders of magnitude compared with measuring the envelope drift. Moreover, merits of our sensor in terms of immune to phase shift of reference arm and the power fluctuation of light source benefit our practical application for such as electric power system monitoring.

A fiber laser curvature sensor based on dual-wavelength gain competitive intensity difference demodulation is proposed and experimentally demonstrated. Here a linear cavity dual-wavelength erbium-doped fiber laser (DWEDFL) is build with two filter components i.e. fiber Bragg gratings (FBG) with very close center wavelengths. Since the dual wavelengths are sharing the same gain medium erbium-doped fiber (EDF), gain competition mechanism is formed with sensitive feature to external measurand curvature. Besides, the curvature information is demodulated by subtracting the power of the dual wavelengths. Experimental results show a total sensitivity as high as -57.22 dB/m(-1). Our scheme not only improves the measuring sensitivity, but also eliminates the effects of source power jitter and external disturbances for example temperature shift since they do almost the same impact on the dual wavelengths.

In order to solve the problem of foundation settlement monitoring, this paper presents a monitoring program of substation foundation settlement, which is based on the distributed optical sensing technology. The composition of the hardware monitoring system and the wiring scheme of stress optical cables were described. The results of simulation experiment showed that the Brillouin optical time domain analysis could well meet the precision requirements of substation settlement monitoring. Moreover, the temperature reference optical fibers should be laid for temperature compensation. This paper can provide the basis for further prevention of substation foundation settlement.

A simple fiber lateral stress sensor is proposed based on polarization-maintaining fiber (PMF) embedded Michelson interferometer (MI). A section of PMF is spliced in the sensing arm of the MI to form the basis of the sensing element. Here the output spectrum will be derived from a two-part interference spectrum: fine part from optical path difference (OPD) of the MI and envelope one from birefringence of the PMF. The PMF is wound into a spiral shape sandwiched by two square silicon rubber sheets, that is the sensing element. Thanks to the low elasticity modulus of silicon rubber material, the experiment show high stress sensitivity of 1.93 nm/kPa in 2.1 kPa stress range by demodulating the envelope shifting. Compared with conventional Sagnac type sensor, the proposed sensor has merits of convenient for application, flexible form, and so on. And this is beneficial for electric power system monitoring