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The strain characteristics of fiber-optic refractive index (RI) is theoretically investigated, combined with practical application situations, including a systematic theoretical model to explain its physical nature and analyze its functional mechanism. The simplified analytical expression of elastic-optical coefficient is obtained, which is more direct than the existing ones. Besides, the change in RI of fiber-optic with strain is measured by a succinct method based on fiber Bragg grating (FBG) that is simple in structure and easy to operate. We got the conclusion that the variation of RI is negative linearly proportional to strain when optical fiber is stretched from the experimental results. As a result, the theoretical and experimental reduction rate of 0.45 × 10−6/μe and 0.44 × 10−6/μe, respectively. The elastic-optical coefficient of fiber-optic is measured and the measurement results agree well with the previous theoretical analysis. Furthermore, our work shows major application potential in fiber-optic strain sensor systems.

The delay of optical signal is determined by the refractive index and length of optical fiber, and temperature would have an intense influence on the index. To establish the relationship between refractive index and temperature, the temperature characteristics of refractive index was analyzed and the thermo-optical coefficient equation was derived according to the polarization of the induced electric dipole moment in SiO2 optical fiber. A measuring system based on optical fiber delay was carried out to measure the index within the temperature range of −30 °C to 70 °C and the experimental result was compared with the theoretical result. The final result shows that the relationship between refractive index and temperature is linear in the temperature range of discussion.

We propose a Mobius-strip-type plasmonic cavity with a silver Mobius strip sandwiched between dielectric layers. By brief theoretical and simulation analyses, we obtain that the factor of the cavity remains about 40 and the mode volume is ultrasmall (less than 1 ) which is more compact than that of the cylindric cavity. This Mobius-strip-type plasmonic cavity supporting the propagation of surface plasmon polaritons owns some unusual properties such as more effective volume and the spatial separation. More potential applications based on this cavity remain to be explored in future nanophotonics.

A high-sensitivity temperature sensor based on optical fiber delay is proposed in this paper. The sensor system is designed and tested in a temperature range of 0°C to 100°C with increments of 5°C. The output delay difference is found to be linearly proportional to the temperature with an average fluctuation less than 0.1 ps. To achieve an overall low cost and practical detection, a simple detection system is developed to measure temperature, and a potential for high temperature sensitivity is shown by analyzing the system. As a result, this sensor system is proven to be feasible and practical, and temperature can be measured in a simple and economical way.