We experimentally demonstrate transverse load and strain sensing based on a fiber optic Fabry-Perot interferometer (FPI) with special air cavity, which was created by fusion splicing single mode fiber (SMF), hollow core fiber (HCF) and several electrical arc discharges. The cavity height of this structure is higher than the cladding diameter of SMF so that it can sense transverse load with high sensitivity. The transverse load sensitivity of this air cavity FPI sensor is 1.31 nm∕N and about 5 times more sensitive compared to the current fiber tip interferometer (0.2526 nm∕N). Meanwhile, this sensor also can measure strain and the strain sensitivity of 3.29 pm∕με is achieved. In addition, the low temperature sensitivity (1.08 pm/°C) of the sensor can reduce the temperature-induced measurement error. This novel air cavity FPI can be developed and used as high-sensitivity transverse load and strain sensor with temperature-insensitive.

The β-NaLuF₄: Yb³⁺/Ho³⁺ nanocrystals have been synthesized via a solvothermal method, which were protected in a SiO₂ capillary tube. Upon 980 nm continuous laser excitation, the micro-tube waveguide characteristic was studied. Additionally, the upconversion emissions from the ⁵F₄, ⁵S₂→⁵I₈ (~545 nm), ⁵F₅→⁵I₈ (~650 nm) and ⁵F₄, ⁵S₂→⁵I₇ (~750 nm) transitions of Ho³⁺ ions in the micro-tube were obtained and studied as a function of temperature in the range of 300~500 K. The maximum sensitivities derived from the fluorescence intensity ratio technique are 1.53% K⁻¹ (I₇₅₀/I₆₅₀) and 0.09% K⁻¹ (I₅₄₅/I₆₅₀) at 300 K. The result demonstrated that the near infrared-red absolute sensitivity is more sensitive as a thermometer than the green-red at the whole temperature range. The device is a promising candidate for high resolution luminescent thermometers operating under temperature of 300~500 K.

We report the experimental observation of enhanced rotation sensing in a slow-light structure. We demonstrate that the differential of the phase difference, introduced by rotation, between the counterpropagating waves is proportional to the group index, and thus we can obtain large rotation sensitivity in the slow-light structure with high dispersion (large group index). The results also predict the realization of highly sensitive and compact integrated rotation sensors and gyroscopes by using microwaveguides.

We propose a high-temperature sensor based on a suspended-core microstructured optical fiber (SCMF). The sensor is constructed by fusion splicing a piece of SCMF between two sections of multimode fibers (MMFs) which act as light beam couplers. The multimode interference is formed by the air cladding modes and the silica core modes in the SCMF. Fast Fourier transform is adapted to filtering the raw transmission spectra of the MMF-SCMF-MMF structure. The wavelength shift of the dominant spatial frequency is monitored as the temperature varies from 50 °C to 800 °C. The sensitivities of 31.6 pm/°C and 51.6 pm/°C in the temperature range of 50 °C-450 °C and 450 °C-800 °C are respectively achieved. Taking advantage of the compact size, good stability and repeatability, easy fabrication, and low cost, this proposed high-temperature sensor has an applicable value.

A simple and highly sensitive temperature sensor based on an isopropanol-sealed optical microfiber coupler (OMC) is reported. Due to the high thermo-optic coefficient of isopropanol, the temperature sensitivity of the OMC can be effectively improved by immersing the OMC into isopropanol. The refractive index change of isopropanol is caused by the surrounding temperature variation which in turn allows highly sensitive temperature sensing. Theoretical analysis demonstrates that the temperature sensitivity increases quickly with the decreasing OMC waist diameter. Temperature sensitivities at different waist diameters exhibit high consistency with the theoretical results. When used for temperature sensing, the transmission spectrum blueshifts as the surrounding temperature increases. The highest sensitivity of −5.89 nm/°C is achieved at the waist diameter of 2.2 μm. This is the most sensitive OMC based temperature sensing device reported so far. Such a compact size, low cost, and highly sensitive device may widen the application range of OMC.