Ultra-compact silicon-microcap based improved Michelson interferometer high-temperature sensor.

An ultra-short high-temperature fiber-optic sensor based on a silicon-microcap created by a single-mode fiber (SMF) and simple fusion splicing technology is proposed and experimentally demonstrated. A section of the SMF with a silicon-microcap at one end is connected to the "peanut" structure to build the microcap-based optical fiber improved Michelson interferometer (MI). The optimal discharge parameters of microcap and length of SMF has been investigated to achieve the best extinction ratio of 6.61 dB. The size of this microcap-based improved MI sensor is 560 µm and about 18 times shorter compared to the current fiber tip interferometers (about 10 mm). Meanwhile, it showed good robustness during the two heating-cooling cycles and the duration period stability test at 900 °C. This microcap-based improved MI sensor with the smaller size, simple fabrication, low cost, high reliability, and good linearity within a large dynamic range is beneficial to practical temperature measurement and massive production.

High-sensitivity transverse-load and high-temperature sensor based on the cascaded Vernier effect.

In this paper, we demonstrate a novel, to the best of our knowledge, transverse-load and high-temperature sensor based on the cascaded Vernier effect. Two Fabry-Perot interferometers fabricated by a piece of hollow-core fiber (HCF) and a piece of polarization-maintaining photonic crystal fiber (PM-PCF) are connected by a long part of single-mode fiber with a length of 1 m, and play the roles of transverse-load sensor and high-temperature sensor, respectively. The sensitivity of not only the transverse load but also that of temperature can be enhanced by the Vernier effect. The sensitivity of the transverse load is raised by 7.7 times to 5.84 nm/N, and the temperature sensitivities increased by 5.5 and 5.9 times to -0.0689nm/∘C and -0.1038nm/∘C within the temperature range of 50-400°C to 400-900°C. Moreover, both the HCF cavity and PM-PCF cavity can be split and combined flexibly. Hence, such a sensor could have great potential in sensing applications.

Three-parameter measurement optical fiber sensor based on a hybrid structure.

We have proposed a hybrid-structured optical fiber sensor that can measure curvature, temperature, and transverse load. The hybrid structure is made by fusing a section of hollow-core fiber (HCF) between an air bubble and an up-taper. The air bubble acts as a Fabry-Perot interferometer (FPI) and at the same time serves as excitation for a Mach-Zehnder interferometer (MZI). HCF is used as an anti-resonant reflected optical waveguide (ARROW), which periodically decreases in the resonant wavelength of the optical transmission spectrum. The transverse load can be measured by demodulating the reflection spectrum of the FPI. By demodulating the wavelength shift of the MZI for temperature sensing and the intensity change of ARROW inclination for curvature sensing, the curvature and temperature can be measured simultaneously. The experimental results show that the transverse load sensitivity of the FPI is 1.53 nm/N. The curvature and temperature sensitivities are 33.23dB/m-1 and 20.3 pm/°C, respectively, and the cross-sensitivity is 0.0003m-1/∘C. Due to its ease of manufacture, low crosstalk, and high sensitivity, the hybrid-structured optical fiber sensor is suitable for multi-parameter measurement applications.

Ultrasensitive strain sensor based on Vernier- effect improved parallel structured fiber-optic Fabry-Perot interferometer.

A novel parallel structured fiber-optic Fabry-Perot interferometer (FPI) based on Vernier-effect is theoretically proposed and experimentally demonstrated for ultrasensitive strain measurement. This proposed sensor consists of open-cavity and closed-cavity fiber-optic FPI, both of which are connected in parallel via a 3 dB coupler. The open-cavity is implemented for sensing, while the closed-cavity for reference. Experimental results show that the proposed parallel structured fiber-optic FPI can provide an ultra-high strain sensitivity of -43.2 pm/µÎµ, which is 4.6 times higher than that of a single open-cavity FPI. Furthermore, the sensor is simple in fabrication, robust in structure, and stable in measurement. Finally, the parallel structured fiber-optic FPI scheme proposed in this paper can also be applied to other sensing field, and provide a new perspective idea for high sensitivity sensing.