Ultrasensitive measurement of tactile force based on a PDMS-embedded microfiber Mach-Zehnder interferometer.

This study investigates the utilization of an in-fiber interferometer embedded in polydimethylsiloxane (PDMS) to develop a highly sensitive tactile sensor. The tapered mode-field mismatch structure is more conducive to stimulating strong high order modes to promote the sensitivity of the sensor. Experimental investigations are conducted to study the sensing performance of the sensor, resulting in a sensitivity of 23.636 nm/N and a detection limit of 0.746 mN. The experiments demonstrate that employing fast Fourier transform (FFT) and inverse FFT (IFFT) methods to filter weak high order modes significantly improves the repeatability of the sensor, resulting in a repeatability error of less than 1%.

Highly sensitive soft optical fiber tactile sensor.

A soft highly sensitive tactile sensor based on an in-fiber interferometer embedded in polydimethylsiloxane (PDMS) structure is studied. Theoretical simulation obtains that the high order sensing modes and PDMS can improve the sensitivity. Experiments show that different order sensing modes, derived by fast Fourier transform (FFT) and inverse FFT methods, present different sensing performance. Corresponding to high order mode, 1.3593 nm/kPa sensitivity and 37 Pa (0.015 N) detection limit is obtained. Meanwhile, it also shows very good stability, reproducibility, and response time. This study not only demonstrates a tactile sensor with high sensitivity but also provides a novel sensing modes analysis method.

Polarization dependence of a graphene-optical fiber hybrid Mach-Zehnder interferometer.

Graphene exhibits a particular optical polarization dependence property, which is that supporting optical polarization states of graphene can be readily altered through tuning the polarity of the imaginary part of its conductivity. The in-fiber Mach-Zehnder interferometer (MZI) possesses extremely high sensitivity to the surrounding refractive index through cladding modes. Combining graphene and the in-fiber interferometer, a graphene-optical fiber hybrid MZI is constructed. Depending on the graphene polarization dependence property, the interference wavelength of the graphene-optical fiber hybrid MZI expresses periodic drift with the in-fiber light linear polarization angle adjusting within 180°. Meanwhile, drift periods corresponding to different interference wavelengths are slightly different, which is primarily due to the superposition of the polarization dependence behaviors of different cladding modes. For different light polarization states, with the in-fiber optical power increasing, the interference wavelengths and contrast intensities of the hybrid MZI transmission spectrum show a polarization independent linear blue shift and a nonlinear decrease, respectively.

In-Fiber Closed Cavity Interferometric High-Resolution Aqueous Solution and Alcohol Gas Refractometer.

An optical fiber interferometric refractometer for alcohol gas concentration and low refractive index (RI) solution (with 1.33-1.38 RI range) measurement is theoretically and experimentally demonstrated. The refractometer is based on a single-mode thin-core single-mode (STS) interferometric structure. By embedding a suitably sized air cavity at the splicing point, high-order cladding modes are successfully excited, which makes the sensor more suitable for low RI solution measurement. The effect of the air cavity's diameter on the sensitivity of alcohol gas concentration was analyzed experimentally, which proved that RI sensitivity will increase with an enlarged diameter of the air cavity. On this basis, the air cavity is filled with graphene in order to improve the sensitivity of the sensor; and the measured sensitivity of the alcohol gas concentration is -1206.1 pm/%. Finally, the characteristics of the single-cavity structure, graphene-filled structure and double-cavity structure sensors are demonstrated, and the linear RI sensitivities are -54.593 nm/RIU (refractive index unit), -85.561 nm/RIU and 359.77 nm/RIU, respectively. Moreover, these sensor structures have the advantages of being compact and easily prepared.

Temperature-insensitive hybrid interferometric liquid refractive index sensor.

A temperature-insensitive all fiber Fabry-Pérot (F-P) and Mach-Zehnder (M-Z) hybrid compact structure and its sensing characteristics are proposed and theoretically and experimentally demonstrated. In one sensor, two kinds of sensing principles are existing, which is shown in the sensing process that with the increase in the refractive index (RI) of the liquid, the dip wavelengths coming from the F-P interference do red-drift, and the dips from the M-Z interference do blue-drift, respectively. Due to the opposite shift and almost the same temperature sensitivities, the dip difference between M-Z and F-P refractometers is used to eliminate temperature cross-sensitivity and improve the RI sensitivity of the sensor. In our experiments, the liquid RI sensitivity is 134.383 nm/RIU, and temperature cross-sensitivity is effectively eliminated within the ±21.74 °C change range at room temperature. This sensing structure also has advantages of simple structure, good integration, and low power loss.