Fabry-Perot cavity-based contact force sensor with high precision and a broad operational range

High-temperature-sensitive and spectrum-contrast-enhanced sensor using a bullet-shaped fiber cavity filled with PDMS

Low temperature sensitivity and low spectral contrast are serious but common issues for most Fabry Perot (FP) sensors with an air cavity. In this paper, a high-temperature-sensitive and spectrum-contrast-enhanced Fabry Perot interferometer (FPI) is proposed and experimentally demonstrated. The device is composed of a hollow cylindrical waveguide (HCW) filled with polydimethylsiloxane (PDMS) and a semi-elliptic PDMS end face. The semi-elliptic PDMS end face increases the spectral contrast significantly due to the focusing effect. Experimentally, the spectral contrast is 11.97 dB, which is two times higher than the sensor without semi-elliptic PDMS end face. Ultra-high temperature sensitivity of 3.1501 nm/°C was demonstrated. The proposed sensor exhibits excellent structural stability, high spectral contrast and high temperature sensitivity, showing great potential in biomedicine, industrial manufacturing, agricultural production and other applications.

Microstructured optical fiber based Fabry-Pérot interferometer as a humidity sensor utilizing chitosan polymeric matrix for breath monitoring

This study reports a method for humidity sensing based on a specialty microstructured optical fiber (MOF). A suspended tri-core MOF was fabricated using the stack and draw technique. A low finesse sensing head was prepared by depositing a chitosan polymer matrix within the holes of the MOF, forming a Fabry-Pérot interferometer as a sensing platform while the chitosan film acts as the sensing material. The use of the probe for real-time breath monitoring was also successfully demonstrated. The probe possessed a maximum sensitivity of 81.05 pm/(%RH) for 90-95%RH range while the linear region of the sensor ranged from 70-95%RH. The temperature cross correlation was also experimented, and a lower influence of external temperature was observed. The probe shows an ultrafast response during human breath monitoring with a rising time and recovery time of 80 ms and 70 ms, respectively.

Bragg labeled wavelength calibrates interferometric sensors in hollow core fiber

A Bragg labeled wavelength (BLW) employed to the sensitivity calibration in an interference pattern has been proposed and experimentally demonstrated. According to the critical condition of Fabry-Perot (FP) interference and the antiresonant (AR) effect, the length of hollow core fiber (HCF) is artificially controlled to form a FP microcavity by collapsed fusion splicing. Dual-spectral features of the BLW and inline multimode interference (IMMI) dominate the transmission spectrum of the collapsed Bragg HCF (BHCF). The location of the BLW remains unchanged once the air-core diameter is selected. Sensing performance is investigated to validate the calibration function of the proposed BHCF. In particular, the temperature sensitivity of the BLW and multimode interference are 12.8 pm/°C and 87.1 pm/°C, respectively, corresponding to the reference sensitivity induced by the Bragg structure and the measurement sensitivity of the IMMI. All these findings highlight the calibration of HCF-based interferometric sensors in practical applications.