A high-sensitivity curvature sensor with dual-parameter measurement ability based on angularly cascaded long-period fiber grating (AC-LPFG) is proposed and experimentally demonstrated, which consists of two titled LPFGs (TLPFGs) with different tilt angles and the same grating period. AC-LPFG was fabricated by using a deep ultraviolet laser and an amplitude-mask in our laboratory. The experimental results show that simultaneous measurement of curvature and temperature can be achieved by monitoring the wavelengths of two resonant peaks for different TLPFGs. The two peaks show opposite shifts with increasing curvature and has a maximum curvature sensitivity of 16.392 nm/m⁻¹. With the advantages of low cost, high sensitivity, and dual-parameter measurements, our sensor has more potential for engineering applications.

An open-cavity optical fiber gas pressure sensor based on the Vernier effect is proposed. The sensor consists of two Fabry-Perot interferometers (FPIs) connected in parallel. As a sensing FPI, FPI-1 is an open-cavity FPI and composed of single-mode fiber (SMF), hollow core capillary (HCC) and twin-hole and dual-core fiber (THDCF). The open-cavity FPI structure is constructed using the air holes of THDCF. FPI-2 consists of SMF and HCC with a large inner diameter and works as a reference FPI. The manufacturing cost of the sensor is low, and easy to manufacture. This study explored the relationship between the magnification factor and the cavity lengths of the sensing FPI and the referencing FPI. After optimizing, the sensor has a sensitivity of -168.82 nm/MPa in the gas pressure range of 0.1-1.6 MPa, which is 48.37 times the sensing sensitivity of single FPI. In addition, the temperature crosstalk of the sensor is 2.285×10 ^-4 MPa/°C. Repeated experiments have demonstrated that the sensor has good repeatability and stability. Therefore, the proposed sensor structure provides a new idea for the design and application of optical fiber gas pressure sensors with ultra-high sensitivity and lower temperature cross-sensitivity.

Ultrafast humidity interrogation is valuable in industrial production, healthcare, and environmental monitoring due to its fast response and high sensitivity. We present an ultrafast humidity sensor based on an agarose-coated fiber Bragg grating (AG-FBG) structure combined with time stretching method. Leveraging AG’s ability to swell or contract in response to humidity variations results in changes to the effective grating period, which in turn causes a shift in the Bragg wavelength. Using a home-made high-power femtosecond all-polarization-maintaining fiber laser, the time-stretching technique can be achieved through a long dispersion-compensating fiber. According to wavelength-to-time mapping, the wavelength shift associated with humidity response can be converted into the time domain, resulting in a humidity sensitivity of −0.017 ns/%RH at an interrogation speed of 76.75 MHz and a humidity resolution of 0.007 %RH. The proposed humidity monitoring system has demonstrated high stability and repeatability. Therefore, with the advantages of high sensitivity, high accuracy and ultrafast response time, our proposed humidity sensor shows significant potential in the field of real-time monitoring.

In the paper, a temperature and relative humidity (RH) sensor based on a half-covered agarose fiber Bragg grating (HC-AFBG) is proposed and experimentally validated. A single fiber Bragg grating (FBG) is utilized as the sensing core for the sensor, with half the length of the FBG coated with humidity-sensitive agarose (AG) material. Utilizing the ability of AG to stretch or shrink with changes in humidity, the grating period of the FBG can be altered, which in turn creates new reflection peaks in the reflection spectrum. We experimented and verified the behavior of the two reflection peaks of HC-AFBG at different humidity and temperature and solved the cross-sensitivity problem. The experimental results show that the humidity sensitivity is 73.0 pm/%RH in the range of 35 %RH 65 %RH. And the temperature sensitivities of the two peaks are 13.3 pm/°C and 9.6 pm/°C in the range of 25 60 °C. Using the obtained temperature and humidity sensitivity to construct a sensitivity measurement matrix, humidity and temperature can be monitored simultaneously. This study presents a HC-AFBG sensor capable of high-sensitivity, simultaneous temperature and humidity sensing, offering a promising tool for various environmental monitoring applications.

A single-polarization solid-core anti-resonant fiber is proposed, and the influence of the fiber core material anisotropy of the solid-core anti-resonant fiber on polarization characteristics is investigated using the finite element method. Single-polarization guidance is achieved by using the anisotropy of optical fiber materials, which also ensures high birefringence. The numerical simulation results indicate that there are two single-polarization intervals (1210–1440 nm and 1490–1560 nm), with a maximum bandwidth of up to 230 nm, when the confinement loss difference between the two orthogonal polarizations exceeds two orders of magnitude. Specifically, when the work wavelength is 1550 nm, a polarization extinction ratio (PER) of 108 is obtained by optimizing the structure parameters. Additionally, the y-polarization fundamental mode (YPFM) can be well confined in the fiber center with a low confinement loss of 0.04 dB/m, while the x-polarization fundamental mode (XPFM) has a huge confinement loss larger than 4.65 dB/m due to the coupling with the tube mode. The proposed single-polarization solid-core anti-resonant fiber has a huge potential in applications such as laser systems, fiber-optic gyroscopes, and optical fiber communications.

Nitrogen dioxide (NO₂) is broadly acknowledged as one of the six key air pollutants, posing a significant threat to environmental stability and human health. The profile of atmospheric nitrogen dioxide is required for quantifying NO₂ emissions from fossil fuel combustion and industry. In continuous-wave differential absorption lidar (CW-DIAL) systems, the laser sources employed are subject to the issues of varying output characteristics and poor instability. This study presents a CW-DIAL system for remote sensing of atmospheric NO₂ that employs a compact grating-based external cavity diode laser (ECDL) and Scheimpflug imaging. The laser in this system utilizes a piezoelectric transducer (PZT) for precise wavelength tuning, emitting at 448.1 nm and 449.7 nm with an output power of 2.97 W and a narrow linewidth of 0.16 nm. Signal capturing was achieved through a Newtonian telescope with a diameter of 200 mm and a 45° inclined CCD image sensor, satisfying the Scheimpflug principle. A case study near road traffic was used to verify the feasibility of ECDL-DIAL, which took place from 1 October to 2 October 2023 over an industrial park. The system generates precise NO₂ distribution maps with sub-50 m resolution over 3 km, updating every 10 min.