In this study, we propose a tilted fiber Bragg grating (TFBG) humidity sensor fabricated using the phase mask method to produce a TFBG that was then etched with five different diameters of 20, 35, 50, 55 and 60 μm, after which piezoelectric inkjet technology was used to coat the grating with graphene oxide. According to the experimental results, the diameter of 20 μm yielded the best sensitivity. In addition, the experimental results showed that the wavelength sensitivity was −0.01 nm/%RH and the linearity was 0.996. Furthermore, the measurement results showed that when the relative humidity was increased, the refractive index of the sensor was decreased, meaning that the TFBG cladding mode spectrum wavelength was shifted. Therefore, the proposed graphene oxide film TFBG humidity sensor has good potential to be an effective relative humidity monitor.

In this study, we proposed a Base S-type, long-period, fiber grating (Base S-type LPFG) coated with graphene oxide (GO) for sensing relative humidity based on the micro-electro-mechanical systems (MEMS) process and piezoelectric inkjet technology. The single mode optical fiber was etched to three different diameters (37, 42 and 60 m) which were evaluated in the Base S-type LPFG. According to the experimental results, the diameter of 37 m yielded the best sensitivity. Humidity sensor experiments showed that the Base S-type LPFG exhibited a high humidity sensitivity in a wide range from 20% RH to 80% RH. These experiments were repeated three times and the results showed that the average value of transmission loss sensitivity was -0.1824 dB/% RH and the average linear response had a correlation coefficient of 95.68%. The sensor exhibits good linearity, high stability, and reversibility in a wide working range. Therefore, the proposed graphene oxide-coated Base S-type LPFG humidity sensor has the potential for monitoring the relative humidity.

This study describes the fabrication of an electrospun, U-shaped optical fiber sensor for temperature measurements. The sensor is based on single mode fibers and was fabricated into a U-shaped optical fiber sensor through flame heating. This study applied electrospinning to coat PVA, a polymer, onto the sensor layer to reduce its sensitivity to humidity. The sensor is used to measure temperature variations ranging from 30 °C to 100 °C. The objectives of this study were to analyze the sensitivity variation of the sensor with different sensor layer thicknesses resulting from different electrospinning durations, as well as to simulate the wavelength signals generated at different electrospinning durations using COMSOL. The results revealed that the maximum wavelength sensitivity, transmission loss sensitivity, and linearity of the sensor were 25 dBm/°C, 70 pm/°C, and 0.956, respectively. Longer electrospinning durations resulted in thicker sensor layers and higher sensor sensitivity, that wavelength sensitivity of the sensor increased by 42%.

This paper presents an optical fiber gas sensor based on sandwiched long-period fiber grating (SLPFG) that is fabricated via the microelectromechanical systems (MEMS) process and coated with amino silica adsorbent for carbon dioxide (CO₂) gas sensing. The amine-modified nanoporous silica foams were coated onto the SLPFG for CO₂ adsorption. To characterize the CO₂ adsorption of the SLPFG sensor, a gas sensing test was conducted with a mixed gas consisting of 15% CO₂ and 85% nitrogen at a flow rate of 0.2 L/min. The results showed that the spectra of the SLPFG were varied with the gas flow within 21 min. After that, the transmission spectra of the SLPFG held steady and exhibited no further change. This phenomenon was caused by the adsorption saturation of the amine-modified nanoporous silica foams which were coated onto the SLPFG. During the absorption process, the transmission was increasing by about 11.27 dB (from −23.11 to −11.84 dB), and the increasing rate of transmission was 0.4598 dB/min. Repeatable adsorption and desorption experiment results showed that the SLPFG CO₂ gas sensor exhibited good repeatability and a short response time. The recovery rate for each cycle was about 85%, and the required recovery time was short. Therefore, elaborated SLPFG gas sensor could potentially be used as a gas sensor for monitoring CO₂ adsorption in the context of various industrial, agricultural, and household applications.

Carbon fiber reinforced plastics (CFRP) have many mechanical properties that are superior to those of conventional structural materials and are becoming more and more widely used. Monitoring the curing process used to produce such composite material is important to ensure the quality of the process, especially for the characterization of residual strains after the material has been manufactured. In this study, we present a tilted fiber Bragg grating (TFBG) sensor used to monitor the curing of CFRP composite materials. The TFBG sensor was embedded into the layers of CFRP laminates to study the curing residual strain of the laminates. The experimental results showed that the curing residual stress was about −22.25 MPa, the axial residual strain was −281.351 με, and lateral residual strain of 89.91 με. The TFBG sensor was found to be sensitive to the curing residual strain of the CFRP, meaning that it has potential for use in applications involving composite curing processes. Moreover, it is indeed possible to improve the properties of composite materials via the optimization and monitoring of their curing parameters.

This paper presents the fabrication and application of a notched long-period fiber grating (NLPFG) with an amine-modified surface nanostructure for carbon dioxide (CO₂) gas sensing. The NLPFG with the modified surface nanostructure was fabricated by using inductively coupled plasma (ICP) etching with an Ag nanoparticle etching barrier. The experimental results show that the spectra were changed with the CO₂ gas flow within 12 min. Thereafter, the spectra of the NLPFG remained steady and unchanged. During the absorption process, the transmission loss was decreased by approximately 2.019 dB, and the decreased rate of transmission loss was 0.163 dB/min. The sensitivity was about −0.089 dB/%. These results demonstrate that the NLPFG CO₂ gas sensor has the advantages of steady performance, repeatability, and low cost. Therefore, the NLPFG can be utilized as a reliable CO₂ gas sensor.