Search

An optical fiber sensor based on a structural modulated ultralong period microfiber grating (SULPMG) for the simultaneous measurement of the refractive index and temperature within a low-refractive-index (RI) range is experimentally demonstrated. By using the arc discharge method followed by hydrogen-oxygen flame drawing technology, an SULPMG with a small waist diameter provides a strong evanescent field. The results show that a sensitivity as high as 2418.6 nm/RIU and −561.4 dB/RIU can be achieved in the low-RI range from 1.3359 to 1.3402. An experimental temperature sensitivity of approximately −0.145 nm/°C can be achieved over an ambient temperature range of 30–80 °C. The theoretical analysis and experimental results are consistent. The proposed sensor with an outstanding response to a low RI can be applied to research in the chemical analysis and biomedical fields.

A structure-modulated ultralong-period microfiber grating (SULPMG) was successfully designed for simultaneous measurement of microdisplacement and temperature. The SULPMG was fabricated based on the standard single-mode fiber using the arc discharge method followed by hydrogenoxygen flame drawing technology. The resonance wavelength of the two notches shifts toward a shorter range when the microdisplacement varies from 0 μm to 65 μm. The results show that the wavelength sensitivity could reach a maximum value of -288.9 pm/μm with a total depth change of 2.95 dB and a high resolution of 69 nm. The temperature sensitivity of the proposed sensor could reach approximately -26.4 pm/°C over an ambient temperature range of 22-90 °C. The proposed sensor can be expected to be applied in fields pertaining to microfabrication and many industrial applications.

A chloride ion sensor based on a microfiber coupler with a Sagnac loop is proposed. Experimental results show that the sensitivity reaches a maximum of 423 pm/‰ and that the detection limit for the chloride ion concentration is 0.447‰ at a wavelength of 1595 nm. The proposed sensor is characterized by simple and easy manufacturing process, compact structure and low cost. This sensing unit has great potential for application in marine chloride detection and environmental safety monitoring, especially for monitoring building corrosion and water pollution.

An optical sensor that simultaneously measures the concentration of the biochemical oxygen demand (BOD) and temperature in water based on a tapered microfiber is proposed for environmental monitoring. The sensor is characterized by a strong evanescent field, which is more sensitive to liquids with a low refractive index and a low transmission loss. The results show that as the BOD concentration increases, the interference spectrum shifts toward longer wavelengths, the spectral loss decreases, and the sensitivities of the BOD are 12.17 nm/mg/mL and − 2.387 d B / m g / m L in the range of 0.25–1 mg/mL, which indicates the extent of the water pollution. The detection limit for the BOD concentration is as low as 0.0016 mg/mL. As the ambient temperature increases, the interference spectrum shifts toward shorter wavelengths, the spectral loss decreases, and the temperature sensitivities are − 0.339 n m / ∘ C and − 0.031 d B / ∘ C in the range of 30°C–60°C. The matrix method can be used to achieve the simultaneous measurement of the BOD concentration and environmental temperature because the spectral interference peaks have different responses to these two parameters. The sensor can not only be used for detecting water pollution in rivers, drinking water, and groundwater but can also be utilized for other types of environmental monitoring. This sensor has great potential to act as a basic sensing unit in fiber-optic sensor networks for multiparameter measurements and intelligent monitoring.

A chloride ion sensor based on a multitaper modulated fiber fabricated via arc discharge is proposed and studied experimentally and theoretically. The sensing unit consists of four periodic tapers with a diameter of 28.24 μm, a period of 676 μm, and a total length of 2.7 mm. The results show that the concentration sensitivity values are 170 pm/(g/L) at a wavelength of 1303.60 nm and 220 pm/(g/L) at a wavelength of 1389.84 nm when the chloride ion concentration is increased from 0 to 40 g/L. The proposed sensor is characterized by a simple manufacturing process, a compact structure, and a low cost, and this sensing unit has great potential for application in marine chloride detection and environmental safety monitoring, especially for monitoring building corrosion and water pollution.

The measurement of chloride ion concentrations has been studied for the purpose of monitoring the quality of water resources. In this paper, a chloride ion sensor based on a microfiber coupler with a Sagnac loop is proposed. The microfiber coupler, which acts as the sensing unit and has a diameter of 10 μm and a length of 1 mm, is fabricated using the flame-brushing technique, and the two ends are connected to form a Sagnac loop, which acts as a reflector to enhance the reflection in the structure. Experimental results show that the sensitivity reaches a maximum of 423 pm/‰ and that the detection limit for the chloride ion concentration is 0.447‰ at a wavelength of 1595 nm. The proposed sensor is characterized by a simple and easy manufacturing process, compact structure, and low cost; further, this sensing unit has great potential for applications in marine chloride detection and environmental safety monitoring, especially for monitoring building corrosion and water pollution.