In this research, we proposed and experimentally verified a compact all-fiber sensor that can measure refractive index (RI) and temperature simultaneously. Two segments of hollow-core fiber (HCF) are connected to the two ends of the four-core fiber (FCF) as a beam splitter and a coupler, and then spliced with two sections of single-mode fibers (lead-in and lead-out SMF), respectively. The two hollow-core fibers can excite the higher-order modes of the four-core fiber and recouple the core modes and higher-order modes into the outgoing single-mode fiber, thereby forming inter-mode interference. The different response sensitivities of two interference dips to RI and temperature manifest that the proposed structure can achieve simultaneous measurement. From the experimental results, it can be seen that the maximum sensitivity of the sensor to RI and temperature is 275.30 nm/RIU and 94.4 pm/°C, respectively. When the wavelength resolution is 0.02 nm, the RI and temperature resolutions of the sensor are 7.74 × 10−5 RIU and 0.335 °C. The proposed dual-parameter optical sensor has the advantages of high sensitivities, good repeatability, simple fabrication, and structure. In addition, it has potential application value in multi-parameter simultaneous measurement.

We have proposed and experimentally demonstrated a dual-parameter optical fiber sensor for simultaneous measurement of magnetic field and temperature. The sensor is a magnetofluid-coated single-mode fiber (SMF)-U-shaped hollow-core fiber (UHCF)-single-mode fiber (SMF) (SMF-UHCF-SMF) fiber structure. Combined with the intermodal interference and the macro-bending loss of the U-shaped fiber structure, the U-shaped fiber sensor with different bend diameters was investigated. In our experiments, the transmission spectra of the sensor varied with magnetic field strength and temperature around the sensing structure, respectively. The dip wavelengths of the interference spectra of the proposed sensor exhibit red shifts with magnetic field strength and temperature, and the maximum sensitivity of magnetic field strength and temperature were 1.0898 nm/mT and 0.324 nm/°C, respectively.

This article proposes and demonstrates a kind of all fiber vector magnetic field sensor based on side-polished hollow-core fiber (SPHCF) coated with magnetic fluid. The magnetic field sensor is composed of a single mode fiber- SPHCF - single mode fiber structure coated with the magnetic fluid. Our designed sensor has good identification of magnetic field orientation. In the experiments, the maximum orientation sensitivity and the intensity sensitivity are 0.19dB/° and -769.05 pm/mT, respectively. Additionally, we found that the changes of the concentration of the magnetic fluid and the sidepolished depth will lead to the change of the higher-order modes involved in the interference as well as the sensitivity of the magnetic field sensor. The proposed vector magnetic field sensor has the advantages of all fiber, simple structure, cost-effective and easy to manufacture, and etc.

We demonstrate an optical fiber vector magnetic field sensor based on Mach-Zehnder interferometer by splicing a section of side-polished hollow-core fiber between two sections of single-mode fiber. As a varied magnetic field is applied to the magnetic fluid encapsulated sandwiched structure, the transmission spectra of the sensor will vary with the intensity and the direction of the magnetic field. In our experiments, at the incident light wavelength around 1510 nm, the magnetic field orientation sensitivity and intensity sensitivity are 180 pm/° and 240 pm/mT, respectively. In addition, a high contrast of about 20 dB between the signal interference dip with the noise interference dip is obtained in our experiments. The proposed all-optical fiber magnetic field sensor has the advantages of simple structure, compact size, low cost and easy fabrication.