A novel compact ultra-high sensitivity optical fiber temperature sensor based on surface plasmon resonance (SPR) is proposed and demonstrated. The sensor is fabricated by employing a helical-core fiber (HCF), which is polished as a D-type fiber on the helical-core region and coated with a layer of Au-film and polydimethylsiloxane (PDMS). The theoretical and experimental results show that the resonant wavelength and sensitivity of the proposed sensor can be effectively adjusted by changing the twisting pitch of HCF. Due to the high refractive index sensitivity of the sensor and the high thermo-optic coefficient of PDMS, the maximum sensitivity can reach -19.56 nm/°C at room temperature when the twist pitch of HCF is 2.1 mm. It is worth noting that the sensitivity can be further improved by using a shorter pitch of HCF. The proposed SPR temperature sensor has adjustable sensitivity, is easy to realize distributed sensing, and has potential application prospects in biomedical, healthcare, and other fields.
The prism‐based surface plasmon resonance (SPR) sensing system provides a flexible way to modulate the resonance wavelength by changing the incident angle. Unfortunately, it is difficult to implement such a type of modulation for optical fiber SPR sensor. Herein, a novel and flexible SPR sensor based on a side‐polishing helical‐core fiber (HCF), which is fabricated by twisting an eccentric core fiber, is presented. For the first time to the best of knowledge, the sensing effect of such a sensor theoretically and experimentally is demonstrated. Two SPR excitation methods based on the cladding whispering gallery modes and the core mode are introduced into studying the sensor. The results show that the resonant wavelength of the HCF SPR sensor can be effectively adjusted by changing the twist pitch of HCF. An average sensitivity of 7400 nm/RIU is achieved for the refractive index sensing from 1.375 to 1.385 with a twist pitch of 1.9 mm. This sensitivity can be further improved by using a shorter pitch of HCF. Those characteristics enable the fabrication of sensor arrays in one helical single‐core or multicore fiber with several different twist pitches for multiparameter measurement and may also find wide application in chemo/biosensing.
A tungsten disulfide (WS2) coated surface plasmon resonance (SPR) sensor based on gradient pitch Mach-Zehnder interferometer (GP-MZI) for measuring ethanol vapor concentration is proposed and verified by experiments. Under continuous CO2 laser heating, a MZI based on GP helix structure is fabricated by twisting single mode fiber (SMF), which can excites multi-order cladding modes. A gold film is deposited on the surface of the GP helix structure by a magnetic sputtering coating machine. WS2 film is coated on the gold film of the GP helix structure, which increases the evanescent field strength of the twisted structure surface and enhances the interaction between SPR wave and ethanol molecules. Since the absorption of ethanol molecules by WS2 sheets will cause the change of effective refractive index (RI) of WS2 film, the intensity of transmission signal can be adjusted accordingly. For multi-order cladding modes, the effective RI and the effective thermo-optic coefficient vary with the modal order, so the RI and temperature sensitivity of different modal orders are also different. So, the ethanol vapor concentration, relative humidity (RH), and temperature can be simultaneously measured by monitoring the intensity of those dips with the resolution of ± 0.030 mg/L, ±0.035%RH, and ± 0.010 ℃, respectively. This sensor structure provides a promising platform for multi-parameter sensing applications.
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