Optical fiber refractive index sensor based on SMF-TCF-NCF-SMF interference structure

A novel optical fiber refractive index (RI) and strain sensor based on the combination of single mode fiber (SMF), thin-core fiber (TCF), and no-core fiber (NCF) was proposed. Due to the inter-mode interference caused by the mode mismatch, the sensor is sensitive to the RI of the environment but insensitive to temperature. The experimental results show that in the RI range of 1.3333-1.3794, the sensitivity of dip A (1543 nm) and dip B (1565 nm) are 101.9446 nm/RIU and 109.9009 nm/RIU, respectively. In the temperature range of 15-85 degrees C, the maximum wavelength shifts are only -3.5 pm/degrees C and -4.9 pm/degrees C respecitvely for dip A and dip B, indicating that the sensor can eliminate the cross-sensitivity of temperature to the RI. The sensor was used to detect alcohol, sucrose, NaCl and glycerin solution with the same RI and there is no obvious dip shift of the interference spectra. This sensor has the advantages of high RI sensitivities, strong anti-temperature interference ability, compact structure and has the potential application in the health and security monitoring.