Liquid sensors using refractive intensity at the end-face of a glass fiber connected to fiber-Bragg grating

All-fiber-optic liquid sensors were developed to detect liquid solutions and monitor the submersion. Their operating principle is based on Fresnel's laws of reflection at the end-face of silica fibers. Two types of sensing probes were fabricated using single-mode and multi-mode fibers. Their spectral responses were measured with respect to the intensity modulation caused by a change in the refractive index of the surrounding media. By comparing the optical output power of the sensor on exposing the probe to air and water, its potential as a sensitive submersion sensor was proved. The difference in the output power levels between exposure to air and water was 10 dB. Further, a fiber-Bragg grating (FBG) spliced to the sensor head was used for remote monitoring of whether the optical fiber or sensor head were damaged or not. The possibility of self-diagnosis of the sensor was demonstrated.