Optical-fiber Temperature Sensor Based on Capillary-sealed MSM Fiber Structure

A high sensitivity temperature sensor based on capillary-sealed multimode-single mode-multimode (MSM) fiber structure is proposed and simulated. Temperature variation is indirectly measured by this sensor probe due to the high thermo-optic coefficient of the alcohol filled in the capillary. The interference spectrum is calculated by beam propagating method (BPM). In order to improve the temperature sensitivity, taper is introduced to the sensing part. To verify the importance of the fiber taper, the sensing structure with tapering is also simulated and the linear relationship between temperature variation and wavelength shifts of spectrum for tapered and no-tapered sensor are obtained to compare the sensitivities. The conclusion is that the temperature sensitivity for tapered structure is significantly higher than that of the no tapered structure. As an 80 mu m-thick taper is fabricated in the middle SMF, the temperature sensitivity is increased from 0.04 nm/degrees C to 0.12 nm/degrees C and as we know it can be further improved by a thinner taper.