Ultra-Compact Optical Thermo-Hygrometer Based on Bilayer Micro-Cap on Fiber Facet

We demonstrate an ultra-compact optical fiber thermo-hygrometer on the base of a bilayer OA (Optical Adhesive, a kind of polymer) micro-cap covering the entire SMF (Single-Mode-Fiber) facet. In fabrication, two types of OA are dispensed to fiber facet successively and stratified distinctly forming the bilayer micro-cap, which contains a flat and 2 spherical interfaces reflecting emitted light. Hence, hybrid interference would occur. The experimental results show that the sensitivity for humidity and temperature reach −3.641deg/%RH and −4.527deg/°C when demodulating interference phase shift, and dual-parameter measurement could also be achieved. The proposed optical fiber thermo-hygrometer is integrated, robust and with high sensitivity, making it satisfy lab-on-tip measuring requirement.