A Novel Visible Light-Excited Interference Behavior Occurred in Capillary Waveguide

In this article we demonstrated a novel interference behavior excited by visible light in the capillary waveguide (CWG). We investigated the sensing principle of CWG with filling liquid and optical characteristics of interference systematically. This CWG-based sensing element is theoretically verified to possess continuously tunable thermal sensitivity by changing the thermo-optic coefficient of the filling liquid. As expected, experimental results show that the proposed sensor possesses sharp interference fringes and the tunable sensitivity of temperature. Unlike most optical fiber interferometers, the optical path difference of our sensing element is generated in the wall of CWG instead of air cavity. Besides, interference occurs in the visible light band, which greatly improves dynamic range and reduces the cost of system setup. The novel optical behavior we investigated offers a way to the utility of the waveguide as an optical interferometer.