A Temperature Sensor Based on a Symmetrical Metal-Cladding Optical Waveguide

A compact temperature sensor based on a symmetrical metal-cladding optical waveguide using free-space coupling is proposed and demonstrated theoretically and experimentally. The symmetrical Au-cladding optical waveguide is based on a thin LiNbO₃ slab sandwiched between two metal films, which serve as the coupling layer and reflecting panel, respectively. The sensitivity of this sensor of 9.08×10⁻² deg/°C, 6.6×10⁻² deg/°C and 4.8×10⁻² deg/°C corresponding to 3238−order, 3237-order and 3236-order modes, respectively, are obtained. Higher resolution is predicted with a larger linear expansion coefficient material and a higher resolution θ/2θ goniometer.