An intensity measurement refractometer based on a symmetric metal-clad waveguide structure

An optical refractometer using intensity measurement to detect minute changes in the refractive index (RI) of aqueous analyte is illustrated in this paper. In this sensor, the analyte, which is sealed by an O-ring between two metal films, serves as the guiding layer of a symmetric metal-clad waveguide. By using the free-space coupling technique, an incident laser beam is coupled into the sensor structure as the sensing probe. The reflected beam intensity is monitored to analysis the sample's RI change. Both theoretical analysis and experimental results show that, due to concentrated power in the sample layer, the sensor exhibits magnificent sensitivity improvement. Besides, it also presents polarization independence.