Demonstration of an optical cavity sensor with a differential detection method by refractive index measurements

This paper describes refractive index measurements for verifying a novel optical cavity based sensor using a differential detection method. Two low cost laser diodes at the wavelengths of 780 nm and 850 nm are used. The optical cavity is created by a SU-8 to SU-8 bonding of two silver sputtered glass substrates. The intensities of two lasers are measured by an sCMOS camera after the cavity is filled with a refractive index of fluid. We employed a differential detection method which calculates differential values using measured intensities in order to enhance sensitivity. Combined with the noise analysis, the limit of detection of refractive index is estimated to be 6.944 × 10^-6 R.I.U.