Based on surface plasmon resonance sensing theory, composite films of gold (Au) and silver (Ag) are used to improve sensing properties. A differential intensity detection method is also presented. Composite films with different thicknesses of Au and Ag are used for detection. Two light sources are used for differential detection, and the reference light path is determined to eliminate fluctuation of the light source. Detection theory is analyzed, and experiments are conducted to detect the refractive indices of glycerin solutions. The sensitivity of the differential-wavelength and single-wavelength methods is simulated. Results show that the use of composite film and the differential-wavelength method can enhance detection sensitivity. The rotating angle detection device and the spectrometer are not used in the experiments. The proposed detection device is small and cheap. The detecting range can be adjusted on the basis of the incident angles and wavelengths of the light sources. Thus, the proposed system can be extensively applied to detection.
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