Design of a small-displacement sensing system based on the surface plasmon resonance technology in heterodyne interferometry

In this paper, a small-displacement sensing system based on the surface plasmon resonance technology in heterodyne interferometry is proposed. The basic sensing unit is composed of a prism assembly and a displacement probe. The prism assembly is composed of a halfwave (λ/2) plate, two right-angle prisms and two rotation stages. In a prism assembly, two right-angle prisms are coated with 2Ti film and 45.5nm Au film. Thus, the surface plasmons are excited when a equals to a resonant angle α_sp, α_sp≈43.813°. In order to achieve the best resolution of the system, both of the initial incident angles are equal to 43.813° on the hypotenuse surfaces of two prisms. The small-displacement sensor is with high sensitivity and resolution due to the attenuated total reflection effect in heterodyne interferometry. Besides, we can obtain the results of the experiment in a distant place by using a ZigBee/Wi-Fi module. It can be found that the displacement resolution of the small-displacement sensor can reach 0.3nm at least by numerical simulation. The small-displacement sensor has some merits, e.g., easy operation, high measurement accuracy, high resolution and rapid measurement, etc.