Coupled Optical Resonances in a Dielectric Microsphere: Physical Concept of a Miniature Optical Pressure Sensor

Optical resonance of the internal field of a dielectric microparticle occurs when the frequency of the incident light wave is tuned to the frequency of one of the particle spatial eigenmodes and leads to a sharp increase in the intensity and localization of the field near the surface with the formation of annular-periodic structures in the form of standing waves, the so-called whispering gallery modes (WGMs). We theoretically consider the case where a dielectric microsphere is placed near a flexible light reflecting membrane which acts as an external pressure sensor. In this case, due to reflection from the reflecting membrane, the WGMs of the sphere are excited twice by direct and backward reflected radiation which then couples within the microparticle volume. The optical intensity of the resulting WGM field carries information about the position of the flexible loaded membrane. This allows one to propose a physical concept of a new miniature all-optical pressure sensor. It is shown that the pressure sensitivity of such a sensor depends on the Q factor of the excited resonance mode, as well as on the geometrical and mechanical parameters of the flexible membrane. Important advantages of the sensor proposed are the miniature design (the size of the sensor is determined by the diameter of the flexible membrane) and the noncontact type of the pressure sensor placement.

Automated summary

This article introduces a miniature all-optical pressure sensor based on optical resonance. By utilizing the resonance mode of microparticles and the reflection effect of a flexible reflecting membrane, pressure sensitivity to the position of the membrane can be achieved. The advantages of this sensor include its compact design and noncontact placement.