Coupled optical resonances in a dielectric microsphere: physical concept of miniature optical pressure sensor
Yu.E. Geints1, I.V. Minin2,3, O.V. Minin2,3
1V.E. Zuev Institute of Atmospheric Optics of Siberian Branch of the Russian Academy of Science, Tomsk, Russia
2Research Tomsk Polytechnic University, Tomsk, Russia
3Siberian State University of Geosystems and Technologies, Novosibirsk, Russia
Keywords: optical resonance, optical pressure sensor, whispering gallery modes, wave reflection, optical wave interference, mesowavelength particle
Abstract
Optical resonance of the internal field of a dielectric microparticle occurs when the frequency of the incident light is tuned to the frequency of one of the particle spatial eigenmodes which leads to a sharp increase in optical intensity and higher field localization near the particle rim providing the formation of annularly-periodic structures in the form of standing waves, the so-called “whispering gallery” modes (WGM). 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 reflected backward radiation, which then couples within the microparticle volume. The optical intensity of the resulting WGM carries enough 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. We show that the pressure sensitivity of such a sensor depends on the quality factor of the excited resonant mode, as well as 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 non-contact type of the pressure sensor placement.
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