High pressure tuning of whispering gallery mode resonances in a neodymium-doped glass microsphere

Abstract

The effects of pressure on the behavior of optical microspherical resonators, prepared from Nd3+ doped, barium titanium silicate glass, have been studied up to 5 GPa inside a diamond anvil cell using silicone oil as the hydrostatic transmission medium and ruby emission lines as the pressure gauge. The optical resonances, known as whispering gallery modes, were observed within the broad emission band of the Nd3+ ions, and the resonances were identified as a function of pressure. By means of simulations, it was found that the average wavelength position of both transverse electric and magnetic modes depended on the radius and refractive index of the sphere, but not on the refractive index of the pressure transmitting medium under the experimental conditions. This was used to define the average sensitivity of the resonant modes with the pressure. Therefore, a value of 6.5×10−4 GPa−1 has been obtained for this sensitivity, which is higher than the value for ruby, the most conventional pressure sensor.