On the theory of whispering-gallery modes in a spherical layer

The theory of whispering-gallery modes (WGMs) in a dielectric spherical layer is developed based on the approximation of Bessel functions by Airy functions. It is shown that the optimal layer thickness exists at which the intensities of WGM fields in the spherical layer are more than an order of magnitude greater than those of WGM fields in a solid sphere.