We have studied transmission spectra of a silicon nitride O-ring resonator with a Ge2Sb2Te5 (GST) thin-film cover. We have performed numerical simulations of the transmission, absorption, reflection, and scattering for the GST cells of various thicknesses and lengths and have also measured transmission spectra O-ring resonators for GST cells of various length and phase states. An analysis of the changes in the Q-factors has enabled us to identify the region of the GST cells where light scattering and absorption dominate and find the size dependence of amorphous and crystalline GST attenuation coefficients. The demonstrated results pave the way to high energy-efficient on-chip devices of a small footprint that can be switched either optically or electrically.
