Reduction in Operation Voltage of Silicon Ring Optical Modulator Using High-k (Ba,Sr)TiO3 Cladding Layer

Abstract

Electric-field drive Si ring optical modulators with a (Ba,Sr)TiO3 (BST) cladding layer have been fabricated. A lateral electric field is applied across the Si ring using the side Pt electrodes, and the optical output from the drop port is measured. It is estimated that an operation voltage of less than 10 V is possible when the relative dielectric constant of the cladding layer is larger than 150 and the quality factor is 5×104. The operation voltage of the fabricated optical modulator with a BST cladding layer is reduced to <1/8 relative to that of the SiO2 and Si3N4 cladding layers. One reason for the still high operation voltage (125 V for 75% modulation) is the low quality factor, which is limited by the light propagation loss of the BST film. It is also estimated that an operation voltage of less than 10 V is achievable when the propagation loss of the cladding layer is improved to less than 28 dB/cm.