Electrically tunable vertically coupled ring resonator based on Si–ITO heterojunction

We numerically propose a vertically coupled ring resonator with a high extinction ratio and tunable group delay based on Silicon (Si)–Indium Tin Oxide (ITO) heterojunction. The vertically coupled ring and bus waveguide configuration offers several advantages including, improved coupling efficiency, and reduced propagation losses, which allows for efficient coupling between the Si-bus waveguide and the Si–ITO ring, leading to stronger light–matter interaction and enhanced light transmission. The Si–ITO heterojunction within the ring resonator enables electrically varying carrier concentration of ITO, thereby reaching the epsilon-near-zero (ENZ) region. The achievement of the ENZ region leads to enhanced optical absorption and improved device performance. The proposed device exhibits a high extinction ratio of 20.5 dB. Moreover, the voltage-dependent group delay of the device exhibited a significant variation of 29 psec when the applied voltage is varied within the range of − 4 V to 4 V. The voltage-tunable vertically coupled Si–ITO heterojunction-based ring modulator offers a promising platform for integrated photonics, with potential applications in optical communication, signal processing, and sensing.