The use of the Silicon-on-Insulator (SOI) platform has been prominent for
realizing CMOS-compatible, high-performance photonic integrated circuits
(PICs). But in recent years, the silicon-nitride-on-silicon-dioxide
(SiN-on-SiO2​) platform has garnered increasing interest as an alternative to
the SOI platform for realizing high-performance PICs. This is because of its
several beneficial properties over the SOI platform, such as low optical
losses, high thermo-optic stability, broader wavelength transparency range, and
high tolerance to fabrication-process variations. However, SiN-on-SiO2​ based
active devices such as modulators are scarce and lack in desired performance,
due to the absence of free-carrier based activity in the SiN material and the
complexity of integrating other active materials with SiN-on-SiO2​ platform.
This shortcoming hinders the SiN-on-SiO2​ platform for realizing active PICs.
To address this shortcoming, we demonstrate a SiN-on-SiO2​ microring
resonator (MRR) based active modulator in this article. Our designed MRR
modulator employs an Indium-Tin-Oxide (ITO)-SiN-ITO thin-film stack, in which
the ITO thin films act as the upper and lower claddings of the SiN MRR. The
ITO-SiN-ITO thin-film stack leverages the free-carrier assisted, high-amplitude
refractive index change in the ITO films to effect a large electro-refractive
optical modulation in the device. Based on the electrostatic, transient, and
finite difference time domain (FDTD) simulations, conducted using photonics
foundry-validated tools, we show that our modulator achieves 280 pm/V resonance
modulation efficiency, 67.8 GHz 3-dB modulation bandwidth, ∼19 nm
free-spectral range (FSR), ∼0.23 dB insertion loss, and 10.31 dB
extinction ratio for optical on-off-keying (OOK) modulation at 30 Gb/s