Molecular-absorption-induced thermal bistablity in PECVD silicon nitride microring resonators

TL;DR

This paper investigates how linear absorption in PECVD silicon nitride microring resonators causes thermal bistability, with absorption and quality factor peaking near 1520 nm, enabling optical switching.

Contribution

It demonstrates the direct link between linear absorption and thermal bistability in PECVD silicon nitride microrings, with experimental calibration and theoretical analysis.

Findings

Linear absorption affects on-resonance transmission and quality factor.

Maximum absorption and quality factor near 1520 nm.

Thermal optical bistability enabled by phonon absorption.

Abstract

The wavelength selective linear absorption in communication C-band is investigated in CMOS-processed PECVD silicon nitride rings. In the overcoupled region, the linear absorption loss lowers the on-resonance transmission of a ring resonator and increases its overall quality factor. Both the linear absorption and ring quality factor are maximized near 1520 nm. The direct heating by phonon absorption leads to thermal optical bistable switching in PECVD silicon nitride based microring resonators. We calibrate the linear absorption rate in the microring resonator by measuring its transmission lineshape at different laser power levels, consistent with coupled mode theory calculations.