On-chip Brillouin notch filter on a silicon nitride ring resonator

TL;DR

This paper presents an integrated silicon nitride ring resonator that acts as a Brillouin notch filter, significantly reducing elastic background light to enable more effective on-chip Brillouin spectroscopy for biomedical imaging.

Contribution

The work introduces a fully integrated, ultra-compact Brillouin notch filter on a silicon nitride platform with high extinction ratio and Q factor, advancing on-chip spectrometer technology.

Findings

Achieved 10 dB extinction ratio in the on-chip filter

Demonstrated a Q factor of 1.9x10^5

Proof-of-concept for attenuating elastic background light

Abstract

Noncontact Brillouin spectroscopy is a purely optical and label-free method to retrieve fundamental material viscoelastic properties. Recently, the extension to a three-dimensional imaging modality has paved the way to novel exciting opportunities in the biomedical field, yet the detection of the Brillouin spectrum remains challenging as a consequence of the dominant elastic background light that typically overwhelms the inelastic Brillouin peaks. In this Letter, we demonstrate a fully integrated and ultra-compact Brillouin notch filter based on an optical ring resonator fabricated on a silicon nitride platform. Our on-chip ring resonator filter was measured to have a 10 dB extinction ratio and a Q factor of 1.9x10^5. The experimental results provide a proof-of-concept on the ability of the on-chip filter to attenuate the elastic background light, heralding future developments of fully integrated, ultra-compact and low-cost Brillouin spectrometers.