Optical Feedback FM-to-AM Conversion with integrated Micro-Ring Resonator for Displacement Sensing Applications

Abstract

Abstract In this study, we show the capability of integrated Micro-Ring Resonators (MRRs) to perform frequency-to-amplitude (FM-to-AM) conversion of optical feedback interferometry (OFI) signals with improved signal-to-noise ratio compared to conventional AM OFI signals. Further, contrary to traditional OFI FM-to-AM conversion techniques using gas cell-based edge filters and free-space or fiber Mach-Zehnder Interferometers (MZI), integrated photonic processing offers greater compactness and perturbation resilience, enhancing noise performance through improved temperature control and immunity to parasitic mechanical vibrations. The OFI FM-to-AM conversion was performed with a fabricated silicon nitride MRR of radius 120 μm and a quality factor of 130,000. The FM-to-AM conversion factor achieved was 0.61 GHz−1, with a noise equivalent displacement of only 4.9 nm for a 1 kHz bandwidth. This demonstration highlights the potential of integrated edge filters to replace traditional freespace and fiber architectures, more prone to environmental perturbations, in OFI signal processing for vibrometric applications.