Silicon Nitride Photonic Waveguide-Based Young's Interferometer for Molecular Sensing

TL;DR

This paper presents a silicon nitride photonic waveguide-based Young's interferometer sensor integrated with CMOS detection, demonstrating sensitive glucose measurements and potential for biosensing applications.

Contribution

It introduces a novel low-cost fabrication method for integrated photonic sensors and demonstrates their application in molecular sensing using interferometry.

Findings

Interference fringe visibility exceeds 0.75.

Phase shift measurement for glucose concentrations around 10 ug/ml.

Sensor design optimized for sensitivity using FDTD analysis.

Abstract

Devices based on photonic integrated circuits play a crucial role in the development of low-cost, high-performance, industry-scale manufacturable sensors. We report the design, fabrication, and application of a silicon nitride waveguide-based integrated photonic sensor in Young's interferometer configuration combined with Complementary Metal-Oxide-Semiconductor (CMOS) imaging detection. We use a finite-difference time-domain method to analyze the performance of the sensor device and optimize the sensitivity of the fundamental transverse-electric (TE) mode. We develop a low-cost fabrication method for the photonic sensor chip, using photolithography-compatible dimensions, and produce the sensing region with wet-etching of silicon dioxide. We demonstrate the sensor's functioning by measuring the optical phase shift with glucose concentration in an aqueous solution. We obtain consistent interference patterns with fringe visibility exceeding 0.75 and measure the phase differences for glucose concentrations in the 10 ug/ml order, corresponding to the order of 10^7 molecules in the sensing volume. We envision extending this work to functionalized surface sensors based on molecular binding. Our work will impact biosensing applications and, more generally, the fabrication of interferometric-based photonic devices.