Simultaneous measurement of refraction and absorption with an integrated near-infrared Mach-Zehnder interferometer

TL;DR

This paper introduces a silicon nitride Mach-Zehnder interferometer capable of simultaneously measuring both refraction and absorption, providing a comprehensive complex refractive index analysis with high sensitivity in the near-infrared range.

Contribution

The work presents the first integrated sensor that directly measures both real and imaginary parts of the complex refractive index simultaneously.

Findings

Achieved detection limits below 2×10⁻⁶ RIU for both parameters.

Demonstrated the sensor as an integrated dispersion spectrometer.

Validated the approach through experimental results.

Abstract

Most integrated evanescent-field photonic sensors measure changes in either the real part or the imaginary part of the complex refractive index of the sample, i.e., refraction or absorption. Here we propose and experimentally demonstrate a near-infrared sensor based on a silicon nitride Mach-Zehnder interferometer which provides a direct measurement of the complex refractive index. Our architecture exhibits a high sensitivity, achieving limits of detection below $2\cdot 10^{-6}\,\mathrm{RIU}$ for both the real and imaginary parts of the refractive index. We furthermore show that our sensor can be employed as an integrated dispersion spectrometer.