Optical sensing with Anderson-localised light

TL;DR

This paper demonstrates that disorder-induced Anderson localisation in silicon nitride photonic crystal waveguides can be harnessed to create high-quality, scalable optical sensors capable of detecting refractive index changes and temperature variations with high sensitivity.

Contribution

It introduces a novel approach to optical sensing using Anderson-localised light in photonic crystals, leveraging fabrication imperfections as a resource rather than a flaw.

Findings

Wavelength shifts of up to 15.2 nm for refractive index changes.

Quality factors increase by over two times at cryogenic temperatures.

Multiple optical resonances enable simultaneous sensing of contaminants and temperature.

Abstract

We show that fabrication imperfections in silicon nitride photonic crystal waveguides can be used as a resource to efficiently confine light in the Anderson-localised regime and add functionalities to photonic devices. Our results prove that disorder-induced localisation of light can be utilised to realise an alternative class of high-quality optical sensors operating at room temperature. We measure wavelength shifts of optical resonances as large as 15.2 nm, more than 100 times the spectral linewidth of 0.15\,nm, for a refractive index change of about 0.38. By studying the temperature dependence of the optical properties of the system, we report wavelength shifts of up to about 2 nm and increases of more than a factor 2 in the quality factor of the cavity resonances, when going from room to cryogenic temperatures. Such a device can allow simultaneous sensing of both local contaminants and temperature variations, monitored by tens of optical resonances spontaneously appearing along a single photonic crystal waveguide. Our findings demonstrate the potential of Anderson-localised light in photonic crystals for scalable and efficient optical sensors operating in the visible and near-infrared range of wavelengths.