Towards Chiral Sensing and Spectroscopy Enabled by All-Dielectric Integrated Photonic Waveguides

Chiral spectroscopy is a powerful technique that enables to identify the chirality of matter through optical means. So far, experiments to check the chirality of matter or nanostructures have been carried out using free-space propagating light beams. However, for the sake of miniaturization, it would be desirable to perform chiral spectroscopy in photonic integrated platforms, with the additional benefit of massive parallel detection, low-cost production, repeatability, and portability of such a chiroptical device. Here we show that all-dielectric integrated photonic waveguides can support chiral modes under proper combination of the fundamental eigenmodes. In particular, we investigate two mainstream configurations: a dielectric wire with square cross-section and a slotted waveguide. We analyze numerically three different scenarios in which such waveguides could be used for chiral detection: all-dielectric waveguides as near-field probes, evanescent-induced chiral fields, and chiroptical interaction in void slots. In all the cases we consider a metallic nanohelix as a chiral probe, though all the approaches can be extended to other kinds of chiral nanostructures as well as matter. Our results establish that chiral applications such as sensing and spectroscopy could be realized in standard integrated optics, in particular, with silicon-based technology.