III-V on CaF2: a possible waveguiding platform for mid-IR photonic devices

TL;DR

This paper presents a novel waveguiding platform using low-index CaF2 or BaF2 materials for mid-IR photonic devices, enabling improved confinement and substrate access, demonstrated through strong light-matter coupling at mid-IR wavelengths.

Contribution

The authors introduce a technique replacing metallic cladding with low-index transparent materials, allowing double-side patterning and strong mid-IR light-matter interactions.

Findings

Successful demonstration of strong light-matter coupling at 10 microns

Losses estimated in the 1-10 cm$^{-1}$ range from simulations

Platform enables substrate access and improved confinement in mid-IR

Abstract

We developed a technique that enables to replace a metallic waveguide cladding with a low-index (n $\sim$ 1.4) material - CaF2 or BaF2 - that in addition is transparent from the mid-IR up to the visible range: elevated confinement is preserved while introducing an optical entryway through the substrate. Replacing the metallic backplane also allows double-side patterning of the active region. Using this approach, we demonstrate strong light-matter coupling between an intersubband transition (lambda $\sim$ 10 microns) and a dispersive resonator, at 300 K and at 78 K. Finally, we evaluate the potential of this approach as a platform for waveguiding in the mid-IR spectral range, with numerical simulations that reveal losses in the 1-10 cm$^{-1}$ range.