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

We developed a technique that enables replacement of a metallic waveguide cladding with a low-index (n≈1.4) material - CaF2 or BaF2. It 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 (λ∼10 µm) and a dispersive resonator at 300 K and at 78 K. Finally, we evaluate this approach's potential as a platform for waveguiding in the mid-IR spectral range, with numerical simulations that reveal losses in the 1-10 cm-1 range.