Mid-infrared high-Q germanium microring resonator

TLDR

Germanium, CMOS‑compatible and transparent across 2–15 µm, is a promising material for mid‑infrared photonics, yet high‑Q on‑chip resonators have been limited by material quality and platform design, making the development of a high‑Q germanium microring a significant step toward on‑chip MIR applications. The device is realized using smart‑cut fabrication of high‑quality Ge‑on‑insulator wafers and a suspended‑membrane structure. Here we experimentally demonstrate an air‑cladding MIR germanium microring resonator with the highest loaded Q‑factor of ~57,000 across all germanium‑based platforms to date, achieving a propagation loss of 5.4 dB/cm and an extinction ratio of 22 dB near critical coupling.

Abstract

Germanium is a promising material for mid-infrared (MIR) integrated photonics due to its CMOS compatibility and wide transparency window covering the fingerprint spectral region (2–15 μm). However, due to the limited quality and structural configurations of conventional germanium-based integration platforms, the realization of high-Q on-chip germanium resonators in the MIR spectral range remains challenging to date. Here we experimentally demonstrate an air-cladding MIR germanium microring resonator with, to the best of our knowledge, the highest loaded Q-factor of ∼57,000 across all germanium-based integration platforms to date. A propagation loss of 5.4 dB/cm and a high extinction ratio of 22 dB approaching the critical coupling condition are experimentally realized. These are enabled by our smart-cut methods for developing high-quality germanium-on-insulator wafers and by implementing our suspended-membrane structure. Our high-Q germanium microring resonator is a promising step towards a number of on-chip applications in the MIR spectral range.