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.
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