Compact silicon-germanium microresonators for long-wave infrared frequencies

We report on the fabrication and investigation of compact microresonators (100 µm radius) operating in the long-wave infrared range, exploiting silicon-germanium graded waveguides. Two designs are considered and demonstrate intrinsic quality factors above 4 × 10⁴ at 7.5 µm wavelength and 2 × 10⁴ at 8 µm wavelength. The resonances measured in these systems attain a 0 dB extinction ratio. These properties could be leveraged for Kerr-comb generation, on-chip optical filtering or multiplexing systems in the long-wave infrared range.