One million quality factor integrated ring resonators in the mid-infrared

Area of Science:

• Integrated Photonics
• Mid-Infrared Optics
• Materials Science

Background:

• Mid-infrared (MIR) integrated photonics is crucial for sensing and spectroscopy.
• Silicon photonics platforms face limitations in the MIR due to silicon's optical losses.
• Silicon Germanium (SiGe) on Silicon offers a promising alternative for MIR applications.

Purpose of the Study:

• To demonstrate high-quality factor (Q-factor) ring resonators on a SiGe-on-Si platform.
• To operate these resonators in the critical 3.5-4.6 µm wavelength range.
• To validate the performance through observable optical phenomena.

Main Methods:

• Fabrication of SiGe-on-Si ring resonators using advanced lithography and etching techniques.
• Characterization of resonator performance in the 3.5-4.6 µm spectral region.
• Analysis of resonance splitting (degeneracy lifting) and optical bistability.

Main Results:

• Achieved record high Q-factors exceeding one million for SiGe ring resonators.
• Demonstrated stable operation and high performance in the target mid-infrared wavelengths.
• Confirmed high Q-factors via clear observation of clockwise (CW) and counter-clockwise (CCW) resonance degeneracy lifting.
• Observed optical bistability, indicative of significant optical power buildup within the resonators.

Conclusions:

• The SiGe-on-Si platform is highly suitable for high-performance mid-infrared integrated photonics.
• The demonstrated Q-factors rival those of other advanced photonic platforms.
• This work establishes SiGe as a leading material for future MIR photonic integrated circuits.