High-quality microresonators in the longwave infrared based on native germanium.

Area of Science:

• Photonics and Optical Engineering
• Materials Science
• Infrared Spectroscopy

Background:

• The longwave infrared (LWIR) spectrum (8–14 μm) is crucial for advanced sensing and imaging.
• Realizing chip-scale LWIR photonic devices requires ultra-low loss and low-dispersion components, which are currently limited.
• Existing LWIR microresonators suffer from high losses and low quality factors.

Purpose of the Study:

• To demonstrate the first high-quality microresonators in the LWIR spectral region.
• To enable ultra low-loss and low-dispersion photonic components for LWIR applications.
• To advance the development of precision sensors and broadband frequency combs in the LWIR.

Main Methods:

• Fabrication of native germanium microresonators.
• Coupling microresonators to partially-suspended germanium waveguides on a glass chip.
• Unambiguous measurement of isolated microresonator linewidths in the LWIR.

Main Results:

• Demonstrated the first high-quality microresonators in the LWIR using native germanium.
• Achieved propagation losses of 0.5 dB/cm at 8 μm.
• Measured intrinsic quality (Q) factors of 2.5 × 10⁵, nearly two orders of magnitude higher than previous LWIR resonators.

Conclusions:

• The developed germanium microresonators represent a significant advancement for LWIR photonics.
• These high-performance components are essential for novel sensing and nonlinear photonic applications in the LWIR.
• This work paves the way for chip-scale LWIR devices with unprecedented performance.