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Crystalline germanium high-Q microresonators for mid-IR
Optics Express
|June 11, 2024
Summary
Researchers developed high-quality germanium microresonators, achieving over 20 million Q-factors for mid-infrared photonics. This breakthrough enhances material potential and enables precise optical loss measurements.
Area of Science:
- Photonics and optical engineering.
- Materials science for nonlinear optics.
Background:
- High-quality-factor optical microresonators are crucial for many applications.
- The mid-infrared (mid-IR) spectrum lacks suitable materials for nonlinear photonics.
- Crystalline germanium offers desirable properties like a high nonlinear refractive index and broad transparency.
Purpose of the Study:
- To fabricate germanium microresonators with ultra-high Q-factors.
- To investigate optical loss mechanisms in germanium microresonators.
- To enable precise measurement of nonlinear absorption coefficients in the mid-IR.
Main Methods:
- Fabrication of crystalline germanium microresonators with radii of 1.35 and 1.5 mm.
- Measurement of optical quality factors (Q-factors) at 2.68 µm wavelength.
- Characterization of two-photon absorption (TPA) and free-carrier absorption using the microresonators.
Main Results:
- Achieved Q-factors exceeding 20 million, a hundredfold improvement over previous reports.
- Q-factors approached the material's absorption limit at 2.68 µm.
- Measured the TPA coefficient as (0.71 ± 0.12) × 10⁻⁸ m/W at 2.68 µm.
Conclusions:
- Ultra-high Q-factor germanium microresonators are demonstrated, overcoming previous loss limitations.
- Whispering gallery mode microresonators are effective tools for material characterization and loss analysis.
- These findings pave the way for advanced germanium-based nonlinear photonics in the mid-IR.
