Mid-IR light modulators enabled by dynamically tunable ultra-high-Q silicon membrane metasurfaces

Area of Science:

• Photonics and Optical Engineering
• Materials Science
• Nanotechnology

Background:

• Metasurfaces offer subwavelength light control but face limitations in Q-factor, amplitude contrast, and static functionality.
• These challenges are amplified in the mid-infrared (mid-IR) due to material constraints.
• Existing metasurfaces are predominantly static, limiting their use in dynamic optical systems.

Purpose of the Study:

• To demonstrate actively tunable single-crystalline silicon membrane metasurfaces for mid-IR applications.
• To overcome the inherent limitations of static metasurfaces, particularly in the mid-IR spectrum.
• To achieve high Q-factors, strong amplitude contrast, and wafer-scale manufacturability in active metasurfaces.

Main Methods:

• Fabrication of single-crystalline silicon membrane metasurfaces.
• Characterization of optical properties, including Q-factors, in the mid-IR.
• Implementation and testing of electro-thermal tuning using Joule heating.
• Demonstration of ultrafast all-optical modulation via photo-generated carriers in silicon.

Main Results:

• Achieved record-high measured Q-factors up to 3000 in the mid-IR.
• Demonstrated electro-thermal tuning with >50% modulation depth at CMOS-compatible voltages and speeds up to 14.5 kHz.
• Showcased ultrafast all-optical modulation with nanosecond response times and estimated sub-GHz rates.
• Confirmed wafer-scale manufacturability of the silicon membrane metasurface platform.

Conclusions:

• Silicon membrane metasurfaces provide a scalable platform for active mid-IR photonics.
• The developed metasurfaces combine high Q-factors, strong amplitude contrast, and dynamic tunability.
• This work overcomes key limitations, paving the way for advanced active optical devices in the mid-IR spectrum.