Grating-Graphene Metamaterial as a Platform for Terahertz Nonlinear Photonics

Area of Science:

• Optics and Photonics
• Materials Science
• Condensed Matter Physics

Background:

• Nonlinear optics is crucial for advanced optical and optoelectronic technologies.
• There's a need for efficient, compact nonlinear materials for chip integration and room-temperature operation.
• Two-dimensional materials like graphene show promise due to large nonlinearity, but suffer from short interaction lengths.

Purpose of the Study:

• To overcome the limited light-matter interaction length in 2D materials for enhanced nonlinear optical conversion.
• To develop a metamaterial platform for efficient terahertz (THz) nonlinear applications.
• To demonstrate chip-integrated, room-temperature THz nonlinear conversion using graphene.

Main Methods:

• Fabrication of a metamaterial platform integrating graphene with a photonic grating structure.
• Measurement of terahertz third-harmonic generation (THG) in the grating-graphene metamaterial.
• Characterization of nonlinear optical properties, including third-order nonlinear susceptibility and conversion efficiency.

Main Results:

• Achieved an effective third-order nonlinear susceptibility of 3 × 10^-8 m²/V² (21 esu) at 0.7 THz, 50 times greater than bare graphene.
• Observed a 3-orders-of-magnitude increase in third-harmonic signal intensity due to the grating.
• Demonstrated up to ~1% field conversion efficiency for third harmonic generation at moderate field strengths (~30 kV/cm).
• Observed enhanced generation of higher-order harmonics, up to the ninth harmonic.

Conclusions:

• Grating-enhanced graphene metamaterials provide a powerful platform for significantly boosting THz nonlinear optical effects.
• This approach overcomes the inherent limitations of 2D materials, enabling efficient nonlinear conversion.
• The developed metamaterials are suitable for commercially viable, CMOS-compatible, room-temperature, chip-integrated THz nonlinear applications.