On-grating graphene surface plasmons enabling spatial differentiation in the terahertz region

Area of Science:

• Plasmonics
• Nanophotonics
• Metamaterials

Background:

• Spatial differentiation is crucial for image processing and optical computing.
• Existing methods often lack compactness or operate at lower frequencies.
• Terahertz (THz) technology offers unique capabilities for non-ionizing imaging and sensing.

Purpose of the Study:

• To propose and demonstrate a novel graphene-on-grating nanostructure for second-order spatial differentiation in the THz region.
• To achieve compact, high-accuracy analog computation for THz wave manipulation.
• To enable real-time imaging applications in THz security detection.

Main Methods:

• Utilizing a graphene-on-grating nanostructure.
• Leveraging interference between direct reflected fields and surface plasmon polaritons (SPPs).
• Applying spatial coupled-mode theory to derive critical coupling conditions for differentiation.

Main Results:

• The proposed structure enables second-order spatial differentiation based on critical coupling.
• Numerical simulations with Gaussian beams show high accuracy (>95%) even for narrow beam waists (w₀=0.68λ).
• The nanostructure is ultra-compact (<0.1λ thickness) and operates in the THz frequency range.

Conclusions:

• The graphene-on-grating nanostructure effectively performs second-order spatial differentiation in the THz region.
• The device's high spatial bandwidth and accuracy make it suitable for advanced THz applications.
• This compact differentiator holds promise for real-time THz imaging and security systems.