Imaging metasurfaces based on graphene-loaded slot antennas

Area of Science:

• Optics and Photonics
• Materials Science
• Infrared Technology

Background:

• Traditional spectral imagers use filter arrays with low efficiency (∼1/N), particularly problematic for sensitive thermal infrared (IR) detection.
• Existing thermal IR sensors have inherently low detectivity, necessitating highly efficient spectral imaging solutions.
• Metasurfaces offer a promising platform for novel optical device functionalities due to their sub-wavelength structures.

Purpose of the Study:

• To propose and demonstrate an efficient, compact thermal infrared spectral imager.
• To overcome the efficiency limitations of conventional filter-based spectral imagers.
• To develop a metasurface-based approach compatible with CMOS integration for thermal IR applications.

Main Methods:

• Designed a metasurface composed of sub-wavelength-spaced, tuned slot antennas coupled to photosensitive graphene elements.
• Utilized graphene for its photoresponse extending to thermal IR wavelengths.
• Developed a circuit model for optical properties and validated with full-wave simulations.

Main Results:

• Achieved broadband absorption in graphene exceeding the 1/N efficiency limit.
• Demonstrated a theoretical free space-to-graphene photodetector coupling efficiency of approximately 58% over a broad wavenumber range (1050–1700 cm⁻¹).
• Showcased a four-spectral-channel gold metasurface with a specific antenna pitch (0.883 µm x 6.0 µm).

Conclusions:

• The proposed metasurface design offers a significant improvement in efficiency for thermal infrared spectral imaging.
• This technology enables the development of compact, CMOS-integrable thermal IR spectral imagers.
• The findings pave the way for advanced sensing applications in the thermal infrared spectrum.