Broadband Achromatic Metasurfaces for Longwave Infrared Applications

Area of Science:

• Optics and Photonics
• Materials Science

Background:

• Longwave infrared (LWIR) optics are crucial for thermal imaging and wireless communication.
• Metasurfaces offer potential for miniaturized LWIR integrated optics.
• Conventional metasurfaces suffer from high chromatic dispersion, limiting broadband applications.

Purpose of the Study:

• To analyze chromatic dispersion in metasurfaces using ray tracing.
• To present a general method for correcting chromatic aberrations in metasurfaces.
• To demonstrate broadband achromatic metasurfaces for LWIR applications.

Main Methods:

• Ray tracing analysis of metasurface chromatic dispersion.
• Combining dynamic and geometric phases to control group delay and phase profiles.
• Fabrication of all-germanium metasurfaces.

Main Results:

• A general method for achieving achromatic performance in metasurfaces was developed.
• Two broadband achromatic metasurfaces were demonstrated in the LWIR spectrum (9.6–11.6 μm).
• A metalens achieved NA of 0.32 with >0.8 Strehl ratio and 31% efficiency.
• A metasurface grating provided a constant 30° deflection angle.

Conclusions:

• The developed metasurfaces significantly advance LWIR optics by correcting chromatic aberrations.
• This work brings achromatic LWIR metasurfaces closer to practical technological implementation.
• The combined phase approach offers a robust strategy for designing achromatic optical components.