Lens Antenna Arrays for THz Superconducting HEB Mixers: A Review and a Metasurface Coupling Approach

Area of Science:

• Astrophysics
• Optical Engineering
• Materials Science

Background:

• Terahertz hot electron bolometer (HEB) mixers provide the highest sensitivity for detecting terahertz radiation from the interstellar medium in space observatories.
• Increasing mapping speed necessitates the development of large HEB mixer arrays.
• Current quasi-optical coupling methods face challenges in achieving both high filling factors and uniform illumination for HEB mixer arrays.

Purpose of the Study:

• To review research on quasi-optical coupled HEB mixer arrays.
• To propose an innovative array coupling scheme to overcome limitations in uniform illumination and filling factor.
• To design and simulate a metasurface beam shaper for uniform local oscillator (LO) distribution.

Main Methods:

• Literature review of quasi-optical coupled HEB mixer arrays.
• Design of a metasurface beam shaper using the Gerchberg-Saxton algorithm.
• Electromagnetic simulation using COMSOL to analyze beam shaping performance at 0.6 THz and 1.6 THz.

Main Results:

• A metasurface beam shaper was designed to transform a Gaussian beam into a flattop beam for uniform illumination.
• Simulations at 0.6 THz showed a 3 mm wide flattop region with only 4.2% intensity variation.
• Simulations at 1.6 THz demonstrated a 1.5 mm wide flattop region with 5.5% intensity variation.

Conclusions:

• Metasurfaces can effectively convert Gaussian beams into flattop beams at terahertz frequencies.
• This approach offers a viable pathway for array-level coupling schemes for HEB mixer arrays.
• The proposed method enables high filling factors and uniform illumination, crucial for advanced astronomical observations.