Proof of concept for continuously-tunable terahertz bandpass filter based on a gradient metal-hole array

Area of Science:

• Optics and Photonics
• Electromagnetics
• Materials Science

Background:

• Terahertz (THz) technology requires advanced optical components for applications like imaging and sensing.
• Existing THz filters often lack continuous tunability and broad operational ranges.

Purpose of the Study:

• To develop and demonstrate a continuously-tunable THz bandpass filter.
• To investigate the tunability and performance of a gradient metal-hole array design.
• To enhance filter performance by suppressing interference patterns.

Main Methods:

• Fabrication of a metal-hole array on a silicon substrate using optical lithography.
• Numerical simulation using the finite element method (FEM).
• Experimental characterization using THz pulsed spectroscopy.
• Application of Kapton-based anti-reflection coating.

Main Results:

• Achieved a continuously-tunable bandpass filter with a wide tuning range of 400-800 μm central wavelength.
• Demonstrated a relative bandwidth of approximately 0.4.
• Successfully suppressed interference patterns in the transmission spectrum with anti-reflection coating.

Conclusions:

• The developed gradient metal-hole array filter offers wide tunability and potential for multispectral THz imaging and sensing.
• The filter's design is conceptually simple and easy to operate.
• The fabrication concept is adaptable to other spectral ranges with appropriate technologies.