Photo-Excited Metasurface for Tunable Terahertz Reflective Circular Polarization Conversion and Anomalous Beam...

Area of Science:

• Terahertz (THz) photonics
• Metamaterials and Plasmonics
• Optoelectronics

Background:

• Terahertz (THz) technology requires advanced functional devices for wave manipulation.
• Metasurfaces (MS) offer promising solutions for controlling THz waves due to their subwavelength structures.
• Achieving independent and tunable control over THz wave properties at multiple frequencies remains a challenge.

Purpose of the Study:

• To propose and demonstrate a photo-excited metasurface (MS) capable of tunable reflective circular polarization (CP) conversion and beam deflection.
• To achieve independent control of these functionalities at two distinct terahertz frequencies.
• To explore the potential applications of such a device in active THz wavefront manipulation.

Main Methods:

• Design of a unit cell comprising hybrid patterned photoconductive silicon (Si) structures (circular-ring, Si ellipse-shaped-patch, circular-double-split-ring) on a dielectric substrate with a ground plane.
• Utilizing an external infrared beam to alter the conductivity of Si components, thereby tuning the MS response.
• Fabrication and characterization of the MS to measure CP conversion efficiency, modulation depth, and phase shift at 0.65 THz and 1.37 THz.
• Construction of a supercell for demonstrating reflective CP beam deflection.

Main Results:

• Demonstrated tunable reflective CP conversion efficiency from 0% to 96.6% at 0.65 THz and 0% to 89.3% at 1.37 THz.
• Achieved high modulation depths of 96.6% and 89.3% at the respective frequencies.
• Obtained a 2π phase shift by rotating Si components at both frequencies.
• Dynamically tuned reflective CP beam deflection efficiency from 0% to 99% at the two independent frequencies.

Conclusions:

• The proposed photo-excited metasurface effectively enables tunable reflective CP conversion and beam deflection at two independent THz frequencies.
• The device exhibits excellent photo-excited response, allowing for dynamic control via infrared beam pumping.
• Potential applications include active functional THz wavefront devices such as modulators, switches, and deflectors.