Optically Controlled Ultrafast Terahertz Metadevices with Ultralow Pump Threshold.

Area of Science:

• Metamaterials and Nanophotonics
• Terahertz (THz) Technology
• Semiconductor Optoelectronics

Background:

• Dynamic control of terahertz (THz) waves is crucial for next-generation telecommunications.
• Current active materials for metasurfaces are limited to single external fields, restricting manipulation flexibility.
• Reducing the energy threshold for metasurface modulation is an unmet challenge.

Purpose of the Study:

• To experimentally demonstrate a germanium (Ge) hybrid Fano metasurface with dual-stimulus control (photoexcitation and current-bias).
• To investigate the impact of dual-stimulus control on THz wave modulation depth, switching speed, and energy efficiency.
• To explore the relationship between Ge film thickness and current-bias modulation effectiveness.

Main Methods:

• Fabrication of a germanium (Ge) hybrid Fano metasurface.
• Application of photoexcitation and current-bias as dual stimuli.
• Measurement of Fano resonance modulation depth, switching time, and pump threshold.
• Analysis of THz amplitude modulation under single and dual-stimulus conditions.

Main Results:

• Photoexcitation achieved 100% modulation depth and ultrafast switching (<10 ps).
• Current-bias significantly reduced the pump threshold from 1600 to 200 µJ cm⁻².
• Current modulation effectiveness was found to be proportional to Ge film thickness.
• Dual-stimulus control increased THz amplitude modulation by 56.3% compared to optical-only stimulus.

Conclusions:

• The developed Ge-based metasurface offers enhanced flexibility and practicality for THz wave manipulation.
• Dual-stimulus control presents a viable strategy for reducing energy consumption in active metasurfaces.
• This work paves the way for advanced applications in switchable sensing, lasing, and nonlinear optics.