# Color coded metadevices toward programmed terahertz switching

## TL;DR

Researchers developed a new terahertz switching system using metasurfaces that allows for ultrafast and programmable control of terahertz signals.

## Contribution

The study introduces a 2-bit dual-channel terahertz encoding system using composite metasurfaces for all-optical programming.

## Key findings

- A terahertz metasurface with semiconductor islands and microstructures enables ultrafast all-optical modulation.
- Color-coded spatial light field distribution is used to achieve 2-bit encoding in terahertz switching.
- Time-domain coupled mode theory explains how energy dissipation modes are independently controlled.

## Abstract

Terahertz modulators play a critical role in high-speed wireless communication, non-destructive imaging, and so on, which have attracted a large amount of research interest. Nevertheless, all-optical terahertz modulation, an ultrafast dynamical control approach, remains to be limited in terms of encoding and multifunction. Here we experimentally demonstrated an optical-programmed terahertz switching realized by combining optical metasurfaces with the terahertz metasurface, resulting in 2-bit dual-channel terahertz encoding. The terahertz metasurface, made up of semiconductor islands and artificial microstructures, enables effective all-optical programming by providing multiple frequency channels with ultrafast modulation at the nanosecond level. Meanwhile, optical metasurfaces covered in terahertz metasurface alter the spatial light field distribution to obtain color code. According to the time-domain coupled mode theory analysis, the energy dissipation modes in terahertz metasurface can be independently controlled by color excitation, which explains the principle of 2-bit encoding well. This work establishes a platform for all-optical programmed terahertz metadevices and may further advance the application of composite metasurface in terahertz manipulation.