Recently, the research group of Situ Guohai from the Information Optics and Optoelectronic Technology Laboratory of the Shanghai Institute of Optics and Mechanics of the Chinese Academy of Sciences and the research group of Professor Zhang Yan from the Department of Physics of Capital Normal University jointly proposed a reconfigurable terahertz metasurface implementation scheme. This technical solution achieves arbitrary and fast wavefronts in the terahertz band, which provides a new idea and experimental verification for the development of reconfigurable metasurfaces.

A metasurface is a planar structure composed of a series of artificially designed subwavelength antennas. Compared with traditional optical components, it has the advantages of ultra-thin, ultra-thin and can realize arbitrary wavefront modulation, and has important applications in optical interconnection, integrated optics, micro-nano optics, etc., but how to achieve its dynamic tunability is still a problem. The main challenges currently facing.

The research team used a high-intensity femtosecond laser, based on the photoconductive effect, to project patterns onto a silicon wafer to produce a metasurface effect to modulate terahertz pulses. The output of terahertz changes correspondingly with the change of the projection pattern, thus realizing a light-controlled reconfigurable terahertz metasurface. When a semiconductor silicon wafer is irradiated with light, carriers are generated and lead to an increase in electrical conductivity. When the conductivity rises to a certain value, the illuminated area can be regarded as a metal or weakly metallized material. Since metallic structures are commonly used in metasurfaces, patterned illuminated semiconductors can perform a similar function; when the illumination light is removed, the carriers rapidly recombine to their initial state.

This scheme can realize the erasing and rewriting of metasurfaces, and has three major advantages: simple structure, only a thin silicon wafer (10 μm); simple operation, arbitrary modulation and conversion can be realized by controlling illumination; high modulation speed, Up to 4000 frames per second. The solution can be used in real-time imaging, optical switching, time-varying materials with nonlinear effects, information processing, point-by-point scanning of microscopes, adaptive optics and other fields.