Towards New Optical Devices: The Electrically-Controlled Dynamic Metasurface

• Operation at visible frequencies
• First pixel level control of a metasurface
• Universal for many active materials
• Highly integrated and compact design possibilities

• Nanophotonic devices
• Data storage
• Optical communications
• Cryptography and security

In a metasurface, meta-atoms, usually consisting of plasmonic or dielectric nanoantennas, can directly change light properties such as phase, amplitude, and polarization. So far, research has mainly been devoted to optical devices in which the individual elements are static, especially at visible frequencies. This leaves out many opportunities that metasurfaces can offer. For reconfigurability, active media can be integrated, for example liquid crystals in response to electric fields or vanadium dioxide in response to temperature tuning. However, this approach fails, because the optical antennas on the metasurface will be tuned simultaneously upon an external input, lacking pixel-level reconfigurability.

A novel electrically-controllable dynamic metasurface has been developed to overcome the aforementioned shortcomings and improve their applicability to future devices.

The pixel-level addressability is achieved by selective combination of geometric phase and propagation phase on individual subwavelength pixels. This concept is universal and works for any active materials, which show refractive index changes upon electrical, light, thermal, or other external influences.

An implementation according to the invention is shown in figure 1. A metasurface is caged in a cell, which is filled with highly birefringent liquid crystals. Some of the antennas, i.e., subwavelength pixels, are selectively covered with dielectric pillars. This introduces an additional propagation phase on such pixels and isolates them from the liquid crystals, deactivating the response of these pixels to electrical control. Completely interchangeable functionalities like switching between different holographic patterns within a hologram, or multi-function switching among beam steering, focusing, holography and optical vortices can be successfully implemented within milliseconds and with excellent reversibility under electrical control at visible frequencies.

This invention features great potentials to achieve diversified optical functions, while keeping individual functions highly independent within a single nanophotonic device.

PCT (WO2021104902A1), EP, CN

Li et al., " Electrically-controlled digital metasurface device for light projection displays", Nature Comunications (2020)