Metasurface Enables Bidirectional Conversion Between Free-space Terahertz Waves and Guided Waves

Known for their precise manipulation of electromagnetic wave properties such as amplitude, polarization, and phase, the metasurfaces, have become increasingly popular in waveguiding applications. In this study, we proposed a wearable metasurface that achieved coupling of terahertz waves from free space to guided waves through polarization conversion and phase manipulation. By designing the phase gradient of the metasurface in the propagation and cross-sectional direction of the waveguide, we can direct the guided waves to exit as plane waves or at a specific angle. Additionally, by compensating for the phase mismatch between the waveguide and free space, we can also convert guided waves back into free space. The investigated metasurface enables bidirectional conversion between free-space terahertz waves and guided waves, contributing to the development of terahertz integrated photonic devices and holding great potential for next-generation communications and terahertz sensing applications.