Broadband on-Chip Terahertz Asymmetric Waveguiding via Phase-Gradient Metasurface

As fundamental elements, optical diodes are required for on-chip optical communications and computing. However, it is still a challenge to realize ultracompact devices working in the terahertz (THz) range. Here an optical diode device with a bandwidth up to 100 GHz that is able to produce a highly asymmetric THz propagation was designed by coupling a gradient metasurface and subwavelength waveguide modes. This system is based on the breaking of the momentum symmetry at the interface with phase discontinuities. The asymmetric transmission process generated by THz mode conversion is detected by employing time-resolved phase contrast imaging. The results agree well with full-wave electromagnetic simulations. Moreover, the performance of the working bandwidth and the ratio of transmission of the device can be optimized by the induced arbitrary scattering phase. These performances indicate that this design provides a very effective method and a versatile platform for on-chip information processing by preventing undesired light interference in the integrated system.