Design of Switchable SHG and THG Using Metasurface-Based Frequency Mixing System

In this letter, we propose a nonlinear reflective metasurface-based frequency mixing system able to perform second-harmonic generation (SHG) and third-harmonic generation (THG). The metasurface consists of a planar bidimensional alignment of unit-cells, each of which encompasses a receiving element at fundamental frequency, and two transmitting elements operating at double and triple the fundamental frequency, respectively. The TX/RX elements within each unit-cell are connected via a microwave network to a radio frequency (RF) mixing circuit that performs the conversion, assisted by an RF amplifier that improves the overall conversion efficiency. Efficient switchable SHG and THG frequency conversions are demonstrated by both full-wave simulations and experiments. For the input fundamental frequency of 3 GHz, the conversion efficiencies for SHG and THG are 55.5% and 42.6%, respectively.