Broadband Terahertz Metalenses Based on Printed Circuit Board Fabrication

Metalenses have provided a good solution to the bulkiness of conventional refractive lenses. Due to the subwavelength feature sizes of the metalens structure, the increasing fabrication difficulties at high frequencies limit its application in the terahertz and optical regime. Moreover, the deeply subwavelength features of the metasurface unit cells usually make the cells strongly resonant, which limits the bandwidth of the metalens. In this paper the usage of aggressive discretization in a metalens design is investigated, and it is found that aggressive discretization can lead to the usage of weakly resonant and relatively large unit cells, which leads to excellent broadband performance and dramatically relaxes the feature size tolerance of the metalens. For examples, two terahertz focusing metalenses are designed which feature large numerical apertures (NA = 0.86), diffraction-limited focusing over a broad bandwidth (240-400 GHz, or 50% bandwidth), and minimum feature sizes of 0.1 mm. These tolerance-relaxed terahertz metalenses are successfully constructed using conventional printed-circuit-board fabrication technology. The experimental measurements validate the simulated performances. Compared to existing terahertz meta-devices based on micro-fabrication or nano-fabrication technologies, this paper opens door to a kind of high-quality terahertz metasurfaces featuring low-cost, rapid, and established fabrication. Aggressive discretization in metalens design dramatically relaxes the feature size tolerance, providing possibility to design and fabricate terahertz meta-devices based on established and cost-efficient printed circuit board (PCB) technology. As examples, two PCB-based metalenses are reported, which feature a very large numerical aperture of 0.86 and achieve diffraction-limited focusing over a broad bandwidth of 240-400 GHz. image