An Ultra-Broadband Modified Moiré Varifocal Metalens with High Alignment Tolerance for Terahertz Wave

Abstract

The Moiré metalens (MML) offers a wide zoom range and easy adjustability, making it an excellent candidate for integrated optical systems. However, the focusing performance of traditional MML rapidly deteriorates under slight perturbations or imprecise settings, and their intrinsic low focusing efficiency further limits their practical applications. To address these challenges, a modified MML is developed with a novel phase distribution. This modified MML exhibits significantly enhanced performances, achieving over 40% focusing efficiency across a ≈17× zoom range, an axial displacement tolerance of 40λ, a lateral misalignment tolerance of 10 units (meta-element size), and an ultra-wide operating bandwidth covering ≈40% of the central frequency. In a proof-of-concept experiment using a frequency-tunable terahertz (THz) free-electron laser, the experimental results aligned well with numerical simulations, demonstrating the exceptional performances of the modified MML in the THz band. Furthermore, its design can extend beyond the THz range, offering a promising approach for the varifocal lens design across the entire electromagnetic spectrum.