Femtosecond Laser Non-Diffracting-Beam Lithography via Phase Modulation for Dielectric Metasurface Fabrication.

Abstract

Dielectric phase-change metasurfaces enable programmable light control and show great application potential in optoelectronics. However, current technologies are limited by challenges in achieving high-uniformity, high-precision fabrication over large areas, as well as selective phase-state modulation of individual meta-atoms. To address these challenges, a femtosecond (fs)-laser phase-modulated non-diffracting-beam lithography (PNDL) technique is proposed. By superimposing axicon and blazed grating phases, the fs-laser beam is shaped into a quasi-Bessel non-diffracting-beam with a depth of focus over 10 times greater than that of a tightly focused Gaussian beam, thereby reducing the need for refocusing and minimizing focal drift. The dynamic beam deflection during fabrication can be controlled with 7 nm precision. The voxel metasurfaces composed of phase-change regions are then chemically processed to achieve maskless lithography. PNDL is used to fabricate a tunable Ge₂Sb₂Te₅ metasurface with a structural feature size of 9 nm. Furthermore, multifunctional programmable photonic logic devices are fabricated and modulated, demonstrating high-precision capabilities. This approach provides a novel paradigm for active metasurface fabrication and modulation, laying the foundation for next-generation photonic devices.