Stretching as a Versatile Tool for Fine-Tuning of THz Optical Elements and Metasurfaces based on Carbon Nanotubes

Active manipulation of electromagnetic waves through changes in nanomaterial properties is a key strategy forintegrating these materials into modern adjustable terahertz (THz) technologies. In this work, this direction is advanced by demonstrating a method for realizing mechanically stretchable THz diffractive elements and metasurfaces built from single-walled carbon nanotubes (SWCNTs). This nature-inspired concept draws an analogy to the dynamic expansion and contraction of the biological eye lens for adaptive wave focusing. Four types of THz elements deposited on a stretchable substrate are presented: a Fresnel zone plate (FZP), spiral zone plates (SZPs) with topological charges 𝑚 = 3 and 𝑚 = 4, and a Pancharatnam–Berry (PB) metasurface. Each device comprises ultrathin SWCNT films with tailored geometries, enabled by a unique deposition technique applicable to diverse element shapes. The FZP exhibits focal distance tuning from 24 to 30 mm under 0–20% strain. The metasurface lens demonstrates focal plane shifting from 17 to 24 mm under 0–20% strain, maintaining stable performance across the 265–441 GHz range. The SZPs preserve their orbital angular momentum states under deformation, with focal positions shifting monotonically with increasing strain. SWCNT films exhibit exceptional mechanical robustness, with less than 10% variation in peak intensity after 1,000 stretch-release cycles at 0–10% strain and 500 cycles at 0–20% strain. The presented devices demonstrate broadband operational stability. We introduce a new Figure of Merit combining mechanical tunability and spectral bandwidth. Developing this concept could lead to varifocal THz lenses, extending the spectral boundaries of modern imaging systems.