In this paper, we designed a terahertz absorber based on vanadium dioxide (VO2) with tunable and ultra-broadband characteristics. The absorber is composed of four identical synthetic VO2 patterns, the dielectric...

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Airy beams exhibit intriguing characteristics, such as diffraction-free propagation, self-acceleration, and self-healing, which have aroused great research interest. However, the spatial light modulator that generates Airy beams has problems such as narrow operational bandwidth, high cost, poor phase discretization, and single realization function. In the visible region (λ∼532 nm), we proposed a switchable all-dielectric metasurface for generating transmissive and reflective two-dimensional (2D) Airy beams. The metasurface was mainly composed of titanium dioxide nanopillars and vanadium dioxide substrate. Based on the Pancharatnam-Berry phase principle, a high-efficient Airy beam can be generated by controlling the phase transition of vanadium dioxide and changing the polarization state of the incident light. The optimized optical intensity conversion efficiencies of the transmissive and reflective metasurfaces were as high as 97% and 70%, respectively. In the field of biomedical and applied physics, our designed switchable metasurface is expected to offer the possibility of creating compact optical and photonic platforms for efficient generation and dynamic modulation of optical beams and open up a novel path for the application of high-resolution optical imaging systems.

Elliptical Airy vortex beams (EAVBs) can spontaneously form easily identifiable topological charge focal spots. They are used for topological charge detection of vortex beams because they have the abruptly autofocusing properties of circular Airy vortex beams and exhibit unique propagation characteristics. In this paper, we study the use of the dynamic phase and Pancharatnam-Berry phase principles for the generation and modulation of EAVBs by designing complex-amplitude metasurface and phase-only metasurface, respectively, at an operating wavelength of 1500 nm. It is found that the focusing pattern of EAVBs in the autofocusing plane splits into |m|+1 tilted bright spots from the original ring, and the tilted direction is related to the sign of the topological charge number m. Due to the advantages of ultra-thin, ultra-light, and small size of the metasurface, our designed metasurface device has potential applications in improving the channel capacity based on orbital angular momentum communication, information coding, and particle capture compared to spatial light modulation systems that generate EAVBs.

In this paper, we designed a terahertz absorber based on vanadium dioxide (VO2) with tunable and ultra-broadband characteristics. The absorber is composed of four identical synthetic VO2 patterns, the dielectric layer and the metal reflector layer from top to bottom. The results indicate that the designed absorber achieves essentially total reflection when VO2 is in the insulated state. The designed absorber has an absorption bandwidth of over 90% absorptance up to 7.7 THz in the frequencies range 5.36 THz-13.06 THz when VO2 is in the metallic state. By adjusting the conductivity of VO2, the absorber realizes near-perfect amplitude modulation with absorbance dynamically tuned from 4.31% to 100%. The operating principle of ultra-broadband absorber is interpreted by wave interference theory, impedance matching theory and electric field analysis, respectively. Compared to previously reported terahertz absorbers, the designed absorber offers significant improvements in the absorption broadband, and it also has many advantages such as simple structure, polarization insensitivity, and flexible incident angle. Such tunable ultra-broadband terahertz absorbers hold great promise in the fields of photochemical energy absorption, thermal emitters, and stealth.