Using the transfer matrix method, a unidirectional absorber with an ultrabroadband absorption bandwidth and angular stability is realized in the graphene-embedded photonic crystals (GPCs) arranged by the cascading structure formed with the periodic sequence and the quasi-periodic Octonacci sequence in the terahertz regime. As a result, the surface conductivity of the graphene sheet can be modulated via the chemical potential, and the characteristics of the proposed absorber are tunable. Compared to the structure spliced by the diverse periodic sequences, the relative absorption bandwidth of the proposed composite construction is up to 94.53%, which far outweighs that of the periodic one. We compare the Octonacci sequence, the Fibonacci sequence, and the Thue–Morse sequence, and the calculated results reveal the advantage of the Octonacci sequence in the expansion of the absorption bandwidth. Under the optimization of the related parameters, the incident wave is primarily reflected in the forward propagation and absorbed in a wide range of θ under the TM mode in backward propagation, which shows the splendid unidirectionality and angular stability. The impacts of the chemical potential, structural thicknesses, and stack numbers on the absorption properties are also investigated in detail. Additionally, the impedance match theory and the interference field theory are introduced to explain the intrinsic absorption mechanism of the presented GPCs. In short, the unidirectional broadband and angle-insensitive absorber has extensive application prospects in optical sensing, optical filtering, photodetection, and solar energy collection.

In this paper, an ultra-wide multiband unidirectional absorber based on 1D gyromagnetic magnetized photonic crystals (GMPCs) comprising ferrite material and isotropic dielectrics is investigated under transverse magnetization for transverse electric mode within the infrared regime by the transfer matrix method. Due to the Voigt magneto-optical effect, the magnetically modulated absorber possesses multiple preeminent one-way absorption bands, which run at 12.24–18.80, 25.25–50.05, 51.13–74.90 and 76.67–93.88 THz and in the reverse propagating direction. The absorber displays a splendid reflection phenomenon. These perfect nonreciprocal results can be ascribed to the destruction of the space-time reversal symmetry on account of the anisotropic gyromagnetic ferrite material and quasi-periodic arrangement of the proposed GMPCs. The comparisons of the absorption capacity among the general Fibonacci sequence, the periodic sequence and Thue–Morse sequence are discussed, and the general Fibonacci sequence has its superiority in the expansion of the one-way absorption bandwidth due to its better self-similarity. Besides, the regulative effects of the magnetic field intensity, damping factor and thicknesses of materials on the one-way absorption features are analyzed specifically. This research provides a promising design approach to the tunable infrared optical isolator, waveguide and circulator through the magnetized materials.

Polaritons are quasi-particles that combine light with matter, enabling precise control of light at deep subwavelength scales. The excitation and propagation of polaritons are closely linked to the structural symmetries of the host materials, resulting in symmetrical polariton propagation in high-symmetry materials. However, in low-symmetry crystals, symmetry-broken polaritons exist, exhibiting enhanced directionality of polariton propagation for nanoscale light manipulation and steering. Here, we theoretically propose and experimentally demonstrate the existence of symmetry-broken polaritons, with hyperbolic dispersion, in a high-symmetry crystal. We show that an optical disk-antenna positioned on the crystal surface can act as an in-plane polarized excitation source, enabling dynamic tailoring of the asymmetry of hyperbolic polariton propagation in the high-symmetry crystal over a broad frequency range. Additionally, we provide an intuitive analysis model that predicts the condition under which the asymmetric polaritonic behavior is maximized, which is corroborated by our simulations and experiments. Our results demonstrate that the directionality of polariton propagation can be conveniently configured, independent of the structure symmetry of crystals, providing a tuning knob for the polaritonic response and in-plane anisotropy in nanophotonic applications.

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