The non-Hermitian skin effect (NHSE), which involves an extensive number of bulk modes collapsing to open boundaries as skin modes, unveils a variety of unprecedented topological physics. However, achieving this effect in photonic waveguides has been challenging due to the difficulty of establishing the required non-Hermitian asymmetric couplings. Here, we investigate NHSE in photonic waveguide arrays via Floquet engineering. By periodically driving the waveguides along the propagation direction, we create an artificial gauge field (AGF) that interacts with on-site dissipation, yielding non-Hermitian asymmetric coupling and eventually giving rise to NHSE. The localization direction of NHSE is tunable by AGFs and can be detected from light propagation. In particular, we explore the interplay between NHSE and dynamical localization, whereby NHSE is suppressed by dynamical localization due to the collapse of quasienergies. Our proposed method can be extended to explore the non-Bloch Su-Schrieffer–Heeger model, with potential implications for steering light transport with the aid of NHSE.

Based on the transfer-matrix method, we theoretically explore the transmission and reflection properties of light waves in a one-dimensional defective photonic crystal composed of superconductor (HgBa₂Ca₂Cu₃O_8+δ) and semiconductor (GaAs) layers. The whole system is centrosymmetric and can generate a defect transmission peak in the photonic band gap. We study the effect of the temperature on the defect mode. Results obtained show that the defect mode shifts to the lower frequency regions as the value of the environmental temperature increases, and the resonance of the defect mode can be strengthened further as the number of periods increases. In addition, our findings reveal that the central wavelength of the defect mode increases with the increase in the environmental temperature and it presents a nearly linear relationship between the central wavelength of the defect mode and the temperature in cryogenic environments. Therefore, we can use the temperature response of the defect mode to detect the temperature. It is hoped that this study has potential applications for the development of cryogenic sensors with high sensitivity.

In this paper, we investigate the nonreciprocity of reflection in parity-time−symmetric (PT-symmetric) Cantor photonic crystals (PCs). Two one-dimensional PCs abiding by the Cantor sequence are PT-symmetric about the center. The PT symmetry and defect cavities in Cantor PCs can induce optical fractal states which are transmission modes. Subsequently, the left and right reflectionless states are located on both sides of a transmission peak. The invisible effect depends on the incident direction and the invisible wavelength can be modulated by the gain–loss factor. This study has potential applications in tunable optical reflectors and invisible cloaks.

We theoretically investigate the optical fractal effect in one-dimensional quasiperiodic photonic crystals (PCs). Dielectric multilayers arrayed alternately submit to the Cantor-like sequence rule. The optical fractal phenomenon is induced by modulating the generation number of the dielectric sequence. The optical fractal effect corresponds to a series of resonant modes, and the Cantor-like PCs approve more resonance modes than those in the Cantor PCs with the same order number. The transmission channels of resonances exponentially increase with the increase in the sequence generation number. Furthermore, the central waves of the transmission channels can be regulated by the incident angle flexibly. We expect this paper may pave a new way for the development of wavelength division multiplexers.

We studied the optical fractal effect of the one-dimensional distributed feedback Bragg photonic crystals formed by semiconductor GaAs and dielectric TiO2. Light wave is transmitted in the intermediate dielectric slab and reflected back by the periodic photonic crystals at both ends, forming multiple fractal resonance output. The transmission channels expand exponentially by thickening the bulk in a cryogenic environment. The quality factor of each fractal resonant state improves with a greater periodic number of crystals. Furthermore, central wave of resonance has a blue-shift as the external pressure increases, while the influence of environment temperature on the fractal resonance could be ignored. It is hoped that our study can highlight the potential of these findings for designing multi-channel communication filters in cryogenic environments.

In this study, we explore the anisotropic reflection of light waves around the exceptional points (EPs) in anti-parity-time−symmetric (APT−symmetric) Cantor dielectric multilayers. This one-dimensional fractal structure governed by the Cantor substitution law is modulated to satisfy APT symmetry. The Cantor multilayers are aperiodic and support optical fractal resonances. The optical fractal effect combined with APT symmetry can induce multiple exceptional points (EPs) in the parameter space by modulating the loss coefficient of materials and optical frequency. Reflection anisotropy for light waves incident from two opposite directions presents unidirectional suppression and enhancement around EPs. This study can be utilized for multiple wavelengths of photonic suppressors and reflectors.