In this paper, the polycyclic tornado circular swallowtail beam (PTCSB) with autofocusing and self-healing properties is generated numerically and experimentally and their properties are investigated. Compared with the circular swallowtail beam (CSB), the optical distribution of the PTCSB presents a tornado pattern during the propagation. The number of spiral stripes, as well as the orientation of the rotation, can be adjusted by the number and the sign of the topological charge. The Poynting vectors and the orbital angular momentum are employed to investigate the physical mechanism of beam-rotating. In addition, we also introduce a sector-shaped opaque obstacle to investigate the self-healing property of the PTCSB, passing through it with different center angles and discuss the influence of the scaling factor along the propagation direction. Our results may expand the potential applications in the optical spanner and material processing.
In this work, we propose a graphene-indium tin oxide (ITO)/TiO2/ITO sandwich structure and theoretically study the Goos-Hänchen (GH) shift within the epsilon-near-zero region of the ITO. The findings show that the sign of GH shifts keeps positive or negative in two different wavelength ranges in the case of the zero graphene conductivity. When the graphene conductivity is non-zero, the influence of the graphene conductivity on the sign of GH shifts is discussed, and we regularly achieve the positive and the negative regulation of GH shifts by adjusting the Fermi energy. Based on the positive and the negative variation of GH shifts in two cases of the zero and the non-zero graphene conductivity, we design a barcode encryption scheme based on the sign of GH shifts, which can simply obtain four groups of the coding state “0 0”, “0 1”, “1 0” and “1 1”, by the means of first adjusting the incident wavelength and then adjusting the Fermi energy. Our research provides a new machanism to realize the potential application of GH shifts.
We theoretically study the Goos-Hänchen (GH) shifts of Gaussian beams reflected in parity-time (PT) symmetric multilayered structure coating graphene structures. And there are the exceptional points (EPs) in this structure, whose position can be adjusted by the real part of the dielectric constant and the incident angle. Moreover, we find that the value and direction of the GH shifts change significantly under different EPs, so we could control the GH shifts by the position of the EPs. When the dielectric constant is fixed, the GH shifts can also be adjusted by the Fermi energy of graphene and the period number of the PT-symmetric structure. With the increase of the period number of the PT system, the system will produce the Bragg resonance, which refers to the phenomenon of total reflection caused by the interaction between the wave and the periodic structure with a specific frequency. And at the Bragg resonance, the special GH shifts independent of the incident direction can be obtained with large reflectivity. In addition, the incident direction of the beam can also affect the GH shifts in this asymmetric structure. Our results may find great applications in highly sensitive sensors, optoelectronic switches, and all-optical devices.
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