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In this paper, the magnetically tunable and enhanced photonic spin Hall effect (PSHE) of reflected light beam at terahertz frequencies is achieved by using a multilayer structure where anisotropic graphene is inserted. This enhanced PSHE phenomenon results from the excitation of surface plasmon polariton (SPP) at the interface between two dielectric materials. By considering the 4×4 transfer matrix method and the quantum response of graphene, the PSHE of the reflected light can be enhanced by harnessing the anisotropic conductivity of graphene. Besides, the PSHE can be tuned through the external magnetic field and structural parameters. This enhanced and tunable PSHE approach is promising for fabricating anisotropic graphene-based terahertz spin devices and other applications in nanophotonics.

In this paper, we present a theoretical analysis of the optical bistability phenomenon of the transmitted light beam in a graphene-based one-dimensional photonic crystal heterostructure in terahertz frequency range. This low-threshold optical bistability originates from the enhancement of the local electric field owing to the excitation of topological edge state at the interface between the two proposed onedimensional photonic crystals. The results of calculation and simulation show that the hysteretic behavior and the threshold of optical bistability can be adjusted continuously by changing the applied voltage of the graphene. Moreover, the optical bistability of this structure also can be modified by the angle of the incident light and the number of graphene layers. Our findings provide a new method for realizing low threshold and tunable optical bistability in terahertz range, indicating excellent application prospects in the field of alloptical switches and other optical bistable devices. INDEX TERMS Graphene, low-threshold, optical bistability, topological edge state modeThis work is licensed under a Creative Commons Attribution-NonCommercial-NoDerivatives 4.

In this paper, the reflected and transmitted group delay from a one-dimensional photonic crystal heterostructure with graphene at communication band are investigated theoretically. It is shown that the negative reflected group delay of the beam in this structure can be significantly enhanced and can be switched to positive. The large reflected group delay originates from the sharp phase change caused by the excitation of topological edge state at the interface between the two one-dimensional photonic crystals. Besides, the introduction of graphene provides an effective approach for the dynamic control of the group delay. It is clear that the positive and negative group delay can be actively manipulated through the Fermi energy and the relaxation time of the graphene. In addition, we also investigate the transmitted group delay of the structure, which is much less than the reflected one. The enhanced and tunable delay scheme is promising for fabricating optical delay devices like optical buffer, all-optical delays and other applications at optical communication band.

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