Omnidirectional terahertz photonic band gap broaden effect in one-dimensional photonic crystal containing few-layer graphene

Chirality has always been a hot research topic because it possesses potential applications in polarization optics, chemical and biosensing. In the previous works, intrinsic chirality has been extensively explored, but its development is limited due to the complexity in fabrication of chiral metamaterials. Therefore, there is an urgent need to simplify fabrication and design of compact devices with chiral response. Extrinsic chirality has shown great potential because it can be realized in nonchiral anisotropic planar structures with low-cost fabrication techniques. In this paper, the extrinsic chirality of biaxial hyperbolic material $\alpha {\text -}{\rm{Mo}}{{\rm{O}}_3}$ with in-plane anisotropy has been investigated. By analyzing the effect of thickness of $\alpha {\text -}{\rm{Mo}}{{\rm{O}}_3}$ film, the angle of incidence, azimuth angle, and wavelength of incidence on the circular dichroism (CD), the maximum CD can reach 0.77. This strong extrinsic chirality of the $\alpha {\text -}{\rm{Mo}}{{\rm{O}}_3}$ film results from the mutual orientation of the $\alpha {\text -}{\rm{Mo}}{{\rm{O}}_3}$ film and the incident light. In addition, $\alpha {\text -}{\rm{Mo}}{{\rm{O}}_3}$ film can still maintain strong extrinsic chirality when the azimuthal angle ranges from approximately 20°–57° and the angle of incidence is from 55°–80°.

Strong extrinsic chirality in biaxial hyperbolic material α-MoO 3 with in-plane anisotropy

Chiral structures are promising in many applications, such as biological sensing and analytical chemistry, and have been extensively explored. In this paper, we theoretically investigate the chiral response of twisted bilayer α -MoO 3 . Firstly, the analytical formula for the transmissivity is derived when the structure is illuminated with circularly polarized plane waves. Furthermore, the results demonstrate that the twisted bilayer α -MoO 3 can excite the strong chirality with the maximum circular dichroism (CD) of 0.89. In this case, the chirality is due to the simultaneous breaking the rotational symmetry and mirror symmetry, which originates from the relative rotation of two α -MoO 3 layers. To better understand the physical mechanism, the polarization conversion between the left-hand circular polarization (LCP) and right-hand circular polarization (RCP) waves is discussed as well. Moreover, it is found that the structure can maintain the strong chirality (CD &gt; 0.8) when the twisted angle varies from 69° to 80°, which effectively reduces the strictness in the requirement for rotation angle. In addition, the CD can be larger than 0.85 when the incidence angle of circularly polarized plane wave is less than 40°, implying that the chirality is robust against the angle of incidence. Our work not only provides an insight into chirality induced by the twisted bilayer α -MoO 3 , but also looks forward to applications in biological sensing. 

Strong chirality in twisted bilayer α-MoO<sub>3</sub>

Strong nonreciprocal thermal radiation in Weyl semimetal-dielectric multilayer structure

Abstract Weyl semimetals are topological materials whose electron quasiparticles obey the Weyl equation. They possess many unusual properties that may lead to new applications. This is a tutorial review of the optical properties and applications of Weyl semimetals. We review the basic concepts and optical responses of Weyl semimetals, and survey their applications in optics and thermal photonics. We hope this pedagogical text will motivate further research on this emerging topic. 

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Light control with Weyl semimetals

Strong optical non-reciprocity in one-dimensional photonic crystal containing a Weyl semimetal-based defect

We theoretically investigated the controllable transition between optical bistability and multistability in graphene/dielectric/graphene structure for TE and TM polarizations. We show such a transition strongly depends on the Fermi energy of graphene, and thus, it can be controlled by adjusting the gate voltage applied on the graphene. In addition, we also show that the transition can be tuned by changing the thickness and permittivity of the dielectric layer, or by varying the wavelength and the incident angle of the input light. Furthermore, three S-type curves appear in our studied structure, which result in quadristability. Our results may find potential applications in optoelectronic devices.

Controllable transition between optical bistability and multistability in graphene/dielectric/graphene structure

We derive an analytical model for calculating the optical activity in monolayer black phosphorus under an external magnetic field. By optimizing the parameters, the circular dichroism can be comparable to that in previously reported chiral metamaterials in a broad angle range. Besides, the optical activity including the circular dichroism, the circular conversion dichroism and the circular birefringence can be tuned almost linearly via changing the applied magnetic field magnitude. These results show that our proposed model would possess potential applications in polarization optics, stereochemistry, and molecular biology.

Theory for optical activity in monolayer black phosphorus under external magnetic field

By means of characteristic matrix method, we make a theoretical investigation on the properties of thermal emission from one-dimensional conjugated photonic crystals heterojunction embedded with graphene. We find that the emissivity plots show sharp spectral peaks and narrow antenna-like angular lobes which show the excellent temporal coherence and spatial coherence. By optimizing the parameters, a close-to-unity emissivity can be achieved in our proposed structure. Furthermore, we demonstrate that the emissivity peak wavelength and emissivity values can be tuned by changing the chemical potential of graphene layer and the center wavelength of conjugated photonic crystals. The study shows that our proposed structure may find great application in infrared spectrometers and infrared gas sensors.

Chengping Yin

Papers

Omnidirectional terahertz photonic band gap broaden effect in one-dimensional photonic crystal containing few-layer graphene

Strong optical non-reciprocity in one-dimensional photonic crystal containing a Weyl semimetal-based defect

Controllable transition between optical bistability and multistability in graphene/dielectric/graphene structure

Theory for optical activity in monolayer black phosphorus under external magnetic field

Thermal emission of one-dimensional conjugated photonic crystals heterojunction embedded with graphene