All-optical logic devices based on black arsenic-phosphorus with strong nonlinear optical response and high stability

The Kerr nonlinearity in two-dimensional(2D)nanomaterials is emerging as an appealing and intriguing research area due to their prominent light processing,modulation,and manipulation abilities.In this contribution,2D black arsenic-phosphorus(B-AsP)nanosheets(NSs)were applied in nonlinear photonic devices based on spatial self-phase modula-tion(SSPM)method.By applying the Kerr nonlinearity in 2D B-AsP,an all-optical phase-modulated system is proposed to realize the functions of“on”and“off”in all-optical switching.By using the same all-optical phase-modulated system,another optical logic gate is proposed,and the logical“or”function is obtained based on the 2D B-AsP NSs dispersions.Moreover,by using the SSPM method,a 2D B-AsP/SnS_(2) hybrid structure is fabricated,and the result illustrates that the hybrid structure possesses the ability of the unidirectional nonlinear excitation,which helps in obtaining the function of spatial asymmetric light propagation.This function is considered an important prerequisite for the realization of diode functionalization,which is believed to be a factor in important basis for the design of isolators as well.The initial investig-ations indicate that 2D B-AsP is applicable for designing optical logical devices,which can be considered as an import-ant development in all-optical information processing.

Tunable and multichannel terahertz perfect absorber due to Tamm surface plasmons with graphene

In this paper, we have shown that perfect absorption at terahertz frequencies can be achieved by using a composite structure where graphene is coated on one-dimensional photonic crystal(1 DPC) separated by a dielectric. Due to the excitation of optical Tamm states(OTSs) at the interface between the graphene and 1 DPC, a strong absorption phenomenon occurs induced by the coupling of the incident light and OTSs. Although the perfect absorption produced by a metal–distributed Bragg reflector structure has been researched extensively, it is generally at a fixed frequency and not tunable. Here, we show that the perfect absorption at terahertz frequency not only can be tuned to different frequencies but also exhibits a high absorption over a wide angle range. In addition,the absorption of the proposed structure is insensitive to the polarization, and multichannel absorption can berealized by controlling the thickness of the top layer.

Octupole corner state in a three-dimensional topological circuit

Higher-order topological insulators(HOTIs)represent a new family of topological materials featuring quantized bulk polarizations and zero-dimensional corner states.In recent years,zero-dimensional corner states have been demonstrated in two-dimensional systems in the form of quadrupole modes or dipole modes.Due to the challenges in designing and constructing three-dimensional systems,octupole corner modes in 3D have not been observed.In this work,we experimentally investigate octupole topological phases in a three-dimensional electrical circuit,which can be viewed as a cubic lattice version of the Hofstadter model with aπ-flux threading each plaquette.We experimentally observe in our higher-order topological circuit a 0D corner state manifested as a localized impedance peak.The observed corner state in the electrical circuit is induced by the octupole moment of the bulk circuit and is topologically protected by anticommuting spatial symmetries of the circuit lattice.Our work provides a platform for investigating higher-order topological effects in three-dimensional electrical circuits.

Ultrasensitive biosensors based on long-range surface plasmon polariton and dielectric waveguide modes

An ultrasensitive biosensor based on hybrid structure and composed of long-range surface plasmon polariton(LRSPP) and dielectric planar waveguide(PWG) modes is proposed. Both PWG and LRSPP modes have strong resonances to form strong coupling between the two modes, and the two modes can couple to enhance sensitivity of sensors. In the hybrid structure, PWG is composed of cytop–Si–cytop multilayers and the LRSPP configuration is composed of cytop–metal–sensing medium multilayer slabs. The highest imaging sensitivities of 2264 and3619 RIU-1were realized in the proposed sensors based on Au and Al-monolayer graphene, respectively, which are nearly 1.2 and 1.9 times larger than the 1910 RIU-1sensitivity of the conventional LRSPR sensor(LRSPP sensor). Moreover, it is demonstrated that the PWG-coupled LRSPP biosensor is applicable to the sensing medium,with refractive index in the vicinity of 1.34.

Broadband nonlinear optical resonance and all-optical switching of liquid phase exfoliated tungsten diselenide

As a kind of two-dimensional transition metal dichalcogenide material, tungsten diselenide(WSe_2) has attracted increasing attention, owing to its gapped electronic structure, relatively high carrier mobility, and valley pseudospin, all of which show its valuable nonlinear optical properties. There are few studies on the nonlinear optical properties of WSe_2 and correlation with its electronic structure. In this paper, the effects of spatial self-phase modulation(SSPM) and distortion influence of WSe_2 ethanol suspensions are systematically studied, namely,the nonlinear refractive index and third-order nonlinear optical effect. We obtained the WSe_2 dispersions SSPM distortion formation mechanism, and through it, we calculated the nonlinear refractive index n_2,nonlinear susceptibility χ^(3), and their wavelength dependence under the excitation of 457 nm, 532 nm, and671 nm lasers. Moreover, by use of its strong and broadband nonlinear optical response, all-optical switching of two different laser beams due to spatial cross-phase modulation has been realized experimentally. Our results are useful for future optical devices, such as all-optical switching and all-optical information conversion.

Graphene Tamm plasmon-induced giant Goos–H?nchen shift at terahertz frequencies

In this Letter, we have shown that a giant Goos–H?nchen shift of a light beam reflected at terahertz frequencies can be achieved by using a composite structure, where monolayer graphene is coated on one-dimensional photonic crystals separated by a dielectric slab. This giant Goos–H?nchen shift originates from the enhancement of the electrical field, owing to the excitation of optical Tamm states at the interface between the graphene and onedimensional photonic crystal. It is shown that the Goos–H?nchen shift in this structure can be significantly enlarged negatively and can be switched from negative to positive due to the tunability of graphene's conductivity. Moreover, the Goos–H?nchen shift of the proposed structure is sensitive to the relaxation time of graphene and the thickness of the top layer, making this structure a good candidate for a dynamic tunable optical shift device in the terahertz regime.

Enhanced spin Hall effect of reflected light with guided-wave surface plasmon resonance

The photonic spin Hall effect(SHE) has been intensively studied and widely applied, especially in spin photonics.However, the SHE is weak and is difficult to detect directly. In this paper, we propose a method to enhance SHE with the guided-wave surface-plasmon resonance(SPR). By covering a dielectric with high refractive index on the surface of silver film, the photonic SHE can be greatly enhanced, and a giant transverse shift of horizontal polarization state is observed due to the evanescent field enhancement near the interface at the top dielectric layer and air. The maximum transverse shift of the horizontal polarization state with 11.5 μm is obtained when the thickness of Si film is optimum. There is at least an order of magnitude enhancement in contrast with the transverse shift in the conventional SPR configuration. Our research is important for providing an effective way to improve the photonic SHE and may offer the opportunity to characterize the parameters of the dielectric layer with the help of weak measurements and development of sensors based on the photonic SHE.

基于液相剥离硼纳米片的全光调制和逻辑门研究

硼纳米片具有独特的光电性能,包括光敏性、光响应和光学非线性.本文通过液相剥离的方法制备了硼纳米片,采用AFM和XRD等方式进行了表征,结果表明制备的硼纳米片具有高质量性质.空间光与硼纳米片相互作用会产生新奇的非线性效应,形成远场的锥形圆环,这归于硼纳米片强大的克尔非线性.文章得到了硼纳米片的光学非线性χ(3)在10-9 esu量级.电子在硼纳米片与激光相互作用后,相位保持一致,形成非局域的相干.文章总结了硼纳米片和其他二维材料的非线性性系数χ(3)与有效质量m*和载流子迁移率μ之间的关系,证实了这种衍射圆环的物理起源,并且作者实现了基于空间自相位调制的全光调制和全光逻辑门.研究表明,基于硼纳米片的被动光子器件具有广阔的应用前景.

Manipulating optical Tamm state in the terahertz frequency range with graphene

The optical Tamm state(OTS), which exists generally at the interface between metal and a dielectric Bragg mirror, has been studied extensively in the visible and near infrared spectra. Nevertheless, OTS in the terahertz(THz) region normally receives far less attention. In this Letter, we demonstrate the physical mechanism of OTS at the interface between graphene and a dielectric Bragg mirror in the THz frequency band by applying the transfer matrix method and dispersion characteristics. Based on such mechanisms, we propose an efficient method that can precisely generate and control OTS at a desired angle and frequency. Moreover, we show that the OTS is dependent on the optical conductivity of graphene, making the graphene–dielectric-Bragg-mirror a good candidate for dynamic tunable OTS device in the THz frequency range.

Photonic topological fermi nodal disk in non-Hermitian magnetic plasma

Topological physics mainly arises as a necessary link between properties of the bulk and the appearance of surface states,and has led to successful discoveries of novel topological surface states in Chern insulators,topological insulators,and topological Fermi arcs in Weyl,Dirac,and Nodal line semimetals owing to their nontrivial bulk topology.In particular,topological phases in non-Hermitian systems have attracted growing interests in recent years.In this work,we predict the emergence of the topologically stable nodal disks where the real part of the eigen frequency is degenerate between two bands in non-ideal magnetohydrodynamics plasma with collision and viscosity dissipations.Each nodal disk possesses continuously distributed topological surface charge density that integrates to unity.It is found that the lossy Fermi arcs at the interface connect to the middle of the projection of the nodal disks.We further show that the emergence,coalescence,and annihilation of the nodal disks can be controlled by plasma parameters and dissipation terms.Our findings contribute to understanding of the linear theory of bulk and surface wave dispersions of non-ideal warm magnetic plasmas from the perspective of topological physics.