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The existence of Weyl nodes in the momentum space is a hallmark of a Weyl semimetal (WSM). A WSM can be confirmed by observing its Fermi arcs with separated Weyl nodes. In this paper, we study the spin–orbit interaction of light on the surface of a WSM thin film. Our results show that the spin-dependent splitting induced by the spin–orbit interaction is related to the separation of Weyl nodes. By proposing an amplification technique called weak measurements, the distance of the nodes can be precisely determined. This system may have an application in characterizing other parameters of WSM. [ABSTRACT FROM AUTHOR]

A cylindrically symmetric plano-concave lens based on a one-dimensional (1D) Thue–Morse photonic quasicrystal (PQC) is proposed. Subwavelength focusing characteristics with an incident cylindrical vector beam are investigated. Numerical results reveal that the lens can exhibit polarization-independent, high-resolution, and low-side-lobe characteristics, simultaneously for near-field and non-near-field. Furthermore, the lens can achieve perfect focusing and size-independent characteristics with equal-proportion scaling of the size of the lens at the corresponding center frequency. The focusing mechanisms of the lens are explained by analyzing the transmission spectrum, dispersion relation of a 1D periodic photonic crystal, and transmission spectrum of the 1D Thue–Morse PQC. [ABSTRACT FROM AUTHOR]

We report a vectorial fiber laser with controlled transverse mode conversion by intra-cavity polarization manipulation. By combining a q-plate and two quarter-wave plates (QWPs), we can generate a switchable polarization state output represented by the higher-order Poincaré sphere (l = +1, l = −1), and distinguish the fourfold degenerate LP11 mode. The four transverse vector modes can be obtained and switched in a flexible way, and the slope efficiency of the fiber laser can reach up to 39.4%. This compactness, high efficiency, and switchable operation potential will benefit a range of applications, such as materials processing, particle manipulation, etc. [ABSTRACT FROM AUTHOR]

The spin Hall effect (SHE) of light, as an analogue of the SHE in electronic systems, is a promising candidate for investigating the SHE in semiconductor spintronics/valleytronics, high-energy physics and condensed matter physics, owing to their similar topological nature in the spin–orbit interaction. The SHE of light exhibits unique potential for exploring the physical properties of nanostructures, such as determining the optical thickness, and the material properties of metallic and magnetic thin films and even atomically thin two-dimensional materials. More importantly, it opens a possible pathway for controlling the spin states of photons and developing next-generation photonic spin Hall devices as a fundamental constituent of the emerging spinoptics. In this review, based on the viewpoint of the geometric phase gradient, we give a detailed presentation of the recent advances in the SHE of light and its applications in precision metrology and future spin-based photonics. [ABSTRACT FROM AUTHOR]

Using the density functional theory (DFT), we systematically study the interfacial interaction in monolayer MX2 (M = Mo, W; X = S, Se)/CeO2 heterostructures and its effects on electronic and optical properties. The interfacial interaction in the MX2/CeO2 heterostructures depends largely on chalcogens, and its strength determines the band gap variation and important electronic states at the band edges of the heterostructures. The MX2/CeO2 heterostructures with the same chalcogen have similar absorption spectra, from ultraviolet to near-infrared regions. These results suggest that chalcogens importantly determine the properties of MX2/metal oxide heterostructures. [ABSTRACT FROM AUTHOR]

In this paper, we propose a modified Otto configuration to realize tunable and low-threshold optical bistability at terahertz frequencies by attaching multilayer graphene sheets to a nonlinear substrate interface. Our work demonstrates that the threshold of optical bistability can be markedly reduced (three orders of magnitude) by covering the nonlinear substrate with multilayer graphene sheets, due to strong local field enhancement with the excitation of surface plasmons. We present the influences of the Fermi energy of graphene, the incident angle, the thickness of air gap and the relaxation time of graphene on the hysteresis phenomenon and give a way to optimize the surface plasmon resonance, which will enable us to further lower the minimal power requirements for realizing optical bistability due to the strong interaction of light with graphene sheets. These results are promising for realization of terahertz optical switches, optical modulators and logical devices. [ABSTRACT FROM AUTHOR]

We experimentally show and report on a high-slope-efficiency, wavelength-locked, narrow-linewidth operation in a resonantly diode-pumped Er-doped yttrium aluminum garnet (Er:Y3Al5O12, Er:YAG) laser by using a volume Bragg grating (VBG) as a wavelength selector and an input mirror simultaneously. In this wavelength-locked operation, a maximum output power of 6.5 W at 1645 nm was achieved, which corresponds to a maximum slope efficiency of 105% with respect to the incident power. The small fluctuation of the lasing spectrum demonstrates good stability, with a 3 dB bandwidth of 0.06 nm at the center wavelength. This result shows potential applications of the VBG for high-efficiency, wavelength-locked, narrow-linewidth, and highly stable Er:YAG lasers. [ABSTRACT FROM AUTHOR]

We propose an ultra-compact polarisation converter based on liquid crystal (LC) material for effectively converting the obliquely incident unpolarised light into horizontal linearly polarised beam within the visible frequency range. Multilayer twisted configuration is introduced here to tackle the inherent dispersion issue from the LC itself and extended Jones matrix is employed to analyse the propagation of the electric field inside the LC medium under possible oblique illumination. Spatial angular separation of orthogonal polarised lights and polarisation conversion into the same polarisation direction are realised through specific patterned structure design, which effectively reduce the thickness of the device without sacrificing performance. Experimental results demonstrated that our fabricated LC-based device can deliver >80% polarisation conversion efficiency at normal illumination and 59%-80.5% efficiency for ±10° oblique incidence over the visible spectrum. Therefore, we envision that our presented device might find numerous potential applications associated with polarisation regulation such as vortex beam generator, augmented reality and optical computing. [ABSTRACT FROM AUTHOR]

We have experimentally investigated a full-duplex radio-over-fiber system transmitting 2.5-Gbitsorthogonal frequency-division multiplexing (OFDM) signals with a 40-GHzoptical millimeter wave as downlink. Meanwhile the central can be reused wavelength as the uplink connection for transmitting 2.5-Gbitson-off keying (OOK) signals. By experimentally comparing the transmission performance of OFDM downstream and OOK upstream signals, it can be seen that the power penalty for the downstream signals is about 1 dBat a bit error rate of 10−3after transmission over a 50-kmstandard mode fiber. However, the power penalty for the upstream signals is less than 0.5 dBat a bit error rate of 10−9after transmission over the same distance. [ABSTRACT FROM AUTHOR]

We present a fully vectorial description of the focusing of electromagnetic beams by a slab of indefinite media, in which waves can exhibit dispersion surfaces in the form of an ellipsoid, a double-sheeted hyperboloid, or a single-sheeted hyperboloid. Firstly, by means of the angular spectrum representation for electromagnetic beams, we analyze the transmission properties of a paraxial beam through a slab of indefinite media with the different dispersion relations, respectively. We found that a paraxial beam undergoes focusing in both x and y axes for the slab with an ellipsoid dispersion relation, and undergoes focusing or dispersion in different axes for the slab exhibiting a dispersion surface of a single-sheeted hyperboloid; while the beam cannot transmit in the slab with a double-sheeted hyperboloid dispersion relation. The inherent physics underlying these phenomena is that the effective refractive indices of indefinite media with different kinds of dispersion relations have different sign combinations. Secondly, the paraxial scheme is generalized to describe the propagation of slightly nonparaxial beams in the indefinite media slabs and the nonparaxial correction to the paraxial solution is derived. It is demonstrated that the contribution of nonparaxial correction to the longitudinal component is greater than the corresponding contribution to the transverse component. Importantly, we find that, due to the coupling effect of vectorial field components in indefinite media, the beam suffers a slight change of polarization state. [ABSTRACT FROM AUTHOR]

The production of broadband, terawatt terahertz (THz) pulses has been demonstrated by irradiating relativistic lasers on solid targets. However, the generation of extremely powerful, narrow-band and frequency-tunable THz pulses remains a challenge. Here, we present a novel approach for such THz pulses, in which a plasma wiggler is elaborated by a table-top laser and a near-critical density plasma. In such a wiggler, the laser-accelerated electrons emit THz radiations with a period closely related to the plasma thickness. The theoretical model and numerical simulations predict that a THz pulse with a laser--THz energy conversion of over 2.0%, an ultra-strong field exceeding 80 GV/m, a divergence angle of approximately 20° and a center frequency tunable from 4.4 to 1.5 THz can be generated from a laser of 430 mJ. Furthermore, we demonstrate that this method can work across a wide range of laser and plasma parameters, offering potential for future applications with extremely powerful THz pulses. [ABSTRACT FROM AUTHOR]

We theoretically demonstrate the perfect absorption phenomena in the hexagonal boron nitride (hBN) crystals in the mid-infrared wavelength ranges by means of critical coupling with a onedimensional photonic crystal spaced by the air. Different from the polymer absorbing layer composed by a metal-dielectric composite film, the hyperbolic dispersion characteristics of hBN can meet the condition of critical coupling and achieve the total absorption in the mid-infrared wavelength ranges. However, the critical coupling phenomenon can only appear in the hBN crystals with the type II dispersion. Moreover, we discuss the influence of the thickness of hBN, the incident angle, and the thickness and permittivity of the space dielectric on the total absorption. Ultimately, the conditions for absorption enhancement and the optimization methods of perfect absorption are proposed, and the design rules for a totally absorbing system under the different conditions are achieved. [ABSTRACT FROM AUTHOR]