Degenerate merging BICs in resonant metasurfaces.

Resonant metasurfaces driven by bound states in the continuum (BIC) offer an intriguing approach to engineering high-Q resonances. Merging multiple BICs in the momentum space could further enhance the Q-factor as well as its robustness to fabrication imperfections. Here, we report the doubly degenerate guided mode resonances (GMR) in a resonant metasurface, whose radiation losses could be totally suppressed due to merging BICs.

An outbreak associated with in a junior high school, China.

is an emerging foodborne enteropathogen associated with infectious diarrhoea in humans. In February 2023, an outbreak of acute gastroenteric cases was reported in a junior high school located in Hangzhou, Zhejiang province, China. Twenty-two investigated patients presented diarrhoea (22/22, 100%), abdominal pain (21/22, 95.

Low-loss chalcogenide photonic devices with a secondary coating method.

In the traditional dry etching process for photonic device fabrication, the etching effect is influenced in many ways, usually resulting in relatively large sidewall roughness and high transmission loss. In this study, an effective method, namely the secondary coating method, is proposed to reduce the transmission loss of a Ge-Sb-Se chalcogenide waveguide and increase the quality factor (Q-factor) of a Ge-Sb-Se chalcogenide micro-ring resonator. The Ge-Sb-Se waveguide and micro-ring resonator are fabricated by ultraviolet exposure/electron beam lithography and inductively coupled plasma etching technology.

Parvalbumin and Somatostatin: Biomarkers for Two Parallel Tectothalamic Pathways in the Auditory Midbrain.

The inferior colliculus (IC) represents a crucial relay station in the auditory pathway, located in the midbrain's tectum and primarily projecting to the thalamus. Despite the identification of distinct cell classes based on various biomarkers in the IC, their specific contributions to the organization of auditory tectothalamic pathways have remained poorly understood. In this study, we demonstrate that IC neurons expressing parvalbumin (IC) or somatostatin (IC) represent two minimally overlapping cell classes throughout the three IC subdivisions in mice of both sexes.

Compact reconfigurable on-chip polarization beam splitters enabled by phase change material.

In this paper, we present the design of a compact reconfigurable polarization beam splitter (PBS) enabled by ultralow-loss phase-changing SbSe. By harnessing the phase-change-mediated mode coupling in a directional coupler (DC), guided light with different polarizations could be routed into different paths and this routing could be dynamically switched upon the phase change of SbSe. With an optimized DC region, the proposed PBS demonstrates efficient polarization splitting with crosstalk less than -21.

A common thalamic hub for general and defensive arousal control.

The expression of defensive responses to alerting sensory cues requires both general arousal and a specific arousal state associated with defensive emotions. However, it remains unclear whether these two forms of arousal can be regulated by common brain regions. We discovered that the medial sector of the auditory thalamus (ATm) in mice is a thalamic hub controlling both general and defensive arousal.

Q-factor mediated quasi-BIC resonances coupling in asymmetric dimer lattices.

Resonance coupling in the regime of bound states in the continuum (BICs) provides an efficient method for engineering nanostructure's optical response with various lineshape while maintaining an ultra-narrow linewidth feature, where the quality factor of resonances plays a crucial role. Independent manipulation of the Q factors of BIC resonances enables full control of interaction behavior as well as both near- and far-field light engineering. In this paper, we harness reflection symmetry (RS) and translational symmetry (TS) protected BIC resonances supported in an asymmetric dimer lattice and investigate Q-factor-mediated resonance coupling behavior under controlled TS and RS perturbations.

Compact nonvolatile 2×2 photonic switch based on two-mode interference.

On-chip nonvolatile photonic switches enabled by phase change materials (PCMs) are promising building blocks for power-efficient programmable photonic integrated circuits. However, large absorption loss in conventional PCMs (such as GeSbTe) interacting with weak evanescent waves in silicon waveguides usually leads to high insertion loss and a large device footprint. In this paper, we propose a 2×2 photonic switch based on two-mode interference in a multimode slot waveguide (MSW) with ultralow loss SbS integrated inside the slot region.

Strong mode coupling-enabled hybrid photon-plasmon laser with a microfiber-coupled nanorod.

Laser based on single plasmonic nanoparticle can provide optical frequency radiation far beyond the diffraction limit and is one of the ultimate goals of nanolasers, yet it remains a challenge to be realized because of the inherently high Ohmic loss. Here, we report the direct observation of lasing in microfiber-coupled single plasmonic nanoparticles enabled by strong mode coupling. We show that, by strongly coupling a gold nanorod (GNR) with the whispering gallery cavity of a dye-doped polymer microfiber (with diameter down to 2.

Mid-infrared biomimetic moth-eye-shaped polarization-maintaining and angle-insensitive metalens.

Metalenses can potentially reduce the size and complexity of existing cameras, displays, and other optical devices, owing to their capability of flexible manipulation of the polarization, amplitude, and phase of light. However, metalenses capable of maintaining polarization and broadband wavefront shaping under arbitrarily polarized excitation have not been studied. In this study, we present the first demonstration of a biomimetic moth-eye-shaped metalens for polarization-maintaining, broadband and angle-insensitive focusing under an arbitrarily polarized excitation in the mid-infrared waveband (3.

Reconfigurable hybrid silicon waveguide Bragg filter using ultralow-loss phase-change material.

Reconfigurable silicon photonic devices attract much research attention, and hybrid integration with tunable phase-change materials (PCMs) exhibiting large refractive index contrast between amorphous (Am) and crystalline (Cr) states is a promising way to achieve this goal. Here, we propose and numerically investigate a -Si hybrid waveguide Bragg filter operating in the telecom C-band on the silicon-on-insulator (SOI) platform. The proposed device consists of a Bragg grating (BG) with a thin top layer of ultralow-loss PCM interacting with evanescent field of the silicon waveguide mode.

Batch Fabrication of High-Quality Infrared Chalcogenide Microsphere Resonators.

Optical microsphere resonators working in the near- and mid-infrared regions are highly required for a variety of applications, such as optical sensors, filters, modulators, and microlasers. Here, a simple and low-cost approach is reported for batch fabrication of high-quality chalcogenide glass (ChG) microsphere resonators by melting high-purity ChG powders in an oil environment. Q factors as high as 1.

Proposed liquid-cooled nanowire lasers.

While the nanowire (NW) lasers have attracted much attentions as nanoscale coherent sources in recent years, the heat accumulation and temperature-rise-induced breakdown remain challenges to improving the lasers for practical applications. Here we propose a microscale liquid-cooled approach to address the issue. Calculated results show that, compared with conventional air-cooled lasing systems, liquid-cooled NW lasers can allow much higher thermal power.

Plasmonic in-plane total internal reflection: azimuthal polarized beam focusing and application.

Due to the characteristic of surface plasmon polaritons (SPP) excitation, radial polarized beams and circular polarized beams are widely used for plasmonic lens and plasmonic near field focusing. In this paper, a plasmonic lens based on in-plane total internal reflection (TIR) scheme is proposed and numerically demonstrated to achieve the simultaneous nanofocusing of azimuthal and radial polarized beams. By means of the in-plane TIR mechanism, the operation bandwidth of lens ranges from visible light to mid-infrared.

Bending effect characterization of individual higher-order modes in few-mode fibers.

We propose an approach to directly measure the bending effect on individual modes in few-mode fibers using a wavelength-scanning spatially and spectrally resolved imaging technique. By collecting a fiber output beam profile with a scanning wavelength at different bending diameters and analyzing the peaks of its Fourier transformation, we have distinguished higher-order modes (HOMs) of the fiber and investigated their group delay, beam profile, bend loss, and mode splitting individually. We have experimentally verified with a multilayer core fiber at 1-8 cm bending diameters that its HOMs experience more loss compared to lower-order modes, but delay at approximately the same speed as the bending diameter decreases.

Guiding terahertz orbital angular momentum beams in multimode Kagome hollow-core fibers.

We explore terahertz (THz) orbital angular momentum (OAM) modes supported in multimode Kagome hollow-core fibers. Numerical models are adopted to characterize the effective indices and confinement losses of vector modes over 0.2-0.

Nonlinear coupling in graphene-coated nanowires.

We propose and analyze nonlinear coupler based on a pair of single mode graphene-coated nanowires. Nonlinear wave interactions in such structure are analyzed by the coupled mode equations derived from the unconjugated Lorentz reciprocity theorem. We show that the routing of plasmons in the proposed structure can be controlled by the input power due to the third order nonlinear response of graphene layer.

Strong light confinement and gradient force in a hexagonal boron nitride slot waveguide.

In this Letter, we show that a hexagonal boron nitride (h-BN) slot waveguide can achieve strong field enhancement and light confinement in a slot region and a giant gradient force between h-BN slabs. Excellent agreement between simulations and results from an analytical model is observed. In a two-dimensional case, a field enhancement ratio near 60, a power confinement ratio of 80%, and a gradient force over -8.

Nanofocusing of hybrid plasmons-phonons-polaritons in a graphene-hexagonal boron nitride heterostructure.

In this Letter, we investigate the nanofocusing of hybrid plasmons-phonons-polaritons (SPP-HPhPs) in a graphene-hexagonal boron nitride (h-BN) heterostructure with a graphene coating on a tapered h-BN slab. Compared with the hyperbolic phonon polariton (HPhP) in h-BN, the hybrid SPP-HPhP in a heterostructure exhibits much smaller losses, which is validated through both analytical and numerical methods. Furthermore, the thickness dependent dispersions of a hybrid SPP-HPhP enable the tapered heterostructure to achieve a function of focusing electromagnetic waves.

Second harmonic generation in graphene-coated nanowires.

We study second harmonic generation in a pair of graphene-coated nanowires. We show that the phase matching condition for harmonic generation can be engineered in a wide range of frequencies by tuning the spacing between graphene nanowires. We derive coupled mode equations describing the process of second harmonic generation using an unconjugated Lorentz reciprocity theorem.

Graphene circular polarization analyzer based on unidirectional excitation of plasmons.

In this paper we propose a method of unidirectional excitation of graphene plasmons via metal nanoantenna arrays and reveal its application in a circular polarization analyzer. For nanoantenna pairs with orthogonal orientations, the graphene plasmons are excited through antenna resonances with the direction of propagation can be controlled by incident polarization. On the other hand, based on the spiral shape distribution of antenna arrays, a circular polarization analyzer can be obtained via the interaction of geometric phase effect of antenna arrays and the chirality carried by incident polarization.

Graphene circular polarization analyzer based on spiral metal triangle antennas arrays.

In this paper we propose a circular polarization analyzer based on spiral metal triangle antenna arrays deposited on graphene. Via the dipole antenna resonances, plasmons are excited on graphene surface and the wavefront can be tailed by arranging metal antennas into linetype, circular or spiral arrays. Especially, for spiral antenna arrays, the geometric phase effect can be cancelled by or superposed on the chirality carried within circular polarization incidence, producing spatially separated solid dot or donut shape fields at the center.

Graphene plasmons isolator based on non-reciprocal coupling.

In this paper we propose a graphene plasmons isolator based on non-reciprocal coupling within double graphene layer waveguide structure on a magneto-optical substrate. The difference in modal indices of graphene plasmons in opposite directions enables non-reciprocal coupling, which is theoretically investigated via coupled mode theory (CMT) and shows good agreement with numerical finite elements methods (FEM). The non-reciprocal coupling endows such system functionalities as magnetically controlled "plasmons circulator" or "plasmons isolator".

Hindering effect of the core-cladding interface in thermally poled optical fibers.

In this paper, the hindering effect of the core-cladding interface (CCI) in thermally poled optical fiber is investigated based on the two-dimensional charge dynamics model. The influence of the mobility of charge carriers at the CCI, and the mobility and concentration of charge carriers in the fiber core on the thermal poling process is presented. It is found that lower mobility of charge carriers at the CCI is responsible for the hindering effect of the CCI.

Tunable graphene-coated spiral dielectric lens as a circular polarization analyzer.

We propose a tunable circular polarization analyzer based on a graphene-coated spiral dielectric lens. Spatially separated solid dot shape (or donut shape) field can be achieved if the geometric shape of analyzer and incident circular polarization possess the opposite (or same) chirality. Moreover, distinct from the narrow working bandwidth of a traditional circular polarization analyzer, the focusing and defocusing effects in the analyzer are independent of the chemical potential of graphene, and depend only on the dielectric permittivities and the grating occupation ratio.