Keya Zhou

Harbin Institute of Technology | HIT · Department of Physics

In the present methods of multiple intensity measurements, the recorded different intensity patterns are supposed to have the identical quality and the contribution of different images to the result is the same. However, intensity patterns are of different quality, since the raw patterns are affected by environment noise and focusing distance in th...

Topological transitions open a fundamentally new route of research with interesting optical phenomena in photonic metamaterials. In this work, we comprehensively investigate the topology of equifrequency surfaces in magnetized plasma. The full topological phase diagrams are shown and the critical points in the topological transitions are given. The...

The reconfigurable higher-order topological states are realized in valley photonic crystals with enhanced optical Kerr nonlinearity. The inversion symmetry of the designed valley photonic crystal is broken due to the difference in optical responses between adjacent elements rather than their geometry structures. Therefore, by constructing photonic...

Recently, topologically nontrivial phases in chiral metamaterials have been proposed. However, a comprehensive description of topological phase diagrams and transitions in chiral metamaterials has not been presented. In this work, we demonstrate several forms of topological phase transitions and study the existence of edge states in different phase...

Spin-dependent nonlinear harmonic generations from nanostructures may provide a new class of design for future applications such as nonlinear optical switching and modulation and nonlinear information processing. Most reported works are based on the utilization of metasurfaces with specific symmetry (such as C 3 and C 4 ) and the application of the...

Magnetized plasma as a topological material has been demonstrated recently. However, a comprehensive description of the bulk-edge correspondence in magnetized plasma is still lacking. In this work, we systematically reveal all types of anomalous bulk-edge correspondence in magnetized plasma. The bulk-edge correspondence can be formally restored by...

Most of the photonic valley-Hall edge states were constructed by changing structures to break the spatial inversion symmetry, restricting the practical application potential. In this paper, we construct a tunable topological valley-Hall edge state based on the large optical Kerr effect. It is demonstrated that topological phase transition happens b...

The recent reported robust surface states in a photonic metamaterial are usually limited to the gapless type. In this work, we propose a photonic topological metamaterial that can support surface states with gaps. The gaps appear when the electromagnetic duality symmetry of the material system is broken. Despite the existence of gaps, the surface w...

Topological one-way surface states allow light to pass through sharp corners without reflection. In order to enhance the capability of surface routing devices, multiple one-way surface modes are usually required. Different from previously reported multiple surface modes achieved with large Chern number photonic media, we realize multiple surface wa...

Topological corner state has attracted much research interests since it does not obey the conventional bulk-edge correspondence and enables tightly confined light within small volumes. In this work, we demonstrate an enhanced second harmonic generation (SHG) from a topological corner state and its directional emission. To this end, we design an all...

Higher‐order topological photonic crystals (TPCs) have attracted much attention in the past several years since they do not obey the conventional bulk‐boundary correspondence in topological insulating phases. This characteristic offers a new dimension with which to trap and manipulate the flow of light. In this work, 2D higher‐order TPCs for engine...

We reveal an interesting phenomenon of enhanced polarization-dependent transverse deflection of scattered light on a meta-atom with bianisotropy. The relationship between the spin-dependent shift and the bianisotropy is demonstrated. Unlike the usual particle, the obvious transverse scattering can be obtained by the bianisotropy. Furthermore, the l...

In this work, we utilize phase change materials to achieve tunable second harmonic generation from magnetic resonance in bianisotropic plasmonic metamolecules. As a proof-of-concept, we fill the gap of gold split ring resonators (SRRs) with Ge 2 Se 2 Te 5 (GST); the second harmonic wavelength can be tuned over 400 nm in the telecom regime when GST...

Topological insulators are internally insulating but allow topologically protected surface waves at the boundary. In this work, the photonic analogue of topologically protected surface states in gyro‐electromagnetic metamaterials are discovered. It is analytically and numerically demonstrated that the surface waves appear not only in the k‐space co...

We propose an orientation-dependent polarization manipulation by Cherenkov radiation (CR) in a silicon-on-insulator (SOI) waveguide with a metasurface. By putting an electron bunch passing near the SOI waveguide, CR excites the fundamental TE-like mode with ultra-high mode purity. The spin state of the decoupled light is determined by the direction...

In this paper, we generalize the principle of a generated first-order acoustic vortex (AV) with the acoustic resonances (AR) of a metasurface, from which we have also proposed a method for generating the higher-order AVs by arranging the sequences of the AR metasurface properly. The usable frequency range of the designed AR metasurface has been inv...

Gratings are commonly used as waveguide couplers because they can provide extra momentum to assist the incident light beam to match the wave vector in the waveguides. Here, we propose two kinds of grating-like nanoantenna arrays which not only satisfies the wavevector matching condition, but also induces the conversion from the spin angular momentu...

We present the photonic spin Hall effect on an ellipsoidal Rayleigh particle, which amounts to a polarization-dependent shift in scattering far-field. Based on the dipole model, we demonstrate that such shift is unavoidable when the light incidence is inclined with respect to the main axis of the ellipsoidal Rayleigh particle. The result has genera...

The vortex beam carrying orbital angular momentum (OAM) has attracted great attentions in optical communication field, which can extend the channel capacity of communication system due to the orthogonality between different OAM modes. Generally, atmospheric turbulence can distort the helical phase fronts of OAM beams, which presents a critical chal...

We present a refined theoretical analysis on the relationship between the optical total angular momenta (TAM) and the optical torque (OT) in a birefringent silicon waveguide. By using the vector angular spectrum method, we demonstrate the dynamic evolutions of the OT, TAM, spin angular momentum (SAM), and orbital angular momentum (OAM). The SAM and...

Weyl points, as linearly double degenerated point of band structures, have been extensively researched in electronic and classical wave systems. However, Weyl points’ realization is always accompanied with delicate “lattice structures”. In this work, frequency-tunable terahertz (THz) generalized Weyl points inside the parameter space have been inve...

Recently, metasurface has attracted lots of attentions because of its great capability in phase engineering for the transmitted cross-polarization light, and many functional optical elements have been designed and investigated. Commonly, the co-polarization and cross-polarization lights will coexist in the transmitted fields. Here, we propose a pla...

It has been recently demonstrated that a metallic surface with periodic grooves can support a laterally-confined surface wave called spoof plasmon polaritons (SSPPs). Here we propose a SSPPs waveguide drilled with L-shaped grooves which can support SSPPs efficiently. Dispersion relations based on the modal expansion method (MEM) are derived and dis...

In microwave and terahertz frequency band, a textured metal surface can support spoof surface plasmon polaritons (SSPPs). In this paper, we explore a SSPPs waveguide composed of a metal block with pyramidal grooves. Under the deep subwavelength condition, theoretical formulas for calculation of dispersion relations are derived based on the modal ex...

In this work, we re-analyze the influence of the loss on the super-resolution imaging of a single metal layer superlens system and reveal its positive role of the imaging. The analysis is based on the surface plasmon polariton (SPP) theory. We show that SPP mode with high loss could suppress the amplification of evanescent waves and concentrate the...

We derive several analytical expressions for the root-meansquare (rms) angular width and the M2-factor of the multi-sinc Schell-model (MSSM) beams propagating in non-Kolmogorov turbulence with the extended Huygens-Fresnel principle and the second-order moments of the Wigner distribution function. Numerical results show that a MSSM beam with dark-ho...

We introduce a new kind of partially coherent beam, non-uniformly Hermite–Gaussian correlated beam, by employing a non-uniformly Hermite function to modulate the spectral degree of coherence. The evolution of such scalar beam on propagation in free space and turbulent atmosphere are investigated. It is demonstrated that the spectral intensity distr...

A thin-film solar cell with dual photonic crystals has been proposed, which shows an advanced light-trapping effect and superior performance in ultimate conversion efficiency (UCE). The shapes of nanocones have been optimized and discussed in detail by self-definition. The optimized shape of nanocone arrays (NCs) is a parabolic shape with a nearly...

A novel multi-focusing metalens in the longitudinal direction has been proposed and investigated based on the equal optical path principle, which is independent on the incident polarizations and can be suitable for both of the linear and circular polarization incidences simultaneously. Here, three novel designing principles: partitioned mode, radia...

A relative broadband circular polarization analyzer based on a single-turn Archimedean nano-pinholes array has been proposed and investigated systematically from visible spectrum to near infrared region. The spiral arrangement of circular nano-pinholes can implement spatially separated fields according to the relationship between the spiral directi...

In this paper, an ultrathin metalens has been proposed based on a holographic metasurface that consists of elongated apertures in 40 nm gold film, which exhibit intriguing properties such as on- and off-axis focusing and also can concentrate light into multiple, discrete spots for circularly polarized incident lights. First, the spatial transmissio...

Surface plasmons, which exist along the interface of a metal and a dielectric, have been proposed as an efficient alternative method for light trapping in solar cells during the past ten years. With unique properties such as superior light scattering, optical trapping, guide mode coupling, near field concentration, and hot-electron generation, meta...

We present dynamics of spatial solitons propagating through a PT symmetric optical lattice with a longitudinal potential barrier. We find that a spatial soliton evolves a transverse drift motion after transmitting through the lattice barrier. The gain/loss coefficient of the PT symmetric potential barrier plays an essential role on such soliton dyn...

In this work, we present a plasmonic photodetector (PPD) with high sensitivity to red light illumination. The ultrasensitive PPD was composed of high-crystalline CdSe nanoribbons (NRs) decorated with plasmonic hollow gold nanoparticles (HGNs) on the surface, which were capable of coupling the incident light due to localized surface plasmon resonanc...

The origin of the photocurrent enhancement and the overpotential reduction in solar water splitting employing nanostructured silicon is still a matter of debate. A set of tapered Si nanowires has been designed for clarifying the impact of nanostructured Si on the hydrogen evolution reactio while precisely tailoring several interference factors such...

Surface plasmons, which exist along the interface of a metal and a dielectric, have been proposed as an efficient alternative method for light trapping in solar cells during the past ten years. With unique properties such as superior light scattering, optical trapping, guide mode coupling, near field concentration, and hot-electron generation, meta...

The optical properties of the various types of tapered silicon nanowires (SiNWs) have been investigated by the phase retrieving method of utilizing the experimental reflec-tion spectra with the aid of the Kramers–Kronig (KK) relation. The effective refractive index (n) and the extinction coefficient (K) of each tapered SiNWs and combined sili-con n...

We suggest a silicon nanowire (SiNW) photodetector side-contacted with hemispherical Au nanoantennas (NAs) that can remarkably amplify the intensity of the near-infrared optical field. The plasmonic NA suppresses visible-range guided mode excitation in SiNW, which enables our photodetector to possess a near-infrared-selective response and overcome...

We suggest a silicon nanowire (SiNW) photodetector side-contacted with hemispherical Au nanoantennas (NAs) that can remarkably amplify the intensity of the near-infrared optical field. The plasmonic NA suppresses visible-range guided mode excitation in SiNW, which enables our photodetector to possess a near-infrared-selective response and overcome...

Metal nanoparticles (NPs) induced surface plasmon resonance (SPR) is of great interest for efficient controlling over light's propagation and absorption in optoelectronic devices applications. In this work, we proposed a simple strategy to improve the photocurrent of planar silicon (Si) p-n junction solar cells by attaching plasmonic Au nanoparticl...

The antireflective characteristics of Si nanocone (NC) arrays were estimated using a theory devised for an inhomogeneous antireflection layer, and further verified by the Fourier modal method (FMM). Considering a better impedance matching from air to Si, a minimum depth of 400 nm is essentially required. Although Si NC arrays have usually been sugg...

Formation of a selective emitter in crystalline silicon solar cells improves photovoltaic conversion efficiency by decoupling emitter regions for light absorption (moderately doped) and metallization (degenerately doped). However, use of a selective emitter in silicon nanowire (Si NW) solar cells is technologically challenging because of difficulti...

An effective photocathode adopting a tapered Si nanohole (SiNH) array has been developed for photoelectrochemical water splitting. The tapered feature of SiNH photocathodes resulted in a gradation of the refractive indices between Si and air, such that the mismatching of optical impedance was alleviated and light absorption was enhanced. Adjusting...

We investigate the influence of Al back reflectors on the optical absorption spectra of Si nanowire (NW) arrays by using the finite-difference time-domain simulation method. A flat Al layer enhances the absorption in the NW array due to not only the reflection-induced optical path length enlargement but also reflection of light between NWs and loca...

Hierarchical nanomaterials have shown unprecedented capabilities in emerging technologies ranging from biosensing and solar energy harvesting to photoelectronics. Developing facile routes for the synthesis of functional semiconductors with controllable size, structure, and means of assembly is of significant importance for optimization of nanoscale...

Metal-assisted chemical etching (MaCE) has been shown to be a powerful and cost-effective method for surface nano-texturing and silicon micromachining. Since the motion of a metal catalyst during the etching process determines the etched morphology, understanding the mobility of the metal catalysts would enable precise control of the silicon struct...

Optimizing the antireflection coatings of porous silicon (PS ARC) is found to be sensitive to their thicknesses. The optimal reflectance for a 400-nm-thin, PS ARC is calculated to be as low as 1.55%.

We investigate optical properties of Si nanowire (NW) array using the FDTD method. Al underlayers can excite localized surface plasmons and surface plasmon polaritons, resulting in enhancement of optical absorption of the NWs.

We have investigated optical characteristics of silicon nanowire (Si NW) on Al disk arrays using the finite-difference time-domain (FDTD) simulations. Without the Al disk, the Si NW arrays alone exhibit strong absorption peaks, originated from guided mode resonance. The arrays of SiNW with Al disk possess additional broad peaks, at slightly larger...

We perform a systematic numerical study to characterize the tradeoff between the plasmonic enhancement and optical loss in periodically aligned, silicon nanowire (SiNW) arrays integrated with a silver back reflector (Ag BR). Optimizing the embedded depth of the wire bottoms into a silver reflector achieved a highly efficient SiNW solar cell. Compar...

The interactions between femtosecond (fs) laser pulses and a thin Au film deposited on a silica glass substrate were systematically investigated based on experimental data. Different structures, including microholes, nanoholes, and nanobumps, are obtained when pulses with different energies are incident on the surface of a gold film. The experiment...

Introducing a ZnSe quantum dot (QD) layer over silicon nanowire (Si NW) solar cells considerably enhances external quantum efficiency (EQE) over broadband wavelengths. This is attributed to the combination of two major benefits of ZnSe QDs: superior light trapping and photon down-conversion. The integration of ZnSe QDs on the Si NW solar cell signi...

The virtual source for generation of rotational symmetric Lorentz-Gaussian (RLG) wave whose propagating dynamics present the rotational symmetry is identified. Closed-form expressions, including integral and differential representations, are derived for this kind of Lorentz-Gaussian (LG) wave, thereby yielding paraxial approximation of the RLG beam...

We found that multi-layer coating of a Si substrate with SiO2 dielectric nanoparticles (NPs) was an effective method to suppress light reflection by silicon solar cells. To suppress light reflection, two conditions are required for the coating: 1) The difference of refractive indexes between air and Si should be alleviated, and 2) the quarter-wavel...

A new mathematical model of dark-hollow beams, described as hollow sinh-Gaussian (HsG) beams, has been introduced. The intensity distributions of HsG beams are characterized by a single bright ring along the propagation whose size is determined by the order of beams; the shape of the ring can be controlled by beam width and this leads to the ellipt...

We report on the growth of GaSb nanotrees on InAs { ̅1 ̅1 ̅1}(B) substrates by chemical beam epitaxy. GaSb nanotrees form by the nucleation of Ga droplets on the surface of < ̅1 ̅1 ̅1>(B) oriented GaSb nanowires followed by the epitaxial growth of branches catalyzed by these Ga droplets. In the tip region, the trunks of the GaSb nanotrees are perio...

A generalized type of spiral Bessel beam has been demonstrated by using a spatially displaced helical axicon (HA). The topological charge of the spiraling Bessel beams is determined by the order of the input Laguerre—Gaussian (LG) beam and the topological charge of the HA. The obtained spiraling Bessel beams have an LG type of modulation along thei...

The relation between filling ratio and length of Si nano wires is investigated via characterizing the optical and electrical performances of solar cells. To enhance photovoltaic performances, we suggest the optimal parameters in nano wired solar cell.

The optical properties of metal nanoparticle (NP)-coated silicon nanowires (Si NWs) are theoretically investigated using COMSOL Multiphysics commercial software. A geometrical array of periodic Si NWs coated with metal NPs is proposed. The simulation demonstrates that light absorption could be enhanced significantly in a long wavelength region of t...

A simple method to extract the optical bandgap of Si nanowire (SiNW) arrays that utilizes the reflection spectra of freestanding SiNW arrays is presented in this Letter. At a fixed nanowire diameter, three different wire lengths reproducibly formed a cross point in their reflectance curve plots. The cross point wavelength corresponded to the optica...

Spiraling Bessel beams of arbitrary order are created by illuminating an apertured axicon and a hologram with a single-ringed Laguerre–Gaussian beam. The high-order beam rotates around the propagating axis with a hollow center and can be regarded as the hollow spiraling beam. Such beams have distinct advantages, which offer a direct method for micr...

We present a new method for determining the trap depth of an atomic or molecular trap of any type and any depth. This method relies on measurements of the trap loss rate induced by elastic collisions of ultracold Rb atoms with room temperature background gases. Because of the long range nature of the Van der Waals force, these loss rates exhibit si...

Silicon microholes array have been fabricated using femtosecond laser directly writing followed by electrochemical etching in a hydrofluoric acid (HF) and the isopropyl alcohol ((CH3)2CHOH) solution. Firstly, the micro size scratches array were directly written on a surface of the n-type, 1–5 Ωcm, Si(100) wafer by using the femtosecond laser pulses...

We present the measurements and calculations of the absolute total collision cross sections for a room-temperature gas of helium using 87Rb atoms confined in either a magneto-optic or a magnetic quadrupole trap. The loss rates from the magneto-optic trap and the pure magnetic trap are compared and show significant differences. The collision cross s...

Defect modes are studied in parity-time (PT) symmetric periodic complex potentials for both positive and negative defects. Such new kinds of linear localized modes may conserve their energy or endure gain or loss upon propagating. The existence domain of the conserved modes would be prolonged by positive defects or shortened by negative defects, an...

The optical properties of the silicon naniwires (SiNWs) fabricated by a method of metal-assisted electroless etching have been investigated. The optical parameters of both SiNWs and the Si wafer, including dielectric function (ɛ (ω) ) and the effective refractive index ( N(ω) ), could be obtained from the light-absorption theory and Kramers-Kronig...

We investigate the dynamics of strongly localized solitons trapped in remote troughs of radially periodic lattices with Kerr-type self-focusing nonlinearity. The rotary motion of solitons is found to be more stable for larger nonlinear wavenumbers, lower rotating velocity, and shorter radius of the trapping troughs. When the lattice is shrunk or ex...

We report on a kind of self-assembled volume grating in silica glass induced by tightly focused femtosecond laser pulses. The formation of the volume grating is attributed to the multiple microexplosion in the transparent materials induced by the femtosecond pulses. The first order diffractive efficiency is in dependence on the energy of the pulses...

In this article, we investigate the N-soliton bound state (BS) motions in photonic lattices. BSs split into their constituent single-solitons when they are incident normally into lattices. The splitting is sensitive to the incident position with respect to the lattices. In such a process, the lattice profile not only provides an antisymmetric frequ...

Discrete plasmonic Talbot effect in the subwavelength metal waveguide arrays (SMWAS) is theoretically analyzed and numerically simulated. Based on the finite-difference time-domain technique, we discuss the influence of the structural parameters on the Talbot distance. By carefully choosing the geometry parameters, the Talbot distance decreases to...