On-chip integrated metasystem for spin-dependent multi-channel color holography.

On-chip integrated metasurface driven by in-plane guided waves is of great interests in various light-field manipulation applications such as colorful augmented reality and holographic display. However, it remains a challenge to design colorful multichannel holography by a single on-chip metasurface. Here we present metasurfaces integrated on top of a guided-wave photonic slab that achieves multi-channel colorful holographic light display. An end-to-end scheme is used to inverse design the metasurface for projecting off-chip preset multiple patterns. Particular examples are presented for customized patterns that were encoded into the metasurface with a single-cell meta-atom, working simultaneously at RGB color channels and for several different diffractive distances, with polarization dependence. Holographic images are generated at 18 independent channels with such a single-cell metasurface. The proposed design scheme is easy to implement, and the resulting device is viable for fabrication, promising plenty of applications in nanophotonics.

Inverse design of a light nanorouter for a spatially multiplexed optical filter.

It is attractive to use an optical nanorouter by artificial nanostructures to substitute the traditional Bayer filter for an image array sensor, which, however, poses great challenges in balancing the design strategy and the ease of fabrication. Here, we implement and compare two inverse design schemes for rapid optimization of RGGB Bayer-type optical nanorouter. One is based on the multiple Mie scattering theory and the adjoint gradient that is applicable to arrays of nanospheres with varying sizes, and the other is based on the rigorous coupled wave analysis and the genetic algorithm. In both cases, we study layered nanostructures that can be efficiently modeled respectively which greatly accelerates the inverse design. It is shown that the color-dependent peak collection efficiencies of nanorouters designed in the two methods for red, green, and blue wavelengths reach 37%, 44%, and 45% and 52%, 50%, and 66%, respectively. We further demonstrate color nanorouters that provide light focusing to four quadrants working in both the visible and infrared bands, which promises multispectral imaging applications.

Square-root topological state of coupled plasmonic nanoparticles in a decorated Su-Schrieffer-Heeger lattice.

The square-root operation can generate systems with new (to the best of our knowledge) topological phases whose topological properties are inherited from the parent Hamiltonian. In this Letter, we introduce the concept of square-root topology in the two-dimensional (2D) Su-Schrieffer-Heeger (SSH) model and construct a square-root topological square nanoparticle lattice (SRTL) by inserting additional sites into the original 2D SSH model. We find that the topological states in the SRTL are intriguingly different from those in the corresponding SSH model (with on-site potential) due to the change in symmetrical characteristics. Plasmonic nanoparticle arrays are used to demonstrate this by including both nearest-neighbor and next-nearest-neighbor interactions within the dipole approximation. These unique topological states, such as the single corner mode and multiple topological edge modes, enrich the topological features produced by square-root operation and expand the scope to apply such topological features into photonic systems.

Nearly dispersionless multicolor metasurface beam deflector for near eye display designed by a physics-driven deep neural network.

Dispersion is one of the most important issues in see-through near eye displays with waveguide technology. In particular, the nanophotonics design is challenging but demanding. In this paper, we propose a design method for a multilayer achromatic metasurface structure for near eye display application by a physics-driven generative neural network. Two in-coupling metagratings under different projector illuminations are presented and numerically verified with the absolute diffraction efficiency over 89%. A beam splitter, which provides a balance between compactness and visual comfort in a single-projector-binocular display, is also designed. Finally, we apply this method to an out-coupling metasurface with the capability of enlarging the visible region by threefold.

Multiple Dirac points by high-order photonic bands in plasmonic-dielectric superlattices.

The emergence of Dirac points (DPs) characterizes the topological phase transition and the gapless interface states in composite metal-dielectric metamaterials. In this work, we study a kind of compound plasmonic-dielectric periodic structure (PDPS) which sustains both plasmonic modes and multiple photonic modes. The structure has primitive cell consisting of four layers made from triple constituent components. Due to the generalized Su-Schrieffer-Heeger, DPs can emerge at the Brillouin zone center. More specifically, in weak plasmonic-photonic mode interaction regime, multiple DPs would emerge at the Brillouin zone center and edge due to the band folding, from the perspective of general effective medium. From the rigorous field analysis, the origin of these DPs is clearly demonstrated. These interleaved DPs behave as the intermediate transitions of the surface impedance for the PDPS and raise fully spanned topological interface states originated from 0 to 2nd-order photonic bands in the PDPS. The cases of combining our PDPS with either a plasmonic or dielectric homogenous medium are presented.

Exploring optical resonances of nanoparticles excited by optical Skyrmion lattices.

Recently, optical Skyrmion lattices (OSLs) have been realized in evanescent electromagnetic fields. OSLs possess topologically stable field configurations, which promise many optics and photonics applications. Here, we demonstrate that OSLs can serve as versatile structured optical near-fields to assist with studies of a variety of photonic modes in nanoparticles. We firstly show that OSL is capable of selectively exciting electric and magnetic multipole modes by placing a nanoparticle at different positions in the lattice. We then disclose that OSLs can efficiently excite some intriguing resonant modes, including toroidal and plasmonic dark modes, in dielectric or metal nanoparticles. Our results may enhance understanding of the interaction between OSLs and nanoparticles and find applications associated with precise control over resonant modes in nanostructures.

Dual-band unidirectional forward scattering with all-dielectric hollow nanodisk in the visible.

High-index dielectric nanoantennas have become an emerging branch of optical nanoantennas, essentially due to their low loss. These types of nanoantennas can achieve both forward and backward unidirectional scattering, enabled by electric dipole and magnetic dipole interaction. Here, we show that the scattering directionality can be further enhanced if higher-order moments are properly balanced and reach the generalized Kerker condition at two different wavelengths in an all-dielectric hollow nanodisk. Moreover, putting the nanodisks in an array of transverse configuration can enhance the unidirectionality to be needle-like, with the main lobe angular beam width α<15°. Finally, we show that such unidirectional radiation properties can be maintained for a local electric dipole source.

Unidirectional excitation of plasmonic waves via a multilayered metal-dielectric-metal Huygens' nanoantenna.

Huygens' nanoantennas maintain orthogonal electric and magnetic dipole resonances satisfying the Kerker condition and can generate directional radiation in both the near-field and far-field regimes. Here we study a multilayered metal-dielectric-metal (MDM) Huygens' type nanoantenna which is capable of launching surface plasmon polaritons (SPPs) unidirectionally when excited by a dipole source. We show that the radiative decay rates of the dipole source are strongly enhanced by the antenna, and the generated SPP waves propagate in opposite directions at two different wavelengths. The directionality of the excited SPPs can be switched by changing the geometry and the material composition. We further demonstrated that the beam width of the SPP waves can be narrowed by arranging the MDM antennas in a chain.

Complex band structure of one-dimensional polariton crystal.

The exceptional point (EP), at which the relevant eigenvalues and eigenstates are simultaneously identical, typically exists in non-Hermitian systems with parity-time (PT) symmetric complex potentials, and gives rise to many intriguing behaviors in various physical realms. In this work, we explore the complex band structure of one-dimensional "polariton crystals" that can be constructed in waveguide-resonator coupled systems, with PT-symmetric potential. Analysis based on the transfer matrix and the coupled mode theory shows that the complex band structure is intimately determined by the interaction between the Bragg resonance and the polariton one, the gain/loss coefficients, in addition to the coupling strength. A miniband is induced due to the interaction of these two resonances, which is a defect-like band and appears quite different for the band structure evolution. Furthermore, PT-symmetric phase transition occurs in the momentum space for certain amounts of non-Hermiticity. As the non-Hermiticity increases, the EP formed in the original polariton gap approaches another EP formed at the touch point of the folded Bragg bands (where the thresholdless transition occurs). Then they coalesce at a specific non-Hermiticity, and finally disappear. Subsequently, the transmission spectra of such polariton crystals show intriguing phenomena induced by the EPs. Our results provide a different perspective to understand PT-symmetric polariton crystals and may find applications in gain/loss induced lasing by 'polaritons'.

Resonance modes in stereometamaterial of square split ring resonators connected by sharing the gap.

Stereometamaerials can fully utilize the 3D degrees of freedom to exploit the coupling and hybridization between multiple split ring resonators (SRRs), enabling more extraordinary resonances and properties over their planar counterparts. Here we propose and numerically study a kind of structure based on connected SRRs sharing their gap in a rotational fashion. It is shown that there are three typical resonance modes in such cage-like SRR (C-SRR) stereometamaterial in the communication and near infrared range. In the order of increasing energy, these modes can be essentially ascribed to magnetic torodial dipole, magnetic dipole, and a mixture of electric-dipole and magnetic toroidal dipole. We show that the latter two are derived from the second-order mode in the corresponding individual SRR, while the first one from the fundamental one. The highest energy mode remains relatively "dark" in an individual C-SRR due to the high-order feature and the rotational symmetry. However, they are all easily excitable in a C-SRR array, offering multiband filtering functionality.

Multiple reversals of optical binding force in plasmonic disk-ring nanostructures with dipole-multipole Fano resonances.

We study the optical far-field and near-field characteristics, and the optical force effects of plasmonic disk-ring nanostructures. There are multiple Fano features resulting from the scattering interferences of the hybridized modes from the disk's dipole and the ring's higher-order modes. In particular, it is found that the optical binding force between the disk and the ring shows multiple sign reversals spectrally, from the dipole-quadrupole regime up to the dipole-decapole regime. We show that the zero-force points can be categorized into two types: the positive-to-negative ones resulting from the Fano dip and the negative-to-positive ones associated with the transitions between dipole-multipole modes. The multiple sign reversals of the optical forces are tunable by the geometrical size and gap of the disk and ring. Such characters make it possible to organize unusual optical matters from individual plasmonic nanoparticles.

In situ preparation of Mn-doped perovskite nanocrystalline films and application to white light emitting devices.

Mn-doped perovskite nanocrystals have promised new optoelectronic applications due to their unique material properties. In the present study, Mn-doped perovskite nanocrystalline films were prepared in situ in a polymer matrix. The Mn-doped perovskite nanocrystals (PNCs) had good crystallinity and uniform size/spatial distributions in the polymer film. Bright dual-color emission and the long lifetime of the excited state of the dopant were observed from the host exciton and the Mn2+ dopant, respectively. Furthermore, magnetism was observed in the optimal Mn2+ concentration, implying that magnetic coupling was achieved in the Mn-doped perovskite lattice. The Mn-doped perovskite films also showed superior stability against moisture. To demonstrate the practicality of this composite film, a white light emitting device was fabricated by combining a single composite film with a blue light emitting diode; the device showed a high-quality white light emission, and the Commission Internationale De L'Eclairage (CIE) chromaticity coordinate of the white light emitting diode (WLED) (0.361, 0.326) was close to the optimal white color index. In this single-layer WLED, self-absorption among the luminous multilayers in traditional white light emitting diodes can be avoided. The study findings revealed that Mn-doped perovskite nanocrystalline films have many exciting properties, which bodes well for the fundamental study and design of high-performance optoelectronic devices.

A robust and dither-free technique for controlling driver signal amplitude for stable and arbitrary optical phase modulation.

We propose a robust and dither-free technique using a delay line interferometer, a balanced detector and simple signal processing to adjust the amplitude of the driver signal of an optical phase modulator automatically for stabilizing the modulated phase of an optical carrier at any arbitrary value. The technique is analytically shown to be robust against practical device imperfections. A stable 45 degrees phase shift with deviation less than ± 0.8 degrees is experimentally demonstrated.

[Cytological study on osteoblasts and in-situ setting calcium phosphate cements].

OBJECTIVE: To evaluate biocompatibility of three kinds of self-developed injectable calcium phosphate cements (CPCs): chitosan microspheres/CPC, ß-tricalcium phosphate (ß-TCP)/CPC, and K(+)/CPC and the viability of the osteogenic cells cultured with CPC pastes and discs for 10 days. METHODS: The rabbit marrow stromal cells (rMSCs), isolated from rabbit bone marrow with density gradient centrifugation and flow cytometer, were cultured, expended and induced into osteoblasts. Alizarin red staining was used to determine the function of ossification. Then, rMSCs were incubated randomly on both the pastes and solidified discs of the 3 kinds of CPCs. The cells cultured on a 24-well plate were as blank control. Each group had 4 samples. The proliferation and differentiation of each group were observed using acid phosphatase assay (APA) and by testing the activity of alkaline phosphatase (ALP) at day 1, 4, 7, and 10. After stained by acridine orange(AO), the cells were observed, counted and analyzed with an epifluorescence microscopy. The morphology of the cells on CPCs was observed with scanning electron microscope(SEM).The data was subjected to two-way ANOVA followed by LSD test to compare between groups. RESULTS: The process of solidification of the three kinds of CPC pastes has the toxic effect on cells, which is irreversible. The proliferation( the average absortion of pastes are 0.049,0.050,0.049; the discs are 0.898,0.867,0.909;P<0.001), function(the average ALP activity of pastes after ten days are 0.775,0.782,0.798 U/g protein; the discs are 49.288,49.631, 49.744 U/g protein;P<0.001) and number of cells(the average number of cells of pastes after ten days are 3.7,3.7,3.7; the discs are 91.1,89.7,93.7;P<0.001) directly exposed to CPC paste significantly decreased compared with those contacting with the discs. By contrast, cells on the three kinds of discs showed better viability, proliferation, and ossification and cell numbers increased obviously with culture days. CONCLUSION: The process of solidification of the three kinds of CPC pastes has toxic effect on cells. Further study needs to explore a method to protect osteoblasts when seeded into the CPC paste.

Average capacity optimization in free-space optical communication system over atmospheric turbulence channels with pointing errors.

A model is proposed to study the average capacity optimization in free-space optical (FSO) channels, accounting for effects of atmospheric turbulence and pointing errors. For a given transmitter laser power, it is shown that both transmitter beam divergence angle and beam waist can be tuned to maximize the average capacity. Meanwhile, their optimum values strongly depend on the jitter and operation wavelength. These results can be helpful for designing FSO communication systems.

Dual-Band Unidirectional Emission in a Multilayered Metal-Dielectric Nanoantenna.

Controlling the emission efficiency, direction, and polarization of optical sources with nanoantennas is of crucial importance in many nanophotonic applications. In this article, we design a subwavelength multilayer metal-dielectric nanoantenna consisting of three identical gold strips that are separated by two dielectric spacers. It is shown that a local dipole source can efficiently excite several hybridized plasmonic modes in the nanoantenna, including one electric dipole (ED) and two magnetic dipole (MD) resonances. The coherent interplay between the ED and MDs leads to unidirectional emissions in opposite directions at different wavelengths. The relative phase difference between these resonant modes determines the exact emission direction. Additionally, with a proper spacer thickness and filling medium, it is possible to control the spectral positions of the forward and backward unidirectional emissions and to exchange the wavelengths for two unidirectional emissions. An analytical dipole model is established, which yields comparable results to those from the full-wave simulation. Furthermore, we show that the wavelength of the peak forward-to-backward unidirectionality is essentially determined by the MD and is approximately predictable by the plasmonic wave dispersion in the corresponding two-dimensional multilayer structure. Our results may be useful to design dual-band unidirectional optical nanoantennas.

Flavonoids isolated from Sinopodophylli Fructus and their bioactivities against human breast cancer cells.

Four prenylated flavonoids compounds 1-4, named sinopodophyllines A-D, and a flavonoid glycoside (compound 13), sinopodophylliside A, together with 19 known compounds (compounds 5-12 and 14-24) were isolated from the fruits of Sinopodophyllum hexandrum. The structures of new compounds were elucidated by extensive spectroscopic analysis, including HRESIMS, 1D and 2D NMR. Compounds 1-6, 9-11, and 14-17 were tested for their cytotoxicity against human breast-cancer T47D, MCF-7 and MDA-MB-231 cells in vitro, and compounds 2, 5, 6, 10 and 11 showed significant cytotoxicity (IC50 values < 10 µmol·L-1) against T47D cells.

[Immune regulating activity of a novel organoselenium compound ethaselen-1 in C57/BL mice].

OBJECTIVE: To detect the Immune regulating activity of ethaselen-1 (Eb1), a novel organoselenium compound, in C57/BL mice transplanted with Lewis lung cancer(LLC). METHODS: The LLC transplanted C57/BL mice models were established, and the mice was randomly divided into four groups, including high dose Eb1 group (25.0 mg/kg),low dose Eb1 group (12.5 mg/kg), positive control group (levamisole, LMS, 2.0 mg/kg) and negative control group(solvent). Intraperitoneal injections (ip.) of the four pharmaceuticals were performed once a day through the abdominal wall separately, from the second to the eighth day after cancer was transplanted. On the eleventh day, six mice of each group were killed and relative weight of spleen, transforming activity of spleen lymphocytes, NK cell activity, LAK cell activity and percentage of CD4(+)CD8(+)T lymphocyte were detect. RESULTS: Compared with the control group, high dose Eb1 could obviously increase the relative weight of spleen (150.59% and 122.55%), transforming activity of spleen lymphocytes(162.25% and 561.98%), NK cell activity(78.60% and 219.42%) and percentage of CD4(-)/CD8(+) T lymphocyte(104.72% and 105.87%) in normal mice and LLC mice. Compared with the control group, high dose Eb1 could also increase LAK cell activity of LLC mice by 195.11%. CONCLUSION: The novel organoselenium compound Eb1 has immune regulating activity in vivo.

Sub-wavelength Unidirectional Antenna Realized by Stacked Spoof Localized Surface Plasmon Resonators.

The use of resonant structures to control scattering strength and directionality is of importance in various electromagnetic systems. Here we propose and demonstrate sub-wavelength unidirectional scattering by two nearby spoof localized surface plasmon resonators for microwave. The principle is that metal surfaces corrugated by grooves can support magnetic dipolar modes, as well as electric dipolar modes. The resonance is essentially dictated by the geometric parameter of the structure, enabling extremely high degrees of freedom for tuning the scattering properties of the resonator. Particularly, by adjusting the thickness of the resonators, we can make the magnetic dipole mode of one resonator have nearly the same resonant frequency with that of the electric dipole mode of the other resonator. We show that nearly zero backscattering happens when the distance between the two resonators is subwavelenght but larger than a certain value, otherwise strong vertical coupling and mode splitting occur. The results can be extended to other frequency bands and might find application in unique resonant devices as a radio frequency (RF) antenna, filter and metasurface.

Absence of Exceptional Points in Square Waveguide Arrays with Apparently Balanced Gain and Loss.

The concept of parity-time (PT) symmetry in the field of optics has been intensively explored. This study shows the absence of exceptional points in a three-dimensional system composed of a square waveguide array with diagonally-balanced gain/loss distribution. More specifically, we show that an array of four coupled waveguides supports eight fundamental propagation supermodes, four of which are singlet, and the other two pairs are double degenerated. It is found that the singlet states follow the routine PT phase transition; however, the double-degenerated modes never coalesce as the gain/loss-to-coupling strength level varies, showing no actual PT symmetry-derived behavior. This is evident in the phase rigidity which does not approach zero. The absence of exceptional points is ascribed to the coupling of non-symmetric supermodes formed in the diagonal waveguide pairs. Our results suggest comprehensive interplay between the mode pattern symmetry, the lattice symmetry, and the PT-symmetry, which should be carefully considered in PT-phenomena design in waveguide arrays.