Near-perfect fidelity polarization-encoded multilayer optical data storage based on aligned gold nanorods

Encoding information in light polarization is of great importance in facilitating optical data storage(ODS)for information security and data storage capacity escalation.However,despite recent advances in nanophotonic techniques vastly en-hancing the feasibility of applying polarization channels,the data fidelity in reconstructed bits has been constrained by severe crosstalks occurring between varied polarization angles during data recording and reading process,which gravely hindered the utilization of this technique in practice.In this paper,we demonstrate an ultra-low crosstalk polarization-en-coding multilayer ODS technique for high-fidelity data recording and retrieving by utilizing a nanofibre-based nanocom-posite film involving highly aligned gold nanorods(GNRs).With parallelizing the gold nanorods in the recording medium,the information carrier configuration minimizes miswriting and misreading possibilities for information input and output,respectively,compared with its randomly self-assembled counterparts.The enhanced data accuracy has significantly im-proved the bit recall fidelity that is quantified by a correlation coefficient higher than 0.99.It is anticipated that the demon-strated technique can facilitate the development of multiplexing ODS for a greener future.

Cylindrical vector beams reveal radiationless anapole condition in a resonant state

Nonscattering optical anapole condition is corresponding to the excitation of radiationless field distributions in open resonators,which offers new degrees of freedom for tailoring light-matter interaction.Conventional mechanisms for achieving such a condition relies on sophisticated manipulation of electromagnetic multipolar moments of all orders to guarantee superpositions of suppressed moment strengths at the same wavelength.In contrast,here we report on the excitation of optical radiationless anapole hidden in a resonant state of a Si nanoparticle utilizing a tightly focused radially polarized(RP)beam.The coexistence of magnetic resonant state and anapole condition at the same wavelength further enables the triggering of resonant state by a tightly focused azimuthally polarized(AP)beam whose corresponding electric multipole coefficient could be zero.As a result,high contrast inter-transition between radiationless anapole condition and ideal magnetic resonant scattering can be achieved experimentally in visible spectrum.The proposed mechanism is general which can be realized in different types of nanostructures.Our results showcase that the unique combination of structured light and structured Mie resonances could provide new degrees of freedom for tailoring light-matter interaction,which might shed new light on functional meta-optics.

Optical storage arrays: a perspective for future big data storage

The advance of nanophotonics has provided a variety of avenues for light–matter interaction at the nanometer scale through the enriched mechanisms for physical and chemical reactions induced by nanometer-confined optical probes in nanocomposite materials.These emerging nanophotonic devices and materials have enabled researchers to develop disruptive methods of tremendously increasing the storage capacity of current optical memory.In this paper,we present a review of the recent advancements in nanophotonics-enabled optical storage techniques.Particularly,we offer our perspective of using them as optical storage arrays for next-generation exabyte data centers.

基于柱状矢量光的大容量光信息存储

在纳米尺度下实现光和物质相互作用的复用调控具有重要的科学意义和应用价值.具有独特偏振涡旋特性的柱状矢量光被认为是一种能够增加信息复用容量的光场调控新自由度.本文基于紧聚焦柱状矢量光电场矢量的不均匀特性实现了高密度的光信息复用存储.该工作将起偏后的多波长柱状矢量光聚焦作用在耦合无序金纳米颗粒上,并利用不同波长和偏振态组合的紧聚焦柱状矢量光在一个存储单元中创造了复用存储通道数目的新纪录,且其复用存储误码率较低.本文不仅为利用结构光调控光和物质相互作用提供新思路,而且有望通过结构光与光纤激光器的兼容性降低多维信息存储系统的成本,有助于实现低系统复杂度的大容量数据存储.

Facile metagrating holograms with broadband and extreme angle tolerance

The emerging meta-holograms rely on arrays of intractable meta-atoms with various geometries and sizes for customized phase profiles that can precisely modulate the phase of a wavefront at an optimal incident angle for given wavelengths.The stringent and band-limited angle tolerance remains a fundamental obstacle for their practical application,in addition to high fabrication precision demands.Utilizing a different design principle,we determined that facile metagrating holograms based on extraordinary optical diffraction can allow the molding of arbitrary wavefronts with extreme angle tolerances(near-grazing incidence)in the visible–near-infrared regime.By modulating the displacements between uniformly sized meta-atoms rather than the geometrical parameters,the metagratings produce a robust detour phase profile that is irrespective of the wavelength or incident angle.The demonstration of high-fidelity meta-holograms and in-site polarization multiplexing significantly simplifies the metasurface design and lowers the fabrication demand,thereby opening new routes for flat optics with high performances and improved practicality.

Arbitrary polarization conversion dichroism metasurfaces for all-in-one full Poincare sphere polarizers

The control of polarization,an essential property of light,is of broad scientific and technological interest.Polarizers are indispensable optical elements for direct polarization generation.However,arbitrary polarization generation,except that of common linear and circular polarization,relies heavily on bulky optical components such as cascading linear polarizers and waveplates.Here,we present an effective strategy for designing all-in-one full Poincare sphere polarizers based on perfect arbitrary polarization conversion dichroism and implement it in a monolayer all-dielectric metasurface.This strategy allows preferential transmission and conversion of one polarization state located at an arbitrary position on the Poincare sphere to its handedness-flipped state while completely blocking its orthogonal state.In contrast to previous methods that were limited to only linear or circular polarization,our method manifests perfect dichroism of nearly 100%in theory and greater than 90%experimentally for arbitrary polarization states.By leveraging this attractive dichroism,our demonstration of the generation of polarization beams located at an arbitrary position on a Poincare sphere directly from unpolarized light can substantially extend the scope of meta-optics and dramatically promote state-of-the-art nanophotonic devices.

等离激元纳米材料超快激光光热形变原理及应用

超快激光具有极短的脉宽和极高的峰值强度,已被广泛应用于等离激元纳米材料的加工。在极高的激光功率密度下,等离激元纳米材料中的自由电子吸收入射光子能量成为热电子,然后通过电子与晶格的耦合作用使得晶格温度升高,诱导等离激元纳米材料产生光热形变。根据激光功率密度与熔化沸腾阈值的关系,综述了等离激元材料的三种光热形变——阈值熔化、表面原子扩散和激光烧蚀的不同原理;同时还介绍了等离激元纳米材料超快激光光热形变在多维光存储、结构色彩色打印和信息加密隐写等领域的应用。

Multifunctional metasurface:from extraordinary optical transmission to extraordinary optical diffraction in a single structure

We show that a metasurface composed of a subwavelength metallic slit array embedded in an asymmetric dielectric environment can exhibit either extraordinary optical transmission(EOT) or extraordinary optical diffraction(EOD). The cascaded refractive indices of the dielectrics can leverage multiple decaying passages into variant subsections with different diffraction order combinations according to the diffraction order chart in the k-vector space, providing a flexible mean to tailor resonance decaying pathways of the metallic slit cavity mode by changing the wavevector of the incident light. As a result, either the zeroth transmission or-1 st reflection efficiencies can be enhanced to near unity by the excitation of the localized slit cavity mode, leading to either EOT or EOD in a single structure, depending on the illumination angle. Based on this appealing feature, a multifunctional metasurface that can switch its functionality between transmission filter, mirror, and off-axis lens is demonstrated. Our findings provide a convenient way to construct multifunctional miniaturized optical components on a single planar device.

Dual-shot dynamics and ultimate frequency of all-optical magnetic recording on GdFeCo

Although photonics presents the fastest and most energy-efficient method of data transfer,magnetism still offers the cheapest and most natural way to store data.The ultrafast and energy-efficient optical control of magnetism is presently a missing technological link that prevents us from reaching the next evolution in information processing.The discovery of all-optical magnetization reversal in GdFeCo with the help of 100fs laser pulses has further aroused intense interest in this compelling problem.Although the applicability of this approach to high-speed data processing depends vitally on the maximum repetition rate of the switching,the latter remains virtually unknown.Here we experimentally unveil the ultimate frequency of repetitive all-optical magnetization reversal through time-resolved studies of the dual-shot magnetization dynamics in Gd27 Fe63.87 C09.T3.Varying the intensities of the shots and the shotto-shot separation,we reveal the conditions for ultrafast writing and the fastest possible restoration of magnetic bits.It is shown that although magnetic writing launched by the first shot is completed after 100 ps,a reliable rewriting of the bit by the second shot requires separating the shots by at least 300 ps.Using two shots partially overlapping in space and minimally separated by 300 ps,we demonstrate an approach for GHz magnetic writing that can be scaled down to sizes below the diffraction limit.

Multifunctional metasurface: from extraordinary optical transmission to extraordinary optical diffraction in a single structure: publisher's note

This publisher＇s note reports the revision of authors＇ name spelling in Photon. Res. 6, 443 （2018）.

Theoretical and practical guide for an axial superresolved focus via Gouy phase steering

Achieving an axial superresolved focus with a single lens by simply inserting a modulation mask in the pupil plane is preferred due to its compact configuration and general applicability. However, lack of a universal theoretical model to manifest the superresolved focusing mechanism vastly complicates the mask design and hinders optimal resolution. Here we establish an interference model and find out that the axial resolution closely relates to the Gouy phase gradient(GPG) at the focal point. Using a GPG tuning-based optimization approach, the axial resolution of a ring-mask-modulated beam is readily improved to attain superresolved focal depth for multiple types of pupil function and polarization. In experiment, a focus with an axial resolution of 27% improved from the diffraction limit and 11% finer than the previously reported record is demonstrated for the radially polarized beam. In simulations, a spherical focus with 3D isotropic resolution and a superoscillation-like axial modulation behavior toward extremely high axial resolution is also presented. This approach can be applied for varied types of pupil function, wavelength, and polarization, and can be easily transferred to other traditional or superresolution microscopes to upgrade their axial resolution.

Two-photon reduction： a cost-effective method for fabrication of functional metallic nanostructures

Metallic nanostructures have underpinned plasmonic-based advanced photonic devices in a broad range of research fields over the last decade including physics,engineering,material science and bioscience.The key to realizing functional plasmonic resonances that can manipulate light at the optical frequencies relies on the creation of conductive metallic structures at the nanoscale with low structural defects.Currently,most plasmonic nanostructures are fabricated either by electron beam lithography(EBL) or by focused ion beam(FIB) milling,which are expensive,complicated and time-consuming.In comparison,the direct laser writing(DLW) technique has demonstrated its high spatial resolution and cost-effectiveness in three-dimensional fabrication of micro/nanostructures.Furthermore,the recent breakthroughs in superresolution nanofabrication and parallel writing have significantly advanced the fabrication resolution and throughput of the DLW method and made it one of the promising future nanofabrication technologies with low-cost and scalability.In this review,we provide a comprehensive summary of the state-of-the-art DLW fabrication technology for nanometer scale metallic structures.The fabrication mechanisms,different material choices,fabrication capability,including resolution,conductivity and structure surface smoothness,as well as the characterization methods and achievable devices for different applications are presented.In particular,the development trends of the field and the perspectives for future opportunities and challenges are provided at the end of the review.It has been demonstrated that the quality of the metallic structures fabricated using the DLW method is excellent compared with other methods providing a new and enabling platform for functional nanophotonic device fabrication.

Laser printing based on curvature-driven shape transition of aluminum nanodiscs[Invited]

Plasmonic structural colors have plenty of advantages over traditional colors based on colorants.The pulsed laser provides an important method generating plasmonic structural colors with high efficiency and low cost.Here,we present plasmonic color printing Al nanodisc structures through curvature-driven shape transition.We systematically study the mechanism of morphologic evolution of the Al nanodisc below the thermal melting threshold.A multi-pulse-induced accumulated photothermal effect and subsequent curvature-driven surface atom diffusion model are adopted to explain the controllable shape transition.The shape transition and corresponding plasmonic resonances of the nanodisc can be independently and precisely modulated by controlled irradiations.This method opens new ways towards high-fidelity color prints in a highly efficient and facile laser writing fashion.