Wenqi Zhu

National Institute of Standards and Technology | NIST

Providing additional degrees of freedom to manipulate light, spatiotemporal optical vortex (STOV) beams carrying transverse orbital angular momentum are of fundamental importance for spatiotemporal control of light-matter interactions. Unfortunately, existing methods to generate STOV are plagued by various limitations such as inefficiency, bulkines...

Dielectric metasurfaces, composed of planar arrays of subwavelength dielectric structures that collectively mimic the operation of conventional bulk optical elements, have revolutionized the field of optics by their potential in constructing high-efficiency and multi-functional optoelectronic systems on chip. The performance of a dielectric metasur...

As increasingly more demanding photonics applications are brought on‐chip, more complex design solutions are employed to deliver enhanced performance: e.g., meta‐molecules, inverse‐designed freeform structures, and multilayer metasurfaces. Instead, this study introduces anti‐reflective metasurfaces fabricated in a single nanolithography step that f...

Polarization, one of the fundamental properties of light, is critical for certain imaging applications because it captures information from the scene that cannot directly be recorded by traditional intensity cameras. Currently, mainstream approaches for polarization imaging rely on strong dichroism of birefringent crystals or artificially fabricate...

The commercialization of atomic technologies requires replacing laboratory-scale laser setups with compact and manufacturable optical platforms. Complex arrangements of free-space beams can be generated on chip through a combination of integrated photonics and metasurface optics. In this work, we combine these two technologies using flip-chip bondi...

The electron vortex beam (EVB)-carrying quantized orbital angular momentum (OAM) plays an essential role in a series of fundamental research. However, the radius of the transverse intensity profile of a doughnut-shaped EVB strongly depends on the topological charge of the OAM, impeding its wide applications in electron microscopy. Inspired by the p...

Coherent light–matter interactions on the femtosecond time scale form the backbone of ultrafast science and technology, where the instantaneous state of light is used to control and detect the interaction of light with matter. Here, the polarization state of light has proven pivotal in unveiling intrinsic chiral or anisotropic optical response in v...

We use metasurfaces to construct a six-beam magneto optical trap for neutral strontium atoms. The configuration consists of a polarization-multiplexed metasurface splitter and three topology-optimized metagratings, requiring only two input beams and no bulk optics.

We report on a strontium optical clock built with integrated photonics. We implement free-space laser beam control of positioning, pointing, shaping, polarization, and integration with metasurface optics, and laser-frequency absolute stabilization with waveguide supercontinuum generators.

Dielectric-metasurface-enabled pulse shaper provides a versatile platform for custom engineering the spatiotemporal evolution of ultrafast optical pulses. Here, we investigate its ability to perform complex optical transformations, such as mathematical operations, on femtosecond timescale pulses.

We introduce a novel multilayer metasurface design paradigm, and leverage it to design and fabricate anti-reflective metalenses at various resolving powers. We demonstrate that transmission and focusing efficiencies of multilayer metalenses outperform their single-layer counterparts.

We demonstrate an algorithm based on reinforcement learning to realize high efficiency multifunctional metagrating devices without the requirement of a training dataset.

We design and fabricate high aspect-ratio dielectric metasurfaces made of wide-bandgap, low-index oxide materials that support quasi-bound states in the continuum. These states could be exploited to achieve high harmonic generation in the deep-UV regime.

We demonstrate arbitrary spatiotemporal synthesis of ultrafast optical transients by leveraging the multifunctional control of light at the nanoscale offered by metasurfaces, enabling ready-synthesis of complex space-time wave packets over an ultrawide bandwidth.

The ability to control the instantaneous state of light, from high-energy pulses down to the single-photon level, is an indispensable requirement in photonics. This has, for example, facilitated spatiotemporal probing and coherent control of ultrafast light-matter interactions, and enabled capabilities such as generation of exotic states of light w...

Surface‐enhanced Raman spectroscopy (SERS) has become a sensitive detection technique for biochemical analysis. Despite significant research efforts, most SERS substrates consisting of single‐resonant plasmonic nanostructures on the planar surface suffer from limitations of narrowband SERS operation and unoptimized nano‐bio interface with living ce...

A unique bifocal compound eye visual system found in the now extinct trilobite, Dalmanitina socialis, may enable them to be sensitive to the light-field information and simultaneously perceive both close and distant objects in the environment. Here, inspired by the optical structure of their eyes, we demonstrate a nanophotonic light-field camera in...

Decoding arbitrary polarization information from an optical field has triggered unprecedented endeavors in polarization imaging, remote sensing, and information processing. Therefore, developing a polarization detection device with full on‐chip integration and miniaturization holds tremendous potential for many areas of optical sciences. Herein, a...

We develop a photonic integrated chip and metasurface platform for collinearly combining laser beams at 813 nm and 698 nm wavelengths for the lattice and clock beams of a miniature atomic clock.

We demonstrate a scalable, integrated photonics infrastructure for optical atomic clocks. We laser cool and trap 4 × 10 5 87 Sr atoms in a magneto-optical trap, using metasurface optics and a compact, single-chamber vacuum system.

Arbitrary spatiotemporal shaping requires complete control of the electric-field vector at each space-time coordinate. Here, we demonstrate simultaneous and independent tailoring of spatial and temporal properties of femtosecond pulses using a single-layer dielectric metasurface.

Arbitrary spatiotemporal shaping requires complete control of the electric-field vector at each space-time coordinate. Here, we demonstrate simultaneous and independent tailoring of spatial and temporal properties of femtosecond pulses using a single-layer dielectric metasurface.

Monochromatic light can be characterized by its three fundamental properties: amplitude, phase, and polarization. In this work, we propose a versatile, transmission-mode all-dielectric metasurface platform that can independently manipulate the phase and amplitude for two orthogonal states of polarization in the visible frequency range. For proof-of...

A perfect vortex beam (PVB) is a propagating optical field carrying orbital angular momentum (OAM) with a radial intensity profile that is independent of topological charge. PVBs can be generated through the Fourier transform of a Bessel–Gaussian beam, which typically requires a well‐aligned optical setup consisting of a spiral phase plate, an axio...

Nanophotonic devices, composed of metals, dielectrics, or semiconductors, enable precise and high-spatial-resolution manipulation of electromagnetic waves by leveraging diverse light–matter interaction mechanisms at subwavelength length scales. Their compact size, light weight, versatile functionality and unprecedented performance are rapidly revol...

The term Poincaré beam, which describes the space-variant polarization of a light beam carrying spin angular momentum (SAM) and orbital angular momentum (OAM), plays an important role in various optical applications. Since the radius of a Poincaré beam conventionally depends on the topological charge number, it is difficult to generate a stable and...

Laser-cooled atoms are a key technology for many calibration-free measurement platforms—including clocks, gyroscopes, and gravimeters—and are a promising system for quantum networking and quantum computing. The optics and vacuum hardware required to prepare these gases are often bulky and not amenable to large-volume manufacturing, limiting the pra...

A dielectric-metasurface-enabled pulse shaper able to tailor the temporal instantaneous polarization states within a near-infrared femtosecond pulse is demonstrated. Simultaneous complex wavefront shaping has been implemented by exploiting metasurfaces’ multi-functionalities within a single-pixel.

We present laser cooling of atomic Rb using a metasurface optic for beam shaping and polarization control. This technology will enable miniaturized quantum devices and calibration-free sensors utilizing the properties of cold atoms.

We photonically generate 12 free-space well-collimated beams at 461 nm and 689 nm wavelengths with customized beam profiles and emission angles needed for a Sr MOT. The device advanced photonics interfaces for atomic physics.

We demonstrate arbitrary control of femtosecond timescale complex electrical-field transients using dielectric metasurfaces, enabling temporal vectorial ultrafast pulses with rich instantaneous polarization states and a simultaneously tailored spatial wavefront.

Large-area inverse-designed photonic gratings and optical metasurfaces directly couple waveguides to wide free-space modes with custom wavefronts and polarizations in the visible and near-infrared. Design, modeling methods and experimental results are discussed.

Shrinking conventional optical systems to chip-scale dimensions will benefit custom applications in imaging, displaying, sensing, spectroscopy, and metrology. Towards this goal, metasurfaces—planar arrays of subwavelength electromagnetic structures that collectively mimic the functionality of thicker conventional optical elements—have been exploite...

Color is a primary attribute of human visual perception and plays a crucial role both in imaging and display technology and in the arts. In work this year, we demonstrated the ability to tune both color hue and brightness in transmitted light with a specially designed metasurface—at a level of detail sufficient to create a “nanopainting” that repro...

We realize a dielectric metasurface that enables full-color generation and ultrasmooth brightness variation. The reproduced artwork “girl with a pearl earring” features photorealistic color representation and stereoscopic image impression, mimicking the texture of an oil-painting.

Light beams carrying spin angular momentum (SAM) and orbital angular momentum (OAM) have created novel opportunities in the areas of optical communications, imaging, micromanipulation, and quantum optics. In article number 2000062, Ting Xu, Yanqing Lu, and co‐workers demonstrate an efficient detection approach for measuring multiple SAM and OAM mod...

Recent advancements in the ability to design, fabricate, and characterize optical and optoelectronic devices at the nanometer scale have led to tremendous developments in the miniaturization of optical systems and circuits. Development of wavelength‐scale optical elements that are able to efficiently generate, manipulate, and detect light, along wi...

Light beams carrying spin angular momentum (SAM) and orbital angular momentum (OAM) have created novel opportunities in the areas of optical communications, imaging, micromanipulation, and quantum optics. However, complex optical setups are required to simultaneously manipulate, measure, and analyze these states, which significantly limit system in...

Manipulation of plasmon modes at ultraviolet wavelengths using engineered nanophotonic devices allows for the development of high-sensitivity chiroptical spectroscopy systems. We present here an experimental framework based on aluminum-based crescent shaped nanostructures that exhibit a strong chiroptical response at ultraviolet wavelengths. Throug...

As the two most representative operation modes in an optical imaging system, bright-field imaging and phase contrast imaging can extract different morphological information on an object. Developing a miniature and low-cost system capable of switching between these two imaging modes is thus very attractive for a number of applications, such as biome...

Dielectric metasurfaces enable control of the temporal profile of large bandwidth, near-infrared femtosecond pulses. Using this approach, we demonstrate shaping of the time-domain polarization state within a single pulse.

We demonstrate a novel all-dielectric, ultraviolet metasurface platform based on Tantalum Pentoxide, enabling high-performance meta-devices operating across the mid- and nearultraviolet frequency regimes.

Dielectric metasurfaces enable control of the temporal profile of large bandwidth, near-infrared femtosecond pulses. Using this approach, we demonstrate shaping of the time-domain polarization state within a single pulse.

We demonstrate a dielectric-metasurface-enabled pulse shaper able to tailor the temporal polarization of near-infrared femtosecond pulses over an ultrawide bandwidth, allowing three-dimensional vector-shaped pulses exhibiting rich time-evolving instantaneous polarization states within a single pulse.

The potential for enhancing the optical activity of natural chiral media using engineered nanophotonic components has been central in the quest toward developing next-generation circular-dichroism spectroscopic techniques. Through confinement and manipulation of optical fields at the nanoscale, ultrathin optical elements have enabled a path toward...

Ultrathin gold films are attractive for plasmonic and metamaterial devices, thanks to their useful optical and optoelectronic properties. However, deposition of ultrathin continuous Au films of few nanometer thickness is challenging and generally requires wetting layers, resulting in increased optical losses and incompatibility with optoelectronic...

Densely integrated photonic circuits enable scalable, complex processing of optical signals, including modulation, multiplexing, wavelength conversion, and detection. Directly interfacing such integrated circuits to free-space optical modes will enable novel optical functions, such as chip-scale sensing, interchip free-space interconnect and coolin...

The photon-drag effect, the rectified current in a medium induced by conservation of momentum of absorbed or redirected light, is a unique probe of the detailed mechanisms underlying radiation pressure. We revisit this effect in gold, a canonical Drude metal. We discover that the signal for p -polarized illumination in ambient air is affected in b...

Metasurfaces get ultrafast pulses into shape Nanostructured metasurfaces have been designed to function as many passive optical elements. Now, Divitt et al. demonstrate that metasurfaces can also be operated as time-dependent active optical elements. They used an array of dielectric metasurfaces to demonstrate pulse shaping of ultrashort (femtoseco...

Metasurfaces offer the ability to control optical dispersion with extreme resolution. Here, we demonstrate reconfigurable dispersion control of ultrafast laser pulses through a set of silicon metasurfaces forming a Taylor series expansion in optical phase.

We report a compact, general photonic-to-free-space coupling via integrating metasurfaces with planar photonics. Demonstrated collimated beam projection and high numerical aperture focusing at long distance may enable trapping and interrogating atoms in chip-scale systems.

We demonstrate low-loss all-dielectric metasurfaces operating down to a record-short deep-ultraviolet wavelength of 266 nm, with an efficiency of 60%.

The photovoltage generated in metal films conflicts with the prevailing intuitive model of light-metal momentum exchange, establishing the need for a new microscopic model of radiation pressure, and newly revealing the distribution of optical forces.

We will explain how optical metasurfaces, planar arrays of subwavelength electromagnetic structures that collectively mimic the functionality of thicker conventional optical elements, can be employed for shaping light in both spatial and temporal domains.

Bending light along arbitrary curvatures is a captivating and popular notion, triggering unprecedented endeavors in achieving diffraction-free propagation along a curved path in free-space. Much effort has been devoted to achieving this goal in homogeneous space, which solely relies on the transverse acceleration of beam centroid exerted by a beam...

The photon-drag effect, the rectified current in a medium induced by conservation of momentum of absorbed or redirected light, is a unique probe of the detailed mechanisms underlying radiation pressure. We revisit this effect in gold, a canonical Drude metal. We discover that the signal for p-polarized illumination in ambient air is affected in bot...

Hyperbolic metamaterials are optical materials characterized by highly anisotropic effective permittivity tensor components having opposite signs along orthogonal directions. The techniques currently employed for characterizing the optical properties of hyperbolic metamaterials are limited in their capability for robust extraction of the complex pe...

Metasurfaces provide extremely fine spatial control over the amplitude and phase of incident light. Here, we demonstrate shaping of <15 femtosecond ultrafast laser pulses using a silicon-metasurface acting as both spectral amplitude and phase mask.

We demonstrate high-efficiency (>70%) all-dielectric Terahertz metasurfaces operating in the transmission mode. Example devices include high numerical-aperture (NA≈0.9) meta-lenses as well as cylindrical vector beam generator.

We present a new plasmonic material termed ‘doped Ag’, and its applications in various optoelectronic and nanophotonic devices with improved performance, including organic solar cells, polymer light emitting diodes, hyperbolic metamaterials, and plasmonic interconnects.

Metasurfaces offer the ability to shape optical pulses with unprecedented resolution. Here, we demonstrate dynamic shaping of <15 femtosecond ultrafast laser pulses using a Taylor series system in conjunction with silicon metasurfaces.

With the development of advanced nanofabrication technologies over the last decade, plasmonic nanostructures have attracted wide attention for their potential in label-free biosensing applications. However, the sensing performance of nanostructured plasmonic sensors is primarily limited by the broad-linewidth features with low peak-to-dip signal ra...

Exploiting the wave-nature of light in its simplest form, periodic architectures have enabled a panoply of tunable optical devices with the ability to perform useful functions such as filtering, spectroscopy, and multiplexing. Here, we remove the constraint of structural periodicity to enhance, simultaneously, the performance and functionality of p...

Recent years have witnessed a growing interest in the development of small-footprint lasers for potential applications in small-volume sensing and on-chip optical communications. Surface plasmons—electromagnetic modes evanescently confined to metal-dielectric interfaces—offer an effective route to achieving lasing at nanometer-scale dimensions when...

We demonstrate a surface-plasmon-polariton laser with narrow linewidth and low threshold based on a low-loss open cavity resonator that leverages grating-coupled SPPs to pump the lasing SPPs with improved spatial overlap and minimum perturbation.

We discuss recent efforts in realizing an optical resonator consisting of a metal-coated dielectric cylinder that supports whispering-gallery-type surface plasmon polaritons capable of exhibiting high quality factors in the visible frequency range.

Recent years have witnessed growing interest in the development of small-footprint lasers for potential applications in small-volume sensing and on-chip optical communications. Surface-plasmons, electromagnetic modes evanescently confined to metal-dielectric interfaces, offer an effective route to achieving lasing at nanometer-scale dimensions when...

Metallic structures with nanogap features have proven highly effective as building blocks for plasmonic systems, as they can provide a wide tuning range of operating frequencies and large near-field enhancements. Recent work has shown that quantum mechanical effects such as electron tunnelling and nonlocal screening become important as the gap dist...

With vibrant colours and simple, room-temperature processing methods, electrochromic polymers have attracted attention as active materials for flexible, low-power-consuming devices. However, slow switching speeds in devices realized to date, as well as the complexity of having to combine several distinct polymers to achieve a full-colour gamut, hav...

Supplementary Figures 1 - 5.

The Supplementary Movie 1 shows the real-time switching of red light transmitted through the Au-nanoslit electrode coated with PANI film as the applied voltage is repeatedly stepped between VON and VOFF.

Using finite-difference time-domain simulations, we designed a high-quality-factor “cup” resonator for surface-plasmon-polaritons operating at visible frequencies. By introducing a 4-level gain medium into the cup-structure, we simulated the lasing action of this novel plasmon laser.

We demonstrate a plasmonic cup resonator exhibiting an ultrahigh-quality-factor fabricated using the template-stripping method. The structure has enabled an optical refractive-index sensor with a record high figure-of-merit and a plasmon laser with record narrow linewidth.

We fabricate a plasmonic cup resonator exhibiting an ultrahigh-quality-factor using the template-stripping method. By introducing a gain medium into the cup-structure, we simulated and demonstrated the lasing action of this novel plasmon laser.

Using planar hyperbolic metamaterials composed of alternating layers of metal (Ag) and dielectric (SiO2), we demonstrate a transmission device for nanoparticle sensing that exhibits extremely high optical contrast.

Plasmonic nanostructures enable light to be concentrated into nanoscale 'hotspots', wherein the intensity of light can be enhanced by orders of magnitude. This plasmonic enhancement significantly boosts the efficiency of nanoscale light-matter interactions, enabling unique linear and nonlinear optical applications. Large enhancements are often obse...

We fabricate plasmonic dimers consisting of two metallic nanostructures spaced by a few angstroms using lithographic methods, and show that quantum mechanical tunneling across the gaps limits the enhancement in surface-enhanced Raman scattering.

Surface enhanced Raman scattering (SERS) is undergoing a renaissance, spurred largely by developments in the burgeoning field of plasmonics. This paper reviews the current status and future directions in plasmonic nanostructures for SERS. We show that engineered plasmonic nanostructures enable exciting new functionalities, including beamed Raman sc...

Enhancement factors (EFs) and angular emission profiles of SERS from molecules on nanoparticles can be modified and optimized by engineering their surrounding environments, namely other nanoparticles, and dielectric and metal films. This chapter discusses structures that are termed “double resonance” SERS substrates. It is known that when SERS is p...

The ability to detect molecules at low concentrations is highly desired for applications that range from basic science to healthcare. Considerable interest also exists for ultrathin materials with high optical absorption, e.g. for microbolometers and thermal emitters. Metal nanostructures present opportunities to achieve both purposes. Metal nanopa...

Silicon microwire arrays have attracted considerable attention recently due to the opportunity they present as highly efficient and cost-effective solar cells. In this study, we report on efficient Si microwire array solar cells with areas of 1 cm(2) and Air Mass 1.5 Global conversion efficiencies of up to 10.6 %. These solar cells show an open-cir...

Controlling light from single emitters is an overarching theme of nano-optics. Antennas are routinely used to modify the angular emission patterns of radio wave sources. "Optical antennas" translate these principles to visible and infrared wavelengths, and have been recently used to modify fluorescence from single quantum dots and single molecules....

We demonstrate a reusable and reconfigurable surface enhanced Raman scattering (SERS) platform by optically trapping Ag nanoparticles with a photonic crystal cavity integrated with a microfluidic chip. High-performance SERS is performed in a very reproducible manner, owing to the fact that Ag aggregates are produced by optical trapping in a control...

Appropriately-designed surface plasmon nanostructures enable the emission patterns of surface-enhanced Raman scattering to be modified to facilitate efficient collection, an effect sometimes termed "beamed Raman scattering". Here, we demonstrate the direct and unambiguous observation of this phenomenon by separating the Raman emission pattern from...

A two-dimensional array of gold optical antennas integrated with a one-dimensional array of gold strips and mirrors is introduced and fabricated. The experimental results show that this design achieves average surface-enhanced Raman scattering (SERS) enhancement factors as high as 1.2 × 10(10) , which is more than two orders of magnitude larger tha...

We demonstrate the collimation of Raman scattering by a SERS substrate consisting of optical antennas, a metallic reflector and a 1D grating of metal strips. A ~6.1° FWHM angle perpendicular to the strips is measured.