Achromatic metalenses for full visible spectrum with extended group delay control via dispersion-matched layers.

Achieving achromaticity across the visible light spectrum is crucial for metalenses in imaging systems. Single-layer metalenses struggle with weak focusing power or small aperture sizes due to inadequate group delay control. Multilayer metalenses offer some improvement but come with increased design and fabrication complexity.

Real-time machine learning-enhanced hyperspectro-polarimetric imaging via an encoding metasurface.

Light fields carry a wealth of information, including intensity, spectrum, and polarization. However, standard cameras capture only the intensity, disregarding other valuable information. While hyperspectral and polarimetric imaging systems capture spectral and polarization information, respectively, in addition to intensity, they are often bulky, slow, and costly.

Enhancing metasurface fabricability through minimum feature size enforcement.

The metasurfaces have shown great potential for miniaturizing conventional optics while offering extended flexibility. Recently, there has been considerable interest in using algorithms to generate meta-atom shapes for these metasurfaces, as they offer vast design freedom and not biased by the human intuition. However, these complex designs significantly increase the difficulty of fabrication.

All-optical geometric image transformations enabled by ultrathin metasurfaces.

Image processing plays a vital role in artificial visual systems, which have diverse applications in areas such as biomedical imaging and machine vision. In particular, optical analog image processing is of great interest because of its parallel processing capability and low power consumption. Here, we present ultra-compact metasurfaces performing all-optical geometric image transformations, which are essential for image processing to correct image distortions, create special image effects, and morph one image into another.

Near-Field GHz Rotation and Sensing with an Optically Levitated Nanodumbbell.

A levitated nonspherical nanoparticle in a vacuum is ideal for studying quantum rotations and is an ultrasensitive torque detector for probing fundamental particle-surface interactions. Here, we optically levitate a silica nanodumbbell in a vacuum at 430 nm away from a sapphire surface and drive it to rotate at GHz frequencies. The relative linear speed between the tip of the nanodumbbell and the surface reaches 1.

Citric Acid-Based Intrinsic Band-Shifting Photoluminescent Materials.

Citric acid, an important metabolite with abundant reactive groups, has been demonstrated as a promising starting material to synthesize diverse photoluminescent materials including small molecules, polymers, and carbon dots. The unique citrate chemistry enables the development of a series of citric acid-based molecules and nanomaterials with intriguing intrinsic band-shifting behavior, where the emission wavelength shifts as the excitation wavelength increases, ideal for chromatic imaging and many other applications. In this review, we discuss the concept of "intrinsic band-shifting photoluminescent materials", introduce the recent advances in citric acid-based intrinsic band-shifting materials, and discuss their potential applications such as chromatic imaging and multimodal sensing.

Special scattering regimes for conical all-dielectric nanoparticles.

All-dielectric nanophotonics opens a venue for a variety of novel phenomena and scattering regimes driven by unique optical effects in semiconductor and dielectric nanoresonators. Their peculiar optical signatures enabled by simultaneous electric and magnetic responses in the visible range pave a way for a plenty of new applications in nano-optics, biology, sensing, etc. In this work, we investigate fabrication-friendly truncated cone resonators and achieve several important scattering regimes due to the inherent property of cones-broken symmetry along the main axis without involving complex geometries or structured beams.

High-Efficiency, 80 mm Aperture Metalens Telescope.

Metalenses promise potential for a paradigm shift of conventional optical devices. However, the aperture sizes of metalenses are usually bound within hundreds of micrometers by the commonly used fabrication methods, limiting their usage on practical optical devices like telescopes. Here, for the first time, we demonstrate a high-efficiency, single-lens, refractive metalens telescope.

Metasurface-Dressed Two-Dimensional on-Chip Waveguide for Free-Space Light Field Manipulation.

We show that a metasurface-coated two-dimensional (2D) slab waveguide enables the generation of arbitrary complex light fields by combining the extreme versatility and freedom on the wavefront control of optical metasurfaces with the compactness of photonic integrated circuits. We demonstrated off-chip 2D focusing and holographic projection with our metasurface-dressed photonic integrated devices. This technology holds the potential for many other optical applications requiring 2D light field manipulation with full on-chip integration, such as solid-state LiDAR and near-eye AR/VR displays.

Optical meta-waveguides for integrated photonics and beyond.

The growing maturity of nanofabrication has ushered massive sophisticated optical structures available on a photonic chip. The integration of subwavelength-structured metasurfaces and metamaterials on the canonical building block of optical waveguides is gradually reshaping the landscape of photonic integrated circuits, giving rise to numerous meta-waveguides with unprecedented strength in controlling guided electromagnetic waves. Here, we review recent advances in meta-structured waveguides that synergize various functional subwavelength photonic architectures with diverse waveguide platforms, such as dielectric or plasmonic waveguides and optical fibers.

Molding free-space light with guided wave-driven metasurfaces.

Metasurfaces with unparalleled controllability of light have shown great potential to revolutionize conventional optics. However, they mainly require external light excitation, which makes it difficult to fully integrate them on-chip. On the other hand, integrated photonics enables packing optical components densely on a chip, but it has limited free-space light controllability.

Nonlinear Chiral Meta-Mirrors: Enabling Technology for Ultrafast Switching of Light Polarization.

Photonic nanostructures that realize ultrafast switching of light polarization are essential to advancements in the area of optical information processing. The unprecedented flexibility of metasurfaces in light manipulation makes them a promising candidate for active polarization control. However, due to the lack of optical materials exhibiting a fast as well as large refractive index change, photonic metadevices capable of ultrafast polarization switching remain elusive.

Nonreciprocal metasurface with space-time phase modulation.

Creating materials with time-variant properties is critical for breaking reciprocity that imposes fundamental limitations on wave propagation. However, it is challenging to realize efficient and ultrafast temporal modulation in a photonic system. Here, leveraging both spatial and temporal phase manipulation offered by an ultrathin nonlinear metasurface, we experimentally demonstrated nonreciprocal light reflection at wavelengths around 860 nm.

Design of random and sparse metalens with matrix pencil method.

We propose a matrix pencil method for designing one- or two- dimensional (1D or 2D) metalenses with randomly distributed meta-atoms. In contrast to the standard random synthesis algorithm that only randomizes the position of the meta-atoms, the proposed method designs both the position and phase of each meta-atom rigorously. Several all-dielectric random metalenses, in both 1D and 2D operating at 220 GHz, are presented by using our proposed algorithm.

Optical modulation of aqueous metamaterial properties at large scale.

Dynamical control of metamaterials by adjusting their shape and structures has been developed to achieve desired optical functionalities and to enable modulation and selection of spectra responses. However it is still challenging to realize such a manipulation at large scale. Recently, it has been shown that the desired high (or low) symmetry metamaterials structure in solution can be self-assembled under external light stimuli.

An ultrathin invisibility skin cloak for visible light.

Metamaterial-based optical cloaks have thus far used volumetric distribution of the material properties to gradually bend light and thereby obscure the cloaked region. Hence, they are bulky and hard to scale up and, more critically, typical carpet cloaks introduce unnecessary phase shifts in the reflected light, making the cloaks detectable. Here, we demonstrate experimentally an ultrathin invisibility skin cloak wrapped over an object.

Metasurface-Enabled Remote Quantum Interference.

An anisotropic quantum vacuum (AQV) opens novel pathways for controlling light-matter interaction in quantum optics, condensed matter physics, etc. Here, we theoretically demonstrate a strong AQV over macroscopic distances enabled by a judiciously designed array of subwavelength-scale nanoantennas-a metasurface. We harness the phase-control ability and the polarization-dependent response of the metasurface to achieve strong anisotropy in the decay rate of a quantum emitter located over distances of hundreds of wavelengths.

Experimental demonstration of in-plane negative-angle refraction with an array of silicon nanoposts.

Controlling an optical beam is fundamental in optics. Recently, unique manipulation of optical wavefronts has been successfully demonstrated by metasurfaces. However, these artificially engineered nanostructures have thus far been limited to operate on light beams propagating out-of-plane.

Feedback-driven self-assembly of symmetry-breaking optical metamaterials in solution.

Thermodynamically driven self-assembly offers a direct route to organize individual nanoscopic components into three-dimensional structures over a large scale. The most thermodynamically favourable configurations, however, may not be ideal for some applications. In plasmonics, for instance, nanophotonic constructs with non-trivial broken symmetries can display optical properties of interest, such as Fano resonance, but are usually not thermodynamically favoured.

Electrically tunable damping of plasmonic resonances with graphene.

Dynamic switching of a plasmonic resonance may find numerous applications in subwavelength optoelectronics, spectroscopy, and sensing. Graphene shows a highly tunable carrier concentration under electrostatic gating, and this could provide an effective route to achieving electrical control of the plasmonic resonance. In this Letter, we demonstrate electrical control of a plasmonic resonance at infrared frequencies using large-area graphene.

Loss-compensated and active hyperbolic metamaterials.

We have studied the dispersion relations of multilayers of silver and a dye-doped dielectric using four methods: standard effective-medium theory (EMT), nonlocal-effect-corrected EMT, nonlinear equations based on the eigenmode method, and a spatial harmonic analysis method. We compare the validity of these methods and show that metallic losses can be greatly compensated by saturated gain. Two realizable applications are also proposed.

Broadband light bending with plasmonic nanoantennas.

The precise manipulation of a propagating wave using phase control is a fundamental building block of optical systems. The wavefront of a light beam propagating across an interface can be modified arbitrarily by introducing abrupt phase changes. We experimentally demonstrated unparalleled wavefront control in a broadband optical wavelength range from 1.

Loss-free and active optical negative-index metamaterials.

The recently emerged fields of metamaterials and transformation optics promise a family of exciting applications such as invisibility, optical imaging with deeply subwavelength resolution and nanophotonics with the potential for much faster information processing. The possibility of creating optical negative-index metamaterials (NIMs) using nanostructured metal-dielectric composites has triggered intense basic and applied research over the past several years. However, the performance of all NIM applications is significantly limited by the inherent and strong energy dissipation in metals, especially in the near-infrared and visible wavelength ranges.