Over the past decade, topology has emerged as a major branch in broad areas of physics, from atomic lattices to condensed matter. In particular, topology has received significant attention in ...photonics because light waves can serve as a platform to investigate nontrivial bulk and edge physics with the aid of carefully engineered photonic crystals and metamaterials. Simultaneously, photonics provides enriched physics that arises from spin-1 vectorial electromagnetic fields. Here, we review recent progress in the growing field of topological photonics in three parts. The first part is dedicated to the basics of topological band theory and introduces various two-dimensional topological phases. The second part reviews three-dimensional topological phases and numerous approaches to achieve them in photonics. Last, we present recently emerging fields in topological photonics that have not yet been reviewed. This part includes topological degeneracies in nonzero dimensions, unidirectional Maxwellian spin waves, higher-order photonic topological phases, and stacking of photonic crystals to attain layer pseudospin. In addition to the various approaches for realizing photonic topological phases, we also discuss the interaction between light and topological matter and the efforts towards practical applications of topological photonics.
Miniaturization is a strong demand of modern scientific technology. However, conventional optical components based on refraction suffer from functional degradation as the device size decreases. ...Metasurfaces consisting of subwavelength optical antenna arrays have emerged as planar optical devices that enable many promising applications in lenses, holograms, and optical cloaks. During recent decades, metasurfaces have been developed for their specific functionalities by exploiting new materials and design algorithms. In this issue of
MRS Bulletin
, progress in metasurfaces is discussed to provide a comprehensive understanding of metasurfaces and their novel applications in optics and photonics.
Metalenses have shown a number of promising functionalities that are comparable with conventional refractive lenses. However, current metalenses are still far from commercialization due to the ...formidable fabrication costs. Here, we demonstrate a low-cost dielectric metalens that works in the visible spectrum. The material of the metalens consists of a matrix-inclusion composite in which a hierarchy satisfies two requirements for the single-step fabrication; a high refractive index and a pattern-transfer capability. We use a UV-curable resin as a matrix to enable direct pattern replication by the composite, and titanium dioxide nanoparticles as inclusions to increase the refractive index of the composite. Therefore, such a dielectric metalens can be fabricated with a single step of UV nanoimprint lithography. An experimental demonstration of the nanoparticle composite-based metalens validates the feasibility of our approach and capability for future applications. Our method allows rapid replication of metalenses repeatedly and thereby provides an advance toward the use of metalenses on a commercial scale.
Abstract
Vectorial holography has gained a lot of attention due to the promise of versatile polarization control of structured light for enhanced optical security and multi-channel optical ...communication. Here, we propose a bifunctional metasurface which combines both structural color printing and vectorial holography with eight polarization channels towards advanced encryption applications. The structural colour prints are observed under white light while the polarization encoded holograms are reconstructed under laser illumination. To encode multiple holographic images for different polarization states, a pixelated metasurface is adopted. As a proof-of-concept, we devise an electrically tunable optical security platform incorporated with liquid crystals. The optical security platform is doubly encrypted: an image under white light is decrypted to provide the first key and the corresponding information is used to fully unlock the encrypted information via projected vectorial holographic images. Such an electrically tunable optical security platform may enable smart labels for security and anticounterfeiting applications.
Recent introduction of data-driven approaches based on deep-learning technology has revolutionized the field of nanophotonics by allowing efficient inverse design methods. In this paper, a ...simultaneous inverse design of materials and structure parameters of core–shell nanoparticles is achieved for the first time using deep learning of a neural network. A neural network to learn the correlation between the extinction spectra of electric and magnetic dipoles and core–shell nanoparticle designs, which include material information and shell thicknesses, is developed and trained. We demonstrate deep-learning-assisted inverse design of core–shell nanoparticles for (1) spectral tuning electric dipole resonances, (2) finding spectrally isolated pure magnetic dipole resonances, and (3) finding spectrally overlapped electric dipole and magnetic dipole resonances. Our finding paves the way for the rapid development of nanophotonics by allowing a practical utilization of deep-learning technology for nanophotonic inverse design.
Light detection and ranging (LiDAR) technology, a laser-based imaging technique for accurate distance measurement, is considered one of the most crucial sensor technologies for autonomous vehicles, ...artificially intelligent robots and unmanned aerial vehicle reconnaissance. Until recently, LiDAR has relied on light sources and detectors mounted on multiple mechanically rotating optical transmitters and receivers to cover an entire scene. Such an architecture gives rise to limitations in terms of the imaging frame rate and resolution. In this Review, we examine how novel nanophotonic platforms could overcome the hardware restrictions of existing LiDAR technologies. After briefly introducing the basic principles of LiDAR, we present the device specifications required by the industrial sector. We then review a variety of LiDAR-relevant nanophotonic approaches such as integrated photonic circuits, optical phased antenna arrays and flat optical devices based on metasurfaces. The latter have already demonstrated exceptional functional beam manipulation properties, such as active beam deflection, point-cloud generation and device integration using scalable manufacturing methods, and are expected to disrupt modern optical technologies. In the outlook, we address the upcoming physics and engineering challenges that must be overcome from the viewpoint of incorporating nanophotonic technologies into commercially viable, fast, ultrathin and lightweight LiDAR systems.
Digital optical holograms can achieve nanometre-scale resolution as a result of recent advances in metasurface technologies. This has raised hopes for applications in data encryption, data storage, ...information processing and displays. However, the hologram bandwidth has remained too low for any practical use. To overcome this limitation, information can be stored in the orbital angular momentum of light, as this degree of freedom has an unbounded set of orthogonal helical modes that could function as information channels. Thus far, orbital angular momentum holography has been achieved using phase-only metasurfaces, which, however, are marred by channel crosstalk. As a result, multiplex information from only four channels has been demonstrated. Here, we demonstrate an orbital angular momentum holography technology that is capable of multiplexing up to 200 independent orbital angular momentum channels. This has been achieved by designing a complex-amplitude metasurface in momentum space capable of complete and independent amplitude and phase manipulation. Information was then extracted by Fourier transform using different orbital angular momentum modes of light, allowing lensless reconstruction and holographic videos to be displayed. Our metasurface can be three-dimensionally printed in a polymer matrix on SiO2 for large-area fabrication.A complex-amplitude metasurface hologram is conceptually designed and three-dimensionally printed. The device allows for high-bandwidth orbital angular momentum multiplexing holography and holographic video displays.
Integration of phase-change materials (PCMs) into electrical/optical circuits has initiated extensive innovation for applications of metamaterials (MMs) including rewritable optical data storage, ...metasurfaces, and optoelectronic devices. PCMs have been studied deeply due to their reversible phase transition, high endurance, switching speed, and data retention. Germanium-antimony-tellurium (GST) is a PCM that has amorphous and crystalline phases with distinct properties, is bistable and nonvolatile, and undergoes a reliable and reproducible phase transition in response to an optical or electrical stimulus; GST may therefore have applications in tunable photonic devices and optoelectronic circuits. In this progress article, we outline recent studies of GST and discuss its advantages and possible applications in reconfigurable metadevices. We also discuss outlooks for integration of GST in active nanophotonic metadevices.
Data-driven design approaches based on deep learning have been introduced in nanophotonics to reduce time-consuming iterative simulations, which have been a major challenge. Here, we report the first ...use of conditional deep convolutional generative adversarial networks to design nanophotonic antennae that are not constrained to predefined shapes. For given input reflection spectra, the network generates desirable designs in the form of images; this allows suggestions of new structures that cannot be represented by structural parameters. Simulation results obtained from the generated designs agree well with the input reflection spectrum. This method opens new avenues toward the development of nanophotonics by providing a fast and convenient approach to the design of complex nanophotonic structures that have desired optical properties.
The spin Hall effect of light refers to a spin-dependent transverse splitting of light at a planar interface. Previous demonstrations to enhance the splitting have suffered from exceedingly low ...efficiency. Achievements of the large splitting with high efficiency have been reported in the microwave, but those in the optical regime remain elusive. Here, an approach to attain the large splitting with high efficiency in the near-infrared is proposed and experimentally demonstrated at 800 nm by using a dielectric metasurface. Modulation of the complex transmission of the metasurface leads to the shifts that reach 10λ along with efficiencies over 70% under two linear polarizations. Our work extends the recent attempts to achieve the large and efficient spin Hall effect of light, which have been limited only to the microwave, to the optical regime.
PDF
