Showing papers on "Wavefront published in 2017"

Metalenses: Versatile multifunctional photonic components

Abstract: BACKGROUND Future high-performance portable and wearable optical devices and systems with small footprints and low weights will require components with small form factors and enhanced functionality. Planar components based on diffractive optics (e.g., gratings, Fresnel lenses) and thin-film optics (e.g., dielectric filters, Bragg reflectors) have been around for decades; however, their limited functionality and difficulty of integration have been key incentives to search for better alternatives. Owing to its potential for vertical integration and marked design flexibility, metasurface-based flat optics provides a rare opportunity to overcome these challenges. The building blocks (BBs) of metasurfaces are subwavelength-spaced scatterers. By suitably adjusting their shape, size, position, and orientation with high spatial resolution, one can control the basic properties of light (phase, amplitude, polarization) and thus engineer its wavefront at will. This possibility greatly expands the frontiers of optical design by enabling multifunctional components with attendant reduction of thickness, size, and complexity. ADVANCES Recent progress in fabrication techniques and in the theory and design of metasurfaces holds promise for this new optical platform (metaoptics) to replace or complement conventional components in many applications. One major advance has been the migration to all-dielectric metasurfaces. Here, we discuss the key advantages of using dielectric phase-shifting elements with low optical loss and strong light confinement in the visible and near-infrared regions as BBs of flat lenses (metalenses). High–numerical aperture metalenses that are free of spherical aberrations have been implemented to achieve diffraction-limited focusing with subwavelength resolution, without requiring the complex shapes of aspherical lenses. Achromatic metalenses at discrete wavelengths and over a bandwidth have been realized by dispersion engineering of the phase shifters. By suitably adjusting the geometrical parameters of the latter, one can impart polarization- and wavelength-dependent phases to realize multifunctional metalenses with only one ultrathin layer. For example, polarization-sensitive flat lenses for chiral imaging and circular dichroism spectroscopy with high resolution have been realized, and off-axis metalenses with large engineered angular dispersion have been used to demonstrate miniature spectrometers. The fabrication of metalenses is straightforward and often requires one-step lithography, which can be based on high-throughput techniques such as deep-ultraviolet and nanoimprint lithography. OUTLOOK In the near future, the ability to fabricate metalenses and other metaoptical components with a planar process using the same lithographic tools for manufacturing integrated circuits (ICs) will have far-reaching implications. We envision that camera modules widely employed in cell phones, laptops, and myriad applications will become thinner and easier to optically align and package, with metalenses and the complementary metal-oxide semiconductor–compatible sensor manufactured by the same foundries. The unprecedented design freedom of metalenses and other metasurface optical components will greatly expand the range of applications of micro-optics and integrated optics. We foresee a rapidly increasing density of nanoscale optical elements on metasurface-based chips, with attendant marked increases in performance and number of functionalities. Such digital optics will probably follow a Moore-like law, similar to that governing the scaling of ICs, leading to a wide range of high-volume applications.

Nonlinear photonic metasurfaces

Abstract: Compared with conventional optical elements, 2D photonic metasurfaces, consisting of arrays of antennas with subwavelength thickness (the ‘meta-atoms’), enable the manipulation of light–matter interactions on more compact platforms. The use of metasurfaces with spatially varying arrangements of meta-atoms that have subwavelength lateral resolution allows control of the polarization, phase and amplitude of light. Many exotic phenomena have been successfully demonstrated in linear optics; however, to meet the growing demand for the integration of more functionalities into a single optoelectronic circuit, the tailorable nonlinear optical properties of metasurfaces will also need to be exploited. In this Review, we discuss the design of nonlinear photonic metasurfaces — in particular, the criteria for choosing the materials and symmetries of the meta-atoms — for the realization of nonlinear optical chirality, nonlinear geometric Berry phase and nonlinear wavefront engineering. Finally, we survey the application of nonlinear photonic metasurfaces in optical switching and modulation, and we conclude with an outlook on their use for terahertz nonlinear optics and quantum information processing. Photonic metasurfaces can be used to control the polarization, phase and amplitude of light. Nonlinear metasurfaces enable giant nonlinear optical chirality, realization of the geometric Berry phase, wavefront engineering, and optical switching and modulation, and hold potential for on-chip applications.

Virtual and augmented reality systems and methods

Abstract: Methods of manufacturing a liquid crystal device including depositing a layer of liquid crystal material on a substrate and imprinting a pattern on the layer of liquid crystal material using an imprint template are disclosed. The liquid crystal material can be jet deposited. The imprint template can include surface relief features, Pancharatnam-Berry Phase Effect (PBPE) structures or diffractive structures. The liquid crystal device manufactured by the methods described herein can be used to manipulate light, such as for beam steering, wavefront shaping, separating wavelengths and/or polarizations, and combining different wavelengths and/or polarizations.

Tomographic flow cytometry by digital holography.

Abstract: High-throughput single-cell analysis is a challenging task. Label-free tomographic phase microscopy is an excellent candidate to perform this task. However, in-line tomography is very difficult to implement in practice because it requires a complex set-up for rotating the sample and examining the cell along several directions. We demonstrate that by exploiting the random rolling of cells while they are flowing along a microfluidic channel, it is possible to obtain in-line phase-contrast tomography, if smart strategies for wavefront analysis are adopted. In fact, surprisingly, a priori knowledge of the three-dimensional position and orientation of rotating cells is no longer needed because this information can be completely retrieved through digital holography wavefront numerical analysis. This approach makes continuous-flow cytotomography suitable for practical operation in real-world, single-cell analysis and with a substantial simplification of the optical system; that is, no mechanical scanning or multi-direction probing is required. A demonstration is given for two completely different classes of biosamples: red blood cells and diatom algae. An accurate characterization of both types of cells is reported, despite their very different nature and material content, thus showing that the proposed method can be extended by adopting two alternate strategies of wavefront analysis to many classes of cells.

From the generalized reflection law to the realization of perfect anomalous reflectors.

Abstract: The use of the generalized Snell's law opens wide possibilities for the manipulation of transmitted and reflected wavefronts. However, known structures designed to shape reflection wavefronts suffer from significant parasitic reflections in undesired directions. We explore the limitations of the existing solutions for the design of passive planar reflectors and demonstrate that strongly nonlocal response is required for perfect performance. A new paradigm for the design of perfect reflectors based on energy surface channeling is introduced. We realize and experimentally verify a perfect design of an anomalously reflective surface using an array of rectangular metal patches backed by a metallic plate. This conceptually new mechanism for wavefront manipulation allows the design of thin perfect reflectors, offering a versatile design method applicable to other scenarios, such as focusing reflectors, surface wave manipulations, or metasurface holograms, extendable to other frequencies.

Controlling propagation and coupling of waveguide modes using phase-gradient metasurfaces.

Abstract: Research on two-dimensional designer optical structures, or metasurfaces, has mainly focused on controlling the wavefronts of light propagating in free space. Here, we show that gradient metasurface structures consisting of phased arrays of plasmonic or dielectric nanoantennas can be used to control guided waves via strong optical scattering at subwavelength intervals. Based on this design principle, we experimentally demonstrate waveguide mode converters, polarization rotators and waveguide devices supporting asymmetric optical power transmission. We also demonstrate all-dielectric on-chip polarization rotators based on phased arrays of Mie resonators with negligible insertion losses. Our gradient metasurfaces can enable small-footprint, broadband and low-loss photonic integrated devices.

All-Dielectric Metasurfaces for Simultaneous Giant Circular Asymmetric Transmission and Wavefront Shaping Based on Asymmetric Photonic Spin–Orbit Interactions

Abstract: The control of polarization and wavefront plays an important role in many optical systems. In this work, a monolayer metasurface is proposed to simultaneously realize circular asymmetric transmission (AT) and wavefront shaping based on asymmetric spin–orbit interactions. Circularly polarized incidence, accompanied with arbitrary wavefront modulation, experiences spin-selected destructive or constructive interference. An extinction ratio of ≈10:1 and an AT parameter of ≈0.69 at 9.6 µm, as well as a full width half-maximum of ≈2.9 µm (≈30% of the peak wavelength), are measured with the designed metasurface. These measured results are more than four times of those achieved with previous monolayer chiral structures. As far as it is known, this is the first report on the realization of simultaneous giant AT and arbitrary wavefront modulation with only one metasurface. Due to its fabrication simplicity and the multifunctionality of the designed metasurface, this work may provide a promising route to replace bulky cascading optical components with only one ultrathin metasurface for chiroptical spectroscopy, chiral imaging, optical communication, and so forth.

Complex wavefront engineering with disorder-engineered metasurfaces

Abstract: Recently, complex wavefront engineering with disordered media has demonstrated optical manipulation capabilities beyond those of conventional optics. These capabilities include extended volume, aberration-free focusing and subwavelength focusing via evanescent mode coupling. However, translating these capabilities to useful applications has remained challenging as the input-output characteristics of the disordered media ($P$ variables) need to be exhaustively determined via $O(P)$ measurements. Here, we propose a paradigm shift where the disorder is specifically designed so that its exact characteristics are known, resulting in an a priori determined transmission matrix that can be utilized with only a few alignment steps. We implement this concept with a disorder-engineered metasurface, which exhibits additional unique features for complex wavefront engineering such as an unprecedented optical memory effect range, excellent stability, and a tailorable angular scattering profile.

Spin-to-orbital angular momentum conversion in dielectric metasurfaces.

Abstract: Vortex beams are characterized by a helical wavefront and a phase singularity point on the propagation axis that results in a doughnut-like intensity profile. These beams carry orbital angular momentum proportional to the number of intertwined helices constituting the wavefront. Vortex beams have many applications in optics, such as optical trapping, quantum optics and microscopy. Although beams with such characteristics can be generated holographically, spin-to-orbital angular momentum conversion has attracted considerable interest as a tool to create vortex beams. In this process, the geometrical phase is exploited to create helical beams whose handedness is determined by the circular polarization (left/right) of the incident light, that is by its spin. Here we demonstrate high-efficiency Spin-to-Orbital angular momentum-Converters (SOCs) at visible wavelengths based on dielectric metasurfaces. With these SOCs we generate vortex beams with high and fractional topological charge and show for the first time the simultaneous generation of collinear helical beams with different and arbitrary orbital angular momentum. This versatile method of creating vortex beams, which circumvents the limitations of liquid crystal SOCs and adds new functionalities, should significantly expand the applications of these beams.

Coding metasurface for broadband microwave scattering reduction with optical transparency.

Abstract: Metasurfaces have promised great possibilities in full control of the electromagnetic wavefront by spatially manipulating the phase characteristics across the interface. Here, we report a scheme to realize broadband backward scattering reduction through diffusion-like microwave reflection by utilizing a flexible indium-tin-oxide (ITO)-based ultrathin coding metasurface (less than 0.1 wavelength thick) with high optical transparence. The diffusion-like scattering is caused by the destructive interference of the scattered far-field electromagnetic wave, which is further attributed to the randomly distributed reflection phases on the metasurface composed of pre-designed meta-atoms arranged with a computer-generated pseudorandom coding sequence. Both simulation and measurement on fabricated prototype sample have been carried out to validate its performance, demonstrating a polarization-independent broadband (nearly from 8 GHz to 15 GHz) 10 dB scattering reduction with good oblique performance. The excellent performances can also be preserved to conformal cases when the flexible metasurface is uniformly wrapped around a metallic cylinder. The proposed metasurface may create new opportunities to tailor the exotic microwave scattering features with simultaneously high transmittance in visible frequencies, which could provide crucial benefits in many practical uses, such as window and solar panel applications.

Metasurface Holograms for Holographic Imaging

Abstract: As a revolutionary three-dimensional (3D) optical imaging technique, optical holography has attracted wide attention for its capability of recording both the amplitude and phase information of light scattered from objects Holograms are designed to transform an incident wave into a desired arbitrary wavefront in the far field, which requires ultimate complex phase control in each hologram pixel Conventional holograms shape the wavefront via the phase accumulation effect during the wave propagation through bulky optical elements, suffering issues of low-resolution imaging and high-order diffraction Recently, metasurfaces, 2D metamaterials with ultrathin thickness, have emerged as an important platform to reproduce computer-generated holograms due to their advantages in manipulating light with well-controlled amplitude, phase, and polarization In this article, the latest research progress in various types of metasurface holograms is reviewed from their design principles to versatile functional applications At the end, more potential applications of metasurface holograms are discussed and some future research directions are also provided

3D computer-generated holography by non-convex optimization

Abstract: 3D computer-generated holography uses a digital phase mask to shape the wavefront of a laser beam into a user-specified 3D intensity pattern. Algorithms take the target 3D intensity as input and compute the hologram that generates it. However, arbitrary patterns are generally infeasible, so solutions are approximate and often sub-optimal. Here, we propose a new non-convex optimization algorithm that computes holograms by minimizing a custom cost function that is tailored to particular applications (e.g., lithography, neural photostimulation) or leverages additional information like sample shape and nonlinearity. Our method is robust and accurate, and it out-performs existing algorithms.

Focusing light inside dynamic scattering media with millisecond digital optical phase conjugation.

Abstract: Wavefront shaping based on digital optical phase conjugation (DOPC) focuses light through or inside scattering media, but the low speed of DOPC prevents it from being applied to thick, living biological tissue. Although a fast DOPC approach was recently developed, the reported single-shot wavefront measurement method does not work when the goal is to focus light inside, instead of through, highly scattering media. Here, using a ferroelectric liquid crystal based spatial light modulator, we develop a simpler but faster DOPC system that focuses light not only through, but also inside scattering media. By controlling 2.6×105 optical degrees of freedom, our system focused light through 3 mm thick moving chicken tissue, with a system latency of 3.0 ms. Using ultrasound-guided DOPC, along with a binary wavefront measurement method, our system focused light inside a scattering medium comprising moving tissue with a latency of 6.0 ms, which is one to two orders of magnitude shorter than those of previous digital wavefront shaping systems. Since the demonstrated speed approaches tissue decorrelation rates, this work is an important step toward in vivo deep-tissue non-invasive optical imaging, manipulation, and therapy.

Observation of acoustic Dirac-like cone and double zero refractive index.

Abstract: Zero index materials where sound propagates without phase variation, holds a great potential for wavefront and dispersion engineering. Recently explored electromagnetic double zero index metamaterials consist of periodic scatterers whose refractive index is significantly larger than that of the surrounding medium. This requirement is fundamentally challenging for airborne acoustics because the sound speed (inversely proportional to the refractive index) in air is among the slowest. Here, we report the first experimental realization of an impedance matched acoustic double zero refractive index metamaterial induced by a Dirac-like cone at the Brillouin zone centre. This is achieved in a two-dimensional waveguide with periodically varying air channel that modulates the effective phase velocity of a high-order waveguide mode. Using such a zero-index medium, we demonstrated acoustic wave collimation emitted from a point source. For the first time, we experimentally confirm the existence of the Dirac-like cone at the Brillouin zone centre.

Ultrathin Complementary Metasurface for Orbital Angular Momentum Generation at Microwave Frequencies

Abstract: Electromagnetic (EM) waves with helical wave front carry orbital angular momentum (OAM), which is associated with the azimuthal phase of the complex electric field. OAM is a new degree of freedom in EM waves and is promising for channel multiplexing in the communication system. Although the OAM-carrying EM wave attracts more and more attention, the method of OAM generation at microwave frequencies still faces challenges, such as efficiency and simulation time. In this communication, by using the circuit theory and equivalence principle, we build two simplified models, one for a single scatter and one for the whole metasurface to predict their EM responses. Both of the models significantly simplify the design procedure and reduce the simulation time. In this communication, we propose an ultrathin complementary metasurface that converts a left-handed (right-handed) circularly polarized plane wave without OAM to a right-handed (left-handed) circularly polarized wave with OAM of arbitrary orders, and a high transmission efficiency can be achieved.

Asymmetric Nanoantennas for Ultrahigh Angle Broadband Visible Light Bending

Abstract: Wavefront manipulation in metasurfaces typically relies on phase mapping with a finite number of elements. In particular, a discretized linear phase profile may be used to obtain a beam bending functionality. However, discretization limits the applicability of this approach for high angle bending due to the drastic efficiency drop when the phase is mapped by a small number of elements. In this work, we discuss a novel concept for energy redistribution in diffraction gratings and its application in the visible spectrum range, which helps overcome the constraints of ultrahigh angle (above 80°) beam bending. Arranging asymmetric dielectric nanoantennas into diffractive gratings, we show that one can efficiently redistribute the power between the grating orders at will. This is achieved by precise engineering of the scattering pattern of the nanoantennas. The concept is numerically and experimentally demonstrated at visible frequencies using several designs of TiO2 (titanium dioxide) nanoantennas for medium (...

Scattering compensation by focus scanning holographic aberration probing (F-SHARP)

Abstract: A long-standing goal in biomedical imaging, the control of light inside turbid media, requires knowledge of how the phase and amplitude of an illuminating wavefront are transformed as the electric field propagates inside a scattering sample onto a target plane. So far, it has proved challenging to non-invasively characterize the scattered optical wavefront inside a disordered medium. Here, we present a non-invasive scattering compensation method, termed F-SHARP, which allows us to measure the scattered electric-field point spread function (E-field PSF) in three dimensions. Knowledge of the phase and amplitude of the E-field PSF makes it possible to optically cancel sample turbulence. We demonstrate the imaging capabilities of this technique on a variety of samples and notably through vertebrate brains and across thinned skull in vivo. A non-invasive scattering compensation method, termed F-SHARP, gives direct access to the phase and amplitude of the electric-field point spread function, enabling fast and high-resolution correction of aberrations and scattering in living tissue.

Active Phase Transition via Loss Engineering in a Terahertz MEMS Metamaterial

Abstract: Controlling the phase of local radiation by using exotic metasurfaces has enabled promising applications in a diversified set of electromagnetic wave manipulation such as anomalous wavefront deflection, flat lenses, and holograms. Here, we theoretically and experimentally demonstrate an active phase transition in a micro-electromechanical system-based metadevice where both the phase response and the dispersion of the metamaterial cavity are dynamically tailored. The phase transition is determined by the radiative and the absorptive losses in a metal-insulator-metal cavity that obeys the coupled-mode theory. The complete understanding of the phase diagram in a reconfigurable configuration would open up avenues for designing multifunctional metadevices that can be actively switched between different phases leading to a plethora of applications in polarization control, beam deflectors, and holographic metamaterials.

Interlaced zone plate optics for hard X-ray imaging in the 10 nm range

Abstract: Multi-keV X-ray microscopy has been particularly successful in bridging the resolution gap between optical and electron microscopy. However, resolutions below 20 nm are still considered challenging, as high throughput direct imaging methods are limited by the availability of suitable optical elements. In order to bridge this gap, we present a new type of Fresnel zone plate lenses aimed at the sub-20 and the sub-10 nm resolution range. By extending the concept of double-sided zone plate stacking, we demonstrate the doubling of the effective line density and thus the resolution and provide large aperture, singlechip optical devices with 15 and 7 nm smallest zone widths. The detailed characterization of these lenses shows excellent optical properties with focal spots down to 7.8 nm. Beyond wave front characterization, the zone plates also excel in typical imaging scenarios, verifying their resolution close to their diffraction limited optical performance.

Reconfigurable metasurfaces that enable light polarization control by light

Abstract: Plasmonic metasurfaces have recently attracted much attention because of their novel characteristics with respect to light polarization and wave front control on deep-subwavelength scales. The development of metasurfaces with reconfigurable optical responses is opening new opportunities in high-capacity communications, real-time holograms and adaptive optics. Such tunable devices have been developed in the mid-infrared spectral range and operated in light intensity modulation schemes. Here we present a novel optically reconfigurable hybrid metasurface that enables polarization tuning at optical frequencies. The functionality of tuning is realized by switching the coupling conditions between the plasmonic modes and the binary isomeric states of an ethyl red switching layer upon light stimulation. We achieved more than 20° nonlinear changes in the transmitted polarization azimuth using just 4 mW of switching light power. Such design schemes and principles could be easily applied to dynamically adjust the functionalities of other metasurfaces. A metasurface whose properties can be optically controlled has been used to vary the polarization of a light beam by over 20 degrees. Metasurfaces — the two-dimensional equivalents of metamaterials—consist of ultrathin arrays of miniature light scatters. The optical properties of most metasurfaces are fixed, but there has been a recent push to produce tunable metasurfaces. Now, by combining a metasurface with a dye that switches between two different structures on light excitation, a team at Nankai University in China has realized a metasurface that can alter the polarization of a light beam in response to a continuous laser beam of just a few milliwatts. The metasurface is promising for optical communications and computing as well as optical display devices, and the principle could potentially be extended to other functionalities.

Active Multifunctional Microelectromechanical System Metadevices: Applications in Polarization Control, Wavefront Deflection, and Holograms

Abstract: Metasurfaces have provided a novel route to control the local phase of electromagnetic radiation through subwavelength scatterers where the properties of each element remain passive. A passive metasurface design can only achieve a specific functionality as it is extremely challenging to reconfigure each element that contributes toward the control of the radiation. In this work, the authors propose a different scheme based on microelectromechanical system (MEMS) to reconfigure the resonance and radiation phase via control of each dipolar element. The suspension angle of the individual bimorph cantilever in air can be precisely controlled through electrostatic actuation that determines the operative phase diagram of the metadevice. The dynamic polarization conversion is demonstrated through global control. In addition, it is proposed that a multifunctional operation such as dynamic wavefront deflection and rewritable holographic display can be accomplished by using 1D and 2D control of the cantilever array when each cantilever in the MEMS metadevice array is uniformly and accurately controlled in the large-area samples. Such a rewritable proposition can enable myriad of applications of MEMS-based metadevices in polarization-division multiplexing and dynamic flat lenses.

Multiwavelength Metasurfaces Based on Single-Layer Dual-Wavelength Meta-Atoms: Toward Complete Phase and Amplitude Modulations at Two Wavelengths

Abstract: Since its invention, metasurface has been widely utilized to achieve nearly arbitrary wavefront control based on phase only modulation at single wavelength. To achieve better performance or exotic functions, it is desirable to demonstrate metasurfaces capable of realizing both phase and amplitude modulations. Meanwhile, the wavelength-dependent behavior of the metasurface is one of the critical limitations in existing metasurface structures. Specifically, single-layer metasurfaces with the capability to tailor both phase and amplitude at multiple wavelengths have not been reported so far. In this paper, a single-layer meta-atom is proposed which can realize ultrathin metasurfaces with complete phase and amplitude modulations at two THz wavelengths. Several dual-wavelength metalenses and a nondiffractive Airy beam generator operating at two THz wavelengths are numerically demonstrated, the simulated results of which are consistent with the theoretical calculations and design goals. The presented dual-wavelength meta-atom can provide a powerful building block in multiwavelength metasurface designs for controlling electromagnetic waves, including focusing, beam steering, beam generations, hologram, etc.

Large-field-of-view imaging by multi-pupil adaptive optics

Abstract: Adaptive optics can correct for optical aberrations. We developed multi-pupil adaptive optics (MPAO), which enables simultaneous wavefront correction over a field of view of 450 × 450 μm2 and expands the correction area to nine times that of conventional methods. MPAO's ability to perform spatially independent wavefront control further enables 3D nonplanar imaging. We applied MPAO to in vivo structural and functional imaging in the mouse brain.

Self-coherent phase reference sharing for continuous-variable quantum key distribution

Abstract: We develop a comprehensive framework to model and optimize the performance of continuous-variable quantum key distribution (CV-QKD) with a local local oscillator (LLO), when phase reference sharing and QKD are jointly implemented. We first analyze the limitations of the only existing approach, called LLO-sequential, and show that it requires high modulation dynamics and can only tolerate small phase noise. Our main contribution is to introduce two designs to perform LLO CV-QKD, respectively called LLO-delayline and LLO-displacement, and to study their performance. Both designs rely on a self-coherent approach, in which phase reference information and quantum information are coherently obtained from a single optical wavefront. We show that these designs can lift some limitations of the existing LLO-sequential approach. The LLO-delayline design can in particular tolerate much stronger phase noise and thus appears to be an appealing alternative to LLO-sequential in terms of network integrability. We also investigate, with the LLO-displacement design, how phase reference information and quantum information can be multiplexed within a single optical pulse. By studying the trade-off between phase reference recovery and phase noise induced by displacement, we, however, demonstrate that this design can only tolerate low phase noise. On the other hand, the LLO-displacement design has the advantage of minimal hardware requirements and provides a simple approach to multiplex classical and quantum communications, opening a practical path towards the development of ubiquitous coherent classical-quantum communications systems compatible with next-generation network requirements.

Gradient Chiral Metamirrors for Spin-Selective Anomalous Reflection

Abstract: Metasurfaces, the phase-engineered quasi-2D interfaces, have attracted intensive interest due to their great capabilities in manipulating the reflection, refraction and transmission of electromagnetic waves. Here, we demonstrate the design and realization of a gradient chiral metamirror tailored for spin-selective anomalous reflection based on the theory of Pancharatnam-Berry phase. Asymmetric split ring resonators are employed as the basic meta-atoms for strong circular dichroism. Dispersionless phase discontinuities are achieved by adjusting the orientation of the meta-atoms, and spin-dependent absorption is realized by introducing a chiral resonance. Theoretical results predict both broadband beam deflection and spin-selective absorption for circularly polarized waves in a designer metamirror. Experimental verification of this bifunctional performance is implemented at microwave frequencies and the measured results agree well with the simulation ones. Such chiral metamirrors could pave an avenue towards spin-selective modulation of the wavefront and might find promising applications in planar electromagnetic devices.

Controlling propagation and coupling of waveguide modes using phase-gradient metasurfaces

Abstract: Research on two-dimensional designer optical structures, or metasurfaces, has mainly focused on controlling the wavefronts of light propagating in free space. Here, we show that gradient metasurface structures consisting of phased arrays of plasmonic or dielectric nanoantennas can be used to control guided waves via strong optical scattering at subwavelength intervals. Based on this design principle, we experimentally demonstrate waveguide mode converters, polarization rotators and waveguide devices supporting asymmetric optical power transmission. We also demonstrate all-dielectric on-chip polarization rotators based on phased arrays of Mie resonators with negligible insertion losses. Our gradient metasurfaces can enable small-footprint, broadband and low-loss photonic integrated devices.

High‐Efficiency All‐Dielectric Metalenses for Mid‐Infrared Imaging

Abstract: Metasurfaces-based flat optics, which can make use of existing foundry planar technology for high-throughput production, allows the arbitrary control of the wavefront and polarization of light within subwavelength thick structures. So far, however, flat optics for the mid-infrared (MIR) has received far less attention than devices operating at visible or near-infrared wavelengths. Here, polarization-insensitive, highly efficient, all-dielectric metalenses operating in the MIR around 4 µm are demonstrated. The metalens is designed using rigorous coupled-wave analysis and is based on hydrogenated amorphous silicon (α-Si:H) nanopillars supported by an MgF2 substrate. The metalenses produce close to a diffraction-limited focal spot and can resolve structures on the wavelength scale where the focusing efficiency reaches 78% at a magnification of 120×. The imaging qualities are comparable with commercial bulk-molded chalcogenide aspheric lenses. These results provide novel solutions for existing MIR technology and nurture new functionalities with the population of miniaturized and planarized optoelectrical devices.

Approaching the diffraction-limited, bandwidth-limited Petawatt

Abstract: J-KAREN-P is a high-power laser facility aiming at the highest beam quality and irradiance for performing state-of-the art experiments at the frontier of modern science. Here we approached the physical limits of the beam quality: diffraction limit of the focal spot and bandwidth limit of the pulse shape, removing the chromatic aberration, angular chirp, wavefront and spectral phase distortions. We performed accurate measurements of the spot and peak fluence after an f/1.3 off-axis parabolic mirror under the full amplification at the power of 0.3 PW attenuated with ten high-quality wedges, resulting in the irradiance of ~1022 W/cm2 and the Strehl ratio of ~0.5.

Implementing Quantum Search Algorithm with Metamaterials.

Abstract: Metamaterials, artificially structured electromagnetic (EM) materials, have enabled the realization of many unconventional EM properties not found in nature, such as negative refractive index, magnetic response, invisibility cloaking, and so on. Based on these man-made materials with novel EM properties, various devices are designed and realized. However, quantum analog devices based on metamaterials have not been achieved so far. Here, metamaterials are designed and printed to perform quantum search algorithm. The structures, comprising of an array of 2D subwavelength air holes with different radii perforated on the dielectric layer, are fabricated using a 3D-printing technique. When an incident wave enters in the designed metamaterials, the profile of beam wavefront is processed iteratively as it propagates through the metamaterial periodically. After ≈N roundtrips, precisely the same as the efficiency of quantum search algorithm, searched items will be found with the incident wave all focusing on the marked positions. Such a metamaterial-based quantum searching simulator may lead to remarkable achievements in wave-based signal processors.