Showing papers by "Din Ping Tsai published in 2017"

Broadband achromatic optical metasurface devices

Abstract: Among various flat optical devices, metasurfaces have presented their great ability in efficient manipulation of light fields and have been proposed for variety of devices with specific functionalities. However, due to the high phase dispersion of their building blocks, metasurfaces significantly suffer from large chromatic aberration. Here we propose a design principle to realize achromatic metasurface devices which successfully eliminate the chromatic aberration over a continuous wavelength region from 1200 to 1680 nm for circularly-polarized incidences in a reflection scheme. For this proof-of-concept, we demonstrate broadband achromatic metalenses (with the efficiency on the order of ∼12%) which are capable of focusing light with arbitrary wavelength at the same focal plane. A broadband achromatic gradient metasurface is also implemented, which is able to deflect wide-band light by the same angle. Through this approach, various flat achromatic devices that were previously impossible can be realized, which will allow innovation in full-color detection and imaging. Metasurfaces suffer from large chromatic aberration due to the high phase dispersion of their building blocks, limiting their applications. Here, Wang et al. design achromatic metasurface devices which eliminate the chromatic aberration over a continuous region from 1200 to 1680 nm in a reflection schleme.

Fundamentals and Applications of Metasurfaces

Abstract: Metasurfaces have become a rapidly growing field of research in recent years due to their exceptional abilities in light manipulation and versatility in ultrathin optical applications. They also significantly benefit from their simplified fabrication process compared to metamaterials and are promising for integration with on-chip nanophotonic devices owing to their planar profiles. The recent progress in metasurfaces is reviewed and they are classified into six categories according to their underlying physics for realizing full 2π phase manipulation. Starting from multi-resonance and gap-plasmon metasurfaces that rely on the geometric effect of plasmonic nanoantennas, Pancharatnam–Berry-phase metasurfaces, on the other hand, use identical nanoantennas with varying rotation angles. The recent development of Huygens' metasurfaces and all-dielectric metasurfaces especially benefit from highly efficient transmission applications. An overview of state-of-the-art fabrication technologies is introduced, ranging from the commonly used processes such as electron beam and focused-ion-beam lithography to some emerging techniques, such as self-assembly and nanoimprint lithography. A variety of functional materials incorporated to reconfigurable or tunable metasurfaces is also presented. Finally, a few of the current intriguing metasurface-based applications are discussed, and opinions on future prospects are provided.

Versatile Polarization Generation with an Aluminum Plasmonic Metasurface

Abstract: All forms of light manipulation rely on light–matter interaction, the primary mechanism of which is the modulation of its electromagnetic fields by the localized electromagnetic fields of atoms. One of the important factors that influence the strength of interaction is the polarization of the electromagnetic field. The generation and manipulation of light polarization have been traditionally accomplished with bulky optical components such as waveplates, polarizers, and polarization beam splitters that are optically thick. The miniaturization of these devices is highly desirable for the development of a new class of compact, flat, and broadband optical components that can be integrated together on a single photonics chip. Here we demonstrate, for the first time, a reflective metasurface polarization generator (MPG) capable of producing light beams of any polarizations all from a linearly polarized light source with a single optically thin chip. Six polarization light beams are achieved simultaneously inclu...

GaN Metalens for Pixel-Level Full-Color Routing at Visible Light

Abstract: Metasurface-based components are known to be one of the promising candidates for developing flat optical systems. However, their low working efficiency highly limits the use of such flat components for feasible applications. Although the introduction of the metallic mirror has been demonstrated to successfully enhance the efficiency, it is still somehow limited for imaging and sensing applications because they are only available for devices operating in a reflection fashion. Here, we demonstrate three individual GaN-based metalenses working in a transmission window with extremely high operation efficiency at visible light (87%, 91.6%, and 50.6% for blue, green, and red light, respectively). For the proof of concept, a multiplex color router with dielectric metalens, which is capable of guiding individual primary colors into different spatial positions, is experimentally verified based on the design of out-of-plane focusing metalens. Our approach with low-cost, semiconductor fabrication compatibility and h...

Broadband Wide‐Angle Multifunctional Polarization Converter via Liquid‐Metal‐Based Metasurface

Abstract: Metasurfaces enable flat optical components with predesigned functionalities, including the polarization conversion using subwavelength elements. However, switching between different functionalities of the metasurface-based optical components is extremely difficult because subwavelength elements have to be finely addressed to change the spatial phase gradient for desired functionality. Here, it is demonstrated, for the first time, a broadband wide-angle multifunctional polarization converter via galinstan-based metasurface with each element array actively addressed. The switching between different functionalities is realized by controlling L-shaped galinstan resonator using microfluidic channels, which maintain the optical performances, that is, broadband and large angular tolerance, of the polarization converter. Furthermore, the galinstan-based metasurface is also demonstrated to function as a broadband optical attenuator, which provides prospects for various applications, such as smart radar, stealth technology, and light manipulation for quantum communication.

Water-Resonator-Based Metasurface: An Ultrabroadband and Near-Unity Absorption

Abstract: Metasurface absorbing material, which obtains near-unity electromagnetic absorption through subwavelength artificial structure, plays an important role in the area of stealth and shielding technology, biological imaging, etc. However, they usually suffer from narrow bandwidth and only work on planar surfaces. Here, for the first time, this study demonstrates a soft water-resonator-based metasurface, which functions as an active absorbing material across an ultrabroadband range of Ku, K, and Ka bands. Distinct from conventional metallic metasurface, the water-resonator-based metasurface absorbs the microwave by dielectric magnetic resonance and periodic grating effect, which has a perfect absorptivity of ≈99% and an absorption bandwidth (absorptivity higher than 90%) that covers 78.9% of the central frequency. Furthermore, near-unity absorption is maintained when the soft metasurface material is bent into different curvatures, promising high potential applications for antennas in reducing side lobe radiation, eliminating wall reflection in anechoic chambers, antiradar detection, and stealth.

Landau Damping and Limit to Field Confinement and Enhancement in Plasmonic Dimers

Abstract: Plasmonic dimers and other similarly shaped plasmonic nanoantennas are capable of achieving large field enhancements inside a narrow gap where surface plasmon polaritons (SPPs) are excited. As the electric field concentration increases, two primary nonlocal effects emerge: an increase in energy dissipation and an expansion of the region in SPP mode (diffusion). While phenomenological theories of nonlocality exist, fundamentally nonlocality is very well-described by Landau damping, i.e. direct excitation of electron–hole pairs in the metal by the highly confined electric field of SPPs. This work verifies and extends our original, simple, self-consistent model by (1) calculating the effect of Landau damping on the field enhancement, effective volume, and line width of the SPP mode in the plasmonic dimer, and (2) demonstrating with extensive numerical simulations that major changes of SPP properties occur in the dimers with gaps as large as 1–2 nm, where they cannot be caused by the electron tunneling. Landa...

Liquid-metal-based metasurface for terahertz absorption material: Frequency-agile and wide-angle

Abstract: Terahertz metasurface absorption materials, which absorb terahertz wave through subwavelength artificial structures, play a key role in terahertz wave shielding and stealth technology, etc. However, most of the metasurface absorption materials in terahertz suffer from limited tuning range and narrow incident angle characteristics. Here, we demonstrate a liquid-metal-based metasurface through microfluidic technology, which functions as a terahertz absorption material with broadband tunability and wide-angle features. The proposed terahertz metasurface absorption material exhibits an experimental tuning range from 0.246 THz to 0.415 THz (the tuning range of central frequency reaches 51.1%), and the tuning range maintains at high level with wide-angle response up to 60°.

Adaptable metasurface for dynamic anomalous reflection

Abstract: In this paper, we demonstrate an adaptable metasurface with a periodic array of liquid-metal ring-shaped resonators Its optical properties can be dynamically controlled by individually reconfiguring the geometry (shape and orientation) of the resonators For the proof of concept, by tailoring the phase profile of the scattered electromagnetic wave, a dynamic anomalous reflection is demonstrated, whereby the reflection angle is fixed at −45° for three different normal incident frequencies of 105, 12, and 14 GHz The demonstrated adaptable metasurfaces pave a way for promising applications in multi-frequency tracking radar systems and broadband scanning systems

Transferring the bendable substrateless GaN LED grown on a thin C-rich SiC buffer layer to flexible dielectric and metallic plates

Abstract: By growing an epitaxial GaN LED on C-rich a-SiC buffer deposited SiO2/Si substrate, the simplified transfer to versatile flexible metallic/dielectric membranes is demonstrated. Both the high growth temperature at 1000 °C and the slow deposition rate played important roles in the meticulous MOCVD growth of n-GaN along the surface normal of the a-SiC at the very beginning. High substrate temperature facilitated the refinement of C-rich SiC buffer from amorphous to partially crystalline with (0004)-orientation, which effectively reduces the lattice mismatch between n-GaN and SiC at the interface so as to gradually improve the crystalline n-GaN regrowth. The substrateless GaN LED transferred to flexible copper plates showed reduced turn-on voltage of 2.6 V, enhanced output power of 370 mW, enlarged power-to-current slope of 1.24 W A−1, increased external quantum efficiency of 45%, and reduced efficiency droop of 15% under a bias of 300 mA. The thermal conductivity of the transferred substrate affected the EL peak wavelength shift of the substrateless GaN LED on SiC buffer. Heating the GaN LED on flexible copper plate to 65 °C only reduced its power by 10% and red-shifted its wavelength by 1 nm under a bias at 100 mA; the Auger effect resulted in a degraded EQE of 39.1% and an enlarged EQE droop of 8.5%. Bending the surface diameter of the curvature of the copper plate to 1.2 cm decayed the output power by 12% and red-shifted the EL peak by 5 nm because of the lattice strain induced quantum confined Stark effect (QCSE). Such a bendable substrateless GaN LED transferred to flexible membrane with superior heat dissipation and bending tolerance is a desired lighting element for green photonics in this era.

Coherent selection of invisible high-order electromagnetic excitations

Abstract: Far-field spectroscopy and mapping of electromagnetic near-field distribution are the two dominant tools for analysis and characterization of the electromagnetic response in nanophotonics. Despite the widespread use, these methods can fail at identifying weak electromagnetic excitations masked by stronger neighboring excitations. This is particularly problematic in ultrafast nanophotonics, including optical sensing, nonlinear optics and nanolasers, where the broad resonant modes can overlap to a significant degree. Here, using plasmonic metamaterials, we demonstrate that coherent spectroscopy can conveniently isolate and detect such hidden high-order photonic excitations. Our results establish that the coherent spectroscopy is a powerful new tool. It complements the conventional methods for analysis of the electromagnetic response, and provides a new route to designing and characterizing novel photonic devices and materials.

Generation of convergent light beams by using surface plasmon locked Smith-Purcell radiation.

Abstract: An electron bunch passing through a periodic metal grating can emit Smith-Purcell radiation (SPR). Recently, it has been found that SPR can be locked and enhanced at some emission wavelength and angle by excitation of surface plasmon (SP) on the metal substrate. In this work, the generation of a convergent light beam via using the SP-locked SPR is proposed and investigated by computer simulations. The proposed structure is composed of an insulator-metal-insulator (IMI) substrate with chirped gratings on the substrate. The chirped gratings are designed such that a convergent beam containing a single wavelength is formed directly above the gratings when an electron bunch passes beneath the substrate. The wavelength of the convergent beam changes with the refractive index of dielectric layer of the IMI structure, which is determined by the frequency of SP on the IMI substrate excited by the electron bunch. Moreover, reversing the direction of electron bunch will make the emitted light from the proposed structure to switch from a convergent beam to a divergent beam. Finally, the formation of a convergent beam containing red, green and blue lights just above the chirped gratings is also demonstrated. This work offers potential applications in the fields of optical imaging, optical beam steering, holography, microdisplay, cryptography and light source.

Plasmon-enhanced optical nonlinearity for femtosecond all-optical switching

Abstract: Ultrafast all-optical switching in metals can be an efficient way for high-speed active photonic devices. However, with the improvement in modulation speed, typically by reducing the optical switching pulse width from picoseconds to femtoseconds, the nonlinear optical response of the metal will decrease significantly, which hinders the realization of the sufficient modulation depth at femtosecond optical control. Here, by combining two optical nonlinear enhancement effects of surface plasmon polaritons, including their extreme sensitivity to refractive index change and their capability to induce strong localized optical fields, we have achieved an ∼50-times enhancement in the modulation depth simultaneously with a switching time of ∼75-fs. Such enhancement was found to be independent of the control intensity, which sets a basis for the future application of femtosecond switching at a minimum power.

Temperature tunability of surface plasmon enhanced Smith-Purcell terahertz radiation for semiconductor-based grating.

Abstract: In this work, the terahertz (THz) Smith-Purcell radiations (SPRs) for the relativistic electron bunch passing over an indium antimonide (InSb)-based substrate with a subwavelength grating under various temperatures of substrate are investigated by FDTD simulations and theoretical analyses. The explored SPR is locked and enhanced at a certain emission wavelength with the emission angle still following the wavelength-angle relation of the traditional SPR. This wavelength agrees with the (vacuum) wavelength of surface plasmons (SPs) at the air-InSb interface excited by the electron bunch. The enhancement of SPR at this wavelength is attributed to the energy from electron concentrated in the excited SPs and then transformed into radiation via the SPR mechanism. When the temperature of InSb increases, the emission wavelength of the enhanced SPR decreases along with the emission angles increasing gradually. This work demonstrates that the emission wavelength and angle of the enhanced SPR from the InSb grating can be manipulated by the temperature of InSb. The temperature tunability of SP-enhanced SPR has potential applications in the fields of optical beam steering and metamaterial light source.

Material-assisted metamaterial: a new dimension to create functional metamaterial

Abstract: A high Q-value reflective type metasurface consisting of 1D Au nanorods, a SiO2 spacer and a Au back reflector is demonstrated. It is shown that the sideband of the resonant mode can be suppressed as the resonant wavelength close to the phonon absorption of SiO2. By combining both designed structured resonance and inherent property of the based materials, a low angle-dependent metasurface with a Q-value of 40 has been demonstrated. The proposed structure will be useful for high sensitivity sensing and narrow band thermal emitter.

Plasmonic multicolor meta-hologram

Abstract: A phase-modulated optical component for the visible spectrum is provided and is capable of producing images in three primary colors The phase-modulated optical component is primarily structured by a plurality of aluminum nanorods that are arranged in several two-dimensional arrays to form a plurality of pixels The nanorods can yield surface plasmon resonances in red, green and blue light By tuning the nanorod size in the arrays, the wavelength-dependent reflectance thereof can be varied across the visible spectrum, thereby realizing wavelength division multiplexing operations for the phase-modulated optical component

Plasmonics: Nanoimaging, Nanofabrication, and Their Applications IV

Abstract: vii Conference Committee xi Introduction xiii Revivals of molecular nonlinear optics in physics, chemistry, and life sciences (Plenary Paper) [7040-100] J. Zyss, Lab. de Photonique Quantique et Moleculaire, CNRS, Institut d’Alembert (France) NANOFABRICATION AND LITHOGRAPHY 7033 05 Hierarchical architectures based on optical near-field interactions (Invited Paper) [7033-04] N. Tate, W. Nomura, Univ. of Tokyo (Japan); T. Yatsui, Japan Science and Technology Agency (Japan); M. Naruse, Univ. of Tokyo (Japan) and National Institute of Information and Communications Technology (Japan); M. Ohtsu, Univ. of Tokyo (Japan) 7033 06 Photochemical nano-scale patterning with Rhodamine 6G dye from aqueous phase [7033-05] A. Kassu, F. A. Calzzani, Jr., J. M. Taguenang, R. K. Sileshi, A. Sharma, Alabama AM N. Hayazawa, RIKEN, The Institute of Physical and Chemical Research (Japan) and CREST, Japan Science and Technology Agency (Japan); M. Motohashi, Osaka Univ. (Japan); S. Kawata, RIKEN, The Institute of Physical and Chemical Research (Japan), Osaka Univ. (Japan), and CREST, Japan Science and Technology Agency (Japan) NANO-IMAGING I 7033 0E Ultra-high resolution Raman imaging by optically trapped dielectric microsphere (Invited Paper) [7033-13] Z. X. Shen, J. Kasim, Nanyang Technological Univ. (Singapore) NANO-IMAGING II 7033 0I Nanoscale coupling effects on single particle microscopy (Invited Paper) [7033-17] K. L. Shuford, K. A. Meyer, Oak Ridge National Lab. (United States); C. Li, S. O. Cho, Korea Advanced Institute of Science and Technology (Korea, Republic of); W. B. Whitten, R. W. Shaw, Oak Ridge National Lab. (United States)

Versatile polarization generation by using aluminum plasmonic metasurface

Abstract: All forms of light manipulation depend on light–matter interaction, the fundamental mechanism is the modulation of its electromagnetic fields by the localized electromagnetic fields of atoms. The polarization of the electromagnetic field is the important factors to influence the strength of interaction. The generation and manipulation of light polarization have been traditionally accomplished with bulky optical components such as waveplates, polarizers, and polarization beam splitters that are optically thick. The miniaturization of these devices is highly desirable for the development of a new class of compact, flat, and broadband optical components that can be integrated together on a single photonics chip. Here we demonstrate a reflective metasurface polarization generator (MPG) capable of producing light beams of any polarizations all from a linearly polarized light source with a single optically thin chip. Six polarization light beams are achieved simultaneously including four linear polarizations along different directions and two circular polarizations, all conveniently separated into different reflection angles. Using the Pancharatnam– Berry phase-modulation method, the MPG sample was fabricated with aluminum as the plasmonic metal instead of the conventional gold or silver, which allowed for its broadband operation covering the entire visible spectrum. The versatility and compactness of the MPG capable of transforming any incident wave into light beams of arbitrary polarizations over a broad spectral range are an important step forward in achieving a complete set of flat optics for integrated photonics with far-reaching applications. [1]

Impact of Landau damping on field enhancement in plasmonic dimers

Abstract: We show that Landau damping presents the most practically-relevant limit to the achievable plasmonic enhancement inside the narrow gaps of plasmonic dimers and other similarly-shaped plasmonic nanoantennas.

Author Correction: Generation of convergent light beams by using surface plasmon locked Smith-Purcell radiation.

Abstract: A correction to this article has been published and is linked from the HTML version of this paper. The error has not been fixed in the paper.

Optical range plasmonics of niobium around the superconducting transition temperature

Abstract: We show that a niobium metamaterial exhibits optical plasmonic resonances which change in a critical way near the superconducting transition temperature of 9K. This suggest a hitherto unknown link between superconductivity and optical range plasmonics.

Plasmonic toroidal excitation with engineering metamaterials

Abstract: Natural toroidal molecules, such as biomolecules and proteins, possess toroidal dipole moments that are hard to be detected, which leads to extensive studies of artificial toroidal materials. Recently, toroidal metamaterials have been widely investigated to enhance toroidal dipole moments while the other multipoles are eliminated due to the spacial symmetry. In this talk, we will show several cases on the plasmonic toroidal excitation by engineering the near-field coupling between metamaterials, including their promising applications. In addition, a novel design for a toroidal metamaterial with engineering anapole mode will also be discussed.

Nonlinear plasmonic sensing with nanographene (Conference Presentation)

Abstract: Plasmons provide excellent sensitivity to detect analyte molecules through their strong interaction with the dielectric environment. Plasmonic sensors based on noble metals are, however, limited by the spectral broadening of these excitations. Here we identify a new mechanism that reveals the presence of individual molecules through the radical changes that they produce in the plasmons of graphene nanoislands. An elementary charge or a weak permanent dipole carried by the molecule are shown to be sufficient to trigger observable modifications in the linear absorption spectra and the nonlinear response of the nanoislands. In particular, a strong second-harmonic signal, forbidden by symmetry in the unexposed graphene nanostructure, emerges due to a redistribution of conduction electrons produced by interaction with the molecule. These results pave the way toward ultrasensitive nonlinear detection of dipolar molecules and molecular radicals that is made possible by the extraordinary optoelectronic properties of graphene.

VSRR for isotropic absorption and nanophotonic sensor

Abstract: Metamaterials have been realized for exotic optical phenomena which can not be found in nature, such as negative refractive index and cloaking. Nowadays, people intend to be more precisely from fundamental physical response to specific functionalities in metamaterials on demand for the development on practical applications, such as optical switches, phase gradient surfaces[1,2], optical modulators, polarizer and wave plate. One of the potential applications is the metamaterial based perfect absorber (MPA)[3]. Due to the strong electromagnetic field confinement arising from surface plasmon resonance, MPA provides a benefitting way for enhancing the efficiency in solar energy capture, nanoplasmonic sensor and bolometer. The commonly utilized structural configuration for MPAs is incorporating a metamaterial array with a perfect reflective mirror separated by a dielectric spacer. Because of the near-field interaction between metamaterials and its mirror images, a strong plasmon field confinement is involved and therefore dramatically enhances the absorption intensity. However, both the electric and magnetic responses play an important role to those of electromagnetic media, especially for the nonlinearity responses. Vertical split-ring resonator (VSRR) attracts a wide interest because it found out that the magnetic reciprocal coupling of incident light [4,5].

Plasmonic properties of superconducting niobium in the optical part of the spectrum

Abstract: We show for the first time that, contrary to common expectations, transition to superconductivity affects plasmonic behaviour of niobium at optical frequencies. This result is unexpected as photon energy is orders of magnitude higher than the binding energy of the Cooper pairs, the superconducting charge carriers.

A deep-UV plasmonic nanolaser with hyperbolic metamaterials

Abstract: In recent years, plasmonic nanostructured materials have been used to enhance light emission by creating localized electric fields that confine light fields to regions below the diffraction limit of the material, resulting in efficient lightmatter interactions.1 Plasmonic nanolasers based on these materials have been developed by using, for example, a dielectric nanowire or nanorod gain material—the laser amplification medium—placed on a metal film or silica/metal structure to form a Fabry-Pérot cavity resonator (an arrangement of mirrors for multiple light reflection).2, 3 However, the nanowire or nanorod length in these plasmonic nanolasers is often fairly long (several micrometers) and it is not easy to control the nanowire/nanorod orientation, which limits the potential applications of these devices. Here, we discuss our recent work using a metal-dielectric hyperbolic metamaterial (HMM)—a material engineered to exhibit extreme anisotropy upon interaction with light—as a plasmonic cavity to demonstrate a 289nm UV plasmonic nanolaser. Although the quantum well heterostructures used in these nanolasers, which increase the strength of electro-optical interactions, have a low internal quantum efficiency of 30%, the strong light-matter coupling introduced by the HMM plasmonic cavity can still bring the devices above the lasing threshold. The dispersion relation (the effect of a dispersive medium on the properties of a light wave) of the stacked metal-dielectric HMM is given by:

Plasmonic Metasurface for Photonic Applications in Demand

Abstract: The functionalities of traditional optical component are mainly based on the phase accumulation through the propagation length, leading to a bulky optical component like lens and waveplate. Plasmonic metasurfaces composed of two-dimensional (2D) artificial structures have attracted a huge number of interests due to their ability on controlling the optical properties including electromagnetic phase as well as amplitude at a subwavelength scale [1]. They therefore pave a promising way for the development of flat optical devices and integrated optoelectronic systems. In this talk, several research topics for photonic applications based on metasurfaces will be performed and discussed: Beas deflection [2], highly dimensional holographic imaging [3], versatile polarization generation and analysis [4], multi-functional and tunable metadevices [5], engineering non-radiating anapole mode in free space [6] and achromatic metasurface devices [7]