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ABSTRACT: Materials research plays a vital role in transforming breakthrough scientific ideas into next-generation technology. Similar to the way silicon revolutionized the microelectronics industry, the proper materials can greatly impact the field of plasmonics and metamaterials. Currently, research in plasmonics and metamaterials lacks good material building blocks in order to realize useful devices. Such devices suffer from many drawbacks arising from the undesirable properties of their material building blocks, especially metals. There are many materials, other than conventional metallic components such as gold and silver, that exhibit metallic properties and provide advantages in device performance, design flexibility, fabrication, integration, and tunability. This review explores different material classes for plasmonic and metamaterial applications, such as conventional semiconductors, transparent conducting oxides, perovskite oxides, metal nitrides, silicides, germanides, and 2D materials such as graphene. This review provides a summary of the recent developments in the search for better plasmonic materials and an outlook of further research directions.
Advanced Materials 05/2013; · 13.88 Impact Factor
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ABSTRACT: Metamaterials, or engineered materials with rationally designed, subwavelength-scale building blocks, allow us to control the behavior of physical fields in optical, microwave, radio, acoustic, heat transfer, and other applications with flexibility and performance that are unattainable with naturally available materials. In turn, metasurfaces-planar, ultrathin metamaterials-extend these capabilities even further. Optical metasurfaces offer the fascinating possibility of controlling light with surface-confined, flat components. In the planar photonics concept, it is the reduced dimensionality of the optical metasurfaces that enables new physics and, therefore, leads to functionalities and applications that are distinctly different from those achievable with bulk, multilayer metamaterials. Here, we review the progress in developing optical metasurfaces that has occurred over the past few years with an eye toward the promising future directions in the field.
Science 03/2013; 339(6125):1232009. · 31.20 Impact Factor
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ABSTRACT: We study a planar, holey-metal lens made as a set of concentric circular arrays (rings) of nano-scale holes milled in a sub-wavelength-thick metal film. Each nanohole - a finite-length, circular, single-mode waveguide with a radius-dependent mode index - is used as a phase-shifting element. Our experimental results confirm that the focusing properties of our polarization-independent, holey-metal lens milled in a 380-nm thick gold film and illuminated with 531-nm light fits the analytical model well. The proposed concept could offer an alternative to conventional refraction micro-lenses and open up a vital path toward on-chip or fiber-end planar photonic devices for bio-sensing and imaging.
Nano Letters 12/2012; · 13.20 Impact Factor
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ABSTRACT: Noble metals such as gold and silver are conventionally used as the primary plasmonic building blocks of optical metamaterials. Making subwavelength-scale structural elements from these metals not only seriously limits the optical performance of a device due to high absorption, it also substantially complicates the manufacturing process of nearly all metamaterial devices in the optical wavelength range. As an alternative to noble metals, we propose to use heavily doped oxide semiconductors that offer both functional and fabrication advantages in the near-infrared wavelength range. In this letter, we replace a metal with aluminum-doped zinc oxide as a new plasmonic material and experimentally demonstrate negative refraction in an Al:ZnO/ZnO metamaterial in the near-infrared range.
Proceedings of the National Academy of Sciences 05/2012; 109(23):8834-8. · 9.68 Impact Factor
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ABSTRACT: 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 1.0 to 1.9 micrometers. This is accomplished by using an extremely thin plasmonic layer (~λ/50) consisting of an optical nanoantenna array that provides subwavelength phase manipulation on light propagating across the interface. Anomalous light-bending phenomena, including negative angles of refraction and reflection, are observed in the operational wavelength range.
Science 12/2011; 335(6067):427. · 31.20 Impact Factor
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ABSTRACT: 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. Loss-compensated metal-dielectric multilayers that have hyperbolic dispersion relationships are beneficial for numerous applications such as subwavelength imaging and quantum optics.
Optics Express 12/2011; 19(25):25242-54. · 3.59 Impact Factor
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ABSTRACT: We present comprehensive studies on thin diffraction lenses made of arrays of subwavelength, parallel nanoslits in a gold film. Such a nanoslit lens can operate either as a conventional convex or concave lens. The lenses can be designed to focus linearly polarized light with polarization either perpendicular (TM-lens) or parallel to the slits (TE-lens), while the orthogonal polarization diverges when passing through the lens. The designs of each lens are initially built on the dispersion relations for wave propagation through a parallel-plate waveguide. Both TM- and TE-lenses were realized experimentally, and full-wave numerical simulations fully support the experimental results.
Optics Letters 02/2011; 36(4):451-3. · 3.40 Impact Factor
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ABSTRACT: We report on the experimental demonstration of the broadband "trapped
rainbow" in the visible range using arrays of adiabatically tapered optical
nano waveguides. Being a distinct case of the slow light phenomenon, the
trapped rainbow effect could be applied to optical signal processing, and
sensing in such applications as spectroscopy on a chip, and to providing
enhanced light-matter interactions. As an example of the latter applications,
we have fabricated a large area array of tapered nano-waveguides, which exhibit
broadband "trapped rainbow" effect. Considerable fluorescence enhancement due
to slow light behavior in the array has been observed.
01/2011;
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ABSTRACT: We have studied the ability of a lamellar near-field superlens to transfer an enhanced electromagnetic field to the far side of the lens. In this work, we have experimentally and numerically investigated superlensing in the visible range. By using the resonant hot-spot field enhancements from optical nanoantennas as sources, we investigated the translation of these sources to the far side of a layered silver-silica superlens operating in the canalization regime. Using near-field scanning optical microscopy (NSOM), we have observed evidence of superlens-enabled enhanced-field translation at a wavelength of about 680 nm. Specifically, we discuss our recent experimental and simulation results on the translation of hot spots using a silver-silica layered superlens design. We compare the experimental results with our numerical simulations and discuss the perspectives and limitations of our approach.
SPIE Optics and Photonics, San Diego; 01/2011
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Journal of Nanophotonics 01/2011; 5:051513. · 1.57 Impact Factor
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ABSTRACT: Despite strong experimental and theoretical evidence supporting superresolution imaging based on microlenses, the imaging mechanisms involved are not well understood. Based on the transformation optics approach, we demonstrate that a microlens may act as a two-dimensional fish-eye or an inverted Eaton lens. An asymmetric inverted Eaton lens may exhibit considerable image magnification, which has been confirmed experimentally.
Optics Letters 10/2010; 35(20):3396-8. · 3.40 Impact Factor
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ABSTRACT: 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. Generally the losses are orders of magnitude too large for the proposed applications, and the reduction of losses with optimized designs seems to be out of reach. One way of addressing this issue is to incorporate gain media into NIM designs. However, whether NIMs with low loss can be achieved has been the subject of theoretical debate. Here we experimentally demonstrate that the incorporation of gain material in the high-local-field areas of a metamaterial makes it possible to fabricate an extremely low-loss and active optical NIM. The original loss-limited negative refractive index and the figure of merit (FOM) of the device have been drastically improved with loss compensation in the visible wavelength range between 722 and 738 nm. In this range, the NIM becomes active such that the sum of the light intensities in transmission and reflection exceeds the intensity of the incident beam. At a wavelength of 737 nm, the negative refractive index improves from -0.66 to -1.017 and the FOM increases from 1 to 26. At 738 nm, the FOM is expected to become macroscopically large, of the order of 10(6). This study demonstrates the possibility of fabricating an optical negative-index metamaterial that is not limited by the inherent loss in its metal constituent.
Nature 08/2010; 466(7307):735-8. · 36.28 Impact Factor
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ABSTRACT: We report a spectroscopic method using coherent random lasers for a simple, yet nanoscale, sensing approach. Unique spectral properties of coherent random laser emission can be detectably altered when introducing nanoscale perturbations to a simple nanocomposite film that consists of dielectric nanospheres and laser-dye-doped polymer to serve as a transducer. Random lasing action provides a means to amplify subtle perturbations to readily detectable spectral shifts in multiple discrete emission peaks. Owing to several advantages, such as large-area detection, narrow and multiple emission peaks, straightforward detection, and simple fabrication, random laser spectroscopy has the potential for ultrasensitive, yet simple, biosensors in various applications.
Optics Letters 08/2010; 35(15):2624-6. · 3.40 Impact Factor
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ABSTRACT: Despite strong experimental and theoretical evidence supporting superresolution imaging based on microlenses, imaging mechanisms involved are not well understood. Based on the transformation optics approach, we demonstrate that microlenses may act as two-dimensional fisheye or Eaton lenses. An asymmetric Eaton lens may exhibit considerable image magnification, which has been confirmed experimentally. Comment: 15 pages, 7 figures
06/2010;
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ABSTRACT: We demonstrate a method to fabricate ultra-thin ultra-smooth and low-loss silver and silver-silica composite films using a germanium wetting layer and a rapid post-annealing treatment. Such achievement satisfies both the demands for superlenses and hyperlenses.
Quantum Electronics and Laser Science Conference, San Jose, CA; 05/2010
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ABSTRACT: Owing to the low-loss and high refractive index variations derived from the basic building block of bone structure, we, for the first time to our knowledge, demonstrate coherent random lasing action originated from the bone structure infiltrated with laser dye, revealing that bone tissue is an ideal biological material for random lasing. Our numerical simulation shows that random lasers are extremely sensitive to subtle structural changes even at nanoscales and can potentially be an excellent tool for probing nanoscale structural alterations in real time as a novel spectroscopic modality.
Optics Letters 05/2010; 35(9):1425-7. · 3.40 Impact Factor
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ABSTRACT: Recent experimental demonstrations of optical metamaterials opened up an entirely new branch of modern optics that can be
described as “refractive index engineering” [1–20]. The refractive index of a material is the factor by which an electromagnetic
wave is slowed down, compared with a vacuum, when it propagates inside the material. The material properties of conventional
materials are largely controlled by the properties of their constituent components, viz., atoms and molecules. Their refractive
indices can be modified to some degree by altering material chemical composition, using thermal or electrical tuning, or through
nonlinear optical effects. Nevertheless, a majority of existing materials possesses positive, and typically greater than one,
index of refraction. In contrast, meta-materials provide almost unlimited opportunities for designing the refractive index
through a careful engineering of their constituent components, or meta-atoms. Several examples of engineered optical structures,
including magnetic metamaterial and negative index metamaterials (NIMs), are shown in Fig. 13.1. Moreover, metamaterial properties
can be tuned [21,22] and even controlled on a level of a single meta-atom [23]. Basic properties of optical metamaterials
will be reviewed in Section 13.1. Additional design flexibility provided by metamaterials (discussed in Section 13.2) gives
rise to new linear and nonlinear optical properties, functionalities, and applications unattainable with conventional materials.
In this chapter, we discuss two examples of refractive index engineering in metamaterials that results in truly fascinating
phenomena.
03/2010: pages 217-240;
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ABSTRACT: The effect of grain boundaries on the electron relaxation rate is significant even for large area noble metal films and more so for plasmonic nanostructures. Optical spectroscopy and X-ray diffraction show a substantial improvement in plasmon resonance quality for square-particle nanoantennas after annealing due to an enlarged grain size from 22 to 40 nm and improved grain boundaries described by the electron reflection coefficient. The electron relaxation rate due to the grains is shown to decrease by a factor of 3.2.
Nano Letters 03/2010; 10(3):916-22. · 13.20 Impact Factor
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ABSTRACT: We demonstrate a method to fabricate ultra-thin, ultra-smooth and low-loss silver (Ag) films using a very thin germanium (Ge) layer as a wetting material and a rapid post-annealing treatment. The addition of a Ge wetting layer greatly reduces the surface roughness of Ag films deposited on a glass substrate by electron-beam evaporation. The percolation threshold of Ag films and the minimal thickness of a uniformly continuous Ag film were significantly reduced using a Ge wetting layer in the fabrication. A rapid post-annealing treatment is demonstrated to reduce the loss of the ultra-thin Ag film to the ideal values allowed by the quantum size effect in smaller grains. Using the same wetting method, we have also extended our studies to ultra-smooth silver-silica lamellar composite films with ultra-thin Ag sublayers.
Optics Express 03/2010; 18(5):5124-34. · 3.59 Impact Factor
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ABSTRACT: Recently we have suggested that two-dimensional broadband transformation optics devices based on metamaterial designs may be built using tapered waveguides. Here we review application of this principle to broadband electromagnetic cloaking, trapped rainbow, and novel microscopy devices.
Materials. 01/2010;
