67 research outputs found
Approaches to Three-Dimensional Transformation Optical Media Using Quasi-Conformal Coordinate Transformations
We introduce an approach to the design of three-dimensional transformation
optical (TO) media based on a generalized quasi-conformal mapping approach. The
generalized quasi-conformal TO (QCTO) approach enables the design of media that
can, in principle, be broadband and low-loss, while controlling the propagation
of waves with arbitrary angles of incidence and polarization. We illustrate the
method in the design of a three-dimensional "carpet" ground plane cloak and of
a flattened Luneburg lens. Ray-trace studies provide a confirmation of the
performance of the QCTO media, while also revealing the limited performance of
index-only versions of these devices
Enhanced sensing and conversion of ultrasonic Rayleigh waves by elastic metasurfaces
Recent years have heralded the introduction of metasurfaces that advantageously combine the vision of sub-wavelength wave manipulation, with the design, fabrication and size advantages associated with surface excitation. An important topic within metasurfaces is the tailored rainbow trapping and selective spatial frequency separation of electromagnetic and acoustic waves using graded metasurfaces. This frequency dependent trapping and spatial frequency segregation has implications for energy concentrators and associated energy harvesting, sensing and wave filtering techniques. Different demonstrations of acoustic and electromagnetic rainbow devices have been performed, however not for deep elastic substrates that support both shear and compressional waves, together with surface Rayleigh waves; these allow not only for Rayleigh wave rainbow effects to exist but also for mode conversion from surface into shear waves. Here we demonstrate experimentally not only elastic Rayleigh wave rainbow trapping, by taking advantage of a stop-band for surface waves, but also selective mode conversion of surface Rayleigh waves to shear waves. These experiments performed at ultrasonic frequencies, in the range of 400–600 kHz, are complemented by time domain numerical simulations. The metasurfaces we design are not limited to guided ultrasonic waves and are a general phenomenon in elastic waves that can be translated across scales
Plasmonic Luneburg and Eaton Lenses
Plasmonics is an interdisciplinary field focusing on the unique properties of
both localized and propagating surface plasmon polaritons (SPPs) -
quasiparticles in which photons are coupled to the quasi-free electrons of
metals. In particular, it allows for confining light in dimensions smaller than
the wavelength of photons in free space, and makes it possible to match the
different length scales associated with photonics and electronics in a single
nanoscale device. Broad applications of plasmonics have been realized including
biological sensing, sub-diffraction-limit imaging, focusing and lithography,
and nano optical circuitry. Plasmonics-based optical elements such as
waveguides, lenses, beam splitters and reflectors have been implemented by
structuring metal surfaces or placing dielectric structures on metals, aiming
to manipulate the two-dimensional surface plasmon waves. However, the abrupt
discontinuities in the material properties or geometries of these elements lead
to increased scattering of SPPs, which significantly reduces the efficiency of
these components. Transformation optics provides an unprecedented approach to
route light at will by spatially varying the optical properties of a material.
Here, motivated by this approach, we use grey-scale lithography to
adiabatically tailor the topology of a dielectric layer adjacent to a metal
surface to demonstrate a plasmonic Luneburg lens that can focus SPPs. We also
realize a plasmonic Eaton lens that can bend SPPs. Since the optical properties
are changed gradually rather than abruptly in these lenses, losses due to
scattering can be significantly reduced in comparison with previously reported
plasmonic elements.Comment: Accepted for publication in Nature Nanotechnolog
Transformational Plasmon Optics
Transformation optics has recently attracted extensive interest, since it
provides a novel design methodology for manipulating light at will. Although
transformation optics in principle embraces all forms of electromagnetic
phenomena on all length scales, so far, much less efforts have been devoted to
near-field optical waves, such as surface plasmon polaritons (SPPs). Due to the
tight confinement and strong field enhancement, SPPs are widely used for
various purposes at the subwavelength scale. Taking advantage of transformation
optics, here we demonstrate that the confinement as well as propagation of SPPs
can be managed in a prescribed manner by careful control of the dielectric
material properties adjacent to a metal. Since the metal properties are
completely unaltered, it provides a straightforward way for practical
realizations. We show that our approach can assist to tightly bound SPPs over a
broad wavelength band at uneven and curved surfaces, where SPPs would normally
suffer significant scattering losses. In addition, a plasmonic waveguide bend
and a plasmonic Luneburg lens with practical designs are proposed. It is
expected that merging the unprecedented design flexibility based on
transformation optics with the unique optical properties of surface modes will
lead to a host of fascinating near-field optical phenomena and devices.Comment: 17 pages, 6 figure
Printable all-dielectric water-based absorber
Abstract The phase interplay between overlapping electric and magnetic dipoles of equal amplitude generated by exclusively alldielectric structures presents an intriguing paradigm in the manipulation of electromagnetic energy. Here, we offer a holistic implementation by proposing an additive manufacturing route and associated design principles that enable the programming and fabrication of synthetic multi-material microstructures. In turn, we compose, manufacture and experimentally validate the first demonstrable 3d printed all-dielectric electromagnetic broadband absorbers that point the way to circumventing the technical limitations of conventional metal-dielectric absorber configurations. One of the key innovations is to judicially distribute a dispersive soft matter with a high-dielectric constant, such as water, in a low-dielectric matrix to enhance wave absorption at a reduced length scale. In part, these results extend the promise of additive manufacturing and illustrate the power of topology optimisation to create carefully crafted magnetic and electric responses that are sure to find new applications across the electromagnetic spectrum
Relaxation approach for the generation of inhomogeneous distributions of uniformly sized particles
For many applications in gradient index devices and photonic crystals, it is necessary to be able to design semicrystalline distributions of particles where the lattice constant of the distribution is an arbitrary function of position. We propose a method to generate such distributions which is physically motivated by a system of interacting particles, and apply it to the design and implementation of a microwave gradient index lens. While the demonstration was preformed at microwave wavelengths, this technique would also be particularly useful for designing devices for operation at IR and visible wavelengths where the fabrication of distributions of uniformly sized holes or columns is very easy. © 2010 American Institute of Physics
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