213 research outputs found
Functional Elements in Three-Dimensional Photonic Bandgap Materials
Functional elements in three-dimensional photonic bandgap materials have the potential to precisely control the flow of light. In this thesis a variety of different functional defect structures embedded into silicon woodpile photonic crystals are realized using a combination of direct laser writing and silicon double inversion. The optical properties of the fabricated structures are investigated both experimentally and by numerical calculations
Bidirectional waveguide coupling with plasmonic Fano nanoantennas
We introduce the concept of a bidirectional, compact single-element Fano nanoantenna that allows for directional coupling of light in opposite directions of a high-index dielectric waveguide for two different operation wavelengths. We utilize a Fano resonance to tailor the radiation phases of a gold nanodisk and a nanoslit that is inscribed into the nanodisk to realize bidirectional scattering. We show that this Fano nanoantenna operates as a bidirectional waveguide coupler at telecommunication wavelengths and, thus, is ideally suitable for integrated wavelength-selective light demultiplexing
Optical Yagi-Uda nanoantennas
Conventional antennas, which are widely employed to transmit radio and TV
signals, can be used at optical frequencies as long as they are shrunk to
nanometer-size dimensions. Optical nanoantennas made of metallic or
high-permittivity dielectric nanoparticles allow for enhancing and manipulating
light on the scale much smaller than wavelength of light. Based on this
ability, optical nanoantennas offer unique opportunities regarding key
applications such as optical communications, photovoltaics, non-classical light
emission, and sensing. From a multitude of suggested nanoantenna concepts the
Yagi-Uda nanoantenna, an optical analogue of the well-established
radio-frequency Yagi-Uda antenna, stands out by its efficient unidirectional
light emission and enhancement. Following a brief introduction to the emerging
field of optical nanoantennas, here we review recent theoretical and
experimental activities on optical Yagi-Uda nanoantennas, including their
design, fabrication, and applications. We also discuss several extensions of
the conventional Yagi-Uda antenna design for broadband and tunable operation,
for applications in nanophotonic circuits and photovoltaic devices
Using effective medium theories to design tailored nanocomposite materials for optical systems
Modern optical systems are subject to very restrictive performance, size and
cost requirements. Especially in portable systems size often is the most
important factor, which necessitates elaborate designs to achieve the desired
specifications. However, current designs already operate very close to the
physical limits and further progress is difficult to achieve by changing only
the complexity of the design. Another way of improving the performance is to
tailor the optical properties of materials specifically to the application at
hand. A class of novel, customizable materials that enables the tailoring of
the optical properties, and promises to overcome many of the intrinsic
disadvantages of polymers, are nanocomposites. However, despite considerable
past research efforts, these types of materials are largely underutilized in
optical systems. To shed light into this issue we, in this paper, discuss how
nanocomposites can be modeled using effective medium theories. In the second
part, we then investigate the fundamental requirements that have to be
fulfilled to make nanocomposites suitable for optical applications, and show
that it is indeed possible to fabricate such a material using existing methods.
Furthermore, we show how nanocomposites can be used to tailor the refractive
index and dispersion properties towards specific applications.Comment: This is a draft manuscript of a paper published in Proc. SPIE
(Proceedings Volume 10745, Current Developments in Lens Design and Optical
Engineering XIX, Event: SPIE Optical Engineering + Applications, 2018
Spectral tuning of a three-dimensional photonic-bandgap waveguide signature by silica atomic-layer deposition
Recent progress in three-dimensional sub-micron fabrication has rendered the introduction of waveguide structures into optical three-dimensional photonic bandgap materials possible. However, spectral tuning of the waveguide modes has not been demonstrated so far. Here, we use atomic-layer deposition of amorphous silica to tune the spectral position of an air-core defect waveguide in a three-dimensional silicon woodpile photonic crystal by 225 nm in wavelength. The measured spectral positions of the waveguide signature are in very good agreement with numerical calculations.We acknowledge support by the Deutsche Forschungsgemeinschaft (DFG) and the State of
Baden-Wurttemberg through the DFG-Center for Functional Nanostructures (CFN) within sub- ¨
project A 1.4. The research of G.v.F. is further supported through a DFG Emmy-Noether fel-lowship (DFG-FR 1671/4-3). We acknowledge support by Deutsche Forschungsgemeinschaft
and Open Access Publishing Fund of Karlsruhe Institute of Technology
Electro-optical switching by liquid-crystal controlled metasurfaces
We study the optical response of a metamaterial surface created by a lattice
of split-ring resonators covered with a nematic liquid crystal and demonstrate
millisecond timescale switching between electric and magnetic resonances of the
metasurface. This is achieved due to a high sensitivity of liquid-crystal
molecular reorientation to the symmetry of the metasurface as well as to the
presence of a bias electric field. Our experiments are complemented by
numerical simulations of the liquid-crystal reorientation.Comment: 6 pages, 3 figure
Lasing modes in ZnO nanowires coupled to planar metals
Semiconductor nanowire lasers can be subject to modifications of their lasing
threshold resulting from a variation of their environment. A promising choice
is to use metallic substrates to gain access to low-volume
Surface-Plasmon-Polariton (SPP) modes. We introduce a simple, yet
quantitatively precise model that can serve to describe mode competition in
nanowire lasers on metallic substrates. We show that an aluminum substrate can
decrease the lasing threshold for ZnO nanowire lasers while for a silver
substrate, the threshold increases compared with a dielectric substrate.
Generalizing from these findings, we make predictions describing the
interaction between planar metals and semiconductor nanowires, which allow to
guide future improvements of highly-integrated laser sources
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