3,898 research outputs found
An optical fiber-based probe for photonic crystal microcavities
We review a novel method for characterizing both the spectral and spatial
properties of resonant cavities within two-dimensional photonic crystals (PCs).
An optical fiber taper serves as an external waveguide probe whose micron-scale
field is used to source and couple light from the cavity modes, which appear as
resonant features in the taper's wavelength-dependent transmission spectrum
when it is placed within the cavity's near field. Studying the linewidth and
depth of these resonances as a function of the taper's position with respect to
the resonator produces quantitative measurements of the quality factor Q and
modal volume Veff of the resonant cavity modes. Polarization information about
the cavity modes can be obtained by studying their depths of coupling when the
cavity is probed along different axes by the taper. This fiber-based technique
has been used to measure Q ~ 40,000 and Veff ~ 0.9 cubic wavelengths in a
graded square lattice PC microcavity fabricated in silicon. The speed and
versatility of this fiber-based probe is highlighted, and a discussion of its
applicability to other wavelength-scale resonant elements is given.Comment: Submitted to special section on photonic crystals from the PECS-V
conference in IEEE Journal on Selected Areas in Communications (J-SAC),
Nanotechnologies for Communications issu
Optimization of Excitation in FDTD Method and Corresponding Source Modeling
Source and excitation modeling in FDTD formulation has a significant impact on the method performance and the required simulation time. Since the abrupt source introduction yields intensive numerical variations in whole computational domain, a generally accepted solution is to slowly introduce the source, using appropriate shaping functions in time. The main goal of the optimization presented in this paper is to find balance between two opposite demands: minimal required computation time and acceptable degradation of simulation performance. Reducing the time necessary for source activation and deactivation is an important issue, especially in design of microwave structures, when the simulation is intensively repeated in the process of device parameter optimization. Here proposed optimized source models are realized and tested within an own developed FDTD simulation environment
Integrated collinear refractive index sensor with Ge PIN photodiodes
Refractive index sensing is a highly sensitive and label-free detection
method for molecular binding events. Commercial implementations of biosensing
concepts based on plasmon resonances typically require significant external
instrumentation such as microscopes and spectrometers. Few concepts exist that
are based on direct integration of plasmonic nanostructures with optoelectronic
devices for on-chip integration. Here, we present a CMOS-compatible refractive
index sensor consisting of a Ge heterostructure PIN diode in combination with a
plasmonic nanohole array structured directly into the diode Al contact
metallization. In our devices, the photocurrent can be used to detect surface
refractive index changes under simple top illumination and without the aid of
signal amplification circuitry. Our devices exhibit large sensitivities > 1000
nm per refractive index unit in bulk refractive index sensing and could serve
as prototypes to leverage the cost-effectiveness of the CMOS platform for
ultra-compact, low-cost biosensors.Comment: 21 pages, 6 figures, supporting information with 11 pages and 11
figures attache
Casimir forces in the time domain II: Applications
Our preceding paper introduced a method to compute Casimir forces in
arbitrary geometries and for arbitrary materials that was based on a
finite-difference time-domain (FDTD) scheme. In this manuscript, we focus on
the efficient implementation of our method for geometries of practical interest
and extend our previous proof-of-concept algorithm in one dimension to problems
in two and three dimensions, introducing a number of new optimizations. We
consider Casimir piston-like problems with nonmonotonic and monotonic force
dependence on sidewall separation, both for previously solved geometries to
validate our method and also for new geometries involving magnetic sidewalls
and/or cylindrical pistons. We include realistic dielectric materials to
calculate the force between suspended silicon waveguides or on a suspended
membrane with periodic grooves, also demonstrating the application of PML
absorbing boundaries and/or periodic boundaries. In addition we apply this
method to a realizable three-dimensional system in which a silica sphere is
stably suspended in a fluid above an indented metallic substrate. More
generally, the method allows off-the-shelf FDTD software, already supporting a
wide variety of materials (including dielectric, magnetic, and even anisotropic
materials) and boundary conditions, to be exploited for the Casimir problem.Comment: 11 pages, 12 figures. Includes additional examples (dispersive
materials and fully three-dimensional systems
Anisotropically Shaped Magnetic/Plasmonic Nanocomposites for Information Encryption and Magnetic-Field-Direction Sensing.
Instantaneous control over the orientation of anisotropically shaped plasmonic nanostructures allows for selective excitation of plasmon modes and enables dynamic tuning of the plasmonic properties. Herein we report the synthesis of rod-shaped magnetic/plasmonic core-shell nanocomposite particles and demonstrate the active tuning of their optical property by manipulating their orientation using an external magnetic field. We further design and construct an IR-photoelectric coupling system, which generates an output voltage depending on the extinction property of the measured nanocomposite sample. We employ the device to demonstrate that the nanocomposite particles can serve as units for information encryption when immobilized in a polymer film and additionally when dispersed in solution can be employed as a new type of magnetic-field-direction sensor
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