22,062 research outputs found
Deformation of lyotropic chromonic liquid crystal induced by cylindrical surface
Department of PhysicsInterfaces, where liquid crystals (LCs) is in contact with other materials, play a pivotal role in most LCbased applications such as displays and sensors. Physicochemical properties of interfaces impose a surface anchoring, and the geometry and topology of confining interfaces determine LC???s director configuration and defects. To our interest, the concavely curved interface with anisotropic curvatures gives rise to a so-called surface-elasticity phenomenon. In this work, we report the director configuration around a cylindrical object embedded in nematic Sunset Yellow (SSY), a representative lyotropic chromonic LC with the large K24 modulus. The nematic SSY is sandwiched between two flat substrates, and a cylinder is placed in the SSY. The flat boundaries induce a homogeneous director field orthogonal to the cylinder???s axis, whereas the cylinder aligns neighboring directors parallel to its axis, based on the theory related with K24. These boundary conditions result in the twist deformation near the cylinder, and we investigate the deformation experimentally and theoretically, and evaluate K24 of SSY.clos
Leveraging Continuous Material Averaging for Inverse Electromagnetic Design
Inverse electromagnetic design has emerged as a way of efficiently designing
active and passive electromagnetic devices. This maturing strategy involves
optimizing the shape or topology of a device in order to improve a figure of
merit--a process which is typically performed using some form of steepest
descent algorithm. Naturally, this requires that we compute the gradient of a
figure of merit which describes device performance, potentially with respect to
many design variables. In this paper, we introduce a new strategy based on
smoothing abrupt material interfaces which enables us to efficiently compute
these gradients with high accuracy irrespective of the resolution of the
underlying simulation. This has advantages over previous approaches to shape
and topology optimization in nanophotonics which are either prone to gradient
errors or place important constraints on the shape of the device. As a
demonstration of this new strategy, we optimize a non-adiabatic waveguide taper
between a narrow and wide waveguide. This optimization leads to a non-intuitive
design with a very low insertion loss of only 0.041 dB at 1550 nm.Comment: 20 pages, 9 figure
Frequency-modulated continuous-wave LiDAR compressive depth-mapping
We present an inexpensive architecture for converting a frequency-modulated
continuous-wave LiDAR system into a compressive-sensing based depth-mapping
camera. Instead of raster scanning to obtain depth-maps, compressive sensing is
used to significantly reduce the number of measurements. Ideally, our approach
requires two difference detectors. % but can operate with only one at the cost
of doubling the number of measurments. Due to the large flux entering the
detectors, the signal amplification from heterodyne detection, and the effects
of background subtraction from compressive sensing, the system can obtain
higher signal-to-noise ratios over detector-array based schemes while scanning
a scene faster than is possible through raster-scanning. %Moreover, we show how
a single total-variation minimization and two fast least-squares minimizations,
instead of a single complex nonlinear minimization, can efficiently recover
high-resolution depth-maps with minimal computational overhead. Moreover, by
efficiently storing only data points from measurements of an
pixel scene, we can easily extract depths by solving only two linear equations
with efficient convex-optimization methods
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