127 research outputs found
Semiconductor split-ring resonators for thermally tunable, terahertz metamaterials
As the variation of temperature alters the intrinsic carrier density in a
semiconductor, numerical simulations indicate that the consequent variation of
the relative permittivity in the terahertz regime provides a way to realize
thermally tunable split-ring resonators. Electromagnetic metasurfaces and
metamaterials that are thermally tunable in the terahertz regime can thus be
implemented.Comment: 9 page
Dielectric response of soft mode in ferroelectric SrTiO3
We report far-infrared dielectric properties of powder form ferroelectric
SrTiO3. Terahertz time-domain spectroscopy (THz-TDS) measurement reveals that
the low-frequency dielectric response of SrTiO3 is a consequence of the lowest
transverse optical (TO) soft mode TO1 at 2.70 THz (90.0 1/cm), which is
directly verified by Raman spectroscopy. This result provides a better
understanding of the relation of low-frequency dielectric function with the
optical phonon soft mode for ferroelectric materials. Combining THz-TDS with
Raman spectra, the overall low-frequency optical phonon response of SrTiO3 is
presented in an extended spectral range from 6.7 1/cm to 1000.0 1/cm.Comment: 14 pages; 4 figure
Rotational Correction on the Morse Potential Through the Pekeris Approximation and Nikiforov-Uvarov Method
The Nikiforov-Uvarov method is employed to calculate the the Schrodinger
equation with a rotation Morse potential. The bound state energy eigenvalues
and the corresponding eigenfunction are obtained. All of these calculation
present an effective and clear method under a Pekeris approximation to solve a
rotation Morse model. Meanwhile the results got here are in a good agreement
with ones before.Comment: 11 pages, no figure, submitted to Chemical Physics Letters, (2005
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All-optical active THz metasurfaces for ultrafast polarization switching and dynamic beam splitting.
Miniaturized ultrafast switchable optical components with an extremely compact size and a high-speed response will be the core of next-generation all-optical devices instead of traditional integrated circuits, which are approaching the bottleneck of Moore's Law. Metasurfaces have emerged as fascinating subwavelength flat optical components and devices for light focusing and holography applications. However, these devices exhibit a severe limitation due to their natural passive response. Here we introduce an active hybrid metasurface integrated with patterned semiconductor inclusions for all-optical active control of terahertz waves. Ultrafast modulation of polarization states and the beam splitting ratio are experimentally demonstrated on a time scale of 667 ps. This scheme of hybrid metasurfaces could also be extended to the design of various free-space all-optical active devices, such as varifocal planar lenses, switchable vector beam generators, and components for holography in ultrafast imaging, display, and high-fidelity terahertz wireless communication systems
Wave dynamics on toroidal surface
Wave dynamics on curved surfaces has attracted growing attention due to its close resemblance to the warped space time governed by general relativity. It also opens up opportunities for designing functional optical devices such as geodesic lenses. In this work we study the wave dynamics on the surface of a torus, a shape of considerable interest due to its nontrivial topology. Governed by the conservation of angular momentum, light propagates on the torus in two different types of modes: one is able to twist around and sweep through the whole surface of the torus; the other is confined within a certain angular range along the torus latitude direction. The confined mode exhibits an interesting self focusing or imaging behavior, which, similar to a geometric lens, shows no dependence of wavelength and thus suffers no chromatic aberration. By changing the geometric parameters of the torus, both the focusing point and the focusing distance can be controlled. Our work provides a new approach to manipulation of light propagation on a curved surface under the conservation of angular momentum
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All-optical active THz metasurfaces for ultrafast polarization switching and dynamic beam splitting.
Miniaturized ultrafast switchable optical components with an extremely compact size and a high-speed response will be the core of next-generation all-optical devices instead of traditional integrated circuits, which are approaching the bottleneck of Moore's Law. Metasurfaces have emerged as fascinating subwavelength flat optical components and devices for light focusing and holography applications. However, these devices exhibit a severe limitation due to their natural passive response. Here we introduce an active hybrid metasurface integrated with patterned semiconductor inclusions for all-optical active control of terahertz waves. Ultrafast modulation of polarization states and the beam splitting ratio are experimentally demonstrated on a time scale of 667 ps. This scheme of hybrid metasurfaces could also be extended to the design of various free-space all-optical active devices, such as varifocal planar lenses, switchable vector beam generators, and components for holography in ultrafast imaging, display, and high-fidelity terahertz wireless communication systems
From stateflow simulation to verified implementation: A verification approach and a real-time train controller design
Simulink is widely used for model driven development (MDD) of industrial software systems. Typically, the Simulink based development is initiated from Stateflow modeling, followed by simulation, validation and code generation mapped to physical execution platforms. However, recent industrial trends have raised the demands of rigorous verification on safety-critical applications, which is unfortunately challenging for Simulink. In this paper, we present an approach to bridge the Stateflow based model driven development and a well- defined rigorous verification. First, we develop a self- contained toolkit to translate Stateflow model into timed automata, where major advanced modeling features in Stateflow are supported. Taking advantage of the strong verification capability of Uppaal, we can not only find bugs in Stateflow models which are missed by Simulink Design Verifier, but also check more important temporal properties. Next, we customize a runtime verifier for the generated nonintrusive VHDL and C code of Stateflow model for monitoring. The major strength of the customization is the flexibility to collect and analyze runtime properties with a pure software monitor, which opens more opportunities for engineers to achieve high reliability of the target system compared with the traditional act that only relies on Simulink Polyspace. We incorporate these two parts into original Stateflow based MDD seamlessly. In this way, safety-critical properties are both verified at the model level, and at the consistent system implementation level with physical execution environment in consideration. We apply our approach on a train controller design, and the verified implementation is tested and deployed on a real hardware platform
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