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[신간안내] Computational Electrodynamics (the finite difference time - domain method)

Modern electronics based on semiconductors is meeting the fundamental speed limit caused by the interconnect delay and large heat generation when the sizes of components reach nanometer scale. Photons as a carrier of the information are superior to electrons in bandwidth, density, speed, and dissipation. More over, photons could carry intensity, polarization, phase, and frequency information which could break through the limitation of binary system as in electronic devices. But due to the diffraction limitation, the photonic components and devices can not be fabricated small enough to be integrated densely. Surface plasmon polariton is quanta of collective oscillations of free electrons excited by photons in metal nanostrucrures, which offers a promising way to manipulate light at the nanoscale and to realize the miniaturization of photonic devices. Hence, plasmonic circuits and devices have been proposed for some time as a potential strategy for advancing semiconductor-based computing beyond the fundamental performance limitations of electronic devices, as epitomized by Moore's law. A variety of individual plasmonic nanodevices have been intensively studied recently, but the crucial and necessary step to enable nanophotonic circuits for future information technology, namely cascade logics integrated on-chip, has not been achieved. Here we demonstrate that a nanophotonic binary logic NOR gate can be realized by cascading plasmonic OR and NOT gates in four-terminal nanowire networks. We explain the operating principle for the device based on quantum dot luminescence imaging, which reveal the interferences for different logic functions between propagating plasmon wave packets in the nanowire network in great detail. Since the NOR gate is logic complete, i.e. any Boolean logic gate can be constructed from it, our results could have a key role in defining a viable path for the development of novel subwavelength optical processor architectures.

Cascaded Logic Gates in Nanophotonic Plasmon Networks

Random fiber lasers blend together attractive features of traditional random lasers, such as low cost and simplicity of fabrication, with high-performance characteristics of conventional fiber lasers, such as good directionality and high efficiency. Low coherence of random lasers is important for speckle-free imaging applications. The random fiber laser with distributed feedback proposed in 2010 led to a quickly developing class of light sources that utilize inherent optical fiber disorder in the form of the Rayleigh scattering and distributed Raman gain. The random fiber laser is an interesting and practically important example of a photonic device based on exploitation of optical medium disorder. We provide an overview of recent advances in this field, including high-power and high-efficiency generation, spectral and statistical properties of random fiber lasers, nonlinear kinetic theory of such systems, and emerging applications in telecommunications and distributed sensing.

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Recent advances in fundamentals and applications of random fiber lasers

The plasmon-induced transparency (PIT), which is destructive interference between the superradiation mode and the subradiation mode, is studied in patterned graphene-based terahertz metasurface composed of graphene ribbons and graphene strips. As the results of finite-difference time-domain (FDTD) simulation and coupled-mode theory (CMT) fitting, the PIT can be dynamically modulated by the dual-mode. The left (right) transmission dip is mainly tailored by the gate voltage applied to graphene ribbons (stripes), respectively, meaning a dual-mode on-to-off modulator is realized. Surprisingly, an absorbance of 50% and slow-light property of 0.7 ps are also achieved, demonstrating the proposed PIT metasurface has important applications in absorption and slow-light. In addition, coupling effects between the graphene ribbons and the graphene strips in PIT metasurface with different structural parameters also are studied in detail. Thus, the proposed structure provides a new basis for the dual-mode on-to-off multi-function modulators.

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Dual-Mode On-to-Off Modulation of Plasmon-Induced Transparency and Coupling Effect in Patterned Graphene-Based Terahertz Metasurface.

A particular photonic crystal fiber (PCF) designed with all circle air holes is proposed. Its characteristics are studied by full-vector finite element method (FEM) with anisotropic perfectly matched layer (PML). The simulation results indicated that the proposed PCF can realize high birefringence (up to 10(-2)), high nonlinearity (50W(-1)·km(-1) and 68W(-1)·km(-1) in X and Y polarizations respectively) and low confinement loss (less than 10(-3)dB/km at 1.55um wavelength).

High birefringence photonic crystal fiber with high nonlinearity and low confinement loss.

A polarization splitter based on a new type of dual-core photonic crystal fiber (DC-PCF) is proposed The effects of geometrical parameters of the DC-PCF on performances of the polarization splitter are investigated by finite element method (FEM) The numerical results demonstrate that the polarization splitter possesses ultra-short length of 1191 μm and high extinction ratio of 1187 dB at the wavelength of 155 μm Moreover, an extinction ratio greater than 20 dB is achieved over a broad bandwidth of 249 nm, ie, from 1417 nm to 1666 nm, covering the S, C and L communication bands

Polarization splitter based on dual-core photonic crystal fiber.

Light trapping within waveguides is a key practice of modern optics, both scientifically and technologically Photonic crystal fibers traditionally rely on total internal reflection (index-guiding fibers) or a photonic bandgap (photonic-bandgap fibers) to achieve field confinement Here, we report the discovery of a new light trapping within fibers by the so-called Dirac point of photonic band structures Our analysis reveals that the Dirac point can establish suppression of radiation losses and consequently a novel guided mode for propagation in photonic crystal fibers What is known as the Dirac point is a conical singularity of a photonic band structure where wave motion obeys the famous Dirac equation We find the unexpected phenomenon of wave localization at this point beyond photonic bandgaps This guiding relies on the Dirac point rather than total internal reflection or photonic bandgaps, thus providing a sort of advancement in conceptual understanding over the traditional fiber guiding The result presented here demonstrates the discovery of a new type of photonic crystal fibers, with unique characteristics that could lead to new applications in fiber sensors and lasers The Dirac equation is a special symbol of relativistic quantum mechanics Because of the similarity between band structures of a solid and a photonic crystal, the discovery of the Dirac-point-induced wave trapping in photonic crystals could provide novel insights into many relativistic quantum effects of the transport phenomena of photons, phonons, and electrons

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Fiber guiding at the Dirac frequency beyond photonic bandgaps

An asymmetrical dual-core photonic crystal fiber (DC-PCF), which possesses all circular air holes, is proposed. By setting appropriate geometrical parameters, the wavelength-selective coupling property is realized, and a compact optical filter with a short length of 1.83 mm based on the DC-PCF is designed. The spectral transmission characteristics of the filter are investigated by the beam propagation method. The results demonstrate that the optical filter possesses a bandwidth of ~58 nm and small sidelobes. The proposed optical filter could be used in the integrated optical systems.

Dual-Core Photonic Crystal Fiber for Use in Fiber Filters

Optical cavities and waveguides are essential building blocks of many modern optical devices. They rely upon photonic bandgaps, or total internal reflections, to achieve field confinement. Here a new phenomenon is reported of wave localization that is attributable to neither of the above light guiding mechanisms. It is found that what is known as the Dirac point within a photonic band structure can play the role of a photonic bandgap with the establishment of field confinement. The new localized mode occurs at a Dirac frequency that is beyond any complete photonic bandgap, and exhibits a unique algebraic profile. The features of this new wave localization will add new capabilities and more flexibility to the design techniques of novel photonic components and photonic chip architectures.

Haiming Jiang

Papers

High birefringence photonic crystal fiber with high nonlinearity and low confinement loss.

Polarization splitter based on dual-core photonic crystal fiber.

Fiber guiding at the Dirac frequency beyond photonic bandgaps

Dual-Core Photonic Crystal Fiber for Use in Fiber Filters

Trapped photons at a Dirac point: a new horizon for photonic crystals