To overcome the crosstalk happening between two degenerately fundamental modes of a fiber in Terahertz (THz) regime, a novel photonic crystal fiber (PCF) that yields a wide range of single-polarization-single-mode (SPSM) propagation with large loss differences (LDs) is designed. The method used to realize this SPSM PCF is to deposit an epsilon-near-zero (ENZ) material in four selected air holes in the cladding, which ends up with four ENZ rings. These ENZ rings introduce significant LDs between the wanted (X-polarized) and unwanted (Y-polarized and high order) modes. Extensive simulation results demonstrate that the LDs between the wanted and unwanted modes vary with the thickness of ENZ rings. With a very short length (4 cm) of the proposed PCF, pure SPSM propagation, i.e., the unwanted modes are 20 dB lower than the wanted mode, can be achieved from 1 to 1.2 THz.
Due to their negative permittivity, plasmonic materials have found increasing number of applications in advanced photonic devices and metamaterials, ranging from visible wavelength through microwave spectrum. In terms of intrinsic loss and permittivity dispersion, however, limitations on available plasmonic materials remain a serious bottleneck preventing practical applications of a few novel nano-photonic device and metamaterial concepts in visible and nearinfrared spectra. To overcome this obstacle, efforts have been made and reported in literature to engineer new plasmonic materials exploring metal alloys, superconductors, graphene, and heavily doped oxide semiconductors. Though promising progress in heavily doped oxide semiconductors was shown in the near-infrared spectrum, there is still no clear path to engineer new plasmonic materials in the visible spectrum that can outperform existing choices noble metals, e.g. gold and silver, due to extremely high free electron density required for high frequency plasma response. This study demonstrates a path to engineer new plasmonic materials in the visible spectrum by significantly altering the electronic properties in existing noble metals through high density charging/discharging and its associated strong local bias effects. A density functional theory model revealed that the optical properties of thin gold films (up to 7 nm thick) can be altered significantly in the visible, in terms of both plasma frequency (up to 12%) and optical permittivity (more than 50%). These corresponding effects were observed in our experiments on surface plasmon resonance of a gold film electrically charged via a high density double layer capacitor induced by a chemically non-reacting electrolyte.
We are exploring the degree to which one can control the spectral emission of heated photonic crystals (or, more
generally, electromagnetic crystal) structures in the THz frequency range. Because THz frequencies are well below the
room temperature thermal emission maximum, this configuration may realize a low power but extremely low cost
incoherent broadband THz source. Electromagnetic crystals are structures whose periodicity either enhances or reduces
the associated photonic density of states over some frequency range. Consequently, they either enhance or reduce its
thermal emission over the same frequency range. Thermal radiation from electromagnetic crystals has been studied
theoretically and experimentally for higher frequency ranges, but usually for infinite lattices. We have experimentally
and theoretically investigated a simple 1D, bi-layered electromagnetic crystal structure composed of air and silicon slabs.
We have calculated the emissivity using Kirchhoff's thermal radiation law, as well as by calculating the density of states
directly, and have compared successfully those results to the experimental values. Our ultimate goal is to be able to
control the spectral emission of an electromagnetic crystal in the THz region (or other wavelength ranges, such as the
infrared) by engineering its band structure. Controlled thermal emission, i.e., thermal management, could be used for
applications as diverse as solar energy convertors, thermoelectric devices, and integrated circuits.
We propose a novel multidimensional dynamical model for description of the coherent interactions of ultrashort high-intensity optical pulses with the resonant nonlinearities in planar optical waveguides and semiconductor microresonators. The model is based on the self-consistent solution of the full-wave vectorial Maxwell’s equations
coupled via polarization source terms to the evolution equations of a discrete multilevel quantum system. The latter are derived employing a group-theoretical approach exploiting symmetric properties of the system Hamiltonian. In particular, the resonant nonlinearity is modelled by a degenerate three-level system of saturable absorbers in order to account for the two-dimensional medium polarization. The resulting Maxwell-pseudospin equations are solved in the time domain using the finite-difference time-domain (FDTD) method. The model
is applied for studying conditions of onset of self-induced transparency (SIT) lossless regime of propagation. Numerical evidence of multidimensional solitons localized both in space and in time is given for the planar optical waveguides. Pattern formation and cavity SIT-soliton formation are demonstrated for the special case of a
passive semiconductor microcavity filled with saturable absorbers.
KEYWORDS: Systems modeling, Data modeling, Data storage, Thermal modeling, Electromagnetism, Finite-difference time-domain method, Optical storage, Polarization, Radio propagation, Numerical modeling
A hybrid finite-difference-time-domain/angular spectrum propagation modeling technique and a finite-difference thermal model are used to study near-field optical and two- photon absorption data storage systems. The electromagnetic model is used to analyze scattering effects in structures where scalar-based theory is not appropriate. The thermal model is used in a near-field magneto optic data storage system to calculate data mark sizes.
A 2D finite difference time domain (FDTD) approach to modeling the push-pull tracking error signals in a rewritable optical drive is presented. The predictions of the model are experimentally confirmed.
Substrate and waveguide cross talk models are presented for CMOS smart detectors arrays. A test chip of linear arrays using both p+n and n+p detectors has been designed and fabricated for characterization of substrate and waveguide cross talk. It is shown that both the substrate and waveguide models agree well with the measured cross talk. Techniques for reducing cross talk in CMOS detector arrays are also presented.
1407_41Several exact, nonseparable, space-time solutions of the scalar wave and Maxwell's equations have been found recently. These localized wave (LW) solutions contain very broad-bandwidth components and can be optimized to exhibit enhanced localization properties. Moreover, by driving an array with these LW solutions, one can generate beams that also exhibit these LW characteristics. A new type of array is required to try to realize these localized wave effects -- one that has independently addressable elements. The enhanced localization effects are intimately coupled to the proper spatial distribution of broad-bandwidth signals driving the array; i.e., by shading not only the amplitudes, but also the frequency spectra of the pulses driving the array. A LW pulse-driven array generates a moving localized, interference pattern, i.e., a set of pulses whose shapes are reconstituted as they propagate by the frequency components arriving at different times from the various aperture sources. Analytical bounds on the characteristics of beams generated by an arbitrary pulse-driven array have been derived and are supported by numerical and experimental values. These bounds extend the meaning of near-field distances or diffraction lengths to the situation where the array driving functions can be broad-bandwidth signals. It has been demonstrated theoretically and experimentally that an acoustic array driven with a designed set of localized wave (LW) solutions of the scalar wave equation generates a robust, well-behaved, transient pencil-beam of ultrasound in water that outperforms the beams generated by related continuous wave excitations of the same array. Numerical models predict similar results for an electromagnetic LW pulse-driven array.
1407_42Localized scalar and electromagnetic wave solutions in a variety of complex environments will be reviewed. Like their free-space counterparts, these acoustic and electromagnetic localized wave (LW) solutions can be optimized so that they are localized near the direction of propagation and their original amplitude is recovered out to extremely large distances from their initial location. Pulses with these very desirable localized transmission characteristics may have a number of potential applications in the areas of directed energy transmission, secure communications, and remote sensing.
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