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In this work an all-optical switch based on array of metal nanoparticles (MNP), imbedded in a medium which shows Electromagnetically Induced Transparency (EIT), has been proposed. By implementing EIT in the host medium of MNP plasmonic waveguide, we can induce a transparency and alter the refractive index, by applying reasonable values of optical pumps. Using Finite-Difference Time-Domain (FDTD) simulation, it is found that the proposed all-optical switching exhibits femtosecond-scale feedback time. Results show that the response time of signal light switching up and down are about 100 fs. The proposed switch has a signal transmission of about 14% for a chain of 20 silver MNPs with a length of about 3 μm. It shows losses about 7.75 dB/μm. The proposed nanoscale plasmonic switch has optical properties that cannot be achieved in any other ways at the nanometer scale, such as overcoming diffraction limit. [ABSTRACT FROM AUTHOR]

In this paper we present a full wave 3D-finite difference time domain (FDTD) optical and electrical simulation study of ultra thin silicon solar cell. We have analyzed the optical generation rate and absorption enhancement in thin film solar cell in which silver nanoparticles are embedded in the depletion region of p-n junction in the active layer of solar cell. Then we investigate efficiency and power output of solar cell by solving the Poisson and drift diffusion equations on a finite element mesh, by considering the extracted generation rate data from FDTD simulations. In this work localized surface plasmons (LSPs) are the key factor for absorption and electron-hole generation rate enhancement in thin film solar cell. We show that these enhancements result from dense near field provided by LSPs and ensuring that a large fraction of the incident optical power (which is considered to be AM1.5) dissipates in the absorbing active layer rather than in the MNPs. We study in detail the effect of metal nanoparticle (MNP) geometry in solar cell performance and optimize geometrical parameters of MNPs through particle swarm (PS) optimization algorithm. The optimized structure of spherical MNPs with a diameter of 70 nm and spacing of 180 nm, and optimized structure of nanorod MNPs with a diameter of 70 nm and center to center spacing of 190 nm and length of 150 nm which are imbedded in depletion layer, provided 32.83% and 39% improvements in the efficiency relative to the reference cell, respectively. [ABSTRACT FROM AUTHOR]

In this paper, we present modal analysis for plasmonics structures exhibiting light confinement in sub wavelength scale, with comparison between different mathematical models for complex dielectric constant of noble metals and finally introduce the best model that compatible with experimental results. For evaluation of this idea, we focus on different parameters such as dispersion relation, frequency dependence propagation and field penetration. All mathematical models such as Drude model, free electron gas model (FEG from Drude model without losses), Lorentz–Drude model (LD) and Brendel–Bormann model (BB) compared with complete numerical analysis based on experimental measurement from Johnson–Christy data (JC) and other reported practical data that appeared in Palik handbook. We illustrate that BB model have good agreement with experimental data and is reliable for Near Infrared, Visible and Near Ultra Violet region of electromagnetic spectra and hence, BB model for modal analysis of layered plasmonics heterostructure and complex plasmonics structures can be used. [ABSTRACT FROM AUTHOR]

Array of micro ring resonators based optical photodetectors is introduced and evaluated in this paper to operate in optical communication windows for broad band situation. In this work, we introduced an array of resonators to engineer the transfer function of the detector for broad band operation as well as very sharp edges. The electron and photon transport in the proposed structure is modeled based on rate equation and then transient and steady state behavior are extracted. Finally nonlinear operation added to the model and its effect on spectral behavior as well as transient operation is investigated. [ABSTRACT FROM AUTHOR]

In this paper we demonstrate an all-fiber dual wavelength ring laser by using chirp fiber Bragg grating (CFBG). A dual wavelength centered at 1500 nm and 1550 nm was operated simultaneously in one beam. Pulse widths are measured at 258 fs and 253 fs, and output power is −19 dBm. In order to generate width spectrum for dual wavelength femtosecond laser, we use extra cavity. Fiber Bragg grating is phase matching and can make passive mode locking. This laser is tunable and stable, and the loss is very low due to its all-fiber structure. To the best of our knowledge this is first dual-wavelength femtosecond fiber ring laser that uses CFBG. [ABSTRACT FROM AUTHOR]

In this paper, a photodetector based on InGaAs micro-ring resonator array with 5µm radius, in telecommunication wavelength region has been investigated. Then for the first time to our knowledge, with the change of refractive index due to optical nonlinear effects (such as: Kerr effect, two photon absorption, free carrier dispersion and free carrier absorption), an all-optical switch, based on pump-probe configuration using this photodetector have been proposed. So, the suggested device, will introduce a dual functionality that is important from view point of economically purposes and in term of integration. By numerically solving the light propagation equations, with FDTD and Crank-Nicolson methods, in addition to steady state and transient response, also we have found the frequency response, in both configurations. With increasing reverse bias voltage, and optimizing the free carrier transportation from absorption region, switching frequency can be increased up to 200GHz. Also by optimal choosing of parameters such as the number of rings and spaces between two adjacent rings and so on, the box-like spectral response of photodetector with high efficiency is achievable. [ABSTRACT FROM AUTHOR]

Abstract: Shift of resonance frequency in microsphere optical resonator due to attachment of a desirable particle is obtained. Our 3-D finite element numerical method (FEM) simulations’ results show the path of light through microsphere and its variation due to attachment of particle. It is apparent that after attachment of particle to microsphere's surface, light is inclined to pass through the particle. Subsequently, the path of light becomes longer than previous. Because of this phenomenon, the resonance wavelength shifts to longer wavelengths. It is shown that microsphere optical resonator is a prominent biosensor for single virus detection since we applied characteristics of virus for particle in our simulations. Response of this biosensor depends on the characteristics of particle like its radius as we show in this article. Transmission spectrum of fiber which reveals a selected resonance frequency, have been studied in the frequency range of 106.3 to 107THz under three different sizes of particles. The results show that the amount of frequency shift rises by enhancement of particle's size. [Copyright &y& Elsevier]

Abstract: In this paper, we investigate the optical bistability induced by optical nonlinearity in a compact parallel array of micro-ring resonators with radius of 5μm. Due to the nature of perfect light confinement in this structure, resonance and accumulation process in a ring resonator and optical nonlinear effects, are observable even at small optical power (a few milliwatts). Different optical applications such as all-optical switching, optical memory devices, logic gates and modulators are possible, due to optical bistability in a ring resonator. Using alternative semiconductor compounds, instead of silicon that have weak nonlinear optical properties, we improve the performance of ring-resonator based devices. Here we use a polymer cladding layer with negative thermo-optic coefficient. Using this structure we can eliminate the temperature created nonlinearity which is a very slow process. Therefore, the switching speed increases from a few MHz to several tens of GHz. By plotting the transfer function of the resonator, a hysteresis loop is observed in a few milliwatts. Although, using a ring resonator array the bandwidth reduces, however, the width of the hysteresis loop and resolution between both steady state increases. [Copyright &y& Elsevier]

A new concept for tuning direction of radiation in nano-antenna with negative and positive polarizability is introduced and evaluated by numerical simulation. It has shown that such a configuration consisted of an array of nanoparticles can tune the direction of radiation pattern successfully. Increasing the number of nanoparticles exhibits more directivity at special direction. Variation in position of nanoparticles is used to tune the angle of maximum radiation. The maximum tunability for special geometry of three particles is about 40°. Angle of maximum radiation pattern for four particles is shifted from interval 150–180° to 0–30°. [ABSTRACT FROM AUTHOR]