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Material point method for simulating nonequilibrium thermal transport in metals irradiated by ultrafast laser

Yong Gan, Chunxia Lei, and Zheng Sun

Doc ID: 304684 Received 11 Aug 2017; Accepted 21 Sep 2017; Posted 21 Sep 2017  View: PDF

Abstract: A material point method (MPM) for the analysis of the two-step heating of the metals subjected to ultrafast laser irradiation is developed based on the weak formulation of the two-temperature model (TTM). The electron and lattice subsystems in the metallic targets are both represented by a finite number of Lagrangian material points to discretize the TTM equations, while a background Eulerian grid mesh is used to solve the spatially discrete TTM equations for the electron and lattice temperatures carried by the material points. The validity, convergence and robustness of the proposed MPM method are demonstrated using the representative examples for femto-/picosecond laser heating of a gold thin film. In addition to avoiding the numerical difficulties due to the mesh distortion and entanglement in the mesh-based method, the presented MPM algorithm can also automatically handle the adiabatic boundary condition without requiring additional boundary treatments, showing its advantage over the mesh-based methods for modeling the energy transfer in metals irradiated by ultrafast laser.

Achromatic critically-coupled racetrack resonators

Clément ARLOTTI, Olivier Gauthier-Lafaye, Antoine Monmayrant, and Stephane Calvez

Doc ID: 300904 Received 26 Jun 2017; Accepted 20 Sep 2017; Posted 21 Sep 2017  View: PDF

Abstract: In this paper, we investigate the spectral response of whispering-gallery-mode (WGM) resonators coupled to their access waveguide with a view to design their constitutive waveguides to promote critical-coupling over a wide spectral range and thereby facilitate their use for high-sensitivity sensing or nonlinear frequency conversion applications. The carried-out theoretical analysis is based on the universal response functions of singlemode and unidirectional devices. A coupled-mode treatment of the coupling region enables to derive two sets of favorable designs. The identified resonator/access waveguide systems exploit waveguides with mismatched propagation constants forming a coupling section exhibiting either an achromatic beat-length or an achromatic power-transfer coefficient. This generic model is followed by a numerical case study of vertically-coupled Si3N4 racetrack resonators. The conventional (quasi-)phase-matched configuration, treated as a reference case, is shown to display a critical-coupling bandwidth of nm at a wavelength of 1550nm, whereas the proposed new designs demonstrate critical bandwidths larger than 330nm, i.e. exhibit bandwidths enhanced by more than one order of magnitude.

Intensity correlation in frequency up-conversion via four-wave mixing in Rb vapor

Yong Sup Ihn, Kwang-Kyoon Park, Yosep Kim, Young-Tak Chough, and Yoon-Ho Kim

Doc ID: 302863 Received 19 Jul 2017; Accepted 19 Sep 2017; Posted 21 Sep 2017  View: PDF

Abstract: We report a study on the transfer of intensity correlation properties in frequency up-conversion via four-wave mixing (FWM) in Rb vapor. The $5S_{1/2} - 5P_{3/2} - 5D_{5/2}$ two-photon transition in $^{85}$Rb leads to collimated blue light (CBL) generation at 420 nm by absorbing two input photons of wavelengths 780 nm and 776 nm. The $g^{(2)}(\tau)$ intensity correlation measurement of the CBL field reveals that the intensity correlations of the input fields are transferred to the CBL field due to strong atomic coherence in the FWM loop. We also demonstrate that the measured values of $g^{(2)}(\tau)$ of the CBL field are reduced by the effect of Doppler broadening of Rb vapor.

Coherent field-controlled rectification and directional emission in one-dimension waveguide

Yong-Yie Li, Long-Zhao Lu, and Xiang-Yang Yu

Doc ID: 301849 Received 06 Jul 2017; Accepted 18 Sep 2017; Posted 18 Sep 2017  View: PDF

Abstract: Derived from the time-dependent Schrödinger equation, we study the single-photon pulse (SPP) propagation through a pair of V-type three-level atoms coupled to one-dimensional (1D) waveguide. Our results demonstrate that the rectification and the directional emission can be achieved and controlled by the phase difference between two external fields in the system under the proper condition. Furthermore, we investigate the impact of Rabi frequency, interatomic distance, the detuning between the SPP and the atoms and the SPP bandwidth on the rectification and the directional emission. We treat the system as a quantum interferometer to explain the rectification and the directional emission. The system has a potential application to be the basis of all-optical devices, such as a diode, isolator, modulator, emitter for the quantum information.

Goos-Hänchen shifts in an epsilon-near-zero slab

Jisen Wen, Junxiang Zhang, Li Wang, and Shiyao Zhu

Doc ID: 302927 Received 21 Jul 2017; Accepted 15 Sep 2017; Posted 18 Sep 2017  View: PDF

Abstract: In this work, we theoretically study the Goos-Hänchen effect of the reflected and transmitted light in an epsilon-near-zero (ENZ) slab. For a lossless ENZ slab, it is found that the Goos-Hänchen shifts are great enhanced near resonances for both TE- and TM-polarized beams, which is approximately inverse to the sufficiently small (but finite) value of permittivity. In a lossy ENZ slab, the reflected and transmitted GH shifts are different near resonances, and there are large negative GH shifts for reflected beam and large positive shifts in transmitted beam, and the detailed properties are discussed. There is similar behavior near Brewster angle for TM-polarized light in both the lossy and lossless ENZ slabs. Compared with the results in the semi-infinite ENZ structure, our results may provide the richer controlling on the GH shifts in ENZ slabs and to design the ENZ-based optical devices.

Spectral filtering effect on mode-locking regimes transition: similariton-dissipative soliton fiber laser

Zhiqiang Wang, Li Zhan, xiao fang, and Hao Luo

Doc ID: 297576 Received 08 Jun 2017; Accepted 15 Sep 2017; Posted 18 Sep 2017  View: PDF

Abstract: We show numerically and experimentally the transition between two distinct mode-locking regimes via spectral filtering of frequency-chirped pulses in passively mode-locked net-normal dispersion fiber lasers (NDFLs), resulting in the realization of similariton-dissipative soliton fiber lasers. Two operating modes, amplifier similaritons (ASs) and dissipative solitons (DSs), can switch to each other through solely altering the filter bandwidth in the laser oscillator. The laser favors ASs operation for small filter bandwidth and it jumps to DSs operation along with increasing the filter bandwidth. A narrow filter narrows both in the time and in frequency domain due to the large chirp pulse and when the pulse re-enters in the gain fiber, it can evolve into an attractive similaritons in a definite gain fiber. For a broadband filter, the weak filtering effect indirectly enhanced the self-phase modulation in the laser oscillator, so as to force the laser working in regimes of DSs. Contrary to the previous reports on pulse shaping in NDFLs based on the shape of spectral filters or filter-induced dispersion change, to the best of our knowledge, it is the first time to definitely put forward that the adjustable-bandwidth filter can be implemented as the key element for realizing switchable AS-DS fiber lasers.

Transmission characteristic of subpicosecond Airy pulses in silicon-on-insulator waveguides

Run Chen, Weiguo Jia, Wang Xuying, and Lu Jiaqi

Doc ID: 297853 Received 16 Jun 2017; Accepted 13 Sep 2017; Posted 14 Sep 2017  View: PDF

Abstract: In this study, we numerically simulated the propagation evolution of a subpicosecond Airy pulse in silicon-on-insulate waveguides. The Airy pulse is compressed after a propagation distance; a new Airy pulse is simultaneously split from the leading edge of the initial Airy pulse. This new Airy pulse is also compressed after a transmission length, and its propagation image is inversely distributed with that of the initial Airy pulse. Our numerical analysis showed that the truncation coefficient, pulse width, initial pulse power, and third-order dispersion coefficient have significant impact on the transmission characteristics of Airy pulses under two-photon absorption and free-carrier effect.

Large time-asymmetric quantum fluctuations in amplitude-intensity correlation measurements of a V-type three-level atom resonance fluorescence

Luis Gutierrez, Hector M. Castro-Beltran, Ricardo Roman, and Levente Horvath

Doc ID: 306298 Received 01 Sep 2017; Accepted 13 Sep 2017; Posted 14 Sep 2017  View: PDF

Abstract: In this paper we show theoretically that the fields scattered by a bichromatically driven V-type three-level atom exhibit large and asymmetric amplitude-intensity correlations. These features result from the different fluctuations of the amplitude and intensity field operators and the competition among transitions. The amplitude-intensity correlations of resonance fluorescence, with its large third-order fluctuations, describe phase-dependent nonclassical features of the emitted field in addition to the second-order measure related to squeezing. We also calculate spectra and variances of these correlations, and intensity-intensity correlations, that provide a wealth of supporting information.

Shaping the spectrum of a down-converted mid-infrared frequency comb

Giulio Campo, Anat Leshem, Francesco Cappelli, Iacopo Galli, Pablo Cancio Pastor, Ady Arie, Paolo De Natale, and Davide Mazzotti

Doc ID: 301386 Received 29 Jun 2017; Accepted 11 Sep 2017; Posted 12 Sep 2017  View: PDF

Abstract: New methods to frequency down-convert a broadband near infrared frequency comb into the mid infrared by three-wave mixing are studied. Modulation of the second-order nonlinear coefficient based on the concepts of either nonlinear spectral holography or quasi-periodic modulation enables to obtain different spectral shapes of the mid infrared comb. It includes flat and broadband single-band or dual-band spectra, or a shape that exhibits two or even three sharp peaks at chosen frequencies. The methods we present can be used to tailor the frequency comb spectra to selected molecular absorption lines in the mid infrared.

Application of polarimetric technique for determining the sign of quadratic electro-optic coefficients in crystals

Marek Izdebski, Rafał Ledzion, and Włodzimierz Kucharczyk

Doc ID: 302386 Received 19 Jul 2017; Accepted 09 Sep 2017; Posted 12 Sep 2017  View: PDF

Abstract: So-called polarimetric methods are based on the measurements of the intensity of light emerging from a modulator composed of a "sandwich" of investigated crystal placed between polarizer and analyzer. The polarimetric technique is known for its high accuracy in determining absolute values of electro-optic coefficients, however, the method is considered unable to find their signs. In this paper we propose an examination of changes in the modulated signal phase that result from a controlled shift through the transmission characteristic of the modulator. We show that the analysis of the changes allows to obtain the sign of the coefficients. The sensitivity of the method is examined in measurements of quadratic electro-optic coefficients. It is found that the technique may be easily applied for crystals for which relatively low values of the coefficients, i.e. of the order of magnitude 10^{-20} m^2/V^2 are observed. Configurations where the light beam is sent along the optical axis and perpendicularly to the axis in an uniaxial crystal are considered. Examples of measurements of the quadratic electro-optic coefficients g_{1111} - g_{1122} in KDP and n_e^3 g_{3333} - n_o^3 g_{1133} in DKDP are presented.

Efficient simulation of multimodal nonlinear propagation in step-index fibers

Jesper Laegsgaard

Doc ID: 300785 Received 22 Jun 2017; Accepted 06 Sep 2017; Posted 07 Sep 2017  View: PDF

Abstract: A numerical approach to nonlinear propagation in waveguides based on real-space gaussian-quadrature integration of the nonlinear polarization during propagation is investigated and compared to the more conventional approach based on expressing the nonlinear polarization by a sum of mode overlap integrals. Using the step-index fiber geometry as an example, it is shown that the gaussian-quadrature approach scales linearly or at most quadratically with the number of guided modes, and that it can account formode profile dispersion without additional computational overhead. Theseproperties makes it superior for multimode nonlinear simulations extending over wide frequency ranges.

Measurement of nonlinear refractive indices of air, O₂ and N₂ in capillary by changing the temporal width of short laser pulses

Tiago Souza, Emerson Barbano, Sergio Zilio, and Lino Misoguti

Doc ID: 298021 Received 14 Jun 2017; Accepted 04 Sep 2017; Posted 07 Sep 2017  View: PDF

Abstract: Nonlinear refractive indices of air and its constituents were measured as a function of the pulse width in a capillary used to confine the gas and to increase the interaction length. This study was carried out with nonlinear ellipse rotation measurements using an amplified Ti:sapphire laser system providing pulses at 800 nm, continuously tunable from ~60 fs up to ~3 ps. Due to the presence of non-instantaneous orientational response, nonlinearities in molecular gases strongly depend on the pulse width. The pulse width dependence and discrimination between instantaneous and non-instantaneous nonlinearities of air gases were obtained with a simple exponential growth model.

Characterization of frequency stability in EIT-based atomic clocks using a differential detection scheme

Melissa Guidry, Elena Kuchina, Irina Novikova, and Eugeniy Mikhailov

Doc ID: 301664 Received 06 Jul 2017; Accepted 04 Sep 2017; Posted 07 Sep 2017  View: PDF

Abstract: We investigate a recently proposed scheme for differential detection of the magneto-opticalrotation effect and its application to electromagnetically induced transparency (EIT) atomic clocks~\cite{SihongGu2015}. This scheme utilizes a linearly polarized bichromatic laser field that is EIT-resonant withalkali atoms. The results of our study reveal that the suppression of the laser noisecan substantially improve the signal-to-noise ratio in EITatomic clocks. Our preliminary results demonstrate an order of magnitude improvement in clock stabilityunder some conditions when incorporating the differential detection scheme.

Finding nanostructures that reproduce colors with adaptive mesh search techniques

Emma Vargo

Doc ID: 300839 Received 26 Jun 2017; Accepted 03 Sep 2017; Posted 06 Sep 2017  View: PDF

Abstract: This paper presents a computational adaptive mesh refinement technique for designing photonic nanostructures with a specific perceived color. This inverse design method can be used for any color-based application of photonic structures, including pigment-free paints, anti-counterfeiting materials, and reflective displays. The adaptive mesh refinement technique is very efficient and results are returned within seconds or minutes on a laptop computer, eliminating the need for cluster computing. This search method can be used for any well-characterized photonic structure, and can even be adapted to accommodate fabrication constraints. In this work, the adaptive mesh search is applied to 1D, 2D, and 3D photonic structures, and the resulting designs are satisfactory matches with the desired colors.

Ultrafast and low power plasmon-solitons switching based on two dimensional MoS2 nanostructure

Abbas Zarifkar and Saeed Farazi

Doc ID: 302970 Received 21 Jul 2017; Accepted 02 Sep 2017; Posted 07 Sep 2017  View: PDF

Abstract: The nonlinear propagation in a plasmonic nanostructure composed of two closely MoS2 sheets is investigated numerically using perturbation expansion of Maxwell equations. Because of the extraordinary nonlinear properties of mono-layer MoS2, in particular significant Kerr effect, the production and propagation of dissipative plasmon-solitons in such nanostructure is demonstrated. Considering the linear and nonlinear operation regimes, it is shown that by increasing the input light intensity, which leads to the appearance of the nonlinear correction terms in the MoS2 conductivity, the symmetry of such coupler is breaking and due to the change of the power coupling rate between two sheets, this nanostructure can operate as an all optical nanoswitch. Compact dimensions and high nonlinearity of the proposed nanoswitch can provide us an ultrahigh speed and low power switching operation.

Single-pulse interference caused by temporal reflection at moving refractive-index boundaries

Brent Plansinis, Govind Agrawal, and William Donaldson

Doc ID: 296906 Received 08 Jun 2017; Accepted 01 Sep 2017; Posted 07 Sep 2017  View: PDF

Abstract: We show numerically and analytically that temporal reflections from a moving refractive-index boundary act as an analog of Lloyd’s mirror, allowing a single pulse to produce interference fringes in time as it propagates inside a dispersive medium. This interference can be viewed as the pulse interfering with a virtual pulse that is identical to the first except for a π-phase shift. Furthermore, if a second moving refractive-index boundary is added to create the analog of an optical waveguide, a single pulse can be self-imaged or made to produce two or more pulses by adjusting the propagation length in a processsimilar to the Talbot effect.

XPM induced modulation instability in negative index metamaterial with saturable nonlinear response

Akhilesh Mishra and Ajit Kumar

Doc ID: 293150 Received 20 Apr 2017; Accepted 30 Aug 2017; Posted 31 Aug 2017  View: PDF

Abstract: The influence of nonlinear dispersion (originating from the dispersive permeability as well as from the nonlinear polarization) on cross-phase modulation (XPM) induced modulational instability (MI) in negative index domain of metamaterials (MMs) with saturable nonlinearity is investigated numerically. The study explores various possible regimes of normal and anomalous group velocity dispersion and their combinations which the two co-propagating waves could experience in negative refractive index domain of a metamaterial (MM). It has been shown that, under certain conditions, the first-order nonlinear dispersion, i.e., self-steepening (SS) and the second order nonlinear dispersion (SOND) may lead to a considerable change in the MI gain spectrum. In addition, it is shown that, at higher perturbation frequencies, the self-steepening effect causes considerable structural changes in the MI gain spectrum. © 2015 Optical Society of America

Efficient Finite-Element Formulation for Analysis of Whispering-Gallery-Mode Optical Resonators

Razi Dehghannasiri, Mohammad Soltani, and Ali Adibi

Doc ID: 298178 Received 16 Jun 2017; Accepted 30 Aug 2017; Posted 07 Sep 2017  View: PDF

Abstract: This paper presents a new formulation for fast and accurate three-dimensional vectorial analysis of dielectric whispering-gallery-mode (WGM) resonators using the finite element method (FEM). This method relies on two properties of the WGM resonators: 1) the axial symmetry to reduce the number of coordinate variables from three to two; and 2) the use of the divergence equation for the magnetic field and its axial symmetry to express the azimuthal magnetic component of the field in terms of its transverse components. As a result, for our FEM analysis, only the transverse part of the magnetic Helmholtz equation is required, which is composed of two field variables and two coordinate variables. The method can use scalar elements without generating any spurious modes and without the need for a penalty function. This can substantially reduce the computational time and complexity. After verifying this FEM formulation through comparing the simulation results with the known analytical solutions for a few special resonators, a variety of WGM resonators in the silicon photonic platform are analyzed in terms of key parameters needed for designing integrated photonic structures.

Design of Polarization Converter Based on PCF with Anisotropic Lattice Core Consisting of Circular Holes

Zhang Zejun, Yasuhide Tsuji, Masashi Eguchi, and Chunping Chen

Doc ID: 300944 Received 26 Jun 2017; Accepted 30 Aug 2017; Posted 07 Sep 2017  View: PDF

Abstract: In this paper, we propose a novel polarization converter (PC) based on a photonic crystal fiber (PCF) with an anisotropic square lattice core consisting of circular air holes. Utilizing the core symmetry oriented at a 45 degree to the principal axes, an incident polarized light beam can be completely rotated 90°. Simulation results by using a vectorial finite element beam propagation method show that the polarization conversion is achieved at a device length of 119 μm. Additionally, an improved PC element that can provide a high-consistent Gaussian-like mode distribution to decrease the splice loss with conventional fibers has also been studied. The polarization conversion efficiency is better than 99% and the corresponding extinction ratio is better than -20dB over a wavelength range of 310 nm.

Anisotropically modulated transparency andabsorption in hybrid waveguide-metallic nanowiresystem

chen xue

Doc ID: 297517 Received 08 Jun 2017; Accepted 28 Aug 2017; Posted 31 Aug 2017  View: PDF

Abstract: We have numerically studied the coupling behaviors between the plasmonic mode inmetallic nanowire and the anisotropic waveguide mode in a hybrid anisotropicwaveguide-plasmon system. It is found that the coupling strength between plasmonicmode and waveguide mode is closely related to the orientation of optical axis in theanisotropic waveguide. By varying the orientation of optical axis, two distinctelectromagnetic coupling phenomena are found. The plasmon induced transparencyand absorption phenomena can be observed by changing the optical axis in thevertical plane. In contrast, these phenomena will disappear as the optical axis is variedin the interface plane. The findings hold promise in applications such as filters,sensors and active tuning plasmonic devices.

Persistent currents of superfluidic light in 4-level coherent atomic medium

Nuno Silva, Ariel Guerreiro, and J. Mendonca

Doc ID: 297580 Received 08 Jun 2017; Accepted 27 Aug 2017; Posted 31 Aug 2017  View: PDF

Abstract: In this work we investigate the superfluidic properties of light propagating on a 4-level coherent atomic medium. The model is derived under the paraxial approximation in the form of a Generalized Nonlinear Schrodinger equation and features spatially controllable and quantum-enhanced optical properties, which can offer new possibilities on the field of optical analogues systems. In particular, we use this versatility to study the dynamics of an optical vortex beam confined in a non-trivial connected geometry, finding numerical evidences of another superfluidic signature analogue: the persistent current of light.

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