1,721,072 research outputs found
Floquet's design and circuit modelling of discontinuous planar waveguides at high frequencies
No full textWe present an accurate theoretical approach in view to design discontinuous optical waveguides at high frequencies. The model is based on the Floquet's theory and on the variational equivalent circuit. The distributed circuit model is developed through the use of the microwave network theory and the optical theory of the step discontinuities. This accurate approach considers dielectric periodic structures with high dielectric contrast and the transmission line model applied to guided modes of a discontinuous slab waveguide. The method is applicable to microwave and optical planar waveguides
Double grating design and modeling of second harmonic enhancement by radiation coupling in nonlinear optical waveguides
No full textWe analyze in this work the design and the modeling of periodical optical waveguides for second harmonic enhancement in χ(2) nonlinear process. We consider in our analysis the fundamental guided mode (λFU = 1.55 μm) and the second harmonic guided mode (λSH = 0.775 μm) as codirectional modes propagating in a symmetrical waveguide. In particular we analyze the second harmonic coupling efficiency in a GaAs/AlGaAs waveguide by studying the coupling effect of two gratings. The gratings consider the quasi phase matching condition between the fundamental and second harmonic modes, and, the coupling with the radiation modes generated by the diffraction effect. The combined effects of the gratings provide an efficient second harmonic field conversion. The numerical results are obtained through the time domain Hertzian potential modeling. A good agreement between numerical and analytical results is found
Artificial anisotropy in circular photonic crystals and applications
No full textIn this paper, we analyze the birefringence effect in circular photonic crystals (CphCs). The studied CphCs are dielectric rings (DRs) and photonic crystals with cylindrical air holes arranged in circular patterns. The dielectric concentric circular patterns admit two preferred propagation directions defined by an extraordinary and an ordinary refractive index, representing two electric field polarizations. These electric fields are diffracted inside the crystal or are localized in a central microcavity region. We prove the induced artificial anisotropy in DRs through the geometrical equivalence with the corresponding thin-film multilayer structure. The equivalence is obtained through the geometrical synthesis of the wavefront propagation inside the artificial anisotropic structure. As applications, we analyze a Si/SiO2 DR Bragg reflector and a GaAs CphC microcavity resonator. The Bragg theory is validated by numerical time-domain approaches that are well suited to solve scattering problems. The microcavity resonance analysis and the Q-factor evaluation are performed by the finite-element method modeling
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
An experimental setup for room temperature waveguide spectroscopy of self-assembled quantum dots
No full textIn this work we present the realization of an experimental setup to measure the absorption spectrum of low planar density active media in nanoscale devices. The experimental technique employs in-plane light transmission through a waveguide embedding the active medium. It has been applied to the investigation of the room temperature optical properties of low density self-assembled InGaAs/GaAs quantum dots (QDs), emitting around 1.3νm. A detailed analysis of the obtained spectra showed the occurrence of a Stokes shift which after inspection turned out to be related to the thermally activated carrier migration throughout the QD ensemble
Novel grating design approach by radiation modes coupling in nonlinear optical waveguides
No full textIn integrated optics the radiation modes represent a negative aspect regarding the propagation of guided modes. They characterize the losses of the substrate region but can contribute to enhance the guided modes by considering the coupling through properly designed gratings arranged at the core/substrate interface. By tailored gratings, the radiation modes become propagating modes and increase the guided power inside the waveguide guiding region. This enhancement is useful especially in low intensity processes such as second harmonic χ(2) conversion process. For this purpose, we analyze accurately the radiation modes contribution in a χ(2) GaAs/AlGaAs nonlinear waveguide where second harmonic signal is characterized by a low power intensity. This analysis considers a new design approach of multiple grating which enhances a fundamental guided mode at λFU =1.55 μm and a codirectional second harmonic guided mode at λSH =0.775 μm. In particular we analyze the second harmonic conversion efficiency by studying the coupling effect of three gratings. The combined effects of the gratings provide an efficient second harmonic field conversion. Design considerations, based on the coupled mode equations analysis, are theoretically discussed. A good agreement between analytical and numerical results is observed
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