The present work deals with the implementation of algorithms based on the techniques of optimization by ant colony (ACO) and Scatter Search (SS) together with the Finite Element method (MEF) for modeling and optimization of Tapers between a continuous 2D waveguide (CWG) and a periodically segmented 2D waveguide (PSW). The issue to be solved fits into combinatorial optimization problems, where in front of a large number of available subsets, it is possible to select the sets that produce the best coupling efficiencies. The proposed metaheuristics create new possibilities for optimizing and designing a variety of photonic devices for information processing.
We proposed a broadband absorber based in rectangular metallic and dielectric grating. The geometric parameters of the proposed structure were optimized to exhibits strong absorption (above 90% for incidence normal) with polarization-independent in the visible spectrum (400-700nm). The proposed structure has demonstrated wide-angle absorption of above 80% for angles of incidence of up to 60° for TM mode and up to 40° for TE mode. The high absorption does not change when we vary other geometric parameters of the structure to analyze the fabrication tolerance.
Asymmetrical absorption plays an important role in applications such as photovoltaics, detectors, modulators and emitters. In this work, we introduce and numerically analyze a broadband device capable of realizing asymmetrical optical absorption depending on the direction of propagation of light. The proposed asymmetrical absorber is designed and optimized by a parametric search based on genetic algorithm.
In this article, we analyze the propagation response of Fibonacci based hypercrystals composed by metallic dielectric multilayered metamaterials. The estructure can be engineered to behave as mirrors or stop band filters and absorbers for visible and infrared radiation. The propagation properties of the proposed hypercrystal can be easily tunned and drastically changed by adjusting their geometrical and optical parameters.
Plasmonic groove structures, which are widely known for its absorbent properties of light, are numerically investigated. Genetic algorithms have been successfully used to aid in the design of two-dimensional high efficiency wide-angle plasmonic groove absorbers for visible wavelengths. The novel periodic groove structure exhibits absorption above 90% for ultra-broadband wavelengths ranging from 300 to 700nm. The resonant modes induce localized zero wavevector plasmon polaritons in the metallic material which favors absorption and may also enhance non-linear optical processes.
We show that a planar metal-dielectric-metal structure has a resonant characteristic that can be used to filter specific colors of the visible spectrum depending of the choice of the material used in the dielectric layer. The resonance occurs when the reflection phase is canceled out with the phase of the propagation. We numerically demonstrate a structure that can be used as an RGB optical filter with three different dielectric materials, with transmission of above 60%. The planar structure exhibits wide-angle transmission for angles of incidence up to 50° for the red and blue colors and up to 30° for the green color.
A multipeak Metasurfaces are the two dimensional equivalents of bulk metamaterials [1, 2], which represent a
sudden variation of optical properties when an incident wave interacts with it, yielding the most exotic optical
phenomena, such as broadband absorption, wavefront shaping or the anomalous refraction and reflection. This paper
proposes, through simulations, a model of a purely dielectric metasurface without losses, allowing the incident
wave’s global phase control, from - π to π, for operation on optical frequencies (1.55 μm) by inserting structures that
have contrasting refractive indexes. To demonstrate the phase control, a linear phase profile has been utilized to
cause the anomalous refraction phenomena, which has applications in wireless optical communications.
Efficient directional couplers composed by parallel dielectric and metallic waveguides have been analyzed in details.
The results show that an efficient power conversion of optical dielectric modes to long range plasmonic ones is
possible in such devices. Low insertion losses in conjunction with short coupling length as well as a broadband
operation can be obtained under certain conditions. This kind of couplers has potential applications for the design of
photonic integrated circuits and for signal routing between dielectric and plasmonic waveguides.
We propose a design for light coupling optimization between an optical fiber and a sub-micrometer waveguide using a subwavelength segmented waveguide taper with subwavelength periodicity. The power coupling and light coupling of the output waveguide are calculated, optimized and compared with other designs and values found in the literature. The optimized tapers has been successfully and efficient designed using evolutionary algorithms based on artificial immune system (AIS), the genetic algorithm (GA) and ant colony optimization (ACO). Power coupling above 75 % have been obtained with the evolutionary algorithms.
We proposed and designed angle insensitive color filter based in metal/dielectric multilayers structures for red electromagnetic radiation (620-750nm). The thickness of the dielectric in the structure is calculated according to the physical theory and the omnidirectional resonance occurs when the reflection phase shift cancels the propagation displacement. The thickness of the metal is chosen analyzing a transmission properties in an interval of thicknesses previously described in the literature. We obtain analytically a highly stable filter with a transmission peak greater than 70% in approximately 634nm. This device can keep the same perceived transmitted color when the incidence angle changes from 0° to 50°, especially for TM polarized light.
The directional dependency of the optical coefficients, such as absorbance and reflectance, of a periodic hole plasmonic structure is numerically simulated and investigated. The tridimensional structure, which is composed of a metallic thin layer on a semiconductor matrix, is polarization independent and exhibits wide angle tolerance. It is found that the optical coefficients of the simulated structure have strong dependency to the radii of the holes due to cavity modes resonance and surface plasmon resonance. Simulations were carried out using gold and silver, varying the holes radii ranging from 40 to 70nm, as well as its depth, from 30 to 60nm of the metallic thin layer and from 100 to 200nm of the semiconductor matrix. A maximum contrast ratio of a unit was obtained. The resonant modes excited in the structure and excitation of surface plasmon polaritons in the metallic side illumination favors absorption, which explains the asymmetric behavior. We also investigate the structure’s fabrication sensitivity by randomizing the generation of center of the holes in a supercell. These findings are significant for a diverse range of applications, ranging from optical integrated circuits to solar and thermovoltaics energy harvesting.
A multipeak polarization independent absorber based on ultrathin metamaterials composed of metal layers (Al) and dielectric (polymer, ZnSe) has been proposed and numerically analyzed. The absorber is composed by a trapezoidal shaped grating filled by a polymer. This structure possess resonant absorption modes at multi-frequencies. Numerical results show that near unity absorption peaks can be obtained for both polarization modes (TM and TE) for visible radiation at normal incidence.
We study the length propagation characteristic of plasmonic waveguides employing metamaterials by means of
numerical approach. The analyzed structures are made of metallic nanowires in a dielectric host or metal and
dielectric thin layers claddings, surrounding a dielectric core. The main parameter to be computed is the length
propagation as a function of the light excitation wavelength, waveguide core dimensions, metal filling ratio or the
effective index of the composite claddings. These structures are intended to exhibit low loss propagation guided
modes from visible light to optical communication infrared radiation.
We present a broadband absorber with the half-cylinder geometry composed of thin film with metallic / dielectric
multilayers. The geometric and physical parameters of the proposed structure were optimized to obtain an average
absorption above 90% for the modes of electric polarization (TE) and magnetic (TM) in the visible spectrum. High
absorption is observed for incident angles of up to 40 degrees in TE mode and 80 degrees for TM mode. The effects
of structure periodicity are also investigated for both modes and the results show small changes over a range of 200
nm . In medium IR (infrared) the structure can be scalable to obtain absorption peaks from its geometry.
A rigorous analysis of two-dimensional segmented waveguide (2D-SWG) crossing using evolutionary algorithms in conjunction with the two-dimensional finite element method (2D-FEM) is presented. The power transmission and crosstalk of the waveguide crossings are calculated, optimized and compared with other designs in the literature. The optimized crossing has been successfully and efficient designed using evolutionary algorithms based on genetic algorithm (GA). Power transmissions above 90 % and crosstalk below 40 dB over a broadband interval of wavelength have been obtained with the evolutionary algorithm.
The propagation properties of 1D waveguides composed by a dielectric core and a multilayered metallic dielectric cladding are numerically analyzed in details for applications covering the O-E-S-C-L-U optical communication bands. The propagation length, penetration depth and the figure of merit as a function of their geometrical and optical parameters are presented. The strong dependence of their properties with their constituent materials has been observed. Long propagation distances with high values of figure of merit can be obtained, opening the possibility to develop devices of high performance in the optical band under inspection.
The transmittance, reflectance and absorption of silver nanowires metamaterial embedded into a semiconductor matrix with optical gain are numerically investigated. Metamaterials may suffer from appreciable dissipative losses which are inherent for all plasmonic structures. The losses can significantly be reduced by introducing optical gain in the dielectric matrix by placing atomic or molecular impurities which are pumped by an external light source to create a population inversion. We numerically analyzed the optical properties when the semiconductor host material represents a gain medium. We calculate the transmittance, reflectance and absorption at normal incidence in the visible and near infrared ranges. We observed a peculiar behavior of their optical coefficients that can be explained by observing the field redistribution on the metamaterial.
We propose a strategy to design broadband absorbers. It is based on the apodization of a supercell composed of an array of subwavelength metallic-insulator gratings. The proposed absorber consists of grooves with variable depths in a metallic substrate filled with a dielectric material. It was demonstrated that the apodization procedure plays an important role in the required broadband operation of the proposed absorbers. The proposed absorber presented averaged values of absorption of the order of 94% for wavelengths from 700 to 2300 nm. The spectral response of the absorption coefficient, for a plane wave under normal incidence, has been calculated by using an efficient frequency-domain finite-element method.
The absorption and reflection characteristics of multilayered nanoplasmonic gratings with sub wavelength sizes are analyzed in details by using an efficient finite element method. The multilayered structures are composed by several layers of nanoparticles of metals such as Silver, Gold and Aluminum embedded in dielectric such as amorphous silicon over a metallic substrate. The propagations characteristics for several geometrical configurations are obtained and a broadband reflection or absorption covering the near infrared wavelengths has been observed. The proposed nanoplasmonic structures have a great potential for applications in photovoltaic cells or polarizers by improving their reflection or absorption efficiency. Peaks of reflection or absorption larger than 80% were obtained and their performance over the near infrared can be improved by adequately tuning their geometrical parameters, the refractive index and thickness of the layers as well as the nanoparticles shape and size.
Broadband nanostructured metallic-dielectric absorbers and reflectors are of great interest in integrated optics and they
have a great potential for applications like polarizers or reflectors for nanoantennas applications operating in optical
frequencies, covering the interval of the O-E-S-C-L-U bands. In this work, novel geometric and optical configurations
are numerically analyzed. The absorber or reflected central frequencies of the analyzed devices can be easily tuned over
the entire communications wavelength band by varying their geometrics and optical parameters Peaks of absorption
larger than 80% were obtained in optical wavelengths by using metals like silver and gold in combination with silica
Due to the promises of ultrahigh speed computation realized in the optical domain, great interest towards alloptical
integrated systems has been shown. A great number of different types of optical logic gates have been proposed
during the last years and the optical diode effect based on photonic crystal is of crucial importance in optical logic gates
and computing integrated optical systems. The diode effect can be achieved by breaking the spatial inversion symmetry
by various ways. Many different linear passive structures that exhibits optical isolation and unidirectional transmission
behavior have been proposed, which exploit the properties of point defects, mode conversion and filtering, chirped
structures or heterojunction slabs (two different 2D Photonic Crystals structures). Further improvements of these
structures are here proposed and enhanced unidirectional behavior was achieved by optimization of the originally
proposed structures where good optical isolation has been achieved. The results were obtained by efficient numerical
simulations and it is shown that these devices are good candidates for building blocks of integrated optical systems.
For advanced photonics networks all kind of optical devices are being developed with the aim of routing high speed
optical signals. The multimode interference MMI principle is becoming important because these devices have a simple
configuration, compactness and are suitable for integration. MMI couplers based on subwavelength periodical gratings
and silicon nanowires are here analyzed based the coupled-mode formulation. Several geometrical configurations were
analyzed as a function of the operating wavelength, by varying the width/radius, the period, the segment length (dutycycle)
and the nanowires radius. It was observed that for some specific configurations a wavelength independent
behavior can be obtained.
Two dimensional photonic crystals slabs can be recorded using a double exposure of a photoresist film to an interference fringe pattern. In order to present an expressive PBG (photonic band gap) for a desired region of the electromagnetic spectrum, the geometry of the 2 dimensional structures must be appropriately defined. Besides the geometric requirements, the material itself, in which the structures are recorded, must be transparent and present high refractive index in electromagnetic region of the PBG. In this paper we design and fabricate two dimensional (PC) Photonic Crystals) in dielectric films on glass substrates. The use of optical materials instead of semiconductors allows the devleopment of processes able to produce P.C. for the visible part of the spectrum.