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Salah Obayya

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Mansoura University

Cairo University

Muntasir Hossain

Firas Faeq K. Hussain

Al-Muthanna University (Iraq)

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Papers by Salah Obayya

Numerically efficient full-vectorial rational Chebyshev pseudo-spectral modal analysis for optical Waveguides

Optical and Quantum Electronics

In this paper, an efficient full-vectorial modal analysis based on the rational Chebyshev pseudo-... more In this paper, an efficient full-vectorial modal analysis based on the rational Chebyshev pseudo-spectral method (V-RCPSM) is introduced to analyze 3 dimensional (3D) structures that are invariant along one spatial variable. Such structures are essential in silicon photonics and plasmonics applications where permittivity profiles with high-index contrast need precise treatment of the interface boundary conditions. Besides, such structures are open in general. Hence, good domain truncation is important. Our method handles these challenges via hybrid usage of the domain decomposition technique where the electromagnetic field is expanded in terms of Chebyshev functions in homogeneous regions, while the rational Chebyshev functions are used for semi-infinite homogeneous domains. The boundary conditions are rigorously imposed along the interfaces, a step that maintains the known exponential convergence rate of Chebyshev functions. Chebyshev functions have the ability to capture the corre...

An efficient FDTD algorithm based on FPGA

Egyptian Journal of Pure and Applied Science

Optimization of locations of diffusion spots in indoor optical wireless local area networks

Optics Communications, 2018

In this paper, optimization of diffuse spots' parameters in indoor optical wireless communication... more In this paper, optimization of diffuse spots' parameters in indoor optical wireless communications (OWC) system is carried out by using the particle swarm optimization (PSO) algorithm. By simultaneously optimizing the diffusion spots' locations and intensities, we show an improvement in the signal-to noise-ratio (SNR) and the delay spread at the receivers, while considering both the background noise and the multipath dispersion. A comparison is made between different optimization scenarios, to illustrate the effect of varying the parameters that are being optimized. We show that the optimization of both intensities and locations of diffuse spots resulted in improvement up to 42% and 23% in the average delay spread and the average SNR, respectively, compared with the centrally located position of diffuse spots' distribution, with respect to the receivers' locations, which has a uniform distribution of power.

Orthogonal quasi-phase-matched superlattice for generation of hyperentangled photons

Scientific Reports, 2017

A crystal superlattice structure featuring nonlinear layers with alternating orthogonal optic axe... more A crystal superlattice structure featuring nonlinear layers with alternating orthogonal optic axes interleaved with orthogonal poling directions, is shown to generate high-quality hyperentangled photon pairs via orthogonal quasi-phase-matched spontaneous parametric downconversion. We demonstrate that orthogonal quasi-phase matching (QPM) processes in a single nonlinear domain structure correct phase and group-velocity mismatches concurrently. Compared with the conventional two-orthogonal-crystals source and the double-nonlinearity single-crystal source, the orthogonal QPM superlattice is shown to suppress the spatial and temporal distinguishability of the generated photon pairs by several orders of magnitude, depending on the number of layers. This enhanced all-over-the-cone indistinguishability enables the generation of higher fluxes of photon-pairs by means of the combined use of (a) long nonlinear crystal in noncollinear geometry, (b) low coherence-time pumping and ultra-wide-ban...

Efficient smoothed finite element time domain analysis for photonic devices

Optics express, Jan 24, 2015

In this paper, a new finite element method (FEM) is proposed to analyse time domain wave propagat... more In this paper, a new finite element method (FEM) is proposed to analyse time domain wave propagation in photonic devices. Dissimilar to conventional FEM, efficient "inter-element" matrices are accurately formed through smoothing the field derivatives across element boundaries. In this sense, the new approach is termed "smoothed FEM" (SFETD). For time domain analysis, the propagation is made via the time domain beam propagation method (TD-BPM). Relying on first order elements, our suggested SFETD-BPM enjoys accuracy levels comparable to second-order conventional FEM; thanks to the element smoothing. The proposed method numerical performance is tested through applicating on analysis of a single mode slab waveguide, optical grating structure, and photonic crystal cavity. It is clearly demonstrated that our method is not only accurate but also more computationally efficient (far few run time, and memory requirements) than the conventional FEM approach. The SFETD-BPM ...

Polarization splitter based on soft glass nematic liquid crystal photonic crystal fiber

IEEE Photonics Journal, 2009

A novel design of a polarization splitter based on index-guiding soft glass nematic liquid crysta... more A novel design of a polarization splitter based on index-guiding soft glass nematic liquid crystal (NLC) photonic crystal fiber is proposed and analyzed. The simulation results are obtained using the full-vectorial finite-difference modal solution along with the fullvectorial finite-difference beam propagation method. The numerical results reveal that the suggested splitter of length 8.227 mm can provide low crosstalk of better than À20 dB with great bandwidths of 30 nm and 75 nm for the quasi TE and TM modes, respectively. In addition, the reported splitter has a tolerance of AE3% in its length, which makes the design less sensitive to the perturbation introduced during the fabrication process.

Optical Nano-Antennas for Energy Harvesting

Innovative Materials and Systems for Energy Harvesting Applications

The solar energy is able to supply humanity energy for almost another 1 billion years. Optical na... more The solar energy is able to supply humanity energy for almost another 1 billion years. Optical nano-antennas (ONAs) are an attractive technology for high efficiency, and low-cost solar cells. These devices can be classified to semiconductor nano-wires and metallic nano-antenna. Extensive studies have been carried out on ONAs to investigate their ability to harvest solar energy. Inspired by these studies, the scope of the chapter is to highlight the latest designs of the two main types of ONAs. The metallic nano-antennas are discussed based on the following points: plasmon, modeling, and performance of antenna designs using different configurations and materials. Moreover, the semiconductor nano-wires are studied thoroughly in terms of photonic crystals, antenna design with different patterns, nano-wire forms and materials. Also, the applications of ONAs and their fabrication aspects such as diode challenges are presented in detail. Finally, three novel designs of ONAs are presented ...

Metal-less Plasmonics: A Study of Plasmonic Effects in Amorphous Silicon at The Edge of UV/VIS Spectrum

Advanced Photonics 2015, 2015

A theoretical study of plasmonic effects in silicon nanostructures is introduced. It is found tha... more

Tunable spatial–spectral phase compensation of type-I (ooe) hyperentangled photons

Journal of the Optical Society of America B, 2015

Analysis of ultra-high birefringent fully-anisotropic photonic crystal fiber

Optical and Quantum Electronics, 2015

Efficient Polarization Filter Design Based on Plasmonic Photonic Crystal Fiber

Journal of Lightwave Technology, 2015

A novel selectively metal filled spiral photonic crystal fiber (PCF) with elliptic core is introd... more A novel selectively metal filled spiral photonic crystal fiber (PCF) with elliptic core is introduced and analyzed. The cladding air holes of the suggested design are arranged in spiral arms that are distributed in an elliptical form. In this work, the dispersion characteristics and loss spectra of the reported design are studied through the full vectorial finite element method (FV-FEM). The suggested design has advantages in terms of highly polarization-dependent coupling between xand y-polarized core modes and higher order surface plasmon polariton(SPP) modes. It is evident from this study that the core modes can be separated from each other by changing the structure parameters. In addition, the resonance points at which the coupling between the core modes and SPP modes occurs can be tuned. Moreover, the coupling tunability of the proposed design can be increased by filling the cladding air hole with multiple metal wires. This novel structure is suitable for the design of filter based applications. At wavelength λ= 1.013 µm, the loss of the x-polarized core mode is equal to 77.04 dB/mm while it is only 2.765 dB/mm for the y-polarized core mode with single metal rod. However, for two metal rods, the losses for x and y-polarized core modes are increased to 94.1 dB/mm and 6.424 dB/mm, respectively at λ= 0.98 µm.

Novel Design of Symmetric Photonic Bandgap Based Image Encryption System

Progress In Electromagnetics Research C, 2012

A novel approach for the design of image encryption system based on one stage of 3D photonic band... more A novel approach for the design of image encryption system based on one stage of 3D photonic bandgap structure is proposed. Using the Finite Integration Time Domain (FITD) method, the performance of the proposed design is optimized through the utilization of the reflection properties from 3D photonic bandgap structure while maintaining constant phase encoding. To demonstrate the robustness of the suggested encryption system, root mean square error is calculated between the original and decrypted images revealing the high accuracy in retrieving the images. In addition, as the proposed system renders itself as easy to fabricate, it has an excellent potential for being very useful in both microwaves and photonics imaging system applications.

Design and Characteristics of Directional Coupler Based Filters

In this paper, an accurate characterization of a novel design of an optical wavelength filter is ... more In this paper, an accurate characterization of a novel design of an optical wavelength filter is investigated and analyzed by the coupled mode theory (CMT). The effect of the different structure geometrical parameters on the filter performance is studied. The crosstalk and bandwidth of the device are also calculated for various separations between the waveguides. The suggested design has a crosstalk of-34.909 dB and bandwidth of 14.8 nm for device length of 1646.26 μm. A bandwidth of 10 nm can also be obtained with a device length of 3.1 mm. In addition, a novel design of cascaded structure of non-identical directional coupler is introduced and analyzed by the CMT. The suggested design offers complete power exchange between two slab waveguides having modes with different propagation constants. The reported coupler exhibits low crosstalk of-38.38dB with a compact device length of 171.54μm.

Nanohole design for high performance polymer solar cell

Numerical Simulation of Optoelectronic Devices, 2014, 2014

A novel design of nanohole polymer solar cell (NHPSC) is reported for light trapping improvement.... more A novel design of nanohole polymer solar cell (NHPSC) is reported for light trapping improvement. The proposed design has shown a considerable enhancement in the optical and electrical parameters of the polymer solar cell based on a conventional blend of poly-3-hexylthiophene/ [6, 6]-phenyl-C61-butyric acid methyl ester (P3HT:PCBM) as an active material. In this study, 3D finite difference time domain method is used to simulate the light absorption in the nanohole structure. In addition, an electrical model is developed to calculate the electrical parameters of the polymer solar cell. The reported design has shown 28% improvement in short circuit current density and overall efficiency alike.

Absorption enhancement in hexagonal plasmonic solar cell

Numerical Simulation of Optoelectronic Devices, 2014, 2014

In this paper, a novel design of hexagonal cylindrical plasmonic solar cell (HC-PSC) is investiga... more In this paper, a novel design of hexagonal cylindrical plasmonic solar cell (HC-PSC) is investigated and analysed by using 3D finite difference time domain method. The aim of our work is to get maximum absorption of thin film solar cell by scattering the light from metal nanoparticles. Therefore the effects of the structure geometrical parameters on the absorption are investigated. The numerical results show around 35% absorption improvement compared to the conventional thin film solar cell without metal nanoparticles.

Iodide-Capped PbS Quantum Dots: Full Optical Characterization of a Versatile Absorber

Advanced materials (Deerfield Beach, Fla.), Jan 21, 2015

Lead sulfide quantum dots represent an emerging photovoltaic absorber material. While their assoc... more Lead sulfide quantum dots represent an emerging photovoltaic absorber material. While their associated optical qualities are true for the colloidal solution phase, they change upon processing into thin-films. A detailed view to the optical key-parameters during solid film development is presented and the limits and outlooks for this versatile and promising absorber are discussed.

<title>Designs of tapered, uniform and compact monolithically integrated semiconductor spot-size converters for efficient laser-fiber coupling</title>

Applications of Photonic Technology 5, 2003

ABSTRACT When a photonic device is directly butt-coupled to a single mode fiber, often there is a... more ABSTRACT When a photonic device is directly butt-coupled to a single mode fiber, often there is a 90% or more optical power loss, due to their highly unequal spot-sizes. Often, by using complex microlenses, the coupling efficiency has been increased, but however at the expense of a sub-micron alignment tolerance requirement, and consequently higher associated cost for a reliable operation. Recently, monolithically integrated devices, mostly using tapered structures, have been reported as useful to modify the spot-size of semiconductor photonic devices, which could assist in the rapid implementation of &#39;fiber-to-the-home&#39;. In this work, spot-size converters with a tapered core, also using novel uniform directional couplers and MMI structures are discussed. A rigorous numerical approach, based on the full vectorial finite element method, is used to design various types of monolithically integrated spot-size converters for efficient coupling to an optical fiber and results of their performance reported.© (2003) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Fully Integrated AND and OR Optical Logic Gates

IEEE Photonics Technology Letters, 2014

We propose two novel designs of compact, linear, and all-optical OR and AND logic gates based on ... more We propose two novel designs of compact, linear, and all-optical OR and AND logic gates based on photonic crystal architecture. The proposed devices are formed by the combination of the ring cavities and Y-shape line defect coupler placed between two waveguides. The performance of the proposed logic gates has been analyzed and investigated using finite difference time domain method. The suggested design for AND gate offers ON to OFF logic level contrast ratio of not less than 6 dB and the suggested design for OR gate offers transmitted power of not less than 0.5. On top of that, the proposed OR and AND logic gates can operate at bit rates of around 0.5 and 0.208 Tb/s, respectively. Further, the calculated fabrication tolerances of the suggested devices show that the rods radii of the ring cavities need to be controlled with no more than ±10% and ±3% fabrication errors for optical OR and AND gates, respectively. It is expected that such designs have the potential to be key components for future photonic integrated circuits due to their simplicity and small size.

Quantum waveguides discontinuities analysis

Numerical Simulation of Optoelectronic Devices, 2014, 2014

A finite-element bidirectional beam propagation method based on Blocked Schur (BS-FE-BiBPM) is pr... more A finite-element bidirectional beam propagation method based on Blocked Schur (BS-FE-BiBPM) is presented for the solution of quantum waveguides discontinuities. By using BS-FE-BiBPM, scattering properties of electron waveguide discontinuities could be accurately calculated based on the 1-D time-independent Schrödinger equation avoiding the use of modal solution stage without affecting the accuracy of the results. As will be shown through the analysis of a quantum resonant cavity, a quantum directional coupler, and a quantum waveguide transistor, the suggested BS-FE-BiBPM is very accurate, versatile, efficient, fast and stable.

Slotted microcavity ring resonators for optical storage applications

Optical and Quantum Electronics, 2013

In this paper, slotted microcavity ring resonators based optical storage devices are proposed and... more In this paper, slotted microcavity ring resonators based optical storage devices are proposed and analyzed by means of multiresolution time domain technique. The effect of the structure geometrical parameters on the coupling efficiency, normalized transmission spectra and quality factor has been thoroughly investigated and compared to that of the conventional no-slot microring resonator. The suggested slotted configurations increase the quality factor at a fixed gap size between the central ring and input/output waveguides. In addition, the desired compromise between the coupling efficiency and resonance effect inside the ring can be achieved by mere optimization of the slot geometrical characteristics.

Numerically efficient full-vectorial rational Chebyshev pseudo-spectral modal analysis for optical Waveguides

Optical and Quantum Electronics

In this paper, an efficient full-vectorial modal analysis based on the rational Chebyshev pseudo-... more In this paper, an efficient full-vectorial modal analysis based on the rational Chebyshev pseudo-spectral method (V-RCPSM) is introduced to analyze 3 dimensional (3D) structures that are invariant along one spatial variable. Such structures are essential in silicon photonics and plasmonics applications where permittivity profiles with high-index contrast need precise treatment of the interface boundary conditions. Besides, such structures are open in general. Hence, good domain truncation is important. Our method handles these challenges via hybrid usage of the domain decomposition technique where the electromagnetic field is expanded in terms of Chebyshev functions in homogeneous regions, while the rational Chebyshev functions are used for semi-infinite homogeneous domains. The boundary conditions are rigorously imposed along the interfaces, a step that maintains the known exponential convergence rate of Chebyshev functions. Chebyshev functions have the ability to capture the corre...

An efficient FDTD algorithm based on FPGA

Egyptian Journal of Pure and Applied Science

Optimization of locations of diffusion spots in indoor optical wireless local area networks

Optics Communications, 2018

In this paper, optimization of diffuse spots' parameters in indoor optical wireless communication... more In this paper, optimization of diffuse spots' parameters in indoor optical wireless communications (OWC) system is carried out by using the particle swarm optimization (PSO) algorithm. By simultaneously optimizing the diffusion spots' locations and intensities, we show an improvement in the signal-to noise-ratio (SNR) and the delay spread at the receivers, while considering both the background noise and the multipath dispersion. A comparison is made between different optimization scenarios, to illustrate the effect of varying the parameters that are being optimized. We show that the optimization of both intensities and locations of diffuse spots resulted in improvement up to 42% and 23% in the average delay spread and the average SNR, respectively, compared with the centrally located position of diffuse spots' distribution, with respect to the receivers' locations, which has a uniform distribution of power.

Orthogonal quasi-phase-matched superlattice for generation of hyperentangled photons

Scientific Reports, 2017

A crystal superlattice structure featuring nonlinear layers with alternating orthogonal optic axe... more A crystal superlattice structure featuring nonlinear layers with alternating orthogonal optic axes interleaved with orthogonal poling directions, is shown to generate high-quality hyperentangled photon pairs via orthogonal quasi-phase-matched spontaneous parametric downconversion. We demonstrate that orthogonal quasi-phase matching (QPM) processes in a single nonlinear domain structure correct phase and group-velocity mismatches concurrently. Compared with the conventional two-orthogonal-crystals source and the double-nonlinearity single-crystal source, the orthogonal QPM superlattice is shown to suppress the spatial and temporal distinguishability of the generated photon pairs by several orders of magnitude, depending on the number of layers. This enhanced all-over-the-cone indistinguishability enables the generation of higher fluxes of photon-pairs by means of the combined use of (a) long nonlinear crystal in noncollinear geometry, (b) low coherence-time pumping and ultra-wide-ban...

Efficient smoothed finite element time domain analysis for photonic devices

Optics express, Jan 24, 2015

In this paper, a new finite element method (FEM) is proposed to analyse time domain wave propagat... more In this paper, a new finite element method (FEM) is proposed to analyse time domain wave propagation in photonic devices. Dissimilar to conventional FEM, efficient "inter-element" matrices are accurately formed through smoothing the field derivatives across element boundaries. In this sense, the new approach is termed "smoothed FEM" (SFETD). For time domain analysis, the propagation is made via the time domain beam propagation method (TD-BPM). Relying on first order elements, our suggested SFETD-BPM enjoys accuracy levels comparable to second-order conventional FEM; thanks to the element smoothing. The proposed method numerical performance is tested through applicating on analysis of a single mode slab waveguide, optical grating structure, and photonic crystal cavity. It is clearly demonstrated that our method is not only accurate but also more computationally efficient (far few run time, and memory requirements) than the conventional FEM approach. The SFETD-BPM ...

Polarization splitter based on soft glass nematic liquid crystal photonic crystal fiber

IEEE Photonics Journal, 2009

A novel design of a polarization splitter based on index-guiding soft glass nematic liquid crysta... more A novel design of a polarization splitter based on index-guiding soft glass nematic liquid crystal (NLC) photonic crystal fiber is proposed and analyzed. The simulation results are obtained using the full-vectorial finite-difference modal solution along with the fullvectorial finite-difference beam propagation method. The numerical results reveal that the suggested splitter of length 8.227 mm can provide low crosstalk of better than À20 dB with great bandwidths of 30 nm and 75 nm for the quasi TE and TM modes, respectively. In addition, the reported splitter has a tolerance of AE3% in its length, which makes the design less sensitive to the perturbation introduced during the fabrication process.

Optical Nano-Antennas for Energy Harvesting

Innovative Materials and Systems for Energy Harvesting Applications

The solar energy is able to supply humanity energy for almost another 1 billion years. Optical na... more The solar energy is able to supply humanity energy for almost another 1 billion years. Optical nano-antennas (ONAs) are an attractive technology for high efficiency, and low-cost solar cells. These devices can be classified to semiconductor nano-wires and metallic nano-antenna. Extensive studies have been carried out on ONAs to investigate their ability to harvest solar energy. Inspired by these studies, the scope of the chapter is to highlight the latest designs of the two main types of ONAs. The metallic nano-antennas are discussed based on the following points: plasmon, modeling, and performance of antenna designs using different configurations and materials. Moreover, the semiconductor nano-wires are studied thoroughly in terms of photonic crystals, antenna design with different patterns, nano-wire forms and materials. Also, the applications of ONAs and their fabrication aspects such as diode challenges are presented in detail. Finally, three novel designs of ONAs are presented ...

Metal-less Plasmonics: A Study of Plasmonic Effects in Amorphous Silicon at The Edge of UV/VIS Spectrum

Advanced Photonics 2015, 2015

A theoretical study of plasmonic effects in silicon nanostructures is introduced. It is found tha... more

Tunable spatial–spectral phase compensation of type-I (ooe) hyperentangled photons

Journal of the Optical Society of America B, 2015

Analysis of ultra-high birefringent fully-anisotropic photonic crystal fiber

Optical and Quantum Electronics, 2015

Efficient Polarization Filter Design Based on Plasmonic Photonic Crystal Fiber

Journal of Lightwave Technology, 2015

A novel selectively metal filled spiral photonic crystal fiber (PCF) with elliptic core is introd... more A novel selectively metal filled spiral photonic crystal fiber (PCF) with elliptic core is introduced and analyzed. The cladding air holes of the suggested design are arranged in spiral arms that are distributed in an elliptical form. In this work, the dispersion characteristics and loss spectra of the reported design are studied through the full vectorial finite element method (FV-FEM). The suggested design has advantages in terms of highly polarization-dependent coupling between xand y-polarized core modes and higher order surface plasmon polariton(SPP) modes. It is evident from this study that the core modes can be separated from each other by changing the structure parameters. In addition, the resonance points at which the coupling between the core modes and SPP modes occurs can be tuned. Moreover, the coupling tunability of the proposed design can be increased by filling the cladding air hole with multiple metal wires. This novel structure is suitable for the design of filter based applications. At wavelength λ= 1.013 µm, the loss of the x-polarized core mode is equal to 77.04 dB/mm while it is only 2.765 dB/mm for the y-polarized core mode with single metal rod. However, for two metal rods, the losses for x and y-polarized core modes are increased to 94.1 dB/mm and 6.424 dB/mm, respectively at λ= 0.98 µm.

Novel Design of Symmetric Photonic Bandgap Based Image Encryption System

Progress In Electromagnetics Research C, 2012

A novel approach for the design of image encryption system based on one stage of 3D photonic band... more A novel approach for the design of image encryption system based on one stage of 3D photonic bandgap structure is proposed. Using the Finite Integration Time Domain (FITD) method, the performance of the proposed design is optimized through the utilization of the reflection properties from 3D photonic bandgap structure while maintaining constant phase encoding. To demonstrate the robustness of the suggested encryption system, root mean square error is calculated between the original and decrypted images revealing the high accuracy in retrieving the images. In addition, as the proposed system renders itself as easy to fabricate, it has an excellent potential for being very useful in both microwaves and photonics imaging system applications.

Design and Characteristics of Directional Coupler Based Filters

In this paper, an accurate characterization of a novel design of an optical wavelength filter is ... more In this paper, an accurate characterization of a novel design of an optical wavelength filter is investigated and analyzed by the coupled mode theory (CMT). The effect of the different structure geometrical parameters on the filter performance is studied. The crosstalk and bandwidth of the device are also calculated for various separations between the waveguides. The suggested design has a crosstalk of-34.909 dB and bandwidth of 14.8 nm for device length of 1646.26 μm. A bandwidth of 10 nm can also be obtained with a device length of 3.1 mm. In addition, a novel design of cascaded structure of non-identical directional coupler is introduced and analyzed by the CMT. The suggested design offers complete power exchange between two slab waveguides having modes with different propagation constants. The reported coupler exhibits low crosstalk of-38.38dB with a compact device length of 171.54μm.

Nanohole design for high performance polymer solar cell

Numerical Simulation of Optoelectronic Devices, 2014, 2014

A novel design of nanohole polymer solar cell (NHPSC) is reported for light trapping improvement.... more A novel design of nanohole polymer solar cell (NHPSC) is reported for light trapping improvement. The proposed design has shown a considerable enhancement in the optical and electrical parameters of the polymer solar cell based on a conventional blend of poly-3-hexylthiophene/ [6, 6]-phenyl-C61-butyric acid methyl ester (P3HT:PCBM) as an active material. In this study, 3D finite difference time domain method is used to simulate the light absorption in the nanohole structure. In addition, an electrical model is developed to calculate the electrical parameters of the polymer solar cell. The reported design has shown 28% improvement in short circuit current density and overall efficiency alike.

Absorption enhancement in hexagonal plasmonic solar cell

Numerical Simulation of Optoelectronic Devices, 2014, 2014

In this paper, a novel design of hexagonal cylindrical plasmonic solar cell (HC-PSC) is investiga... more In this paper, a novel design of hexagonal cylindrical plasmonic solar cell (HC-PSC) is investigated and analysed by using 3D finite difference time domain method. The aim of our work is to get maximum absorption of thin film solar cell by scattering the light from metal nanoparticles. Therefore the effects of the structure geometrical parameters on the absorption are investigated. The numerical results show around 35% absorption improvement compared to the conventional thin film solar cell without metal nanoparticles.

Iodide-Capped PbS Quantum Dots: Full Optical Characterization of a Versatile Absorber

Advanced materials (Deerfield Beach, Fla.), Jan 21, 2015

Lead sulfide quantum dots represent an emerging photovoltaic absorber material. While their assoc... more Lead sulfide quantum dots represent an emerging photovoltaic absorber material. While their associated optical qualities are true for the colloidal solution phase, they change upon processing into thin-films. A detailed view to the optical key-parameters during solid film development is presented and the limits and outlooks for this versatile and promising absorber are discussed.

<title>Designs of tapered, uniform and compact monolithically integrated semiconductor spot-size converters for efficient laser-fiber coupling</title>

Applications of Photonic Technology 5, 2003

ABSTRACT When a photonic device is directly butt-coupled to a single mode fiber, often there is a... more ABSTRACT When a photonic device is directly butt-coupled to a single mode fiber, often there is a 90% or more optical power loss, due to their highly unequal spot-sizes. Often, by using complex microlenses, the coupling efficiency has been increased, but however at the expense of a sub-micron alignment tolerance requirement, and consequently higher associated cost for a reliable operation. Recently, monolithically integrated devices, mostly using tapered structures, have been reported as useful to modify the spot-size of semiconductor photonic devices, which could assist in the rapid implementation of &#39;fiber-to-the-home&#39;. In this work, spot-size converters with a tapered core, also using novel uniform directional couplers and MMI structures are discussed. A rigorous numerical approach, based on the full vectorial finite element method, is used to design various types of monolithically integrated spot-size converters for efficient coupling to an optical fiber and results of their performance reported.© (2003) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Fully Integrated AND and OR Optical Logic Gates

IEEE Photonics Technology Letters, 2014

We propose two novel designs of compact, linear, and all-optical OR and AND logic gates based on ... more We propose two novel designs of compact, linear, and all-optical OR and AND logic gates based on photonic crystal architecture. The proposed devices are formed by the combination of the ring cavities and Y-shape line defect coupler placed between two waveguides. The performance of the proposed logic gates has been analyzed and investigated using finite difference time domain method. The suggested design for AND gate offers ON to OFF logic level contrast ratio of not less than 6 dB and the suggested design for OR gate offers transmitted power of not less than 0.5. On top of that, the proposed OR and AND logic gates can operate at bit rates of around 0.5 and 0.208 Tb/s, respectively. Further, the calculated fabrication tolerances of the suggested devices show that the rods radii of the ring cavities need to be controlled with no more than ±10% and ±3% fabrication errors for optical OR and AND gates, respectively. It is expected that such designs have the potential to be key components for future photonic integrated circuits due to their simplicity and small size.

Quantum waveguides discontinuities analysis

Numerical Simulation of Optoelectronic Devices, 2014, 2014

A finite-element bidirectional beam propagation method based on Blocked Schur (BS-FE-BiBPM) is pr... more A finite-element bidirectional beam propagation method based on Blocked Schur (BS-FE-BiBPM) is presented for the solution of quantum waveguides discontinuities. By using BS-FE-BiBPM, scattering properties of electron waveguide discontinuities could be accurately calculated based on the 1-D time-independent Schrödinger equation avoiding the use of modal solution stage without affecting the accuracy of the results. As will be shown through the analysis of a quantum resonant cavity, a quantum directional coupler, and a quantum waveguide transistor, the suggested BS-FE-BiBPM is very accurate, versatile, efficient, fast and stable.

Slotted microcavity ring resonators for optical storage applications

Optical and Quantum Electronics, 2013

In this paper, slotted microcavity ring resonators based optical storage devices are proposed and... more In this paper, slotted microcavity ring resonators based optical storage devices are proposed and analyzed by means of multiresolution time domain technique. The effect of the structure geometrical parameters on the coupling efficiency, normalized transmission spectra and quality factor has been thoroughly investigated and compared to that of the conventional no-slot microring resonator. The suggested slotted configurations increase the quality factor at a fixed gap size between the central ring and input/output waveguides. In addition, the desired compromise between the coupling efficiency and resonance effect inside the ring can be achieved by mere optimization of the slot geometrical characteristics.