arXiv subjects

Moustafa Ahmed

Publications and source records attributed to Moustafa Ahmed.

9 recordsLinked to original sources

arXiv2023

Towards Developing Mid-Infrared Photonics Using Mxenes

Recent research and development in the mid-infrared (IR) wavelength range (2-20 um) for a variety of applications, such as trace gas monitoring, thermal imaging, and free space communications have shown tremendous and fascinating progress. MXenes, which mainly refer to two-dimensional (2D) transition-metal carbides, nitrides, and carbonitrides, have drawn a lot of interest since their first investigation in 2011. MXenes project enormous potential for use in optoelectronics, photonics, catalysis, and energy harvesting fields proven by extensive experimental and theoretical studies over a decade. MXenes offers a novel 2D nano platform for cutting-edge optoelectronics devices due to their interesting mechanical, optical, and electrical capabilities, along with their elemental and chemical composition. We here discuss the key developments of MXene emphasizing the evolution of material synthesis methods over time and the resulting device applications. Photonic and optoelectronic device design and fabrication for mid-IR photonics are demonstrated by integrating MXene materials with various electrical and photonic platforms. Here, we show the potential of using Mxene in photonics for mid-IR applications and a pathway toward achieving next-generation devices for various applications.

physics.optics↗

arXiv2021

On-chip Nanophotonic Broadband Wavelength Detector with 2D-Electron Gas

Miniaturized, low-cost wavelength detectors are gaining enormous interest as we step into the new age of photonics. Incompatibility with integrated circuits or complex fabrication requirement in most of the conventionally used filters necessitates the development of a simple, on-chip platform for easy-to-use wavelength detection system. Also, intensity fluctuations hinder precise, noise free detection of spectral information. Here we propose a novel approach of utilizing wavelength sensitive photocurrent across semiconductor heterojunctions to experimentally validate broadband wavelength detection on an on-chip platform with simple fabrication process. The proposed device utilizes linear frequency response of internal photoemission via 2-D electron gas in a ZnO based heterojunction along with a reference junction for coherent common mode rejection. We report sensitivity of 0.96 uA/nm for a broad wavelength-range of 280 nm from 660-940 nm. Simple fabrication process, efficient intensity noise cancelation along with heat resistance and radiation hardness of ZnO makes the proposed platform simple, low-cost and efficient alternative for several applications such as optical spectrometers, sensing and IOTs.

physics.optics↗

arXiv2020

The Main Role of Thermal Annealing in Controlling the Structural and Optical Properties of ITO Thin Film Layer

Here we report on studying the electronic and optical material properties of the technologically-relevant material indium tin oxide (ITO) as a function of thermal annealing. In this work, ITO powder has been prepared utilizing solid-state reaction methods. An electron beam gun technology has been used to prepare a ITO film (325 nm). The ITO window layer has been investigated at various temperatures. The effects of absolute temperature on the structural, optical, and electrical properties of the prepared ITO thin film layer are investigated. The energy band type corresponding to the orbital transitions has been determined, and the energies of the orbital transitions have been calculated in the Tauc region, HOMO/LUMO gap, and charge transfer gap. In additions, the exciton and Urbach energies have been computed. It has been found that these energies increase with increasing the annealing temperature, except for Urbach's energies which behave differently. Thin-film quality coefficient, surface resistance, and thermal emission in addition to the angle of refraction as a function of wavelength, have been determined.

physics.gen-ph↗

arXiv2020

Influence of Asymmetric Gain Suppression on Relative Intensity Noise Properties of Multimode Semiconductor Lasers

We introduce modeling and simulation of the noise properties associated with types of modal oscillations induced by scaling the asymmetric gain suppression (AGS) in multimode semiconductor lasers. The study is based on numerical integration of a system of rate equations of 21-oscillating modes taking account of the self- and cross-modal gain suppression mechanisms. AGS is varied in terms of a pre-defined parameter, which is controlled by the linewidth enhancement factor and differential gain. Basing on intensive simulation of the mode dynamics, we present a mapping (AGS versus current) diagram of the possible types of modal oscillations. When the laser oscillation is hopping multimode oscillation (HMMO), the spectra of relative intensity noise (RIN) of the total output and hopping modes are characterized by a sharp peak around the relaxation oscillation (RO) frequency and a broad peak around the hopping frequency. The levels of RIN in the regimes of single-mode oscillation (SMO) are much lower than those under HMMO, and the mode-partition noise is two order of magnitudes lower.

physics.optics↗

arXiv2020

Structure, Electrical and Optical Properties of ITO Thin Films and their Influence on Performance of CdS/CdTe Thin-Film Solar Cells

In terms of mixing graded TiO2 and SnO2 powders by solid-state reaction method, ITO was prepared. Using electron beam gun technology, ITO films with different thicknesses were prepared. The influence of film thickness on structure, electrical and optical properties was studied. The XRD patterns were utilized to determine the structural parameters (lattice strain and crystallite size) of ITO with different thicknesses. It is observed that the average crystallite size increases as the film thickness increases, but the lattice strain decreases. SEM shows that as the film thickness increases, the grain size of ITO increases and improves. The electrical properties of ITO films with different thicknesses were measured by the standard four-point probe method. It can be seen that as the thickness of the ITO film increases from 75 nm to 325 nm, the resistivity decreases from 29x10^-4 Ohm/cm to 1.65x10^-4 Ohm/cm. This means that ITO films with lower electrical properties will be more suitable for high-efficiency CdTe solar cells. Three optical layer models (adhesive layer of the substrate/B-spline layer of ITO film/surface roughness layer) are used to calculate the film thickness with high-precision ellipsometry. In the higher T(lambda) and R(lambda) absorption regions, the absorption coefficient is determined to calculate the optical energy gap, which increases from 3.56 eV to 3.69 eV. Finally, the effects of ITO layers of various thicknesses on the performance of CdS/CdTe solar cells are also studied. When the thickness of the ITO window layer is 325 nm, Voc = 0.82 V, Jsc = 17 mA/cm2, and FF = 57.4%, the highest power conversion efficiency (PCE) is 8.6%.

cond-mat.mtrl-sci↗

arXiv2020

Transverse Coupled Cavity VCSEL: Making 100 GHz Bandwidth Achievable

Enhancing the modulation bandwidth (MBW) of semiconductor lasers has been the challenge of research and technology to meet the need of high-speed photonic applications. In this paper, we propose the design of vertical-cavity surface-emitting laser integrated with multiple transverse coupled cavities (MTCCs) as a promising device with ultra-high 3-dB bandwidth. The laser features high modulation performance because of the accumulated strong coupling of the slow-light feedback from the surrounding lateral TCCs into the VCSEL cavity. Photon-photon resonance (PPR) is predicted to occur at ultra-high frequencies exceeding 145 GHz due to the optical feedback from short TCCs, which achieves 3-dB MBW reaching 170 GHz. The study is based on the modeling of the VCSEL dynamics under multiple transverse slow-light feedback from the surrounding TCCs. We show that the integration of the VCSEL with four or six feedback cavities is advantageous over the TCC-VCSEL in achieving much higher MBW enhancement under weaker coupling of slow-light into the VCSEL cavity. We also characterize the noise properties of the promising MTCC-VCSEL in the regime of ultra-high bandwidth in terms of the Fourier spectrum of the relative intensity noise (RIN).

physics.optics↗

arXiv2020

Stabilizing Multimode Hopping Oscillations and Reducing Associated Noise in Long Wavelength Laser Diode Using External Optical Feedback

We report on converting the multimode hopping oscillation (MHO) in long-wavelength semiconductor laser into single-mode oscillation (SMO) by applying external optical feedback (OFB). We characterize and compare the noise performance of the laser when supporting SMO and multimode oscillations. The study is based on a modified time-delay multimode rate-equation model of the laser that includes mechanisms of spectral gain suppression along with OFB induced due to multiple reflections by an external reflector. The study is applied to 1.55um-InGaAsP laser that exhibits multimode hopping in its solitary version and supports wide bandwidth. The noise is evaluated in terms of the relative intensity noise (RIN). We show that when OFB synchronizes with the asymmetric gain suppression (AGS), it enhances the gain of one longer wavelength mode and supports SMO. In this case OFB improves the noise performance of the laser. On the other hand, when OFB works against AGS, it sustains hopping multimode oscillation (HMMO) and deteriorates the side-mode suppression ratio (SMSR) and the noise performance.

physics.optics↗

arXiv2020

Hexagonal Transverse Coupled Cavity VCSEL Redefining the High-Speed Lasers

The vertical-cavity surface-emitting lasers (VCSELs) have emerged as a vital approach for realizing energy efficient, high speed optical interconnects in the data center and supercomputers. As of today, VCSEL is the most suitable for mass production in terms of cost-effectiveness and reliability. However, there are still key challenges for higher speed modulation above 40 GHz. Here, a hexagonal transverse coupled cavity VCSEL adiabatically coupled through the center cavity is proposed. A 3-dB roll-off modulation bandwidth of 45 GHz is demonstrated, which is five times greater than a conventional VCSEL fabricated on the same epi-wafer structure. While a parity time (PT) symmetry approaches add loss to engineer the topological state of the laser system, here, a radical paradigm shift with gain introduces symmetry breaking. This idea, then enables a single mode operation with a side-mode suppression-ratio (SMSR) of > 30 decibels and signal-to-noise ratio (SNR) of > 45 decibels. The energy distribution inside the coupled cavity system is also redistributed to provide a coherent gain in a spatially separated system. Consequently, throughput power is three times higher than that of the conventional VCSEL.

physics.optics↗

arXiv2020

Integrated Photonic FFT for Optical Convolutions towards Efficient and High-Speed Neural Networks

The technologically-relevant task of feature extraction from data performed in deep-learning systems is routinely accomplished as repeated fast Fourier transforms (FFT) electronically in prevalent domain-specific architectures such as in graphics processing units (GPUs). However, electronics systems are limited with respect to power dissipation and delay, both, due to wire-charging challenges related to interconnect capacitance. Here we present a silicon photonics-based architecture for convolutional neural networks that harnesses the phase property of light to perform FFTs efficiently by executing the convolution as a multiplication in the Fourier-domain. The algorithmic executing time is determined by the time-of-flight of the signal through this photonic reconfigurable passive FFT filter circuit and is on the order of 10s of picosecond. A sensitivity analysis shows that this optical processor must be thermally phase stabilized corresponding to a few degrees. Furthermore, we find that for a small sample number, the obtainable number of convolutions per {time-power-chip area) outperforms GPUs by about 2 orders of magnitude. Lastly, we show that, conceptually, the optical FFT and convolution-processing performance is indeed directly linked to optoelectronic device-level, and improvements in plasmonics, metamaterials or nanophotonics are fueling next generation densely interconnected intelligent photonic circuits with relevance for edge-computing 5G networks.

physics.optics↗