Optimization techniques have been indispensable for designing high-performance meta-devices targeted to a wide range of applications. In fact, today optimization is no longer an afterthought and is a fundamental tool for many optical and RF designers. Still, many devices presented in recent literature do not take advantage of optimization techniques. This paper seeks to address this by presenting both an introduction to and a review of several of the most popular techniques currently used for meta-device design. Additionally, emerging techniques like topology optimization and multi-objective optimization and their context to device design are thoroughly discussed. Moreover, attention is given to future directions in meta-device optimization such as surrogate-modeling and deep learning which have the potential to disrupt the fields of optical and radio frequency (RF) inverse-design. Finally, many design examples from the literature are presented and a flow-chart that provides guidance on how best to apply these optimization algorithms to a given problem is provided for the reader.

Review of numerical optimization techniques for meta-device design [Invited]

In this work, we demonstrate that the performance of c-Si/ZnO heterojunction ultrathin-film solar cells (SCs) is enhanced by an integrated structure of c-Si trapezoidal pyramids on the top of a c-Si active layer and Al pyramids in the active layer on the Al back electrode. The top c-Si trapezoidal pyramid (TTP) increases the absorption of short wavelengths by lengthening the propagation distance of incident light and coupling the incident light into photonic modes in the active layer. The bottom Al pyramid (BP) improves the overall optical absorption performance especially for the long wavelength band by forming the surface plasmon resonance (SPR) mode in the active layer. As a result, the average absorption in the entire wavelength range (300-1400 nm) reaches 93.16%. The optimized short-circuit current density (Jsc) and photoelectric conversion efficiency (PCE) of ultra-thin film c-Si/ZnO SCs are 41.94 mA cm-2 and 18.97%, respectively. Moreover, the effect of different illumination angles on the optical absorption of the SCs was explored. The SCs have good absorption when the incident angles are in the range from 0 degrees to 60 degrees. Furthermore, the underlying mechanism for the enhancement of photon absorption in the SCs was discussed through careful analysis of the electric field intensity profile at different wavelengths. It was found that the electric field tends to concentrate around the bottom pyramids and top trapezoidal pyramids even for the long-wave band, which results in an excellent light-trapping performance.

Realization of 18.97% theoretical efficiency of 0.9 μm thick c-Si/ZnO heterojunction ultrathin-film solar cells via surface plasmon resonance enhancement.

A novel design of nearly perfect metamaterial absorber is proposed and analyzed for terahertz sensing applications. The full vectorial finite element method is used to simulate and analyze the reported design. The suggested structure is based on increasing the confinement of both electric and magnetic fields simultaneously at the resonance frequency. Therefore, an absorptivity of 0.99 is achieved at 2.249 THz with a narrow resonant peak and a $Q$ -factor of 22.05. The resonance frequency is sensitive to the surrounding medium refractive index at fixed analyte thickness. Consequently, the reported metamaterial design can be used as a refractive index (RI) sensor with the high sensitivity of 300 GHz/RIU and the figure of merit (FoM) of 2.94 through an RI range from 1.0 to 1.39 at the analyte thickness of $1.0~ \mu \text{m}$ . Furthermore, the proposed sensor has a sensitivity of 23.7 GHz/ $\mu \text{m}$ for the detection of the sensing layer thickness variation at the fixed analyte RI of 1.35. It is worth noting that most of the biomedical samples have a refractive index range from 1.3 to 1.39. Therefore, the reported sensor can be used for biomedical applications with high sensitivity.

Highly Sensitive Terahertz Metamaterial Sensor

Polyphenolic extracts from pomegranate and watermelon wastes as substrate to fabricate sustainable silver nanoparticles with larvicidal effect against Spodoptera littoralis.

Integration of silicon nanowires in solar cell structure for efficiency enhancement: A review

In this study, a novel design of nano-antenna for energy harvesting is proposed and analysed using three-dimensional finite difference time-domain method. The new design consists of three elements nano-antenna with elliptical shape and with air gap. The numerical simulations are investigated for improving the harvesting efficiency of the nano-antennas within the wavelength range from 400 to 1400 nm. The suggested design has high efficiency of 74.6% at 500 nm where the irradiance of the sun is maximum. The proposed nano-antenna shows an improvement in the harvesting and the total harvesting efficiency over the conventional dipole antenna by 15 and 32.7%, respectively.

https://ietresearch.onlinelibrary.wiley.com/doi/pdf/10.1049/iet-opt.2013.0108

Design of flower-shaped dipole nano-antenna for energy harvesting

In this Letter, funnel-shaped silicon nanowires (SiNWs) are newly introduced for highly efficient light trapping. The proposed designs of nanowires are inspired by the funnel shape, which enhances the light trapping with reduced reflections in the wavelength range from 300 to 1100 nm. Composed of both cylindrical and conical units, the funnel nanowires increase the number of leaky mode resonances, yielding an absorption enhancement relative to a uniform nanowire array. The optical properties of the suggested nanowires have been numerically investigated using the 3D finite difference time domain (FDTD) method and compared to cylindrical and conical counterparts. The structural geometrical parameters are studied to maximize the ultimate efficiency and hence the short-circuit current. Carefully engineered structure geometry is shown to yield improved light absorption useful for solar cell applications. The proposed funnel-shaped SiNWs offer an ultimate efficiency of 41.8%, with an enhancement of 54.8% relative to conventional cylindrical SiNWs. Additionally, short-circuit current of 34.2  mA/cm2 is achieved using the suggested design.

Funnel-shaped silicon nanowire for highly efficient light trapping.

In this paper, a novel design of tapered dipole nanoantenna is introduced and numerically analyzed for energy harvesting applications. The proposed design consists of three steps tapered dipole nanoantenna with rectangular shape. Full systematic analysis is carried out where the antenna impedance, return loss, harvesting efficiency and field confinement are calculated using 3D finite element frequency domain method (3D-FEFD). The structure geometrical parameters are optimized using particle swarm algorithm (PSO) to improve the harvesting efficiency and reduce the return loss at wavelength of 500 nm. A harvesting efficiency of 55.3% is achieved which is higher than that of conventional dipole counterpart by 29%. This enhancement is attributed to the high field confinement in the dipole gap as a result of multiple tips created in the nanoantenna design. Furthermore, the antenna input impedance is tuned to match a wide range of fabricated diode based upon the multi-resonance characteristic of the proposed structure.

Optimized tapered dipole nanoantenna as efficient energy harvester.

In this paper, a novel design of Yagi–Uda nanoantenna is introduced and numerically analyzed using finite integration technique via computer simulation technology software. The proposed nanoantenna consists of five core-shell nanowires with silicon cladding and silver core to achieve high directivity for wireless point to point applications. The proposed design shows a high directivity of 17.21 at a wavelength of 500 nm, which exceeds the spherical dielectric counterparts with directivity of 12. Therefore, an enhancement of 43.41% is achieved, which is mainly useful for spontaneous emission manipulation and photon detection. This enhancement is attributed to the silicon dielectric shell that exhibits magnetic mode with high refractive index, as well as the surface plasmon mode supported by the silver core. Additionally, the proposed cylindrical design has advantages in terms of high homogeneity of the field distribution, which overcomes the inhomogeneity field distribution of the nanosphere-based design.

Highly Directive Hybrid Yagi-Uda Nanoantenna for Radition Emission Enhancement

An approach to enhance the ultimate efficiency of the silicon nanowires (Si NWs) solar cell is proposed based on a hybrid population-based algorithm. The suggested technique integrates the ability of exploration in a gravitational search algorithm (GSA) with the exploitation capability of particle swarm optimization (PSO) to synthesize both algorithms’ strengths. The hybrid GSA-PSO algorithm in MATLAB® code is linked to finite-difference time-domain solution technique based on Lumerical-software to simulate and optimize the Si NWs’ geometrical parameters. The suggested GSA-PSO algorithm has advantages in terms of better convergence and final fitness values than that of the PSO algorithm. Further, the Si NWs lattice with optimized diameters and heights shows a high ultimate efficiency of 42.5% with an improvement of 42.8% over the Si NWs lattice with the same diameters and heights. This enhancement is attributed to the different generated optical modes combined with multiple scattering and reduced reflection due to the different heights and different diameters, respectively.

Mohamed Hussein

Papers

Design of flower-shaped dipole nano-antenna for energy harvesting

Funnel-shaped silicon nanowire for highly efficient light trapping.

Optimized tapered dipole nanoantenna as efficient energy harvester.

Highly Directive Hybrid Yagi-Uda Nanoantenna for Radition Emission Enhancement

Optimal design of vertical silicon nanowires solar cell using hybrid optimization algorithm