Author Archives: Leyla

Our Paper on “Far-field sub-wavelength imaging”was accepted for publication in Optics Express.

Abstract

Due to the wave nature of light, the resolution achieved in conventional imaging systems is limited to around half of the wavelength. The reason behind this limitation, called diffraction limit, is that part of the information of the object carried by the evanescent waves scattered from an abject. Although retrieving information from propagating waves is not difficult in the far-field region, it is very challenging in the case of evanescent waves, which decay exponentially as travel and lose their power in the far-field region. In this paper, we design a high-order continuous dielectric metasurface to convert evanescent waves into propagating modes and subsequently to reconstruct super-resolution images in the far field. The designed metasurface is characterized and its performance for sub-wavelength imaging is verified using full wave numerical simulations. Simulation results show that the designed continuous high-order metasurface can convert a large group of evanescent waves into propagating ones. The designed metasurface is then used to reconstruct the image of objects with sub-wavelength features, and an image with the resolution of λ/5.5 is achieved.

link:

https://opg.optica.org/oe/fulltext.cfm?uri=oe-30-21-39025&id=509746

Our Paper on “Thermal insulator film with transparency to visible light”was accepted for publication in JOSA B.

Abstract

A method to develop an insulator window film which is able to filter thermal emission while transmitting the visible spectrum of sunlight is proposed. The proposed film is constructed from engineered metallic nano-spheres randomly distributed in SiO2SiO2, as a host medium. The performance of the designed film is investigated using both analytical models and numerical full-wave simulations. The analytical analysis shows that the thermal emission (the wavelengths in the range of 6–16 µm) is suppressed by more than 10 dB when going through the designed film, meaning that more than 90% of the thermal power is filtered by the film. This is while more than 50% of the visible light passes through the film. Similar results are obtained using numerical full-wave simulations. Moreover, to have a more comprehensive study on the ability of our method, the illuminance due to the insulator window film is calculated and compared with illuminance in different places. This comparison shows that the resultant illuminance in a typical room at the distance of 4 m from the designed window is in the range of illuminance required in a typical office room.

link:

https://opg.optica.org/josab/fulltext.cfm?uri=josab-39-10-2760&id=506490#

Our Paper on “Design and analysis of multi-layer silicon nanoparticle solar cells”was accepted for publication in Scientific Reports.

Abstract

We investigate the concept of nanoparticle-based solar cells composed of a silicon nanoparticle stack as a light trapping absorber for ultrathin photovoltaics. We study the potential of using these inherently nanotextured structures in enhancing the light absorption. For this, a detailed optical analysis is performed on dependency of the cell response to parameters such as the number of particle layers, lattice structure and angle of incidence; Optical response of these cells are then compared with the results in conventional silicon solar cells. Moreover, we propose various configurations to apply these submicron particles as a p–n junction solar cell. We also compute the electrical performance of selected configurations. In doing so, key issues including the effect of contact points between nanoparticles and impact of loss are addressed. In the end, we show how SiO2SiO2 nanoparticles on top of the cell structure can enhance the photocurrent. The appropriate range of SiO2SiO2 particle size is also obtained for the typical cell structures.

 

link:

https://www.nature.com/articles/s41598-022-17677-z

Our Paper on “A periodic perforated graphene in optical nanocavity absorbers”was accepted for publication in Materials Science and Engineering.

Abstract

Aperiodic perforated graphene layers were synthesized and used in fabrication of optical nanocavity absorbers. Chemical vapor deposition-grown graphene (Gr) layers were exposed to oxygen plasma etching to obtain the perforated graphene (pGr). The fabricated pGr/SiO2 (68 nm)/Ag (150 nm) nanocavity could present significant higher optical absorption, especially at around 530 nm wavelength region, as compared to a benchmark Gr/SiO2 (68 nm)/Ag (150 nm) sample. The effect of pore size of the pGr layer on the absorption property of the nanocavity has been studied by both experimental and numerical methods. The dependence of the absorption property of the nanocavity on the incident angles of unpolarized light and also the electrical/magnetical portion of transverse polarized light have been examined. The electrical interaction between the nanopores of the pGr and the incident light was found as the main reason for the absorption. The proposed graphene-based nanocavity resonator can further excite designing high efficient electromagnetic wave absorbers highly demanding two-dimensional coatings with effective optical absorption features.

link:

https://www.sciencedirect.com/science/article/abs/pii/S0921510721005110

Our Paper on “A Novel Plasmonic Bio-Sensor Operating Based on Optical Beam Steering”was accepted for publication in IEEE,Journal of Lightwave Technology.

Abstract

In this paper, a new architecture for developing plasmonic bio-sensors is proposed in which sensing is achieved through optical beam steering. The proposed structure consists of an array of nano-antennas that generate an outcoming optical beam whose direction varies when the material under test or its volume changes. This mechanism of sensing eliminates the requirement for complex instruments such as optical spectrum analyzers. For realization of the proposed bio-sensor, both 1-D and 2-D configurations for the nano-antenna array are designed and numerically studied. The full wave numerical simulation results show that the designed bio-sensor provides a very high sensitivity of 3333∘ per unit refractive index, and also the output light has an enough intensity to be observed by a naked eye. The final results show that although both versions have the same sensitivity, the 2-D structure can project the results with much higher intensity. It is also theoretically shown that the performance of the biosensor will be subject to the size of the array, and therefore, a practical large-scale version of the numerically studied structure would significantly outperform the simulated structure.

link:

https://opg.optica.org/jlt/abstract.cfm?uri=jlt-40-1-277

Our Paper on “Light trapping in thin film crystalline silicon solar cells”was accepted for publication in Optics & Laser Technology.

Abstract

In this paper, a new method is proposed to trap sunlight in the active layer of thin film solar cells. In the proposed technique, multi-scale photonic topological insulators (PTI) realized by photonic crystals, are integrated inside the active layer of a thin film solar cell in order to trap sunlight in the cell. The trapping is realized by excitation of edge states supported by the designed topological insulator. The performance of the proposed solar cell with the topological insulator inside is investigated through full wave numerical analysis. Numerical results show that the proposed method enhances the absorption of the solar spectrum inside the cell in a wide range of wavelengths, and also for different angles of incidence. The short circuit current provided by the proposed solar cell is numerically calculated illustrating a value of 27.72 mA/cm2 for a normally incident light which is 47% higher than a simple solar cell without topological insulator inside.

link:

https://www.sciencedirect.com/science/article/abs/pii/S0030399221005454

Our Paper on “Absorption enhanced thin-film solar cells”was accepted for publication in IET Optoelectronics.

Abstract

In this article, a new structure for development of thin film solar cells is proposed in which elements with fractal shapes are integrated inside the cell to enhance its performance in a wide range of wavelengths. Two different structures are studied. In the first structure, a metallic fractal nano-carpet is integrated inside the silicon layer in order to trap and absorb sunlight by exciting surface plasmon polaritons and local surface plasmons at different wavelengths. Numerical analysis shows that this technique increases the short circuit current provided by the cell by a factor of 2.40 for both TM and TE polarisations of the incident light. The second structure has an active layer shaped as a fractal structure, and absorbs sunlight through Mie and Fabry-Perot resonances occurring at different wavelengths. The short circuit current enhancement for this structure is 2.97 for both TM and TE polarisations of the incident light, representing a significant improvement when compared with the previous works.

link:

https://ietresearch.onlinelibrary.wiley.com/doi/full/10.1049/ote2.12036

Our Paper on “Developing an optimized metasurface for light trapping in thin-film solar cells”was accepted for publication in JOSA B.

Abstract

 

In this paper, using a deep neural network and a genetic algorithm, an optimized digital metasurface is designed to trap sunlight in thin-film solar cells. The deep neural network is trained using full-wave numerical simulation results as the training dataset, and it is designed to predict the electromagnetic response of thin-film solar cells whose active layers are shaped as a digital metasurface. The developed neural network can predict the results much faster than full-wave solvers and therefore can be used for optimization purposes. Using the results generated by the trained neural network, an evolutionary procedure based on the genetic algorithm is developed to find the optimum structure for the digital metasurface, which provides the highest short circuit current inside the thin-film solar cell. The performance of the resultant optimum design is validated using full-wave numerical simulation illustrating a short circuit current of 15.39mA/cm215.39mA/cm2 and 13.30mA/cm213.30mA/cm2 for TE and TM polarization of the incident light, respectively. The resultant short circuit current is 2.47 and 2.13 times higher than a simple thin-film solar cell with the same amount of silicon inside, for TE and TM polarization of the incident light, respectively. To have a more comprehensive comparison, the designed optimum structure is compared with several standard shapes for the metasurface, such as star and plus sign. This comparison showed that the optimum structure provides a short circuit current which is much higher than the current achieved by standard shapes.

link:

https://opg.optica.org/josab/abstract.cfm?uri=josab-38-9-2728

Our Paper on “Distributed silicon nanoparticles”was accepted for publication in Optical Society of America.

Abstract

In this paper, a new architecture comprising silicon nanoparticles inside a hole transport layer laid on a thin silicon layer is proposed to develop ultrathin film solar cells. Using generalized Mie theory, a fast analytical approach is developed to evaluate the optical absorption of the proposed structure for various geometries, polarizations and angles of incidence. The analytical results are verified through comparison with full-wave simulations, illustrating a reasonable agreement. The electrical performance of a distributed silicon nanoparticle solar cell is determined for selected configurations. To be able to predict the light-trapping in a solar cell comprising randomly distributed nanospheres, a new technique based on probability theory is developed and validated through comparison with the simulation results. Both analytical and numerical results show that the excited Mie resonant modes in the proposed structure lead to a significant enhancement in both absorption and the photo-generated current, in comparison to a conventional silicon solar cell with an equivalent volume of the active layer. In the case of random distributions, other advantages, including the simple fabrication process, indicate that the cell is a promising structure for ultrathin photovoltaics.

link:

https://opg.optica.org/oe/fulltext.cfm?uri=oe-29-18-28037&id=457250

Our Paper on “Analysis of wave scattering from 2D curved metasurfaces”was accepted for publication in IET Microwaves, Antennas & Propagation.

Abstract

An efficient technique for calculating the scattering from curved metasurfaces using the extinction theorem in conjunction with the Floquet and Fourier series expansions is presented. Here, we treat the two-dimensional metasurfaces that have transversal polarizabilities with no variation along the y-axis. The boundary conditions at the metasurface are given by the generalized sheet transition conditions (GSTCs) whose susceptibilities are given in an arbitrary local coordinate system. First, we use the extinction theorem to provide integral equations of the scattering problem. The integral equations involve the Green’s functions, tangential electric and magnetic fields and their normal derivatives in regions above and below the metasurface. Then, we employ the Floquet theorem that gives us the analytical periodic Green’s functions of each region. Next, we employ the Fourier theorem to expand the tangential fields in terms of unknown Fourier coefficients. The GSTCs and the integral equations provide equations to be solved for the unknowns. The method can calculate scattering from both periodic and non-periodic metasurfaces. The technique is used to analyse different applied problems such as carpet cloaking, illusion, and radar echo width reduction. The method is fast and accurate and can efficiently treat metasurfaces with electrically large curved geometries with dimensions as large as 120 times the wavelength.

link:

https://ietresearch.onlinelibrary.wiley.com/doi/full/10.1049/mia2.12115