Sharif Digital Repository

The equivalent circuit approach (ECA) is used in this work to analyze and design a previously proposed one-dimensional planar blazed grating of the resonant type. The analysis covers both the classical Littrow configuration, when the direction of the relevant diffracted order coincides with that of the incident wave (Bragg blazing), and when these directions are different (off-Bragg blazing). Once the scattering problem of the grating structure is posed as a discontinuity problem inside an equivalent generalized waveguide (corresponding to the unit cell of the original structure) and studied in terms of its equivalent circuit network, the possibility of transferring all the power of the... 

In a recently published article by Backer [Opt. Express 27(21), 30308 (2019).], a computational inverse design method is developed for designing optical systems composed of multiple metasurfaces. The forward propagation model used in this method was a discretized version of the angular spectrum propagator described by Goodman [Introduction to Fourier Optics, 1996]. However, slight modifications are necessary to increase the accuracy of this inverse design method. This comment examines the accuracy of the results obtained by the above-mentioned method by a full-wave electromagnetic solver and explains the reason of their difference. Thereafter, slight modifications to the method proposed by... 

We investigate the possibility of frequency conversion in time-varying metasurfaces, composed of graphene microribbon arrays (GMRAs) with time-periodic modulation of their conductivity. We present a quasi-static model for the interaction of light with a temporally modulated metasurface, as well as an accurate analytical treatment of the problem of time-varying GMRAs. Results coming from numerical simulations are also available. We provide corrections to a previous related proposal for frequency conversion and refute the possibility of attaining frequency shifts not equal to an integral multiple of modulation frequency. Contrary to the preceding results, our findings show that efficient... 

Traditional analog computers that perform mathematical operations electronically or mechanically suffer from their relatively large size and slow response. Recently, the idea of spatial analog optical computing has overcome these restrictions. The different techniques to implement spatial analog optical computation can be categorized into two fundamental approaches: (I) metasurface (MS) approach and (II) Green's function (GF) approach. In the first approach, a metasurface is designed to implement the Green's function of the desired operator in the spatial domain. This means that this approach needs two sub-blocks to perform Fourier and inverse Fourier transform. On the other hand, in the... 

Recently, an approximate formalism [Opt. Express 23, 2764, (2015)] called diffractive interface theory has been reported for the fast analysis of the optical response of metasurfaces, subwavelength two-dimensional periodic arrays. In this method, the electromagnetic boundary conditions are derived using the susceptibility distribution of the metasurface, such that the analysis of metasurface is possible without solving any eigenvalue equation inside the grating layer. In this paper, we modify the boundary conditions to achieve more accurate results. In addition, in this paper, correct Fourier factorization rules are also applied leading to faster convergence rate. The obtained results are... 

A new resonance phenomenon is discussed and demonstrated by experiment in a dual-polarization cavity. The resonance is formed by waves bouncing between two anisotropic metasurfaces placed at the cavity ends. The simple metasurfaces are designed to preserve the handedness of circularly polarized waves upon reflection. The standing waves resulting from such reflections do not have nodes and antinodes. A theoretical solution to the resonance condition is discussed, both for plane-waves and equivalent guided waves. The concept is then experimentally applied to dual-mode guided waves, demonstrating a very short cavity at X-band. This brings new possibilities for resonator design and can... 

A new resonance phenomenon is demonstrated in waveguide cavities, which simultaneously uses two orthogonal modes (polarizations). This resonance is formed by bouncing waves with similar handedness, between two simple anisotropic metasurfaces having a relative rotation angle. The rotated anisotropic metasurfaces can cross couple the waves from one polarization to the other at the cavity end. The field profile of the resonant mode does not exhibit nodes and antinodes, thus the resonant frequency is not solely determined by the cavity length, unlike common resonators. The resonance condition is theoretically demonstrated from both field and transmission line perspectives, and is validated by... 

In this letter, a new approach to perform edge detection is presented using an all-dielectric complimentary metal-oxide-semiconductor-compatible metasurface. Our design is based on the guided-mode resonance, which provides a high quality factor resonance to make the edge detection experimentally realizable. The proposed structure is easy to fabricate, and it can be exploited for detection of edges in two dimensions due to its symmetry. In addition, a tradeoff between gain and the resolution of edge detection is discussed, which can be adjusted using appropriate design parameters. The proposed edge detector potentially can be used in ultrafast analog computing and image processing. ©... 

We propose a novel graphene-dielectric-based metasurface for manipulating the polarization of the incident light in the terahertz regime. The proposed structure comprised two orthogonally oriented periodic array of graphene ribbons (PAGRs) which are separated by a dielectric spacer and deposited on an Au-backed dielectric substrate. Based on the transmission line theory, an equivalent model with excellent accuracy is suggested for the proposed structure. By leveraging the simplicity of the model, we design a three-state quarter wave plate that is able to dynamically switch the polarization of the reflected wave to linear, right-, and left-hand polarizations while keeping the reflected... 

In this paper, we present a Gaussian to tophat beam shaper (GTBS) based on an all-dielectric metasurface lens for sub terahertz (sub-THz) applications. In order to calculate the required phase profile of the GTBS, we use an analytical procedure based on the geometrical transformation technique. The calculated phase profile is then realized by a silicon (Si) metasurface lens consisting of rectangular-shaped pillars of subwavelength dimensions. Because of large solution domain relative to the operation wavelength, we combined the beam envelope and the finite element methods to simulate the structure with a high precision. By designing an anti-reflection metasurface made up of periodically... 

Recently, metasurfaces capable of manipulating the amplitude and the phase of an incident wave in a broad frequency band have been employed for femtosecond optical pulse shaping purposes. In this study, we introduce a phase-only pulse shaper based on an all-dielectric CMOS-compatible polarization-insensitive metasurface, composed of Si nano cylinders sitting on a fused silica substrate. The required phase profile of the metasurface for desired waveforms are calculated using an iterative Fourier transform algorithm, and the performance of the pulse shaper metasurface in implementing the phase masks was assessed using full-wave simulations. Such approach for realizing a... 

Recently, metasurfaces capable of manipulating the amplitude and the phase of an incident wave in a broad frequency band have been employed for femtosecond optical pulse shaping purposes. In this study, we introduce a phase-only pulse shaper based on an all-dielectric CMOS-compatible polarization-insensitive metasurface, composed of Si nano cylinders sitting on a fused silica substrate. The required phase profile of the metasurface for desired waveforms are calculated using an iterative Fourier transform algorithm, and the performance of the pulse shaper metasurface in implementing the phase masks was assessed using full-wave simulations. Such approach for realizing a... 

Multiband absorption is the interest of the microwave communities due to several applications in sensing, filtering, and stealth. Usually, the stacking of metal and dielectric multilayered structures form a multiband absorber which makes the device bulky and costly. In this paper, we investigate a multiband absorber based on a single-layered fractal metasurface for the 5G applications. The unit cell of the fractal metasurface is comprised of six ring-shaped symmetric split-ring resonators (SRRs) connected back-to-back with each other. The absorptivity is investigated in the 5G microwave regime (22–36 GHz) for various obliquities at different substrate thicknesses. Simulation results show... 

Due to the wide range of applications of metal/graphene-based plasmonic metasurfaces (sensors, absorbers, polarizers), it has become essential to provide an analytical method for modeling these structures. An analytical solution simplified into a circuit model, in addition to greatly reducing the simulation time, can become an essential tool for designing and predicting the behaviors of these structures. This paper presents a high-precision equivalent circuit model to study these structures in one-dimensional and two-dimensional periodic arrays. In the developed model, metallic patches similar to graphene patches are modeled as surface conductivity and with the help of current modes induced... 

We present an emulation design method for converting asymmetrical transmitters to nonreciprocal isolators equipped with time-varying metasurfaces. To illustrate the model, we design a structure using a combination of the photonic crystal (PhC) and time-varying metasurface. Moreover, we propose a general approach for numerical analysis of the time-modulated proposed structure using the extension of the transfer matrix method (TMM) which consists of working through the device one layer at a time and calculating an overall transfer matrix including the time-variation of the permittivity and permeability in each layer. Also, we use an optimization algorithm that is less used in the field of... 

In this paper, a novel method is exposed to improve the performance of the Golden code. In fact, we recommend using the octagonal reconfigurable isolated orthogonal element (ORIOL) antennas instead of a conventional microstrip patch antenna. In order to obtain a dramatic improvement, the ORIOL antenna should be employed in both the transmitter and the receiver sides. Accordingly, in this paper, we recommend space-time-polarization diversity instead of space-time singly; therefore, it is obvious that by employing this technique, the system obtains more strength against destructive fading. The simulations for different rates have confirmed that utilizing the ORIOL antenna outperforms patch...