Dr Maryam Khodadadi

This work introduces an innovative miniaturized transverse electromagnetic (TEM) waveguide design, which is 60% smaller than conventional metal waveguides. The proposed waveguide offers two distinct electronically reconfigurable passbands well below the cutoff frequency. This has been achieved by using sidewalls composed of reconfigurable artificial magnetic conductors (AMC), optimized to operate at 3.51 GHz and 4.37 GHz. By replacing the metal sidewalls with an AMC structure, a TEM mode can be sustained within the confined space enclosed by the waveguide structure, which otherwise would not exist in a conventional metal waveguide. This eliminates typical cut-off frequency constraints that limit the size of conventional waveguides, thereby enabling a significant miniaturization of the waveguide design. The work also proposes a reconfigurable AMC design whose operating frequency can be dynamically adjusted by applying or removing a direct current (DC) bias across the integrated PIN diodes. Additionally, this work utilizes 3D printing technology to fabricate a functional waveguide, highlighting the design’s compactness, cost-effectiveness, versatility, and fast prototyping capabilities for a wide range of microwave applications. This study therefore demonstrates the potential of using reconfigurable AMCs for compact and versatile waveguide designs that can be 3D-printed for various practical use cases and modern microwave applications.

The characteristics of a super-mode waveguide-fed nano-antenna composed of a complementary triangular hybrid plasmonic radiation part have been investigated by two methods of finite element and finite-difference time-domain. Also, a symmetric hybrid plasmonic waveguide (SHPW) has been studied theoretically and numerically to analyze short- and long-range fundamental TM super-modes (TM SR and TM LR ) that excite the nano-antenna. The obtained propagation length and figure of merit at 193.5 THz are 150.6 μm (1.27 μm) and 691.77 (16.94) for TM LR (TM SR ) super-mode, respectively, which confirm the inevitable loss-confinement trade-off of SHPW. These super-modes cause the nano-antenna to have horizontal and bidirectional radiation patterns due to the existence of the in-phase and out-of phase super-modes. The obtained directivities and efficiencies are 9.34 dBi (7.01 dBi) and 96.82% (9.66%) for TM LR (TM SR ) super-mode, respectively, at 193.5 THz. Moreover, the horizontal and bidirectional radiation patterns are appropriate for on-chip wireless links with the quality factor of 69.18 and target tracking systems, respectively. The performance of a single row array of nano-antenna on improving the directivity and efficiency has been studied. The proposed SHPW-fed nano-antenna is quite tolerant to practical fabrication errors and compatible with lift-off and electron beam lithography fabrication processes.

In this paper, a smart multi-user wireless link based on a graphene quantum well vertical hybrid plasmonic waveguide-fed nano-antenna is proposed. The theoretical method and finite element method (FEM) are used to verify that the vertical hybrid plasmonic waveguide (VHPW) supports both even and odd fundamental modes. Utilizing multi-mode graphene quantum well VHPW leads to the design of a selective mode nano-antenna with intermediate broadside and end -fire radiation patterns with high directivities of 9.38 dBi and 11.8 dBi at 193.5 THz, respectively, obtained by the finite-difference time domain method. Also, to verify the accuracy of nano-antenna results, the FEM approach is used. The nano-antenna performance as a wireless inter/intra-chip link is investigated, which confirms the even mode plays a key role to create a multiple-access wireless system. Based on the amazing features of graphene as an epsilon-near-zero and absorptive/transparent material, the accessibility of receivers is easily controlled. The effect of a single row array structure and its application as beam steering is studied. Finally, to estimate the performance of quantum well nano-antenna as a real device, which is compatible with electron-beam lithography and lift-off fabrication techniques, the effect of metal layer roughness and 5% tolerance for geometrical parameters are investigated. (c) 2021 Elsevier Ltd. All rights reserved.

In this paper, we have proposed AND and XOR logic gates simultaneously in one structure. The presented structure is based on two-dimensional (2D) nonlinear photonic crystal with T-shaped waveguide and micro-ring resonator. In the proposed structure, the power consumption is 2.5 x 107 W/mthat is lower than similar logic gates and the extinction ratio is about 6.5 dB. Also, the switching time is attained to be 0.2 and 0.26 ps for AND and XOR logic gates, respectively. Simplicity and small size (18.4 mu mx18.4 mu m) of the structure make it suitable for photonic integrated circuits (PICs). All simulations are based on finite-difference time-domain (FDTD) and plane wave expansion (PWE) numerical methods.

— This paper presents a novel leaky-wave antenna based on utilizing the high bandwidth and low loss ridge gap waveguide concept, featuring a cosecant squared radiation pattern. The antenna is designed to operate within the frequency range of 25 GHz to 29 GHz. At the center frequency of 28 GHz, the antenna achieves a maximum gain of 10 dBi. Additionally, at a frequency of 28.8 GHz, the antenna exhibits a maximum return loss of-16.9 dB. Moreover, the proposed leaky-wave antenna demonstrates the potential of the radiation technology for 5G systems by enabling scanning angles ranging from approximately 5 ֯ to 20֯ across the specified frequency range. This feature highlights the versatility and suitability of the antenna for various applications in 5G communication systems.

In this paper, the idea of square fractal geometry has been utilized to introduce a tunable wideband graphene-based perfect plasmonic absorber in the near-infrared region. It consists of a MgF2 layer and an array of gold squares fractal loaded on a graphene layer. In the designed absorber a single layer of graphene has been used instead of multilayered graphene structures. The structure is polarization-insensitive under normal incidence due to the geometric symmetry. The absorption and bandwidth of the structure are almost insensitive to the incident angle up to 15 degrees and 45 degrees for TE and TM polarizations, respectively. Moreover, by choosing appropriate structural parameters, the resonance wavelength of the desired plasmonic absorber can be controlled. The absorption of the introduced structure can be tuned by changing the chemical potential of the graphene. Therefore, the proposed fractal absorber can act as switch and inverter at lambda = 1995 nm. Furthermore, the equivalent circuit model of the absorber has been derived to confirm the validity of the simulation results. The superiorities of our fractal absorber are wide full-width at half-maximum of 406 nm, multi-applicant, perfect absorption, and fabrication feasibility due to the simple structure with the maximum absorption tolerance error of 5.12%.

In this paper, an all-optical plasmonic multi-wavelength switch based on Kerr nonlinear material is proposed. It consists of circular waveguides wrapped around three side-coupled nano-ring resonators. Fundamentally, introducing the circular waveguide increases the coupling coefficient and switching modulation depth. The transmission response of the proposed multi-switching structure is studied theoretically based on coupled mode and transfer matrix theories. The validity of the derived transmission formula is confirmed by the numerical result obtained by the finite element method. Also, based on the self-phase modulation and cross-phase modulation (XPM) nonlinear effects, the resonance wavelengths are effortlessly tuned by changing the intensity of the incident lightwave without changing the dimensions of the structure. As a result, by utilizing the XPM effect, the required input signal intensity is significantly decreased to 6.5 MW/cm(2). The obtained modulation depths are 18.08, 31.83, and 28.40 dB at wavelengths of 850, 1310, and 1550 nm, respectively. Finally, to show the application of the proposed switch, the simultaneous AND and NOR logic gates are designed with intensity contrast ratios of 78.81 and 85.49 dB, respectively. The proposed plasmonic switch has many advantages such as being multi-wavelength and having low required switching intensity, ultra-fast switching time of 23 fs, and optical bistability. These features are promising for future integrated plasmonic devices for applications such as communications, signal processing, and sensing. (C) 2020 Optical Society of America

In this paper, a wideband InP-based hybrid plasmonic nano-antenna (HPNA) operating at telecommunication wavelengths has been proposed. Monolithically integrating InP-based lasers with hybrid plasmonic waveguide (HPW) as a feed line of the proposed HPNA on the same InGaAsP/InP wafer can increase the antenna efficiency. A new vertical director has been employed to have a highly directive horizontal radiation pattern. This enhancement is attributed to the efficient coupling between the radiation patterns of arm elements as well as reduced side lobes and back-lobes levels due to the achieved impedance matching. As a result, the directivity has been increased considerably, 3.6 dBi at 193.5 THz (1550 nm) and 1.1 dBi at 229 THz (1310 nm). The HPNA shows the high directivity, total efficiency and quality factor of 11.8, 97.49% and 94.57, respectively. Further, to verify the validity of confining the fundamental TM mode to a thin layer with the lower refractive index, both theoretical and numerical methods have been employed. Therefore, we have derived an analytical formula to investigate the HPW dispersion relation based on the transfer matrix theory and genetic algorithm. Moreover, due to the HPNA ability to receive an optical signal from free space and transmit it to the waveguide based on the reciprocity theorem, the HPNA performance as an optical wireless on-chip nano-link has been investigated analytically and numerically. Additionally, to obtain a high optical power signal and steering the beam angle, the antenna gain and directivity have been calculated with two different types of array structure by controlling the relative phase shift between the array elements and elements number. To validate the array design performance, a three dimensional full-wave numerical simulation and array factor theory have been exploited. The HPNA fabrication is compatible with generic foundry technology. (C) 2020 Optical Society of America under the terms of the OSA Open Access Publishing Agreement

In this paper, we have investigated two unique wideband (WB) bandpass filters (BPFs) based on composite right/left-handed (CRLH) structure that have high performance in C-band. The proposed filters have been implemented with stepped-impedance resonator (SIR) section and interdigital capacitors on it with a parallel coupled-shorted stub (CSS). High selectivity, high out-of-band rejection, low loss and two transmission zeroes at the lower and upper passband/stopband edges have been observed. The out-of-band rejection levels in two filters are better than 17 dB and 20 dB at the lower and upper band edges, respectively. In addition, the return loss and insertion loss of the proposed CSS filter are greater than 17 dB and less than 0.7 dB, respectively. Also, the return loss and insertion loss of the proposed spiral CSS (SCSS) filter are greater than 20 dB and less than of 0.5 dB, respectively. The presented structures have been investigated analytically and experimentally in order to verify balance between the results of the full-wave simulation and the equivalent circuit model with the experimental ones. The dimensions of the suggested filters are 21.6 x 3.06 mm(2) and 14.6 x 4.2 mm(2). The specifications and compact size of the filters make them suitable for wideband wireless communication systems. (C) 2019 Elsevier GmbH. All rights reserved.

A simultaneous plasmonic refractive index and thickness bio-sensor has been investigated theoretically and numerically to detect DNA hybridization and biomolecules attached to the inner wall of nano-ring resonators. The finite element method has been used to better appreciate the derived transmission formula based on both transfer matrix and coupled mode theories. For the first time, by applying a monolayer of graphene around the nano-ring resonators and introducing a MIM circular coupled waveguide, the power coupling coefficient, figure of merit and efficiency of the bio-sensor have been enhanced. Also, the coupling distance and optical properties including the chemical potential of graphene have been considered and studied to obtain optimal results. The maximum attained sensitivity and figure of merit of the bio-sensor are 1100 nm/RIU and 200 RIU −1 , respectively. By employing a strong coupling condition, the full-width at half-maximum and extinction ratio have been obtained as 5 nm and 40 dB, respectively. Finally, the potential of the proposed structure as simultaneous AND and NOR logic gates have been studied with the intensity contrast ratios of 57 and 102.6 dB, respectively. Due to the excellent performance of the graphene-based circular plasmonic structure, it can find significant applications in photonic integrated circuits and on-chip nano-sensors.

One of the most controversial issues in Reconfig-urable Intelligent Surfaces (RIS) is how to localize users. A potential solution is to integrate sensing and communication into the RIS platform to simultaneously detect a target and establish a communication link. By utilizing a shared spectrum, it is possible to optimize the channel with little to no mutual interference. To this end, a hybrid metasurface layout is proposed that supports beamforming while also enabling the sensing of incident signals from the user. This hybrid technology couples a small portion of the incident signal into a sensing layer. In the next step, a sensing scheme is introduced that leverages the inherent multiplexing of information within the metasurface's substrate to retrieve relevant information using a few sensing elements. The proposed metasurface can generate desired radiation patterns, and the addition of sensing capabilities has minimal impact on its primary functionality.

In this paper, for the first time, the idea of a dielectric director has been utilized to improve the directivity and gain of the proposed hybrid plasmonic rhombic nano-antenna (HPRNA). The proposed HPRNA can support a horizontal radiation pattern to flourish the concept of wireless transmission link. The horizontal radiation pattern has a 3 dB beamwidth of 43.5°, side lobe level of −11.9 dB, and a directivity and gain of 10.5 dBi and 10.3 dB, respectively, at the operating frequency of 193.5 THz. Moreover, the effects of geometric parameters to verify the functionality of the proposed nano-antenna have been investigated. Finally, the idea of an on-chip wireless transmission link based on transmitting and receiving HPRNAs has been developed and studied theoretically and numerically. The fabrication of the proposed nano-antenna can be done by the typical e-beam lithography (EBL) technique, which is easier than the complicated X-ray method because of its suitable aspect ratio.

In this paper, a wideband hybrid plasmonic V-shaped nano-antenna is proposed based on coupled hybrid plasmonic waveguide (CHPW) feeding to increase the surface plasmon propagation length. The CHPW specifications are investigated analytically and numerically to obtain the dispersion relation and propagation length using the genetic algorithm and the finite element method, respectively. Moreover, the proposed V-shaped nano-antenna, with a fractional bandwidth of similar to 86% and a maximum efficiency of 98%, is able to receive/transmit optical signals at three telecommunication wavelengths of 850, 1310, and 1550 nm with high realized gains of 10.5, 9.39, and 9.05 dB, respectively. The shape of the radiation pattern, with a main lobe along the antenna axis, makes this antenna appropriate for point-to-point connections in inter- or intra-chip optical wireless links and networks, which is studied comprehensively in this article. Furthermore, to obtain a high optical power signal and tune the antenna orientation, the performance of the antenna is investigated with two different types of array structure, single row and square, and its applications for energy harvesting and beam steering are studied. The fabrication feasibility of the nano-antenna is realizable based on complementary metal-oxide-semiconductor technology.

In this paper, for the first time, a dynamic tunable graphene-based cross Yagi-Uda antenna in the terahertz region has been investigated comprehensively by two numerical methods and analytical analysis. To verify the accuracy of the analytical solution based on the coupled dipole method to obtain the directivity pattern, two numerical methods of finite-element and finite-difference time-domain have been used. Numerical results are well matched with the theoretical ones. By introducing the tunable cross Yagi-Uda antenna with graphene-coated spheres, different directivity radiation patterns such as omni-, vertical and horizontal bi- and quad-directional have been obtained with the maximum directivities of 2.42, 12.4, 12.3, and 10.5 dBi, respectively. Moreover, the effect of different element shapes including cube and cylinder on the directivity and radiation efficiency has been studied. Also, the new idea of multiple-access and controlling the user's access to the radiated optical electromagnetic waves from the transmitting antenna has been studied as an optical wireless on-chip link. Finally, the effect of structural parameters on the directivity of the proposed antenna has been surveyed with the tolerance of ±5% to investigate the imperfections that may appear in the fabrication process.

In this paper, a circular hybrid plasmonic waveguide-fed nano-antenna (CHPWFNA) has been introduced for operating at the standard telecommunication wavelength of 1,550 nm. For the first time, the dispersion relation of a circular hybrid plasmonic waveguide as the feed line of the proposed nano-antenna has been derived, analytically. To verify the accuracy of the analytical solution, two numerical techniques of finite element method (FEM) and finite-difference time-domain (FDTD) method have been used. Numerical results are well-matched with the theoretical ones. The characteristics of the CHPWFNA have been studied by two mentioned methods. The obtained realized gains (directivities) by the FDTD and FEM simulations are 9.03 dB (9.38 dBi) and 10.00 dB (10.32 dBi), respectively, at 1,550 nm wavelength. For on-chip point-to-point wireless link performance, the obtained quality factor by the FDTD method (FEM) is 63.97 (100). The obtained radiation characteristics and link performance reveal that at 1,550 nm, the proposed antenna has the best performance. Besides, the frequency bandwidth of the antenna (185-200 THz) covers the low-loss optical frequency range. Also, paying attention to the laser eye safety is so important. Consequently, the wavelength of 1,550 nm has been chosen as the target wavelength. Moreover, the array configuration has been studied and the directivity and realized gain have been obtained based on the array factor theory and numerical methods, which are agree with each other. The attained realized gain by the FDTD method (FEM) for the considered single row array, at 1,550 nm, is 11.20 dB (11.30 dB). There is a little difference between the numerical results due to the total mesh size, the grid size refinement and the relative error of the numerical methods convergence. Finally, as one of the most important challenges in fabrication is the gold surface quality, we have studied the effect of gold surface roughness and its pentagonal cross section on the antenna performance.

In this paper, synthesis of the flat-top radiation pattern with sharp cutoff for reducing the lobing fades due to the presence of the earth is investigated. To this end, first the propagation factor is investigated. Then based on the propagation factor, the antenna pattern is examined at different levels of the cutoff to achieve a flat-top radiation with low level of lobing fades. Finally, synthesizing the desired radiation pattern is investigated through Woodward-Lawson method. Our studies reveal that that antenna with large length (> 12λ) provides the desired flat-top pattern with the appropriate cutoff. The aperture distribution of the desired pattern is provided and discussed.

his paper presents a new dual and complementaryimpedance metasurface platform for studying Line Waves (LWs), electromagnetic modes at interfaces of different metasurfaces like capacitive and inductive types. The excited states, characterized by efficient one-dimensional propagation and tight interface confinement, hold promise for robust waveguide applications, especially within fifth-generation (5G) technology. The research shows that LW, supporting broadband frequencies, can be tuned through capacitive or inductive properties, with a semi-analytical model developed for in-depth analysis. Additionally, a parallel plate waveguide composed of four metasurfaces demonstrates LW robust transmission capabilities, even under longitudinal warping. This highlights their potential in wearable wireless communications and flexible electronics, showcasing their adaptability and efficiency.