Dr. Saghaei's academic websitete

Saghaei's papers published in 2021

[1] M. Hosseinzadeh Sani, H. Saghaei, M. A. Mehranpour, and A. Asgariyan Tabrizi, “A novel all-optical sensor design based on a tunable resonant nanocavity in photonic crystal microstructure applicable in MEMS accelerometers,” Photonic Sensors, vol. 11, no. 4, pp. 457–471, 2021, doi: 10.1007/s13320-020-0607-0.

In view of the large scientific and technical interest in the MEMS accelerometer sensor and the limitations of capacitive, resistive piezo, and piezoelectric methods, we focus on the measurement of the seismic mass displacement using a novel design of the all-optical sensor (AOS). The proposed AOS consists of two waveguides and a ring resonator in a two-dimensional rod-based photonic crystal (PhC) microstructure, and a holder which connects the central rod of a nanocavity to a proof mass. The photonic band structure of the AOS is calculated with the plane-wave expansion approach for TE and TM polarization modes, and the light wave propagation inside the sensor is analyzed by solving Maxwell’s equations using the finite-difference time-domain method. The results of our simulations demonstrate that the fundamental PhC has a free spectral range of about 730 nm covering the optical communication wavelength-bands. Simulations also show that the AOS has the resonant peak of 0.8 at 1.644µm, quality factor of 3288, full width at half maximum of 0.5nm, and figure of merit of 0.97. Furthermore, for the maximum 200nm nanocavity displacements in the x- or y-direction, the resonant wavelengths shift to 1.618µm and 1.547µm, respectively. We also calculate all characteristics of the nanocavity displacement in positive and negative directions of the x-axis and y-axis. The small area of 104.35 µm2 and short propagation time of the AOS make it an interesting sensor for various applications, especially in the vehicle navigation systems and aviation safety tools.

[2] S. Naghizade and H. Saghaei, “Tunable electro-optic analog-to-digital converter using graphene nanoshells in photonic crystal ring resonators,” Journal of the Optical Society of America B, vol. 38, no. 7, pp. 2127–2134, 2021, doi: 10.1364/JOSAB.423088.

In this paper, we propose a novel design of a tunable electro-optic analog-to-digital converter. The proposed structure consists of a tunable three-channel demultiplexer and an optical encoder. The first part provides sampling and quantization of the input electrical analog signal based on the applied potential to the graphene nanoshells (GNSs), while the second part converts the quantized levels into two-bit binary code. The electro-optic demultiplexer is realized using three GNS-based photonic crystal resonant cavities and can be tuned by applying different biasing of the gate voltage to the GNSs. For appropriate chemical potential values of GNS, each resonant cavity can drop the optical beam into its corresponding output port. This tunable ultrafast device supports a maximum sampling rate of up to 222 GS/s, whereas its compact footprint is about 692µm2. The proposed device opens a new window to the design and fabrication of tunable graphene-based photonic crystal circuits to develop electro-optic on-chip processing systems.

[3] A. A. Tabrizi, H. Saghaei, M. A. Mehranpour, and M. Jahangiri, “Enhancement of absorption and effectiveness of a perovskite thin-film solar cell embedded with Gold nanospheres,” Plasmonics, vol. 16, pp. 747–760, 2021, doi: 10.1007/s11468-020-01341-1.

This paper proposes a novel design of plasmonic perovskite solar cell (PSC). It consists of an anti-reflective glass of fluorine-doped tin oxide (FTO), a compact buffer layer of n-type titanium dioxide (TiO2), an absorbing thin-film layer of perovskite (MAPbI3) integrated with gold (Au) nanospheres, a layer of p-type doped spiro-OMeTAD, and a layer of the cathode on aluminum (Al). This multilayer design’s primary purpose is to allow the light to enter the PSC with the minimum reflection and trap it in the active layer due to the presence of Au nanospheres. In this layer, the higher efficiency of PSC is achieved by localized surface plasmon resonances (LSPRs) in the wavelength range from 300 to 1100 nm. A reflective Al layer is used at the bottom of the device to reflect the light into the upper layers to considerably enhance the PSC absorption. The three-dimensional finite-difference time-domain method was conducted to find the best solution to Maxwell’s equations so that the best thickness and radius can be selected for each layer and Au nanospheres, respectively. Proper physical dimensions and Au nanospheres played a significant role in numerically indicating that the proposed structures are 60% more absorbent than the other conventional PSCs. In-house simulation software is used to approximate the solar cell by applying the finite element method to develop solutions for the drift–diffusion and Poisson’s equations. The examinations of the previous studies revealed that the current study is the first study that has simulated the real model of Auger recombination in perovskite. The results indicated that the proposed PSC embedded with Au nanospheres has the following properties: the built-in potential of 3.16 V, short-circuit current of 27.97 mA/cm2, the open-circuit voltage of 1 V, maximum power of 24.84 mW/cm2, fill-factor of 0.88, the conduction band of 3 eV, electron quasi-Fermi level of 2.5 eV, the hole quasi-Fermi level of 0.6 eV, and efficiency of 24.84%. Finally, the suggested PSC has performed 62% more efficient than conventional PSCs.

[4] S. Naghizade and H. Saghaei, “Ultra-fast tunable optoelectronic half adder/subtractor based on photonic crystal ring resonators covered by graphene nanoshells,” Optical and Quantum Electronics, vol. 53, no. 7, p. 380, 2021, doi: 10.1007/s11082-021-03071-y.

This paper reports a new design of a tunable optoelectronic half adder/subtractor. Two photonic crystal (PhC) ring resonators are used to realize the proposed structure. Several silicon rods surrounded by silica rods covered with graphene nanoshells (GNSs) form every PhC ring resonator. Setting the chemical potential of GNS with an appropriate gate voltage, we can tune the PhC resonant mode as desired. The plane wave expansion technique is used to study the photonic band structure of the fundamental PC microstructure, and the finite-difference time-domain method is employed in the final design for solving Maxwell's equations to analyze the light propagation inside the structure. We systematically study the effects of physical parameters on the transmission reflection and absorption spectra. By optimizing the geometric dimensions, resonant absorption peaks can be excited at the same time for GNSs. Our numerical results also reveal the maximum time response is about 0.8 ps. The 200 µm2 area of the proposed half adder/subtractor makes it the building block of every photonic integrated circuit. Also, the design of various fast signal processing systems in optical communication networks is possible due to using tunable GNSs in PhC ring resonators. This study can introduce the use of two-dimensional materials in the design and implementation of logic circuits.

[5] S. Naghizade and H. Saghaei, “A novel design of fast and compact all-optical full-adder using nonlinear resonant cavities,” Optical and Quantum Electronics, vol. 53, no. 5, p. 262, 2021, doi: 10.1007/s11082-021-02929-5.

[6] M. Jahangiri, A. Mostafaeipour, H. U. Rahman Habib, H. Saghaei, and A. Waqar, “Effect of emission penalty and annual interest rate on cogeneration of electricity, heat, and hydrogen in Karachi: 3E assessment and sensitivity analysis,” Journal of Engineering, vol. 2021, p. 6679358, 2021, doi: 10.1155/2021/6679358.

Pakistan is the world’s sixth-most populous country with a semi-industrialized economy. It has been always an energy importer and dependent on fossil fuels. Great pressure is imposed on Pakistan’s national grid from the rise in fossil fuel costs, variations in the annual interest rate, and increased costs of greenhouse emissions. To meet the ever-increasing energy demand, the Government of Pakistan has decided to further harness wind and solar energies currently having a negligible share in Pakistan’s energy portfolio. Despite the importance of this issue, no study has been conducted so far on the cogeneration of power, heat, and hydrogen in Pakistan. Accordingly, this study is aimed at technical–economic–environmental sensitivity analysis of supplying electric and thermal loads of a residential building in Karachi by an off-grid wind-solar-fuel cell system. To this end, 4500000 possible cases were analyzed, simulated, and optimized with the HOMER software using 20-year average meteorological data from the NASA website. A sensitivity analysis was performed on this system for the first time in Pakistan. The other novelties are the use of dump loads for converting the surplus electricity into heat and also heat recovering in the fuel cells. The results showed the great potential of the station understudy for supplying the required power and heat by renewable energies. Hydrogen production was also affordable at every emission penalty price with an interest rate of less than 9%. Moreover, dump loads play a key role in supplying the thermal demand. Comparison of the wind turbine–solar cell–fuel cell–battery system with the wind turbine–solar cell–battery and solar cell–battery systems indicated that the internal rate of return and the payback period were, respectively, 9.39% and 11.4 years and 11.7% and 11 years. According to these results, it is recommend that Pakistani authorities promote the use of renewable energies through incentives and investment subsidies.

[7] M. Balaei, R. Karimzadeh, H. Saghaei, and S. Ghayeb-Zamharir, “The effect of laser wavelength and concentration on the optical limiting response of exfoliated MoS2 in the NMP solvent,” The European Physical Journal Plus, vol. 136, no. 3, p. 296, 2021, doi: 10.1140/epjp/s13360-021-01259-5.

This study investigated the optical limiting (OL) response of the dispersion of MoS2 nanosheets in N-methyl-2-pyrrolidone (NMP) which was made by liquid-phase exfoliation. We measured the OL response of different concentrations of the samples at two wavelengths of 405 nm and 532 nm using a continuous wave (CW) laser irradiation. It was observed that the value of the OL threshold changes by changing the laser wavelength and MoS2 concentration. To understand the mechanisms underlying these results, we use the spatial self-phase modulation (SSPM) and the Z-scan methods to measure the nonlinear absorption and refraction coefficients. It was revealed that the nonlinear absorption response is too weak. These findings highlight the significant role of the nonlinear refraction effect in the spatial self-phase modulation and the OL response of MoS2 dispersion under low-power laser irradiation.

[8] S. Naghizade and H. Saghaei, “An ultra-fast optical analog-to-digital converter using nonlinear X-shaped photonic crystal ring resonators,” Optical and Quantum Electronics, vol. 53, no. 3, pp. 1–16, 2021, doi: 10.1007/s11082-021-02798-y.

This paper reports a new optical analog-to-digital converter (OADC) design based on nonlinear X-shaped photonic crystal ring resonators (X-PCRRs). The dielectric rods made of silicon and nonlinear rods composed of doped glass are used to form X-PCRRs. The proposed structure consists of a nonlinear three-channel demultiplexer and an optical encoder. The nonlinear demultiplexer converts the continuous input signal into three quantized discrete levels, and the optical encoder generates two-bit binary codes depending on the output channel number of the demultiplexer. Two well-known plane wave expansion and finite difference time domain methods are applied to study and analyze the photonic band structure and light propagation inside the PhC-based structure, respectively. The wide TM photonic band gap of the fundamental PhC covers the second window of telecommunication in the C-band. Our calculations reveal that the proposed OADC has a maximum response time of about 4 ps and a sampling rate of 125 GS/s that is much faster than the designed ADC in previous studies. The proposed ADC also has a total footprint of 1785 μm2 with a minimum leakage loss.

[9] S. Naghizade and H. Saghaei, “A novel design of all-optical full-adder using nonlinear X-shaped photonic crystal resonators,” Optical and Quantum Electronics, vol. 53, no. 3, pp. 1–13, 2021. doi: 10.1007/s11082-021-02805-2.

This paper proposes a new all-optical full-adder design based on nonlinear X-shaped photonic crystal (PhC) resonators. The PhC-based full-adder consists of three input ports, two X-shaped PhC resonators (X-PCRs), and two output ports. The dielectric rods made of silicon and nonlinear rods composed of doped glass are used to design the X-PCRs. Two well-known plane wave expansion and finite difference time domain methods are applied to study and analyze the photonic band structure and light propagation inside the PhC, respectively. Our numerical results demonstrate when the incoming light intensity increases, the nonlinear Kerr effect appears and manages the direction of light propagation inside the structure. The maximum time delay and footprint of the proposed full-adder are about 2.5 ps and 663 μm2, making it an appropriate adder for high-speed data processing systems.

[10] A. Foroughifar, H. Saghaei, and E. Veisi, “Design and analysis of a novel four-channel optical filter using ring resonators and line defects in photonic crystal microstructure,” Optical and Quantum Electronics, vol. 53, no. 2, p. 101, 2021. doi: 10.1007/s11082-021-02743-z .

In this paper, we report a new design of an all-optical filter using photonic crystal microstructure. Ring resonators, line defects, scatterer rods, microcavities, and coupling rods are used to form the filter in order to extract specific wavelengths at the output channels. The well-known plane wave expansion method is used to calculate the photonic band diagram. The widely used finite-difference time-domain method is also applied to study the light propagation inside the filter. Our numerical results demonstrate that the proposed structure has high transmission power, high-quality factor, and low cross-talk. They reveal an optical signal centered at 1522 nm exits the first output channel, which has an output-to-input ratio (OIR) of 95 % with a bandwidth (FWHM) of 0.4 nm, and an optical signal centered at 1520.8 nm exits the second output channel with an OIR of 98 % and an FWHM of 0.5 nm. The third output channel can exit the optical signal centered at 1518.2 nm with an OIR of 78 % and an FWHM of 0.4 nm. Furthermore, the fourth channel will exit the optical signal at 1519.3 nm with an OIR of 56 % and an FWHM of 0.4 nm. Therefore, the quality factors of the first to fourth outputs of the filter are equal to 3805, 3041, 3795, and 3798, respectively. The first to fourth outputs’ cross-talk values are also − 37 dB, − 36 dB, − 41 dB, and − 38 dB, respectively, which confirm the least interference between output channels. Besides, linear dielectric rods form the filter design that leads to the filter’s appropriate performance at a low input power which is the most important benefit of this work compared to other recently published articles. The maximum rise time of the proposed filter for all output ports is less than 8 ps. The structure also has 375.84 µm2, which makes the filter easy to use in photonic integrated circuits.

[11] S. M. Alden Mostaan and H. Saghaei, “A tunable broadband graphene-based metamaterial absorber in the far-infrared region,” Optical and Quantum Electronics, vol. 53, no. 2, p. 96, 2021, doi: 10.1007/s11082-021-02744-y.

This paper reports a new design of a broadband absorber composed of graphene, dielectric, and gold layers. The designed absorber has four absorbent modes close to each other, which results in the formation of broadband absorption. The relative bandwidth, a key parameter to assess the bandwidth improvement, shows a significant increase in the proposed design compared to similar structures published in recent years. The numerical results also reveal this metamaterial absorber can be used for applications in the far-infrared frequency range due to choosing optimized dimensions and the graphene Fermi level. Unlike other graphene-based metamaterials, which require complicated structures to be able to attain broadband absorption, the physical structure of the proposed design has a relatively simple fabrication process. For further investigations, the effect of split geometry on the absorption spectrum is studied. Also, the use of graphene in this metamaterial absorber provides dynamic adjustability through electrostatic doping in order to tune the amount of absorption. This characteristic has been studied by changing the graphene Fermi level. This feature can be widely used in electro-absorption switches and modulators.

[12] S. Naghizade and H. Saghaei, “A novel design for an all-optical half adder using linear defects in photonic crystal microstructure,” Journal of Applied Research in Electrical Engineering, vol. 1, no. 1, 2021, doi: 10.22055/jaree.2020.34466.1010.

This paper reports a new optical half-adder design using linear defects in a photonic crystal (PhC) structure. The half adder's proper design obviates the need to increase the input signal's intensity for the nonlinear optical Kerr effect's appearance, which leads to the diversion of the incoming light toward the desired output. The proposed device is composed of silicon rods consisting of four optical waveguides and a defect in a PhC. Two well-known plane wave expansion and finite difference time domain methods are used to study and analyze photonic band structure and light propagation inside the PhC, respectively. The numerical results demonstrate that the ON-OFF contrast ratios are 16 dB for “Sum” and about 14 dB for "Carry". They also reveal that the proposed half-adder has a maximum time delay of 0.8 ps with a total footprint of 158 µm2. Due to very low delay time, high contrast ratio, and small footprint, they are more crucial in modern optoelectronic technologies, so this structure can be used in the next generation of all-optical high-speed central processing units.

[13] H. Saghaei, “Design and simulation of an ultra-fast all-optical single-bit comparator based on photonic crystal ring resonators,” Scientific Journal of Applied Electromagnetics, vol. 9, no. 2, pp. 99–106, 2021, [Online]. Available: https://elemag.ihu.ac.ir/article_206353.html.

A digital comparator is a logic circuit used to compare two binary numbers. So far, various designs have been proposed using logic gates, which are mainly based on electrical signals and lack the desired high speed. This paper presents a new design of an ultra-fast all-optical single-bit comparator based on photonic crystal ring resonators consisting of highly nonlinear glass. The structure of this comparator consists of two inputs, four ring resonators with a number of waveguides for comparison and three outputs for displaying the result, all created in a photon crystal bed. Using the plane wave expansion method, its band structure is calculated and the results show that the fundamental photonic crystal has a photonic band gap in the polarized TM mode in S, C and L bands that is a suitable tool for telecommunication applications. To solve the Maxwell's equations, the finite-difference time-domain method is used, which aims to investigate the light propagation inside the final structure. The results of numerical studies show that the designed structure has a very short response time of 3 ps, making it faster than all the comparators designed so far, including electronic, electro-optical and all-optical comparators. Also, its relatively small area of 826 μm2 makes it applicable in the design of photonic integrated circuits.