Papers by fakhroddin nazari
IEEE Journal of Quantum Electronics, Aug 1, 2016
We report the design procedure for a broadband multichannel cavity-less optical isolator composed... more We report the design procedure for a broadband multichannel cavity-less optical isolator composed of a triangular perturbed nonlinear Parity Time (PT) symmetric lattice. The interplay between the nonlinearity and PT-symmetric lattice that results in nonreciprocal transmission enables us to design the isolator outputs and inputs positions as desired. In the transmitting regime, a number of solitons that are simultaneously launched into individual inputs positioned appropriately, on the waveguides' gain sides in the periodic lattice, swing along the waveguide until they are self-trapped along the respective waveguides axes, where the isolator outputs are located. In the isolating regime, however, the solitons that are launched into the inputsi.e., the outputs of the transmitting regime-propagate along the waveguides axes, until they exit from the new outputs. Simulations show that the neighboring soliton trajectories in each regime are completely isolated and so are the forward and reverse trajectories in each waveguide cell. Moreover, operation of this cavity-less PT-symmetric isolator that is designed on an inhomogeneous slab waveguide does not suffer from the narrow frequency band limitation, unlike their cavity-based counterparts.
Solid–liquid modulator via phononic crystal-based Mach–Zehnder interferometer
The European Physical Journal Plus
This paper introduces a solid–liquid modulator for the first time in a solid–liquid phononic crys... more This paper introduces a solid–liquid modulator for the first time in a solid–liquid phononic crystal (PnC). Adjusting and designing of the liquid-based Mach–Zehnder interferometer (MZI) in a solid phononic crystal play the key role to realize the novel proposed modulator. The proposed PnC configuration is a square lattice composed of the circular vacuum cylinders immersed in an aluminum background. This structure consists of several line defects creating the symmetric Y -shape MZI with the water inclusions. The variations of water properties in the sensing arm of MZI result in changing the acoustic pressure in the output of the modulator. The simulation results reveal that changing the temperature of the water inclusions in the sensing arm leads to the different output phase shifts. This phase variation induces the destructive and constructive interference between two arms, where the modulator output yields the maximum and the minimum values in a specific frequency ( f s = 233.9 kHz). Moreover, a high average quality factor of 1700, and the ultra-high extinction ratio of − 25.12 dB result in the output profile of the proposed modulator. Besides, the admirable insertion losses are obtained − 0.25, and − 21.53 dB for ON and Off modes, respectively.
Design And simulation of device with asymmetric Transmission Based on Nonlinear Photonic Crystal
Tunable optical isolator using Graphene-photonic crystal-based hybrid system
Physica Scripta, 2021
In this article, an optical isolator is designed and simulated based on a hybrid configuration of... more In this article, an optical isolator is designed and simulated based on a hybrid configuration of the photonic crystal (PhC) and graphene. The PhC membrane is a hexagonal lattice of air holes arranged in a nonlinear silicon substrate. To provide a nonreciprocal transmission (optical isolator), breaking the symmetry of the light propagation path (the forth and back routes) is an essential condition. Here, the asymmetrical round trip of the light propagation and the Kerr-nonlinear effect are employed to obtain asymmetric propagation. The isolator structure includes a PhC waveguide that asymmetrically side-coupled to a specific embedded cavity. Then, to attain a tunable asymmetric transmission, a Nano-layer of graphene is located on the top of the mentioned PhC configuration. By altering the chemical potential of graphene one can control the isolation rate, frequency, and bandwidth of offered structure and thus possess a tunable optical isolator. The simulation results show that a 0.5 ...
Tunable Optical Demultiplexer for Dense Wavelength Division Multiplexing Systems Using Graphene–Silicon Microring Resonators
Journal of Electronic Materials, 2020
An ultracompact tunable optical dense wavelength division demultiplexer (DWDM) compatible with co... more An ultracompact tunable optical dense wavelength division demultiplexer (DWDM) compatible with complementary metal–oxide–semiconductor technology is proposed, consisting of a central bus waveguide coupled to two drop waveguides through two ring resonators, all made of silicon (Si). Each Si ring resonator is topped by a graphene microribbon whose chemical potential can be tuned as desired. The center wavelength of each drop channel is determined by the resonant wavelength of the adjacent ring resonator, which in turn is tuned by modifying the conductivity of the graphene. Simulations show that the proposed structure with two graphene–Si ring resonators (GSRRs) having a chemical potential difference of 210 meV demultiplexes a broad optical signal into two narrow channels centered at about 1552.42 nm and 1552.85 nm (with a channel spacing of less than 0.43 nm), each emerging from one drop waveguide, with a transmission efficiency above 64%. The full-width at half-maximum values of the channels are 160 pm and 250 pm, providing quality factors of ∼ 9705 and 6209 with crosstalk of less than − 13.3 dB. By exchanging the chemical potentials of the GSRRs, the drop channels can be swapped dynamically without mechanical manipulation of the device. The proposed ultracompact graphene-based demultiplexer enables electrically tuned optical demultiplexing for DWDM systems as a potential alternative to the thermooptically tuned demultiplexers employed in long-haul optical communications.
Heterostructure based demultiplexer using solid–solid phononic crystal ring resonators
Journal of Physics D: Applied Physics, 2020
This paper presents a novel approach to design a heterostructure demultiplexer using a solid-soli... more This paper presents a novel approach to design a heterostructure demultiplexer using a solid-solid phononic crystal (PnC). The proposed PnC structure is a square lattice contained circular tungsten cylinders embedded in a polycrystalline silicon background. Heterostructure based demultiplexer consists of three different parts, which every part includes a bus waveguide and an output waveguide coupled to each other through a special ring resonator. The simulation results show that different frequencies emitted from the heterostructure demultiplexer outputs in the range of GHz. The achieved maximum and minimum transmissions are about 88% and 42%. Furthermore, the very-high average quality factor of 7807 results among output channels. Moreover, the maximum crosstalk (the worst one) among the outputs is -13 dB, which is a desirable value. Finally, the effect of temperature variations on the demultiplexer performance is explored. It is revealed that by enhancing the constituted material temperature the resonance frequencies decrease almost linearly. Thus, the proposed phononic crystal based structure can operate as a temperature or pressure sensor.
International Journal of Engineering, 2020
Recently, blind multiuser detection has become an important topic in code division multiple acces... more Recently, blind multiuser detection has become an important topic in code division multiple access (CDMA) systems. Direct-Sequence Spread Spectrum (DSSS) signals are well-known due to their low probability of detection, and secure communication. In this article, the problem of blind multiuser detection is studied in variable processing gain direct-sequence code division multiple access (VPG DS-CDMA). The method based on the fluctuations of autocorrelation estimators,which previously described in a single and multiuser context, is extended to an asynchronous variable processing gain (VPG) DS/CDMA systems without restrictions on the processing gains in multi-path channel condition. According to the proposed algorithm, not only the presence of the common peaks in the second-order statistic of the received signal is proved, but the relationship between these peaks and the spreading code length is also derived. The simulation results show that the proposed algorithm even in the presence a very low signal-to-noise ratio (SNR) is completely efficient in signal detection. It is remarkable that the minimum description length (MDL) method is used to determine the number of users.
Physics Letters A, 2018
We propose a tunable Autler-Townes splitting (ATS) window using the electro-optic effect. The pro... more We propose a tunable Autler-Townes splitting (ATS) window using the electro-optic effect. The proposed structure includes two cascaded silicon ring resonators side coupled to a straight waveguide. The electrooptic effect is created by a nano-layer graphene located on half of lower silicon ring resonator. Here for the first time, ATS window frequency location is adjusted by utilizing a graphene nano-sheet, so that its wavelength shift is more than 0.24 nm via changing the graphene chemical potential level from 0.445 eV to 0.667 eV. Moreover, we simulate and show the phase changes of the transmission curves around ATS frequency window and their corresponding group delays. Furthermore, switching from slow (fast) to fast (slow) light is another interesting phenomenon of the proposed structure.
Applied Physics B, 2018
This paper introduces a novel approach based on linear parity-time (PT) symmetry for realization ... more This paper introduces a novel approach based on linear parity-time (PT) symmetry for realization of an optical modulator. The suggested optical modulator is attained by embedding PT-symmetric couplers within the arms of a Mach-Zehnder interferometer configuration. The asymmetric evolution behavior of light propagation and interference effect play the key role in the proposed PT-symmetric based modulator. The extinction ratio of the proposed modulator is as high as 56.97 dB. Moreover, it is shown that the normalized light intensity of the modulator output exponentially varies by increasing the gain/ loss coefficients. Finally, it is demonstrated that just by an active arm (the gain waveguide) of the PT-symmetric coupler, a similar evolution of the light propagation can be achieved along the modulator structure.
Control of slow/fast light frequency via tunable EIT window
Journal of Optics, 2019
Journal of Molecular Liquids, 2019
We propose a tunable four-channel acoustic demultiplexer, based on a fork-shaped phononic crystal... more We propose a tunable four-channel acoustic demultiplexer, based on a fork-shaped phononic crystal (PnC) structure, having four output ports. A square lattice of cylindrical water inclusions in a mercury matrix, separate by ultra-thin elastically solid shells, characterizes the PnC platform. We used a plane wave expansion (PWE) method to calculate the PnC band diagram. There are four cylindrical resonant cavities of different inner radii, filled with the methyl nonafluorobutyl ether (MNE), placed in correspondence of the throat of each output port. Using the finite difference time domain (FDTD) numerical approach, we show that the proposed device can demultiplex a given broadband acoustic signal to four narrowband channels of ultra-high quality factors and interchannel cross talks less than −32 dB. Moreover, simulations show that the proposed device besides its demultiplexing functionality has the potential of sensing pressure and temperature and also the capability of determining the properties of the cavity fluid.
Traveling wave solutions for density-dependent conformable fractional diffusion–reaction equation by the first integral method and the improved $$\textbf{tan}\left( {{\mathbf{\frac{1}{2}}}{\boldsymbol{\varphi }}\left({\boldsymbol{\upxi}} \right)} \right)$$ tan 1 2 φ ξ -expansion method
Optical and Quantum Electronics, 2018
In this paper, we propose the first integral method (FIM) and the improved $$\text{tan}\left( {\f... more In this paper, we propose the first integral method (FIM) and the improved $$\text{tan}\left( {\frac{1}{2}{\varphi }\left(\upxi \right)} \right)$$tan12φξ-expansion method (ITEM) for solving the density-dependent conformable fractional diffusion–reaction equation (CFDRE) which is commonly applied in mathematical biology. We received many new exact soliton solutions for the density-dependent CFDRE which are expressed by exponential function, rational function and hyperbolic function forms. The results show that FIM and ITEM are powerful mathematical tools and efficient techniques for solving the fractional nonlinear partial differential equations.
Optical and Quantum Electronics, 2017
In this article, the Riccati sub equation method is employed to solve fractional Zakharov-Kuznets... more In this article, the Riccati sub equation method is employed to solve fractional Zakharov-Kuznetsov equation with dual-power law nonlinearity in the sense of the conformable derivative. By using this method, new exact solutions involving parameters, expressed by generalized hyperbolic functions are obtained. This method presents a wider applicability for handling nonlinear fractional wave equations.
Journal of the Optical Society of America B, 2017
We present a new bias-free antenna-coupled CW terahertz photomixer with interdigitated electrodes... more We present a new bias-free antenna-coupled CW terahertz photomixer with interdigitated electrodes. Each finger pair is made of metal/semiconductor/metal (MSM) electrodes with dissimilar Schottky barriers. The two dissimilar metals in each MSM have a barrier height of difference (ΔΦ B) and a finite lateral spacing (s). In the proposed teraheretz emitter, not only is the optical absorption and hence photogeneration enhanced by the surface resonant modes, but also the high built-in field increases the terahertz current. Furthermore, by having a large radiation resistance of the antenna integrated to the array electrodes, based on our simulations, it is possible to achieve the maximum power of 35 μW from a dipole antenna coupled to the proposed electrode array with 10 μm × 10 μm active area and pitch of Λ 800 nm. This is more than 196 times larger terahertz power than the highest terahertz power radiated from the array emitters of the same area that contains the bias-free antennaless array of farfield emitters with double pitch size. We have also investigated the limits of thermal breakdown and efficiency degradation of the proposed emitter that play an important role due to the reduction of the active area. Such terahertz sources can pave the way to various biomedical applications such as endoscopic imaging without a need for hazardous external circuitry for biasing, reducing patient health risk.
Broadband all-optical isolator based on all-passive graded index
Superlattices and Microstructures, 2017
Abstract We propose an all optical isolator based on a passive nonlinear graded refractive index.... more Abstract We propose an all optical isolator based on a passive nonlinear graded refractive index. The proposed optical isolator is fully passive and also cavity-less based structure which causes the suggested isolator to operate in a wide frequency rang. The transmission contrast between the forward and backward directions is 81.9 dB and also the transmission intensity is large at the desirable ports. Moreover, the proposed isolator can simultaneously support two incident ports without altering the structure in the forward direction and works as a 2 × 1 optical isolator. Furthermore, the graded waveguide can be easily realized and fabricated by GaAs-based waveguide in the infrared optical frequency regime.
Applied Optics, 2016
We present a wideband and low-dispersion slow-light photonic crystal waveguide with a large norma... more We present a wideband and low-dispersion slow-light photonic crystal waveguide with a large normalized delaybandwidth product that can be exploited in many ultra-compact all-optical devices, such as modulators and switches. The proposed new approach is based on infiltrating optical fluid into the first and second rows of the shifted air holes adjacent to the line-defect waveguide in a hexagonal lattice of photonic crystal. The simulation results show that the normalized delay-bandwidth product can be enhanced to a large value of 0.469 with a wide bandwidth operation of 36.8 nm in the C-band frequency optical communication window. Furthermore, by means of two-dimensional finite-difference time-domain calculations, the low-dispersion slowlight propagation is demonstrated by simulating the temporal Gaussian pulse width broadening.
Journal of Modern Optics, 2016
We propose an optical isolator formed in a nanoscale structure based on non-linear silicon photon... more We propose an optical isolator formed in a nanoscale structure based on non-linear silicon photonic crystal that can be easily realized on an optical integrated chip. The structure comprises an engineered waveguide that is coupled to a L 2 cavity. By using a passive ultra-compact cavity-based isolator, without changing incident characteristics such as mode or frequency in outputs, an admirable transmission contrast of 20.5 dB with a small insertion loss (in the forward direction) of −14.8 dB is achieved. The isolator attains a broad isolating linewidth operation of 0.9 nm without bistability response that is outstanding in comparison with the currently proposed cavity-based isolators. The non-linear Fano resonances that are created by the interplay between the non-linearity and spatial asymmetry notion in the structure play a critical role in the isolator efficiency. In this study, the finitedifference time-domain and finite element methods are used for simulations.
Designing Switchable Phononic Crystal-Based Acoustic Demultiplexer
IEEE Transactions on Ultrasonics, Ferroelectrics, and Frequency Control, 2016
We present the design procedure for switchable acoustic demultiplexers based on a fluid-fluid pho... more We present the design procedure for switchable acoustic demultiplexers based on a fluid-fluid phononic crystal (PnC) platform. It consists of a T-shaped PnC waveguide coupled to two output waveguide ports through two dissimilar point-defect cavities. The PnC platform consists of a periodic array of infinitely long rods of water (inclusions) embedded in mercury background. The waveguides are made by removal of a row or a column of inclusions from the PnC, while the fluid in one of the two dissimilar cavities is methyl nonafluorobutyl ether (MNE) and in the other is ethyl nonafluorobutyl ether (ENE). The difference in the sound velocity in MNE and ENE provides an adequate difference in the dissimilar cavities resonant modes, required for the demultiplexing functionality of the designed structure. The different dependencies of the sound velocities in these two fluids on temperature have also enabled the switching of the multiplexed channel, simply by appropriately changing the cavities temperature.
Physical Review B, 2016
We report the design procedure for an acoustic add-drop filter (ADF) composed of two line-defect ... more We report the design procedure for an acoustic add-drop filter (ADF) composed of two line-defect waveguides coupled through a ring resonator cavity (RRC) all based on a phononic crystal (PnC) platform. Using finite difference time domain and plane wave expansion methods, we study the propagation of acoustic waves through the PnC based ADF structures. Numerical results show that the quality factor for the ADF with a quasisquare ring resonator with a frequency band of 95 Hz centered about 75.21 kHz is Q ∼ 800. We show that the addition of an appropriate scatterer at each RRC corner can reduce the scattering loss, enhancing the quality factor and the transmission efficiency. Moreover, it is also shown that by increasing the coupling gaps between the RRC and waveguides the quality factor can be increased by ∼25 times, at the expense of a significant reduction in the transmission efficiency this is attributed to the enhanced selectivity in expense of weakened coupling. Finally, by varying the effective path length of the acoustic wave in the RRC, via selectively varying the inclusions physical and geometrical properties, we show how one can ultra-fine and fine-tune the resonant frequency of the ADF.
An all optical OR logic gate based on a nonlinear optical parity time (PT) symmetric waveguide wi... more An all optical OR logic gate based on a nonlinear optical parity time (PT) symmetric waveguide with triangular index profile is designed. In this design, we have taken the advantage of the non-reciprocity of PT symmetric systems as well as the asymmetric evolution of interacting solitons in such waveguides in nonlinear regime. The results demonstrate the potential appli-cations of PT symmetric optical systems.
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Papers by fakhroddin nazari