Mohammad K Moravvej-Farshi | Tarbiat Modares University (original) (raw)

Papers by Mohammad K Moravvej-Farshi

Optics and Photonics Society of Iran, Mar 10, 2016

There are various methods to treat degeneracy in Monte Carlo simulation. Lugli-Ferry method is a ... more There are various methods to treat degeneracy in Monte Carlo simulation. Lugli-Ferry method is a more precise method, which is also compatible with Monte Carlo simulation. However, it has shown that the Lugli-Ferry method creates a non-physical behavior in average energy characteristic, at low fields. A new method has already proposed to overcome this problem in a 1-D bulk region. In this article, we present a mathematical and numerical technique to improve the proposed method, useful for 2-D Monte Carlo ...

Optics Express, Aug 24, 2021

Taking advantage of highly confined evanescent fields to overcome the free-space diffraction limi... more Taking advantage of highly confined evanescent fields to overcome the free-space diffraction limit, we show plasmonic tweezers enable efficient trapping and manipulation of nanometric particles by low optical powers. In typical plasmonic tweezers, trapping/releasing particles is carried out by turning the laser power on and off, which cannot be achieved quickly and repeatedly during the experiment. We introduce hybrid gold-graphene plasmonic tweezers in which the trap stiffness is varied electrostatically by applying suitable voltages to a graphene layer. We show how the graphene layer absorbs the plasmonic field around the gold nanostructures in particular chemical potentials, allowing us to modulate the plasmonic force components and the trapping potential. We show graphene monolayer (bilayer) with excellent thermal properties enables more efficient heat transfer throughout the plasmonic tweezers, reducing the magnitude of thermophoretic force by about 23 (36) times. This thermophoresis suppression eliminates the risk of photothermal damage to the target sample. Our proposed plasmonic tweezers open up possibilities to develop tunable plasmonic tweezers with high-speed and versatile force-switching functionality and more efficient thermal performance.

Proceedings of SPIE, Jun 1, 2012

We design an ultra-compact low power all-optical modulator by applying dispersion engineered slow... more We design an ultra-compact low power all-optical modulator by applying dispersion engineered slow-light waveguuide in photonic crystal Mach-Zehnder interferometer (PhC-MZI) arms, which are infiltrated by optofluidic having high nonlinearities. Nearly zero dispersion regime brings us a 22-μm long PhC-MZI to operate as a modulator with an input power as low as 3 mW/μm. By attaching a coupling section about 3.36 μm long and inserting the light through a directional coupler with the lenght of 2.1 μm, losing power from the input port has been decreased.

OSA continuum, Jul 26, 2020

We are proposing next-generation lab-on-a-chip plasmonic tweezers with a built-in optical source ... more We are proposing next-generation lab-on-a-chip plasmonic tweezers with a built-in optical source that can be activated electrically. The building block of these tweezers is composed of an Au/p+-InAs/p+-AlAs0.16Sb0.84 Schottky diode, with a circular air-hole opened in the Au layer. Under an appropriate forward bias, the interband optical transitions in InAs, acting as a built-in optical source that can excite the localized surface plasmons (LSPs) around the edge of the hole. Numerical simulations show that the LSPs mode penetrates a chamber that is filled with water and electrically isolated from the top gold layer, providing the gradient force components desired for trapping the target nanoparticles suspended in the water. Moreover, we show that tweezers with air-holes of radius 90 nm under an applied bias of −1.6 V, can trap polystyrene nanoparticles of radius as small as 93 nm. The proposed structure provides a new platform for developing the next-generation compact on-chip plasmonic tweezers with no need for any external optical pump.

Journal of Lightwave Technology, May 1, 2019

Organic Electronics, Mar 1, 2018

Journal of The Optical Society of America B-optical Physics, Oct 28, 2015

Optics continuum, Feb 7, 2022

We propose a dual−purpose sensor to detect ammonia besides relative humidity with tapered multimo... more We propose a dual−purpose sensor to detect ammonia besides relative humidity with tapered multimode fiber (TMMF) as the sensor structure and silica gel as the sensing layer. In achieving the desired TMMF, we heated and pulled a few pieces of multimode fibers to obtain 9-mm long tapered regions with different diameters in the range of 4−40 µm. Then synthesized silica gel by sol-gel method and passed the tapered section of the TMMFs through drops of silica gel to form the sensing layers. Using the wavelength shift and output power reduction appearing in the fiber transmission spectrum, we determine the sensor response to the alteration of ammonia concentration and relative humidity in the environment. Our experimental results reveal that a decrease in the tapered waist gives rise to an increase in the sensor sensitivity. The same results show that the highest measured sensitivity is 14.8 pm/ppm (for ammonia) and 0.435 dB/%RH (for relative humidity) when we coat the tapered region of a TMMF of 4−µm waist diameter with silica gel. Moreover, the time responses for relative humidity and ammonia sensors are 10 and 32 s, and their corresponding recovery times are 8 and 19.5 s.

IEEE Journal of Selected Topics in Quantum Electronics, May 1, 2021

We are reporting the design procedure for a narrow-band ultra-low-power reflective optical modula... more We are reporting the design procedure for a narrow-band ultra-low-power reflective optical modulator that operates at the critical coupling of an appropriately designed two-dimensional grating with the center frequency of a quarter wavelength distributed Bragg reflector (DBR). By sandwiching a three-layer stack of gated ITO/HfO2/ITO between the DBR and the grating, we can make the optical modulator operational, taking advantage of the tunable property of the ultrathin layer at the ITO/HfO2 interface accumulated by electrons under an ultra-low applied voltage (−0.1 V). The corresponding energy consumption is ∼5.5 fJ/bit. Moreover, our simulations show that the capacitance limited modulation speed is more than 80 Mbps. Our numerical results also predict the influence of possible fabrication errors on the guided-mode resonance wavelength. This investigation shows that a ±3 nm deviation in the grating pitch affects the modulator performance profoundly. Furthermore, the numerical results demonstrate the modulation depth of ∼24 dB is achievable for an appropriately designed modulator with an acceptable insertion loss of ∼0.05 dB. This paper paves the way for developing next-generation optical modulators with high modulation depth, low insertion loss, and ultra-low energy consumption.

Optics Express, Sep 9, 2019

Using a plasmonic graphene ring resonator of resonant frequency 10.38 THz coupled to a plasmonic ... more Using a plasmonic graphene ring resonator of resonant frequency 10.38 THz coupled to a plasmonic graphene waveguide, we design a lab-on-a-chip optophoresis system that can function as an efficient plasmonic force switch. Finite difference time domain numerical simulations reveal that an appropriate choice of chemical potentials of the waveguide and ring resonator keeps the proposed structure in on-resonance condition, enabling the system to selectively trap a nanoparticle. Moreover, a change of 250 meV in the ring chemical potential (i.e., equivalent to 2.029 V change in the corresponding applied bias) switches the structure to a nearly perfect off-resonance condition, releasing the trapped particle. The equivalent plasmonic switch ON/OFF ratio at the waveguide output is -15.519 dB. The designed system has the capability of trapping, sorting, controlling, and separating PS nanoparticles of diameters ≥30 nm with a THz source intensity of 14.78 mW/µm2 and ≥22 nm with 29.33 mW/µm2.

Journal of Physics: Condensed Matter, Sep 21, 2020

Hydrogenation and fluorination have been presented as two possible methods to open a bandgap in g... more Hydrogenation and fluorination have been presented as two possible methods to open a bandgap in graphene, required for field-effect transistor applications. In this work, we present a detailed study of the phonon-limited mobility of electrons and holes in hydrogenated graphene (graphane) and fluorinated graphene (graphene fluoride). We pay special attention to the out-of-plane acoustic (ZA) phonons, responsible for the highest scattering rates in graphane and graphene fluoride. Considering the most adverse cut-off for long-wavelength ZA phonons, we have obtained electron (hole) mobilities of 28 (41) cm2 V-1 s-1 for graphane and 96 (30) cm2 V-1 s-1 for graphene fluoride. Nonetheless, for a more favorable cut-off wavelength of ∼2.6 nm, significantly higher electron (hole) mobilities of 233 (389) cm2 V-1 s-1 for graphane and 460 (105) cm2 V-1 s-1 for graphene fluoride are achieved. Moreover, while complete suppression of ZA phonons can increase the electron (hole) mobility in graphane up to 278 (391) cm2 V-1 s-1, it does not affect the carrier mobilities in graphene fluoride. Velocity-field characteristics reveal that the electron velocity in graphane saturates at an electric field of ∼4 × 105 V cm-1. Comparing the mobilities with other two-dimensional (2D) semiconductors, we find that hydrogenation and fluorination are two promising avenues to realize a 2D semiconductor while providing good carrier mobilities.

$Research paper thumbnail of Analysis of Multimode Interference in a Fabricated Fiber Optic Refractive Index Sensor$

A single-mode-multimode-single-mode (SMS) structure is fabricated by splicing 60 mm of a multimod... more A single-mode-multimode-single-mode (SMS) structure is fabricated by splicing 60 mm of a multimode fiber (MMF) between two single-mode fibers (SMFs). The MMF, which is the sensing part, is chemically etched and bent to form a If-shaped multimode interference (MMI) sensor for measuring the external liquid refractive index. The first SMF that has smaller core than the MMF diffracts the light into the MMF and excites higher modes in the sensing section. To characterize the sensor, the middle part of the sensor was immersed in solutions with different refractive indices and the output spectrum was recorded while changing the liquid refractive index from 1.33 to 1.364. The experimentally achieved sensitivity for indices up to 1.363 is 380.25 nm/RIV.

We report demonstration of four-wave mixing based mid-span optical phase conjugation (OPC) in sho... more We report demonstration of four-wave mixing based mid-span optical phase conjugation (OPC) in short dispersion engineered slow-light chalcogenide and silicon photonic crystal waveguides for dispersion compensation of 4 ps, 40 Gb/s return to zero pseudorandom signals transmission through an 2 km of standard optical fiber link. We take into account the impact of two photon absorption, free carrier absorption, free carrier dispersion, and repetition rate effects in our numerical simulations. We achieve conversion efficiency of -28.26 and -19.68 dB between idler and probe in Si and chalcogenide OPC using a CW pump with the power of 100 mW.

Optics Express, Apr 22, 2022

The presence of species other than the target biomolecules in the fluidic analyte used in the ref... more The presence of species other than the target biomolecules in the fluidic analyte used in the refractive index biosensor based on the surface plasmon resonances (SPRs) can lead to measurement ambiguity. Using graphene-based acousto-plasmonic biosensors, we propose two methods to eliminate any possible ambiguity in interpreting the measured results. First, we take advantage of the dynamic tunability of graphene SPRs in the acousto-plasmonic biosensor with a surface acoustic wave (SAW) induced uniform grating, performing measurements at different applied voltages. Second, a single measurement employing a similar biosensor but with SAW-induced dual-segment gratings. The numerical results show the capability of both methods in decoupling the effect of the target analyte from the other species in the fluid, enabling interpreting the measurement results with no ambiguity. We also report the results of our numerical investigation on the effect of measuring parameters like the target layer effective refractive index and thickness, and the fluid effective refractive index, in addition to the controlling parameters of the proposed acousto-plasmonic biosensor, including graphene Fermi energy and electrical signaling on the sensing characteristics. Both types of proposed biosensors show promising features for developing the next generation lab-on-a-chip biosensors with minimal cross-sensitivities to non-target biomolecules.

Micro & Nano Letters, Jun 1, 2019

Laser Physics, Feb 19, 2019