Showing 5 results for Keshavarz
Alireza Keshavarz, Zahra Abbasi, Mohsen Hatami,
Volume 6, Issue 1 (International Journal of Optics and Photonics (IJOP) Vol 6, No 1, Winter-Spring 2012)
Abstract
Propagation of incoherently soliton pairs in photorefractive crystals under steady-state conditions is studied. These soliton states can be generated when the two mutually incoherent optical beams with the same polarization and wavelength incident on the biased photorefractive crystal. Such soliton pairs can exist in bright-bright, dark-dark, gray-gray as well as in bright-dark types. In this paper the stability against small perturbation in amplitude is investigated while they do not break up, and instead oscillates around the soliton solution. Results show that the bright-bright pairs can travel a longer distance without broadening in comparison with the other types. Finally the effect of self-deflection is simulated numerically.
Keshavarz, Kazempour,
Volume 6, Issue 2 (International Journal of Optics and Photonics (IJOP) Vol 6, No 2, Summer-Fall 2012)
Abstract
The ABCD matrix method is used to simplifying the theoretical coupling efficiency calculation of Elegant Hermite-Cosh-Gaussian (EHChG) laser beams to a Single Mode Fiber (SMF) with a quadric lens formed on the tip. The integrals of coupling efficiency relation are calculated numerically by Boole method. Meanwhile, the structure parameters of surface-lensed fiber are optimized in numerical simulation to achieve maximum coupling efficiency. Results can give some guidance suggestions for designing suitable micro lenses in order to coupling the EHChG laser beams to the SMF.
Reza Ghayoor, Alireza Keshavarz,
Volume 13, Issue 1 (International Journal of Optics and Photonics (IJOP) Vol 13, No 1, Winter-Spring 2019)
Abstract
By developing the terahertz (THz) technology, in addition to generators and detectors of THz waves, the existence of some tools such as modulators and filters are needed. THz filters are important tools for various applications in the field of chemical and biological sensors. Linear and nonlinear optical properties of the graphene have attracted lots of attention. In fact graphene exhibits various nonlinear phenomena. Hence in this paper, by entering the graphene to the field of THz and using the graphene nonlinear properties with utilizing the transfer matrix method and transmission properties of a periodic structure containing graphene are investigated. A fairly straightforward computational method allows us to examine the effect of different structural parameters on the transmittance spectrum. Simulation results show that if the graphene nonlinear response in a periodic structure in the presence of a high-intensity THz field is considered, the proposed structure displays two bands of passes and stopping which can improve the design of the filters and controllers of THz waves.
Maryam Soltani, Alireza Keshavarz, Gholamreza Honarasa, Reza Ghayoor,
Volume 13, Issue 1 (International Journal of Optics and Photonics (IJOP) Vol 13, No 1, Winter-Spring 2019)
Abstract
In a ring laser gyroscope, due to the rotation and the Sagnac effect, a phase difference between the two counter-propagating beams is generated. In this device, the higher phase difference between these two beams causes the better the interference pattern detection, and thus the sensitivity is increased. In this paper, the effect of inserting a dielectric-graphene photonic crystal inside a ring laser gyroscope on the interference pattern and the sensitivity of the device are studied and simulated using ABCD propagation matrix method. Results show that dielectric-graphene photonic crystal has a high transmission and therefore high efficiency in the wavelength of ring laser gyroscope. So it is a suitable choice to use in the ring laser gyroscope. Also, a comparison between ring laser gyroscope with and without dielectric-graphene photonic crystal shows that when the dielectric-graphene photonic crystal is in the system it is possible to build gyroscope with smaller lengths and high sensitivity.
Mohammad Javad Azarm, Alireza Keshavarz, Gholamreza Honarasa,
Volume 15, Issue 1 (Winter-Spring 2021)
Abstract
The absorption cross-section of gold and silver nanoparticles has been demonstrated in confined wavelength spectra based on Mie's theory. For this purpose, the numerical study performed with COMSOL for defined particle size to clarify absorption spectra and final results have been compared with experimental data to express the absorption peak occurs in higher wavelength for large particle size which is in around 530 nanometers for gold and 400 nanometer for silver particles. These results show that particle size affects directly on absorption spectra of metallic nanoparticles.
