Showing 5 results for Hatami
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.
Dr. Mohsen Hatami, Ms. Elham Yousefi,
Volume 7, Issue 2 (International Journal of Optics and Photonics (IJOP) Vol 7, No 2, Summer-Fall 2013)
Abstract
In this study, a new numerical method is introduced to obtain the exact shape of output pulse in the chalcogenide fiber Bragg grating (FBG). A Gaussian pulse shape with 173 ps width is used as an input pulse for lunching to a 6.6 mm nonlinear FBG. Because of bistable and hysteresis nature of nonlinear FBG the time sequence of each portion of pulse is affected the shape of output pulse. So we divide the pulse to leading and trailing portion in time. By using bistability curve and Fourier transformation, the exact shape of output pulse is simulated. In comparison of non-unique solution for output pulse in the previous papers, the results of this study have an optional merit.
Dr. Mahmoud Nikoufard, Mohsen Hatami,
Volume 10, Issue 2 (International Journal of Optics and Photonics (IJOP) Vol 10, No 2, Summer-Fall 2016)
Abstract
A photonic crystal-based TE to TM polarization converter for integrated optical communication is proposed in this paper. The photonic crystal consists of air circular-holes in slab waveguide. The radius of holes are determined to be 291nm having lattice constant of 640nm using the gap map and band diagram. The polarization converter is composed of an InGaAsP triangular-shaped waveguide on SiO2 substrate. At first, the bandgap wavelengths of two-dimensional structure are determined using finite difference method and then polarization conversion length, polarization conversion efficiency and rotation are determined as a function of the ratio of height to width of the triangle waveguide. The simulation results show a minimum conversion length of 750nm with a conversion efficiency of about 90% could be obtained.
Elham Yousefi, Mohsen Hatami, Sajjad Dehghani,
Volume 11, Issue 1 (International Journal of Optics and Photonics (IJOP) Vol 11, No 1, Winter-Spring 2017 2017)
Abstract
We solve the coupled mode equations governing the chalcogenide nonlinear fiber Bragg gratings (FBGs) numerically, and obtain the bistability characteristics. The characteristics of the chalcogenide nonlinear FBGs such as: switching threshold intensity, bistability interval and on-off switching ratio are studied. The effects of FBG length and its third order nonlinear refractive index on FBG characteristics are investigated. We obtain an interesting result that independent of the third order nonlinear refractive index; there exists an optimum FBG length of about 6 mm at which the on-off switching ratio becomes maximized. It is also found that by increasing the nonlinearity, the maximum value of on-off switching ratio decreases. The results of this paper can be mainly used for designing all-optical switches and memories.
Elham Yousefi, Mohsen Hatami, Amin Torabi Jahromi, Sajjad Dehghani,
Volume 13, Issue 2 (International Journal of Optics and Photonics (IJOP) Vol 13, No 2, Summer-Fall 2019)
Abstract
In recent decades, fiber Bragg gratings (FBGs) have been very much considered for their many applications in optical communication systems, as well as due to their bistability and multi stability properties. In this paper, the formation of ternary stability (TS) in nonlinear chalcogenide fiber Bragg gratings (NCFBGs) is investigated via numerical simulations. Effective parameters on TS such as the FBG length, input wavelength and nonlinear property (or nonlinearity) on TS formation are introduced and studied. It is found that there exists a minimum length for each third order nonlinear coefficient that TS phenomena can be observed. Also, the threshold intensity for TS formation is calculated with respect to the length, input wavelength and third order nonlinearity. In addition, the relevance between the minimum length for TS formation and the third order nonlinearity in the range of chalcogenide nonlinearities are looked into. It is numerically confirmed that increasing the input wavelength (in a valid FBG input wavelength range) increases the TS formation threshold intensity, while decreases the needed FBG length. Because of using experimental values in this paper, it has valuable information about designing the all-optical device with three - level stability which makes NCFBG a suitable option for all-optical ternary switching and all-optical memory in the integrated optical circuits.
