Showing 242 results for Type of Study: Research
Supriya Patil, A.d. Shaligram,
Volume 5, Issue 2 (7-2011)
Abstract
A novel geometry for enhancing the sensitivity of intensity modulated refractometric fiber optic sensor for detection of adulteration level in diesel by kerosene is proposed. In this multimode plastic optical fiber is uncladded for specific length and bent into S shape. This geometry is simulated and analyzed using Beam Propagation Method in Beam prop RSOFT software. When sensor is immersed in the diesel then diesel acts as a cladding for uncladded S shape portion of optical fiber. As diesel is adulterated by different volumes of kerosene, refractive index of cladding changes which in turn affects the output intensity of the sensor. The investigation revealed that when such structure of sensor is used to detect the adulteration level in diesel then sensitivity gets improved 4 times for two fold increase in bend curvature of fiber. Thus it is highly sensitive mechanism to determine on line adulteration of diesel and also can be used for other applications.
G. Vidya, Rani Joseph, S. Prathapan, P. Radhakrishnan, C. P.g. Vallabhan, V.p.n. Nampoori, G. Sreelekha ,
Volume 5, Issue 2 (7-2011)
Abstract
In the context of conjugated polymers, especially those of the poly (phenylenevinylene) (PPV) family, which are promising candidates as emission material in light emitting devices such as LEDs, field effect transistors and photovoltaic devices, we have, in the present study, prepared MEH-PPV [Poly [2- methoxy-5-(2’-ethyl-hexyloxy)-1,4-phenylen-evinylene] of low molecular weight and low polydispersity index. We discuss the thickness dependent fluorescence emission from the film waveguides fabricated with the above blends.Of the two peaks observed in this fluorescence spectrum, the shorter wavelength peak (562nm) is dominant in the range of lower thickness and as thickness is increased the longer wavelength peak (600nm) predominates. We also discuss the multimode laser emission from free standing MEH-PPV/Polystyrene film waveguides blends which show the nature of improvement in lasing behavior. The gain studies show that free standing film of MEH-PPV blended with Polystyrene can be used as a compact solid state laser.
Hojjat Amrollahi Bioki, Mahmood Borhani Zarandi,
Volume 5, Issue 2 (7-2011)
Abstract
Zinc Sulfide (ZnS) thin films were deposited on glass substrates at the pressure of 10-6 mbar by thermal resistor evaporation technique. The effects of annealing on the structural, optical properties of ZnS films were studied. Crystalline ZnS films have been analyzed by X-ray diffraction. Only cubic phase with the preferred (111) plane was found in ZnS films. Optical characteristics were studied as a function of annealing temperature and thickness in air. The results show that the energy band gap was found to be about 3.5 eV. It was observed that the energy gap decreases with the increase in the film thickness and increases with the increase in the annealing temperature.
Tahereh Nemati Aram, Saeed Batebi, Massoud Mohebbi,
Volume 6, Issue 1 (10-2012)
Abstract
We investigate theoretically the high-order harmonic spectrum extension and numerical generation of an intense isolated attosecond pulse from He+ ion irradiated by a two-color laser field. Our simulation results show that the chirp of the fundamental field can control HHG cutoff position. Also, these results show that the envelope forms of two fields are important factors for controlling the resultant attosecond pulses. Besides, the effects of relative intensity are investigated. As a result, by using the optimized conditions an intense isolated 126-as (attosecond) pulse can be observed
Alireza Keshavarz, Zahra Abbasi, Mohsen Hatami,
Volume 6, Issue 1 (10-2012)
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.
Hamid Pashaei Adl, Samad Roshan Entezar,
Volume 6, Issue 1 (10-2012)
Abstract
In this paper, the optical properties of one dimensional fractal structures are investigated. We consider six typical fractal photonic structures: the symmetric dual cantor-like fractal structure, the asymmetric dual cantor-like fractal structure, the single cantor-like fractal structure, the symmetric dual golden-section fractal structure, the asymmetric dual golden-section fractal structure and the single golden-section fractal structure. By using the transfer matrix method the transmission spectra of these structures are simulated. The calculation results shows that the transmission spectrum of the symmetric dual cantor-like fractal structure is self-similar and the peak numbers in the transmission spectra of the SDGSFS also follow the principals of special fractal structures. It is also shown that in the symmetric dual golden-section fractal structure the localization of modes which appears within the stop band increases and getting closer to the middle of the gap by increasing the number of string.
Hamed Amin Pour, Alireza Hojabri,
Volume 6, Issue 1 (10-2012)
Abstract
We present a novel slanted faces of thin-disk composite Yb:YAG YAG laser which is side-pumped by four non-symmetric hollow- ducts. The pump light distribution in the disk is modeled by using Monte-Carlo ray tracing method. The temperature distribution inside the crystal is calculated by taking into account either the concentration of Yb+3 ion or the different transmission of laser output coupler. By using Finite Element Analysis (FEA) method, we calculated the absorption efficiency through the disk. The resonator is simulated by self consistently method. The resulting of optical efficiency and the output power of our laser have been modeled.
M. R Ostovari, R Safaiee, M.m Golshan,
Volume 6, Issue 1 (10-2012)
Abstract
In the present article we report the dynamical behavior of entanglement between π-electrons and photons in Graphene. It is shown that the degree of such entanglements depend on the orientation of π-electron momenta relative to the photonic polarization. Moreover, we show that as the detuning between the π-electron transition frequencies and that of the photons is increased, the degree of entanglement decreases.
Mina Eslamifar, Nastaran Mansour,
Volume 6, Issue 1 (10-2012)
Abstract
In this work, thermo-optical properties of gold nanoparticle colloids are studied using continuous wave (CW) laser irradiation at 532 nm. The nanoparticle colloids are fabricated by 18 ns pulsed laser ablation of pure gold plate in the distilled water. The formation of the nanoparticles has been evidenced by optical absorption spectra and transmission electron microscopy. The nonlinear optical properties of gold nanoparticles colloids are investigated by closed Z-scan under irradiation of a low power CW laser. It will be shown that the thermal lens model is in excellent agreement with the experimental results of samples. The aperture-limitted optical limiters based on the nonlinear refraction of colloidal solution are presented. The tunability of limiting threshold of optical limiters can be accomplished by engineering of the experimental geometry.
Mojtaba Sadeghi, Saeed Olyaee, Fahimeh Taghipour,
Volume 6, Issue 1 (10-2012)
Abstract
In this paper, a fractal photonic crystal fiber (F-PCF) based on the 1st iteration of Koch fractal configuration for optical communication systems is presented. Complex structure of fractal shape is build up through replication of a base shape. Nowadays, fractal shapes are used widely in antenna topics and its usage in PCF has not been investigated yet. The purpose of this research is to compare normal photonic crystal fibers (N-PCFs) with F-PCFs through the simulation and optimization procedure based on the finite element method (FEM). The effective mode index of the fundamental mode is found for different PCF structures. In addition, dispersion properties of F-PCF are numerically calculated and compared with N-PCF.
H Pakarzadeh, K Nielsen, A. C Brunetti, K Rottwitt, A Zakery,
Volume 6, Issue 2 (10-2012)
Abstract
A polymethylmethacrylate (PMMA) microstructured polymer
optical fiber (mPOF) is fabricated and characterized. Using the cut-back
technique the fiber loss is measured which is higher than the step-index silica
fibers. Through a novel experimental scheme, the backward Stokes spectrum of
the fabricated mPOF is recorded over a range exceeding 3000 cm‑1
during the cut-back method and compared with that of step-index silica fiber.
Especially, the gain coefficient of the Raman peak at 2950 cm‑1
is directly measured, that is without comparing with other known material. The
results show a very good agreement with those obtained through other
experimental schemes.
Keshavarz, Kazempour,
Volume 6, Issue 2 (10-2012)
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.
Mr. Farshid Koohi-Kamali, Dr. Majid Ebnali-Heidari, Mohammad Kazem Moravvej-Farshi,
Volume 6, Issue 2 (10-2012)
Abstract
We report the results of our study on the role of microfluidic infiltration technique in improving the coupling characteristics of dual-core photonic crystal fiber (PCF) couplers. Using the finite element method (FEM), we evaluate the effective mode area, dispersion and coupling parameters of an infiltrated dual-core PCF. We use these parameters to design a compact and reconfigurable coupler by solving a set of coupled generalized nonlinear Schrödinger equations. This approach allows one to obtain wavelength-flattened dispersion characteristics with bandwidth of in the ITU region, and large walk-off length simply by choosing a suitable infiltrated refractive index. We also demonstrate that under certain conditions one can observe a pulse break-up effect to generate pulse trains with high repetition rate.
Mohammad Ali Ansari,
Volume 6, Issue 2 (10-2012)
Abstract
In this paper, the evaluation of time profile of a femtosecond pulse laser propagated through biological tissues is studied. The majority of the biological tissues with a high scattering anisotropy must be considered as turbid media, that their optical responses are complicated. To study the propagation of ultra-short pulse in turbid media, the diffuse equation is used. In this study, the analytical and numerical solution for diffuse equation is investigated. The numerical method is based on Boundary Integral method (BIM), and also, the time evaluation of propagating pulse is studied.
Mohsen Dehbashi, Mousa Aliahmad,
Volume 6, Issue 2 (10-2012)
Abstract
Sn 0.986 Ni 0.014 O nanoparticles have been synthesized by a simple co-precipitation method. Nanoparticles crystallize in lower temperature (350°C) and shorter time (2h) respect to other methods. The sample characterized by various standard techniques such as Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), Atomic absorption spectroscopy (AAS) and UV–Vis spectroscopy. The X-ray diffraction reveals that sample is pure rutile-type tetragonal phase, the crystalline size Sn0.986Ni0.014O nanoparticles is 27 nm. UV-Vis spectroscopy is revealed the optical band gap to be 3.98 eV for Sn0.986Ni0.014O nanoparticles that is higher than the bulk value of SnO (2.5–3 eV).
Ashkan Horri, Rahim Faez,
Volume 6, Issue 2 (10-2012)
Abstract
In this paper, transistor lasers (TLs) are used as an optical modulator for generation of ASK(Amplitude Shift Keying) and FSK (Frequency Shift Keying) optical signals. Our analysis is based on continuity equation, rate equations, and the theory of discontinuity of quasi-fermi level at the abrupt junction. Our simulation results indicate that, the specification of ASK and FSK optical signals, are affected by dynamical behavior of TL. Also our simulation results indicate that, the collector-emitter voltage amplitude should be small enough that the nonlinear properties of TLs do not destroy the modulated optical signals.
Maral Ghoshani, Abbas Behjat, Fatemeh Jafari, Naimeh Torabi,
Volume 7, Issue 1 (6-2013)
Abstract
In this research, the lifetime of green organic light emitting diodes (OLEDs) is studied using four passivation layers. To encapsulate the OLEDs, MgF2, YF3, composed of alternating MgF2/ZnS and YF3/ZnS layers were grown by thermal vacuum deposition. Measurements show that the device lifetime is significantly improved by using YF3 and ZnS as passivation layers. However, diodes encapsulated by MgF2/ZnS and YF3/ZnS nano-structures show a highly efficient gas diffusion barrier that results in a longer lifetime of the devices. The half lifetime of the green OLEDs reached 1200 minutes using YF3/ZnS layers. The electroluminescence (EL) and current-voltage characteristics of the devices were also examined to compare the electrical and the emissivity properties of the devices before and after encapsulation. This simple and inexpensive thin-film encapsulation method would be potentially employed to capsulate top emitting OLEDs and flexible OLEDs due to their good performance and easy fabrication.
Rasoul Roknizadeh, Malek Bagheri Harouni,
Volume 7, Issue 1 (6-2013)
Abstract
We consider the interaction of quantum light with an ideal semiconductor microcavity. We investigate photon statistics in different conditions and the presence of detuning and exciton-exciton interaction. We show that in the resonant interaction and absence of the exciton-exciton interaction, the state of the whole system can be considered as coherent state. According to our results, it turns out that photon statistics strongly depends on the initial state of the system. It is found that it is possible to generate squeezed light in the presence of the exciton-exciton interaction.
Miss Elnaz Aleebrahim, Mr Fardin Kheirandish,
Volume 7, Issue 1 (6-2013)
Abstract
In this paper, we clarify the applicability of the super operator technique for describing the dissipative quantum dynamics of a system consists of two qubits coupled with a thermal bath at finite temperature. By using super operator technique, we solve the master equation and find the matrix elements of the density operator.
Considering the qubits to be initially prepared in a general mixed state, we explore the influence of dissipation on dynamical behavior of system. As expected, we obtain analytical evidence that the thermal photons and spontaneous emission of atoms are responsible for dissipation of entanglement of system.
Dr Roghaieh Parvizi,
Volume 7, Issue 1 (6-2013)
Abstract
We have investigated and developed a theoretical approach to explore stimulated Brillouin scattering (SBS) phenomena in single mode fiber. SBS happening threshold power condition has been studied in terms of fiber parameters and input pump power. To assess threshold power precisely, the pump depletion effect and fiber loss has been included by employing 1% criterion. The threshold exponential gain Gth can be anticipated by this simulation which strongly depends on the fiber length Brillouin gain content and effective area. The value of Gth is not a constant as usually assumed in the literature and its value is 4 for the longer lengths and between 10 and 18 is for relatively shorter lengths. This simulation can anticipate the optimum length of fiber against the every launched pump power to generate SBS effect.
