International Journal of

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Larger width of P-cladding layer in p-i-n waveguide of traveling wave electroabsorption modulator (TWEAM) results in lower resistance and microwave propagation loss which provides an enhanced high speed electro-optical response. In this paper, a fullvectorial finite-difference-based optical mode solver is presented to analyze mushroom-type TWEAM for the first time. In this analysis, the discontinuities of the normal components of the electric field across abrupt dielectric interfaces which are known as the limitations of scalar and semivectorial approximation methods are considered. The optical field distributions in mushroom-type TWEAM and conventional ridge-type TWEAM of the same active region for 1.55 μm operation are presented. The important parameters in the high-frequency TWEAM design such as optical effective index which defines optical velocity and transverse mode confinement factor are calculated. The modulation response of mushroom-type TWEAM is calculated by considering interaction of microwave and optical fields in waveguide and compared to that of conventional ridge-type TWEAM. The calculated 3dB bandwidths for ridge-type and mushroom-type TWEAM are about 139 GHz and 166 GHz for 200 μm and 114 GHz and 126 GHz for 300 μm waveguide length, respectively.

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Time resolved laser induced incandescence (LII) technique is used to measure size distribution of soot nanoparticles of candle's flame. Pulsed Nd:YAG laser is used to heat nanoparticles to incandescence temperature and the resulting signal is measured. Mass and energy balance equations are numerically solved to calculate temperature of soot particles in low fluence regime. Assuming Plank black body radiation and lognormal size distribution for soot particles, the intensity of LII signals are calculated. Using Levenberg-Marquart nonlinear regression algorithm and numerical and experimental LII signals, mean particle size and distribution width of soot nanoparticles are obtained.

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In this paper, we have reported the fabrication of two-dimensional photonic crystals, using a direct writing method in azo polymers. Periodic structures have been fabricated using the interference patterns of two coherent laser beams. The frequency response of the initial one-dimensional structure shows an attenuation of 19.3dB at 1554nm. The twodimensional structure shows 8.3dB and 11.3dB of attenuation at 1554nm in two perpendicular main axes of the structure. The diffraction pattern shows the characteristic rectangular pattern.

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In this paper the Phase-Matching bandwidth, effective nonlinear coefficient and the walk-off angle within the effective bandwidth of the LiGa(SexS1-x)2 biaxial nonlinear crystals are calculated using the Genetic algorithm (GA). This calculation is held for all tree principle XY, YZ and XZ planes individually. The results are shown the accuracy of the applied algorithm is quite qualified.

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In this article, we report the studies of various device architectures of organic lightemitting devices (OLEDs) incorporating highly efficient blue-emitting and ambipolar carriertransport ter(9,9-diarylfluorene)s, and their influences on device characteristics. The device structures investigated include single-layer devices and multilayer heterostructure devices employing the terfluorene as one functional layer. It is found that, although these terfluorenes are capable of bipolar carrier transport, rather poor device performance of single-layer devices in comparison with multilayer devices indicates that the heterostructure is still essential for balancing hole/electron injection and currents, for achieving high emission efficiencies, and for full utilization of high luminescence efficiency of these terfluorenes. With the heterostructure of hole-transport layer/terfluorene/electrontransport layer and careful choice of carriertransport materials, effective hole and electron injection, confinement of carriers, and confinement of excitons in terfluorenes are achieved. As a consequence, a highly efficient (4.1% quantum efficiency), low-voltage (~2.5 V turn-on voltage), and color-saturated nondoped blue-emitting device is demonstrated. Such high electroluminescent efficiency is consistent with high photoluminescent quantum yields of these terfluorenes and is competitive with those of efficient doped blue OLEDs.

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Micro-channels are made over the Ag+/Na+ ion-exchanged soda-lime glass surface by interaction of an intense Ar+ laser beam and the silver ions inside the glass matrix. The Ar+ laser beam reduces the Ag+ ions inside the matrix. The Ag+ atoms aggregate into silver nano-clusters around the interaction area, inside the glass matrix. Aggregation of the silver atoms and the thermal effects of the interaction, changes the geometrical profile of the glass surface. This phenomenon has been used to produce micro-sized channels over the glass surface. During the interaction the glass has moved under the focused laser beam in two dimensions by resolution of 300 nm via a computer controlled xyz sub-micro-positioner to produce the channel walls. Using this technique, micro-channels of 0.3 μm deep and arbitrary width have been made. The height of the produced wall has been determined by interferometry techniques.

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The composite cavity fiber laser (CCFL) is relatively simple in its fabrication, as it is essentially three wavelength matched Bragg gratings in a section of doped fiber. By using internal feedback with unequal sub-cavity lengths, unidirectional CCFLs with significantly asymmetric output power from its two outputs can be achieved. Preliminary results also show that it is possible for the lasing frequency of the two outputs to be different by a few GHz.

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In this work the effects of heat generation on the modes of Yb:Glass double clad fiber laser were investigated. The thermal dispersion and thermally-induced birefringence were considered when the gain medium becomes an anisotropic medium. The results showed considerable modifications of laser modes profiles, in particular for transfer magnetic (TM) and transfer electric (TE) modes which their polarization vectors possess radial and azimuthal components.

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In this paper, we present a comparative numerical analysis to determine the refractive index of photonic crystal fibers (PCFs) by using FDFD method and used the results to evaluate the confinement losses of PCFs by considering the effects of air-hole rings in the cladding. It is shown that by increasing the wavelength, the imaginary part of refraction index rises, resulting in increase of confinement losses nearly by order of 10. In lower wavelengths over the range of 0.2 to 1 μm, these losses were shown to be negligible. The obtained results show that as the number of air-hole ring in the cladding increases, the confinement losses over wavelengths would reduce. To show the effect of air-hole rings on confinement losses in PCFs, the FDFD method yielded accurate results that agree well with results of FEM method and source–model technique reported by others.

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In this paper we consider electromagnetic field quantization in the presence of a dispersive and absorbing semiconductor quantum dot. By using macroscopic approach and Green's function method, quantization of electromagnetic field is investigated. Interaction of a two-level atom , which is doped in a semiconductor quantum dot, with the quantized field is considered and its spontaneous emission rate is calculated. Comparing with the same condition for an excited atom inside the bulk, it is shown that the spontaneous emission rate of an atom will decrease.

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This paper describes the passive Qswitch, based on polymer and organic dye BDN, of a pulsed Nd:YAG laser. Pulses of 27ns duration and peak power of 1.7MW for initial transmission of Q-switch 18.4% 0 T = have been obtained. We have obtained Q-switching efficiency of 77% for train of pulses of 31 and 76.2% 0 T = at the pump energy of 98J. We have also obtained the dependency of laser pulse characteristics on pump energy and initial transmission of Q-switch. We have obtained the damage threshold of this Q-switch at the pulse duration of 27ns to be13J cm2 .

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Electronic absorption, florescence excitation and AFM studies of selected homogeneous solutions and thin films of mesotetrakis (parahydroxyphenyl) porphyrin (THPP) (1), mesotetrakis (2, 3- dihydroxyphenyl) porphyrin 2, 3-OHPP) (2), mesotetrakis (3, 4-dihydroxyphenyl) porphyrin (3, 4-OHPP) (3) as well as Zn(II) derivative of 2, 3-OHPP (4) under UV lamp and green laser irradiation (532 nm) are acquired and analyzed.Our results indicate that in irradiation experiments, the products of the resulting porphyrins strongly depend on the careful choice of the light source. UV lamp irradiation produced J-type aggregated diacid porphyrins from free base porphyrins by simple photochemical technique. The stabilization of the aggregates structure may be achieved through hydrogen bonding between the protonated core and the peripheral hydroxyl groups, mediated by the chloride anions. The results of laser irradiation experiments shown the formation of J-aggregated porphyrin upon green laser (532 nm) irradiation.Green laser irradiation has been caused the hydrogen bonding interactions between neighboring porphyrin molecules through hydroxyl moieties to produce J-aggregated supramolecular porphyrins. The AFM topographic images and Dynamic Light Scattering (DLS) of THPP(1) under green laser irradiation have been indicated nano-structured porphyrin wires about 5 nm high approximately.

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In this work, using perturbation technique we have developed an approximate analytic model for evaluating the band structure of a 2-D octagonal photonic quasicrystal (PQC). Although numerical techniques are being used for evaluating such band structures, developing a numerical model to the best of our knowledge this work is the first instance of reporting helps to understand the physical properties of the structure more easily. Use of perturbation technique can be beneficial in approximating the photonic band structures, in PQCs made with low-dielectric contrast materials, with high accuracy. To the best of our knowledge this work is the first instance of reporting the development of such an analytic model for octagonal PQCs. In addition, we have studied the effect of variations in the dielectric contrast on the photonic band structure.

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In this paper, a brief summary of different methods of fabrication of optical preform and fiber is reviewed. Several methods of incorporation of erbium ions into optical preforms are studied. Characterization of the fabricated erbium doped fibers including measurements of refractive index profile, absorption, fluorescence and gain spectra and metastable lifetime are described. It is also expressed that many of these fabrication and characterization methods are feasible to be carried out in Iran.

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The average velocity of water flow has been simultaneously measured with fluorescent and speckle imaging methods. The measured velocities with two methods are in good agreement with each other and it confirms that the speckle imaging method can be used as a confident method to measure the velocity of water flow in a dry leaf. Also the velocity of water flow through thick and thin xylems of a leaf can be measured with speckle imaging method and the ratio of thick xylem’s radius to thin xylem’s radius can be estimated with this method. Also the ratio was measured by monitoring the cross section of the leaf. The two measurements were in agreement.

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We generalized the squeeze and displacement operators of the one-dimensional harmonic oscillator to the three-dimensional case and based on these operators we construct the corresponding coherent and squeezed states. We have also calculated the Wigner function for the three-dimensional harmonic oscillator and from the analysis of time evolution of this function, the quantum Liouville equation is also presented. Further properties of the quantum states including Mandel’s 􀡽 and quadrature squeezing parameters are discussed as well.

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We have studied light-induced birefringence (LIB) and surface relief grating (SRG) formation in the series of methylacrylate polymers. The effect of material structure such as length of photochromic side chain, glass transition temperature and molecular structure of azo units on LIB and SRG are studied. The optical formation of self-induced SRG on films of these materials is also presented.

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In this paper, by including Raman scattering in the coupled-mode equations, the scalar modulation instability in photonic crystal fibers is investigated. The evolution of the pump, Stokes and anti-Stokes waves along the fiber as well as the conversion efficiency for two cases, with and without Raman effect, are studied. The effect of anti-Stokes seed and the pump depletion on the evolution of Stokes wave is also considered. Moreover, the parametric gain when it is affected by Raman gain is dealt with. The results show that it is important to take into account Raman scattering, especially for wide-bandwidth parametric amplifiers which results in an asymmetric spectrum and more amplification of the Stokes wave.

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We proposed and analyzed implementation of the single-qutrit quantum gates based on stimulated Raman adiabatic passage (STIRAP) between magnetic sublevels in atoms coupled by pulsed laser fields. This technique requires only the control of the relative phase of the driving fields but do not involve any dynamical or geometrical phases, which make it independent of the other interaction details: detuning and pulse shapes, areas and durations. The suggested techniques are immune to spontaneous emission since the qubit and qutrit manipulation proceeds through non-absorbing dark states. In this paper, taking proper timing of the Rabi frequencies allows us to transfer the population of the system to a desired superposition of the ground states with the highest fidelity. We also obtained and implemented single-qutrit unitary gates, for transferring of the population of the system with different initial and final states.

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The refraction phenomenon at the interface of an ordinary material and a lossy metamaterial has been investigated. For oblique incidence on the lossy metamaterial, the planes of constant amplitude of the refracted wave are parallel to the interface and the plane of constant phases make a real angle with the interface (real refraction angle). The real refraction angle and hence, the real refraction index corresponds to the real refraction angle which satisfies the real version of Snell's law are negative in two different regimes. In one regime, the metamaterial is double-negative, while in the other one it is single-negative. Moreover, we show that the plane wave solution for the refracted wave is causal in both double-negative and single-negative regimes