International Journal of

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A novel design of Dual-Core Photonic Crystal Fiber (DC-PCF) with silica-air microstructures is proposed in this paper. Nonlinearity and confinement loss of DC-PCF are evaluated by using a Full-Vectorial Finite Element Method (FV-FEM) successfully. By optimizing the geometry of three ring DC-PCFs, a high nonlinearity (52w-1km-1) and low confinement loss (0.001dB/km) can be achieved at 1.55μm wavelength when diameter to pitch ratio (d/Λ) is 0.70.

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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.

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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.

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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.

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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.

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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.

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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.

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The performance of a polarizing beam splitter based on the one-dimensional photonic crystals (1D-PCs), is theoretically investigated. The polarizing beam splitter consists of a symmetric stack of the low-index quarter-wave plates and the high-index half-wave plates with a central defect layer of air. The linear transmission properties of the polarizing beam splitter are numerically simulated by the transfer matrix method. The results show that the wavelength of the polarizing beam splitter can be tuned by adjusting the thickness of the defect layer of air and the incident angle of light due to the resonant couple of the evanescent waves localized at the interfaces between neighboring layers.

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Thanks to their unique optical and electromagnetic properties, noble-metal nanoparticles are proven very useful in many scientific fields, from nanotechnology to biology, including detection of cancer cells. Irradiated gold nanoparticles, as a nano-smolder could be widely used in biomedical contexts such as tumor therapy. Laser destruction of a cancerous tissue depends on thermal and physical properties of the tissue, therefore temperature quantification of an irradiated metallic nanoparticle in different materials could be followed by interesting applications. In this research we quantify the temperature of irradiated gold nanoparticles in paraffin which is the most commonly used material for embedding of biological tissues in pathology. We have shown that the temperature increase rate for irradiated gold nanoparticles with diameters of 78 nm, 97 nm, and 149 nm are 1.31, 1.40, and 2.28 ◦C/mW, respectively. Considering that the conductivity of a biological tissue is an important parameter on temperature raise and destruction, these results could yield a valuable insight into the cancer therapy.

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In this study, Highly Oriented Pyrolytic Graphite was ablated in various polar and nonpolar solvents by Q-switched neodymium: yttrium-aluminum-garnet laser (wavelength=1064 nm, frequency=2 kHz, pulse duration=240 ns). Then, the products were examined using Scanning Electron Microscopy and UV-Vis spectroscopy. The images showed that different carbon structures such as cauliflower-like structures in benzene, spiral integrated forms in toluene, organic integrated networks in hexane, and nanoparticles in ethanol were formed. In n-methyl-2-pyrrolidone (NMP), sheets and bulk deformed structures were seen. Also, in Dimethylacetamide, particles in different stages of growth could be detected. The nonlinear optical absorption (NLA) behaviors of the products were investigated by exposing them to a 532 nm nanosecond laser using the Z-scan technique. The saturated NLA coefficient, obtained from structures of NMP and hexane-based synthesized samples, are 1.1×10-8 and 2.4×10-8 cm W-1, respectively. The saturable absorption responses of these samples were switched to the reverse saturable absorption responses in the other synthesis mediums. The maximum nonlinear absorption coefficient of 10.2×10-8 cm W 1 was measured for spiral integrated superstructures, produced in the toluene medium.

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We study the focusing properties of a two dimensional complex square-lattice photonic crystal (PC) comprising air holes immersed in Ge medium. The finite difference time domain (FDTD) method is utilized to calculate the dispersion band diagram and to simulate the image formation incorporating the perfectly matched layer (PML) boundary condition. In contrast to the common square PCs with the same air filling factor, the frequency corresponding to the effective negative refraction occurs in the second photonic band and the spatial image resolution is improved.

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The Image reconstruction is an important problem in optical tomography. The process of the image processing requires the study of photon migration in biological tissue. There are several approaches to study and simulate propagation of photons in biological tissues. These approaches are categorized into stochastic and analytical groups. The Monte Carlo method as a stochastic method is widely used to simulate the propagation of photons in biological tissues which is time consuming. In other hand, the diffuse equation can be also applied to simulate the migration of photons in tissues. In this study, a solution to diffuse equation based on green theorem is applied to study the diffusion of photon in biological tissue. The precision and accuracy of this presented method is evaluated by comparing with Monte Carlo method and experimental Data.

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In this paper, properties of reflection phase in one-dimensional quaternary photonic crystals combining dispersive meta-materials and positive index materials are investigated by transfer matrix method. Two omnidirectional band gaps are located in the band structure of considered structure. However, we limit our studies to the frequency range of the second wide band gap. We observe that the value of the reflection phase difference between TE and TM waves can be controlled by changing the incident angle and frequency. Also, the results show that the reflection phase difference in the second band gap increases by increasing the incident angle, and remains almost unchanged in a broad frequency band. Furthermore, at two points near to the edges of the gap the reflection phase difference keeps almost zero in spite of the change of incident angle. Based on these properties, phase compensators and omni-directionally synchronous reflectors and also polarizers can be designed.

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In this work, potential of the nanosecond laser processing technique on manipulating the surface wettability of 316L bio grade stainless steel is investigated. Results show that the steel wettability toward water, improves significantly after the laser treatment. Different analyses are assessed in correlation with wettability using Scanning Electron Microscope (SEM), Scanning Tunneling Microscope (STM) and Energy Dispersive X-ray spectroscopy (EDX). It is found that the improvement in the wettability relates to the combined effects of the increase in the surface roughness, oxygen content and the form of the created surface morphologies. Laser fluence is found as the most dominant processing parameter and the higher the incident fluence results in the higher surface roughness and improvement of the wettability. However, measurements indicate that all the treated surfaces become hydrophobic after air exposure for a few days. It is shown that the time dependency of the surface wettability relates to the chemical activity and the reduction of the Oxygen/Carbon (O/C) ratio on the treated surfaces. The behaviors are further studied with investigating the effects of the keeping environment. The long-term wettability alteration differs for the samples that are kept in different mediums. Results indicate that the nanosecond pulsed laser treatment is a versatile approach to create either hydrophobic or hydrophilic steel surfaces for industrial and medical applications.

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In this paper a resonant tunnelling quantum well infrared photodetector (RT-QWIP) is discussed. Each period of this photodetector structure comprises of a resonant tunnelling structure (AlAs/AlGaAs/AlAs) nearby a quantum well (AlGaAs/GaAs). In this photodetector, photocurrent is produced when an electron makes a transition from the ground state of the well to an excited state which is coupled to the resonant state of the resonant tunnelling structure. The effect of structural parameters of the photodetector on the electronic states and oscillator strength of transitions between energy subbands of the structure is investigated. Then using the obtained results, an appropriate structure for the RT-QWIP is determined which exhibits a photoresponse peak at 7.3 μm at 77 K.

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In this paper, the magnetic properties of carbon based material, graphene is studied, which is generated by laser ablation in cryogenic media. Transmission electron microscopy (TEM) and alternating gradient force magnetometer (AGFM) are applied to investigate the graphene morphology and magnetic properties, respectively. The graphene synthesized by the laser ablation method exhibits diamagnetic behavior. However the magnetic transition from diamagnetic to paramagnetic effect is lucidly observed by functionalizing the graphene sample with silver atoms.

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Photonic crystal design procedure for negative refraction has so far been based on trial and error. In this paper, for the first time, a novel and systematic design procedure based on physical and mathematical properties of photonic crystals is proposed to design crystal equi-frequency contours (EFCs) to produce negative refraction. The EFC design is performed by the help of rectangular stair-case (RSC) photonic crystals. The RSC crystal is then converted to more common structures like pillar crystals by matching Fourier coefficients of periodic electric permittivity. Methods to design common crystals which have approximately equal Fourier components to the RSC crystal are also discussed. The proposed procedure can be used to design metamaterials without the difficulties of large trial and error. The devised procedure can also be applied in designing other structures involving photonic crystals.

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Glassy samples with a composition of 40P2O5–30V2O5–(30-x)Li2O– xK2O, 0<x<30 (mol %) were prepared by the conventional melt quenching technique in two forms of bulk and blown film. X-ray diffraction patterns corroborated the amorphous feature of the samples. Density of samples was investigated by using Archimedes principle. Based on absorption and reflection spectra, indirect allowed optical gaps, Urbach energies, refractive index and dielectric coefficients were calculated. Study of FTIR spectra revealed that all of the samples mainly contain metaphosphate and pyrophosphate units. Glass transition temperatures were also evaluated using DSC curves. Non-linear variation of many physical properties by gradually substitution of Li ions with K, confirmed the existence of mixed alkali effect in glassy system.​

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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.

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In this paper, homogeneous, wavelength shift biosensor is designed for sensing the protein concentration using two dimensional Photonic Crystal Ring Resonator (PCRR). The sensor is designed to monitor the protein concentration from 0% to 100%. The proposed sensor is composed of periodic Si rods embedded in an air host with a circular PCRR that is placed between the inline quasi waveguides. It is observed that the resonant wavelength of the sensor is shifted (0.9 nm) to higher wavelength while increasing the protein concentration (5%) as the protein has a unique refractive index for each level. With this underlying principle, the performance of the sensor is analyzed for different protein concentration.