International Journal of

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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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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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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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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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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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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.

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In this paper, we report the numerical analysis of a photonic crystal fiber (PCF) for generating an efficient supercontinuum medium. For our computational studies, the core of the proposed structure is made up of As₂Se₃ and the cladding structure consists of an inner ring of holes made up As₂Se₃ and four outer rings of air holes in MgF₂. The proposed structure provides excellent nonlinear coefficient and dispersion optimization. For the analysis, finite difference frequency domain (FDFD) method is employed. Because of the high nonlinear refractive index of the chalcogenide glass and high difference between the refractive index of the core and the cladding, a small effective mode area of 0.68 μm² is obtained. The nonlinear coefficient is 14.98 W^-1m^-1 at the wavelength of 1.8 μm. Dispersion is almost flat from 1.6 μm up to 2.8 μm. The supercontinuum spectrum calculated ranges from 1 μm to 6 μm. The presented structure is appropriate for medical imaging, optical coherence tomography and optical communications

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In this paper, a Y-shaped power splitter based on a two dimensional photonic crystal (PhC) for TE modes is designed and optimized. A triangular lattice of air holes is used for Y-shaped power divider. For analyzing these structures, plane wave expansion (PWE) and finite difference time domain (FDTD) methods are used. The simulation results show that more than 98% of the input power is transmitted to the outputs and the structure has just less than 2% reflected power. According to the simulation results this structure is suitable for high bandwidth optical integrated circuit at the 1550 nm wavelength.

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In this paper, a new structure is provided for the dispersion compensating photonic crystal fibers in order to broaden the chromatic dispersion and increase the dispersion compensating capability in a wide wavelength range. In the structure, putting elliptical holes in the first ring of the inner core clad of a dispersion compensating fiber of the hexagonal lattice, increases the wavelength range of the dispersion compensation, and causes this fiber to have the capability of dispersion compensation in the whole E to U telecommunication bands. In this fiber, the minimal dispersion will be -1006 ps/(nm.km) at the 1.68 μm wavelength and at the 1.55 μm wavelength the dispersion coefficient will be -710 ps/(nm.km). The simulations are all done using the finite difference time domain numerical method.

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We present the procedure for designing a high speed and low power all-optical analog to digital converter (AO-ADC), by integrating InGaAsP semiconductor optical amplifier (SOA) with InP based photonic crystal (PhC) drop filters. The self-phase modulation in the SOA can shift the frequency of the Gaussian input pulse. The two output PhC based drop filters are designed to appropriately code the frequency-shifted analog signals by the SOA, converting them to four desired digital output levels. Our numerical results show that in an appropriately designed AO-ADC, the center wavelength (1572 nm) of an amplitude modulated Gaussian pulse of 1.8 ps width and 1.56 pJ energy can be shifted by 6.7 nm, by the SOA, and then be quantized and coded to four digital levels (00, 01, 10, and 11). The two point-defect PhC drop filters, compensating the effect of the frequency shift by SOA, minimize the AO-ADC integral and differential nonlinearity errors.

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Topological Insulators are systems where the broken time reversal symmetry gives rise to protected edge modes that support backscatter-free and one-way propagation of electromagnetic waves by opening non-trivial bandgaps. In this study we investigate a one-way topologically protected waveguide in the frequency range of f=6.0 to 8.0 GHz. The time reversal symmetry is broken by an applied magnetic field in the z direction. We show that the waveguide propagates the light in only one direction that can be controlled by the applied magnetic field and no backscattering is present in the waveguide which results in a near 100% transmission of light to the output. Furthermore, we investigate effect of the applied magnetic field on the topological properties of the system by considering the material dispersion of the rods. Our results show that 3 different frequency ranges will be supported by the edge modes at each given magnetic field. By increasing the magnitude of the applied magnetic field, a blue shift in the non-trivial bandgap is seen, where it can be used to tailor the modes for the waveguide.

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In this paper, a thin film silicon solar cell with anti-reflection coatings on front surface and the combination of periodic grating and photonic crystal on its back surface has been considered. The thickness and number of anti-reflection coatings, as well as the geometric and physical parameters of photonic crystal and grating are optimized to increase the optical absorption of solar cell. The simulations have been performed using the finite difference time domain method with Lumercial software. The results show that the optical absorption of solar cell has been increased significantly by utilizing the anti-reflection coatings, photonic crystal and grating.

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In this paper, we propose a D-shaped plasmonic optical biosensor based on photonic crystal fiber (PCF) to detecting of the different materials such as water, blood plasma, Yd-10B and hemoglobin by using of the refractive index. The gold layer is coated on the polished surface of D-shaped fiber. To achieve the highest sensitivity of the proposed biosensor, we investigated the effects of variation of the gold layer thickness and the other structure parameters such as hole diameter (d) and the distance between two holes or Pitch (L). The results show that the most sensitivity of the proposed biosensor is 2506 nm per refractive index unit (nm/RIU) with the resolution of 1.25×10^-5 RIU, when d=1.4 µm and Λ=1.9 µm with the gold layer thickness of 45nm.

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We theoretically analyze the sensing properties of a one-dimensional photonic crystal-based biosensor for detecting cancer cells infiltrated in a defect cavity layer. The biosensor consists of a sample cavity layer sandwiched between two identical photonic crystals of Hgba₂Ca₂Cu₃O_8+d and GaAs. We use the transfer matrix method to evaluate the performance of the biosensor. We show that a defect mode appears in the transmission spectrum of the biosensor that its position depends on the type of cancer cells in the cavity layer. The analysis is carried out by comparing the transmittance peaks of the cancer cells with the normal cells. We investigate the performance of the biosensor under different hydrostatic pressures and temperatures. We show that one can use temperature change to fine-tune the frequency of the defect modes. In addition, we can adjust the working area of the biosensor by changing the hydrostatic pressure. It is shown that the sensitivity of the biosensor is independent of the temperature, while it strongly depends on the hydrostatic pressure.

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In this paper, a structure is proposed using ring resonator created on 2D photonic crystal (PC) that acts as an add-drop filter (ADF) in all-optical communication systems. The same structure can also act as refractive index (RI) and temperature sensor. The structure is made up of a hexagonal lattice of air holes in a dielectric slab of silicon with the refractive index of 3.46. The band diagram of the considered structure is obtained using plane wave expansion (PWE) method, and optical propagation through it is simulated using finite difference time domain (FDTD) method. The computational analysis is performed on different structural and physical parameters. Transmission efficiency, quality factor and bandwidth are investigated by varying (i) lattice constant (ii) radius of holes of different parts of the structure and (iii) refractive index of different parts of the structure. The chosen parameters result in operating wavelength around 1550 nm. The designed ADF has a footprint of only 68µm² and a dropping efficiency of 100%. The sensitivity of the structure is determined by determining shifts in the resonance wavelength as a function of the RI of the holes/slab. The designed structure exhibits desirable features like (i) narrow bandwidth of 1.5 nm, (ii) high-quality factor of 1033, (iii) low detection limit of 3.6´10^-4 RIU, (iv) high RI sensitivity of 407 nm/RIU, and (v) high temperature sensitivity of 104 pm/K.

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In this article, we provide a theoretical investigation into the reshaping of flat-top pulses in a one-dimensional, homogeneous, isotropic, finite-size photonic crystal with two defect layers. We use Fourier transform to find frequency and time spectra, and transfer matrix to determine transmission spectra to find the average duration and power of the output pulse. The pulses with a carrier frequency near the defect mode center and a wide frequency spectrum, undergo the most significant reshaping. Reshaping is strongest for narrow pulses with a carrier frequency at defect mode peaks. The maximum power and duration of the output pulse of a spectrally narrow pulse are all proportional to the pulse duration and exhibit extremes at the frequencies of the defect mode peaks. The power and average duration of a spectrally wide pulse's output pulse are not affected by the carrier frequency.