International Journal of

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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.