Observation of electromagnetically induced photonic band gaps in hot two-level atoms

In this paper, two-level thermal Cs atoms are used to observe electromagnetically induced photonic band gaps with a strong symmetric and two types of asymmetric standing-wave (SW) driving fields. One main band and two sidebands are measured for the transmitted and reflected spectra. We carry out physical interpretation about the observations in SW-dressed atom picture and employ method of Fourier transformation to solve density-matrix equations for hot two-level system to simulate the experimental results. The numerical analyses are consistent with the experimental observations for properties of electromagnetically induced photonic band gaps.     

Low-power optical switching with Kerr nonlinear material in two-dimensional photonic crystal nanocavity

We investigate numerically optical bistability in direct-coupled cavity–waveguide photonic crystal system using the finite-difference time-domain method. The quality factor of the cavity is optimized by engineering the geometrical parameters. Numerical results indicate that the threshold power of optical bistability can be reduced greatly due to the increased quality factor.     

Design of ultra-low and ultra-flattened dispersion single mode photonic crystal fiber by DE/EDA algorithm

This paper proposes a combination of differential evolution (DE) and estimation of distribution algorithm (EDA) to design photonic crystal fiber structures with desired properties over the C communication band. In order to determine the effective index of propagation of the mode and then, the other properties of structure, a finite difference frequency domain (FDFD) solver is applied. The results revealed that the proposed method is a powerful tool for solving this optimization problem. The optimized PCF exhibits a dispersion of 0.22 ps nm^?1 km^?1 at 1.55 µm wavelength with a variance of ±0.4 ps nm^?1 km^?1 over the C communication band and a nearly zero dispersion slope.     

Fictitious Rayleigh expansions

Scattering matrix and transfer matrix methods are widely used in the frame of scattering from a stack of thin films, a stack of periodic grids or photonic crystals. They allow one to reduce significantly computation time and memory storage. However, these methods have well-known theoretical limits since they require the field to take the form of plane wave expansions (Rayleigh expansions) on both sides of each element of the stack. It will be shown that, in fact, the domain of validity of these methods can be considerably extended by defining fictitious Rayleigh expansions between two consecutive elements, even when they are not separated by a homogeneous region. Numerical results confirm this prediction.     

Tunable ultracompact electro-optical photonic crystal ring resonator

A tunable ultracompact electro-optical photonic crystal ring resonator with high transmission is reported. The photonic crystal ring resonator is obtained by removing a ring shape of cylinders from a square lattice of dielectric cylinders in air. The transmission spectra of this ring resonator have been investigated by using the finite-difference time-domain technique. The general characteristics of the ring elements to achieve resonant tunneling are determined. By modulating the conductibility of the inner cylinders in the ring resonator, the electrical tunability of the resonant modes is observed in the transmission spectrum. The research results should open opportunities for this ring resonator as ultracompact filters, optical add-drop multiplexers, electro-optical N × N switches, and modulators.     

Structural and optical quality of binary photonic crystal heterostructures fabricated by the modified self-assembly method

Photonic crystal heterostructures constituting of two photonic crystals with different lattice constants are fabricated using the modified self-assembly method and their structural and optical properties are investigated. The results show that these photonic crystal heterostructures of high quality possess deep photonic band gaps and steep photonic band edges in their transmission spectra. Deep double photonic band gaps, steep photonic band edges and high transmittance in the pass band show good ordering of the heterostructure and may offer a probability for studying late-model ultra-fast all-optical switches.     

Modeling of dispersion and nonlinear characteristics of tapered photonic crystal fibers for applications in nonlinear optics

In this article, we investigate for the first time the dispersion and the nonlinear characteristics of the tapered photonic crystal fibers (PCFs) as a function of length z, via solving the eigenvalue equation of the guided mode using the finite-difference frequency-domain method. Since the structural parameters such as the air-hole diameter and the pitch of the microstructured cladding change along the tapered PCFs, dispersion and nonlinear properties change with the length as well. Therefore, it is important to know the exact behavior of such fiber parameters along z which is necessary for nonlinear optics applications. We simulate the z dependency of the zero-dispersion wavelength, dispersion slope, effective mode area, nonlinear parameter, and the confinement loss along the tapered PCFs and propose useful relations for describing dispersion and nonlinear parameters. The results of this article, which are in a very good agreement with the available experimental data, are important for simulating pulse propagation as well as investigating nonlinear effects such as supercontinuum generation and parametric amplification in tapered PCFs.     

Design of omnidirectional reflectors based on a cascaded one-dimensional photonic crystal structure

The omnidirectional transmission properties of photonic heterostructures composed of cascaded one-dimensional photonic crystals (1DPCs) with the same materials and different thickness ratios of the alternate high- and low-refractive index layers were studied theoretically. A criterion for designing omnidirectional reflectors with a maximum bandgap width is presented for heterostructures with an arbitrary number of cascaded 1DPCs. Omnidirectional reflectors based on two and three cascaded 1DPCs are designed according to the criterion.     

Ultrashort pulse compression by using one-dimensional inhomogeneous photonic crystal

Ultrashort pulse compression by propagation in one-dimensional inhomogeneous photonic crystals with symmetric and asymmetric refractive index profiles are studied by using the transfer matrix method and Fourier analysis. The effect of different parameters, like chirp value of the incident pulse, angle of incidence, and number of unit cells on the compress factors, are investigated and temporal evolution of the reflected pulse is calculated. Compress factors as low as 32% for a sinusoidal profile are obtained using this structure.