Narrow Results

We examine the impact of the non-Markovian environment on the dynamical behavior of the quantum coherence and entropy squeezing considering a two-level atomic system (qubit) immersed in a reservoir with zero-temperature for two types of non-Markovian environments. We consider a cavity little off-resonance with the transition frequency of the qubit and the case of a non-perfect photonic band gap (PBG). We show that the amount of coherence is dependent on the structure of the environment and influenced through the memory effects. We obtain that the delay and revival of the coherence loss might take place by controlling the detuning of the cavity-qubit system. Whereas, a partial coherence trapping occurs in non-ideal PBG and the decrease of the gap width will destroy the coherence. On the other hand, we show the situation for which the squeezing is occurring and enhanced with respect to the main parameters for the system. Finally, we display the monotonic dependence of the quantum coherence and squeezing on the main model parameters.

The size influence of silica microspheres on the photonic band gap (PBG) of three-dimensional face-centered-cubic (fcc) photonic crystals (PCs) is studied by means of colloidal photonic crystals, which are self-assembled by the vertical deposition technique. Monodispersed SiO₂ microspheres with a diameter of 220–320 nm are synthesized using tetraethylorthosilicate (TEOS) as a precursor material. We find that the PBG of the PCs shifts from 450 nm to 680 nm with silica spheres increasing from 220 to 320 nm. In addition, the PBG moves to higher photon energy when the samples are annealed in a temperature range of 200–700°C. The large shift results from the decrease in refraction index of silica due to moisture evaporation.

The transmission properties of one-dimensional quasi-periodic Fibonacci photonic crystal containing negative permittivity/permeability material are investigated by use of the transfer matrix method. We find that perfect transmission peaks exist at a series of dimensionless wavelength points in the transmission spectra, and the discrete localized modes appear inside the photonic band gap in the case of normal incidence. In the case of oblique incidence, the detailed numerical calculations show that the transmission peaks and angles strongly depend on the polarization of incident waves and the periodicity of the photonic crystals. In addition, we notice that the one-dimensional quasi-periodic photonic crystal can exhibit omni-directional reflection in a certain frequency region for all incident angles and polarizations. We also investigate the possibility of realizing the omni-directional reflection by means of the simple one-dimensional quasi-periodic Fibonacci photonic crystal.

A complex hexagonal lattice photonic crystal with a two-dimensional (2D) periodic dielectric background is proposed. The photonic band modulation effects due to the 2D periodic dielectric background are investigated. We find that the position and width of the complete photonic band gap (PBG) sensitively depend on the dielectric constants of the 2D periodic dielectric background. The radii of the two alternating air holes have significant influence on the relative width of the complete PBG.

Two-dimensional photonic crystals (2D-PCs) with Ge₂Sb₂Te₅ (GST) nanohole arrays were prepared by the nanosphere lithography (NSL) process. A primary factor of PCs is that the refractive index (n) and the n-modulation can be realized by using the GST films, which exhibit a reversible phase transformation between amorphous and crystalline states by laser illumination. The polystyrene (PS) spheres with a diameter of 500 nm were spin-coated on Si substrate and subsequently reduced by O₂-plasma treatment. The reduced spheres were utilized as a lift-off mask of the NSL process and their size and separation could be precisely controlled. Amorphous GST films were thermally evaporated and then the reduced PS spheres were removed. The fabricated GST nanohole arrays were observed by SEM and AFM. The nanohole diameters are nearly linearly reduced with increasing plasma-treatment time (t). The reduction rate (δ) for the conditions of this work was evaluated to be ~ 0.92 nm/s. The period (Λ) and filling factor (η) of PCs are structure parameters that determine their photonic bandgaps (PBGs). η-modulation can be easily achieved via a control of t and the Λ can be also modulated by the use of PS spheres with specific diameter. In addition, the PBGs for the fabricated GST 2D PC were calculated by considering the amorphous and crystalline states of GST.

The effect of nonlinear interactions in a crystal on the polariton behavior has been investigated. A new mode in the photonic band gap in LiNbO₃ is obtained, as suggested by some recent literature. This mode is shown to be almost dispersionless, which may find application in optical communication. The Raman scattering and parametric amplification are interpreted in terms of a dielectric function, which includes nonlinearity. The scattering efficiency is shown to be a consequence of the photonic band gap. The nonlinearity is shown to lead to a soft mode-like behavior in polar crystals.

In the present work, we discuss the transmittance properties of one-dimensional (1D) superconductor nanocomposite photonic crystals (PCs) in THz frequency regions. Our modeling is essentially based on the two-fluid model, Maxwell–Garnett model and the characteristic matrix method. The numerical results investigate the appearance of the so-called cutoff frequency. We have obtained the significant effect of some parameters such as the volume fraction, the permittivity of the host material, the size of the nanoparticles and the permittivity of the superconductor material on the properties of the cutoff frequency. The present results may be useful in the optical communications and photonic applications to act as tunable antenna in THz, reflectors and high-pass filter.

In this study, we investigated the sensing capabilities of 1D defective photonic crystal designs composed of single and double defect layers. These structures can detect and distinguish minor refractive index changes of various organic samples infiltrated one by one into defect layer regions of the respective designs. We have used the standard transfer matrix method to analyze the transmission properties of both structures at normal incidence. The normal incidence has been chosen to overcome the experimental difficulties associated with oblique incidence. The performance of the proposed designs has been examined by measuring the shift in the position of the defect modes inside PBGs of respective structures depending upon the change in the refractive index of various organic solvents, called samples. We can also find adulteration in the organic samples by comparing the observed data with the experimentally available standard data of pure organic samples. Moreover, double defect photonic structure possesses pair of two defect modes inside PBG. These pair of defect modes are located on either side of bandgap edges that cannot be found in 1D defective PCs composed of a single defect. This intriguing property of double defect PC structure is due to the quasi Fabry–Perot cavity nature of the structure. Finally, we have compared sensing and detection features of both the designs made up of single and double defect photonic structures. It has been noticed that the double defect photonic structure also improves the transmittance of defect peak to unity compared to the single defect photonic structure. Moreover, the FWHM of two pairs of defect modes in double defect PC are opposite in nature. This remarkable feature of double defect photonic design may be very useful for improving the performance of photonic bio-sensors. It may be very helpful for designing some advanced bio-sensing designs whose defect mode properties are mirror image in nature.

The reflected properties of one-dimensional frequency-dependent metallic-dielectric photonic crystals are investigated when disorders are introduced for the first time. It is demonstrated that disordered metallic-dielectric photonic crystal provides remarkably high reflection range compared with the corresponding period metallic-dielectric one when the degree of disorder is moderately chosen, and a wider stop band will be obtained with the increasing of periods. At last, the reflected properties influenced by incident angle for different polarizations are also calculated and discussed.

Oblique light propagation through a chiral photonic crystal (PC) layer with gradient parameters of modulation is considered. The problem is solved by Ambartsumian's layer addition modified method. It is shown that suppressing of diffraction oscillations near the photonic band gap (PBG) is possible at certain conditions. Thus, at certain conditions, the spectra for the finite PC layer is the same as that for the half space.

Peculiarities of the defect modes of cholesteric liquid crystals (CLCs) with an isotropic/anisotropic defect inside are investigated. The influence of the defect layer thickness and its anisotropy of refraction, the influence of the system thickness and of the defect layer position in the system, as well as the influence of the dielectric borders on the defect modes are investigated. It is shown that it is possible to change reflection at the defect modes in wide intervals and change the defect mode wavelength, by tuning the defect location and its thickness. Such a system possesses transmission asymmetry. Also, the CLC system thickness and the refraction coefficient of the medium bordering the CLC layer on its both sides have essential influence on the reflection at the defect mode and on the reflection frequency.

The energy transfer from Tb³⁺ to Eu³⁺ co-doped TiO₂(TiO₂:Tb, Eu) inverse opal photonic crystals was investigated by photoluminescence. The results showed that the photonic band gap enhanced energy transfer from the donor Tb³⁺ to the acceptor Eu³⁺. When the fluorescence emission wavelength of Tb³⁺ overlaps with the photonic band gap, the fluorescence intensity of Tb³⁺ is suppressed, while the fluorescence intensity of Eu³⁺ is enhanced. Energy transfer efficiencies were attributed to the tuning effects of energy transfer in the photoluminescence process by photonic crystal structure.

Using the plane wave expansion method, we have calculated, for both E and H polarizations, the band structure of 2D anisotropic photonic crystals with honeycomb lattice composed of anisotropic tellurium (Te) rods embedded in air background. The two rods in the unit cell are chosen square and circular in shape. Here, from a practical point of view, in order to obtain maximum band gaps, we have also studied the band structure as a function of size of rods.

In this paper, extraction efficiency in simplified and layered light-emitting diodes (LEDs) of GaN photonic crystal with periodic air holes is studied by three-dimensional finite-difference time-domain method. Photonic band structures of the photonic crystal are obtained by plane-wave expansion method. The results about simplified GaN-LED show that extraction efficiency is very sensitive to the structure parameters tuning, and increases considerably inside the transverse-electric-like gap region. A maximum extraction efficiency above 90% can be achieved. The effects of the PC thickness and air-hole radius on relative extraction efficiency of layered GaN-LED are analyzed. They show optimal values to obtain high relative extraction efficiency.

The transmission properties of one-dimensional novel photonic crystal having silver-doped novel piezoelectric superlattice and air as the two constituent layers have been investigated by means of transfer matrix method. By changing the appropriate thickness of the layers and filling factor of nanocomposite system, the variation in the photonic band gap can be studied. It is found that the photonic band gap increases with the filling factor of the metal nanocomposite and with the thickness of the layer. These structures possess unique characteristics enabling one to operate as optical waveguides, selective filters, optical switches, integrated piezoelectric microactuators, etc.

Tunable photonic crystal has been developed by infiltration of nematic liquid crystal (NLC) and different organic liquids in the void of silica microspheres. Optical properties were investigated by ultraviolet–visible (UV–Vis) spectroscopy. It has been observed that the position of photonic band gap (PBG) shifts from 336nm to 326nm with the increase of applied field from 0V to 9V and 316nm to 324nm after the infiltration of the organic liquids. The refractive index of infiltrated liquid crystal (LC) is calculated at different applied electric field. The present results could be suited for implementation of low cost and compact design tunable devices with low power consumption for high density integrated optics.

A derivation of approximate analytical expressions for band edges ω^± of the first band gap of a multilayer periodic structure is presented for both TE and TM waves at arbitrary angles of incidence. It is found that the approximate expressions give an excellent agreement with the numerical results as verified by the band edge variation with respect to the filling fraction and refractive index contrast Δn. The analytical expressions for the band edges are further employed to derive a semi numerical optimization of the relative gap width with respect to the filling fraction ν. The result is again shown to be in good agreement with the numerical result.

In this paper, the channel drop filter based on two dimensional photonic crystal is proposed. The structure is made of silicon rods with the refractive index n₁ = 3.4641 which are perforated in air with refractive index n₂ = 1. The simulation results are obtained using 2D finite difference time domain (FDTD) method. The photonic band gap is calculated by plane wave expansion solver method. Resonant mode of the ring resonator and the filter transmission spectrum is calculated using 2D FDTD method. Full width half maximum (FWHM) bandwidth of the filter at the output transmission spectrum from 1.508 μm to 1.512 μm is 4 nm. The quality factor of the filter is 377.5 and the proposed filter design is around 21 × 15 μm which is suitable for photonic integrated circuits.

We report the modeling and optimization of 1D periodic structures for second-order nonlinear effects. We present the work done in modeling to determine the location of the electromagnetic field in periodic structures. This modeling, carried out in a simple one dimension, makes it possible to mastery the properties of these structures and to study the influence of the different physical parameters on these properties. It allowed us to optimize structures for second-order nonlinear effects by focusing on the two essential factors of nonlinear polarization intensity and phase matching. This study, carried out in 1D structures, was extended to 1D planar structures (called 1.5D) used in guided optics and applied to the design of a 1.5D photonic crystal structure made in a Gallium Nitride layer for the second harmonic generation.

A method of laser control of absorption and dispersion of two-level quantum system (atoms, ions, quantum dots) embedded into photonic band gap (PBG) material via variation of intensity and frequency of an external laser field is proposed. It is shown that in order to provide an effective control, the frequency of atomic transition should be located at the photonic band edge near the bottom of the PBG. The method is based on the laser induced Mollow splitting of the atomic energy levels and strong dependence of the decay rates of the so-called dressed states on the frequency of the Mollow splitting due to photonic band edge. This enables us to control absorption and dispersion of a signal laser field, which is near-resonant to the quantum transition of dopant.