H. Bouchriha

Enhanced Effective Area Photonic Crystal Fiber With Novel Air Hole Design

There is interest in photonic crystal fibers (PCFs) that possess a large effective area. We demonstrate that it is possible to design a PCF structure configuration with an effective mode area as high as 3000 μm2. The proposed PCF structures consist of five air-hole rings, where the air hole diameters are different from one ring to another. In the second ring six air holes are alternatively removed. The effective mode area of the proposed structure was calculated and compared with effective mode areas reported in literature. It is shown that the effective mode area is enhanced compared to other structures. Additionally, critical propagation properties such as chromatic dispersion, confinement losses, bend losses and nonlinear coefficient of proposed PCF structures are reported thoroughly.

Realization of a High Coupling Efficiency by Employing a Concave Lens Based on Two-Dimensional Photonic Crystals With a Negative Refractive Index

A study of the interaction of a continuous-wave Gaussian beam with a concave lens used as a spot-size converter (SSC) is presented. The lens is based on a 2-D photonic crystal (PC) structure with a negative refractive index. A numerical method based on a 2-D finite-difference time domain was employed to investigate the light propagation in a photonic integrated circuitry (PIC). The PIC consisted of a single-mode fiber, an SSC, and a PC waveguide (PCW). By employing an optimized planoconcave lens, a large spot-size area of the Gaussian beam was focused/transformed into a very small spot-size area, which is even smaller than the order of the operating wavelength. Optimization of the proposed device parameters has also been reported. A significant reduction in the device size, transmission efficiency, and coupling efficiency has been achieved by optimizing the planoconcave lens and the PCW.

Energy-band structure and optical gain in strained InAs"N…/GaSb/InAs"N… quantum well lasers.

We present a theoretical study of band structure and optical gain spectra of dilute-N InAsN/GaSb/InAsN and the similar N-free InAs/GaSb/InAs laser structures, which have a “W” band alignment. Calculations are based on a 10×10 k⋅p model incorporating valence, conduction, and nitrogen-induced bands. The two laser diodes are designed to operate at 3.3 μm at room temperature. We find that the incorporation of a few percent of nitrogen in the laser active region improves optical gain performance, which leads to a peak gain value of approximately 1000 cm−1 for a typical injection carrier concentration of 1×1012 cm−2 and a carrier transparent density of 0.54×1018 cm−3.

Hole intersubband transitions in wurtzite and zinc-blende strained AlGaN/GaN quantum wells and its interband interaction dependence

Valence intersubband transitions of the wurtzite (WZ) strained AlGaN/GaN quantum wells are examined theoretically and compared with those of the zinc-blende (ZB) ones. In particular, the effect of the interband interaction between conduction (CB) and valence (VB) bands has been taken into account explicitly. We have used the 8-bands k.p model for both WZ and ZB structures to calculate subband energies and wavefunctions of Al0.3Ga0.7N/GaN quantum wells (QWs). The results indicate that, the prominent transitions for both ZB and WZ QWs were found to be essentially related to the heavy- and light-hole subbands. For the x-polarization, we have shown that it is necessary to take into account explicitly the interband interaction between CB and VB. Finally, we can predict that WZ QWs are more convenient than ZB QWs in most applications involving intersubband transitions, especially for the z-polarized light.

Photonic Crystal Fiber With an Ultrahigh Birefringence and Flattened Dispersion by Using Genetic Algorithms

We developed a high-throughput technique to design photonic crystal fiber (PCF) structures with desired properties and functionalities. By using a genetic algorithm, a high birefringence and an ultra-flattened chromatic dispersion over a large wavelength range are achieved. It is shown that a low confinement loss can be obtained while the birefringence remains the same. The numerical results show that the presented PCF structure can be successfully employed as maintaining polarization devices working in a large zero- chromatic dispersion region.

Band Structure, Optical Transition, and Optical Gain of Type-II InAs(N)/GaSb Quantum Wells Laser Diodes Modeled Within 16-Band and 14-Band

We have used both 16-band and 14-band kp Hamiltonians to investigate electronic band-structure, optical gain and transitions of two type-II quantum wells with InAs and InAs0.98N0.02 as the active layers surrounded by a GaSb layer, respectively. The obtained results are discussed in the context of the importance of the contribution of the p-type conduction band nonparabolicity. The results are given explicitly in the [001] and [111] directions. We have also reported a comparison between the results obtained within the 16-band and 10-band kp models in terms of optical gain and threshold current density for [111]-oriented laser structure. For typical carrier concentration of 8 × 1012 cm-2 at 300 K, we achieved an emission wavelength of ~2.55 μm with a peak gain of order 1400 cm-1 obtained within 16-band kp model while for the 10-band kp model, a peak gain of order 564 cm-1 is reached providing an emission wavelength at ~2.04 μm.

kp

A new design of an optical isolator based on photonic transitions in the interbands of a honeycomb structure that generates a dual negative refraction in a photonic crystal is presented. The involved photonic transition is associated to the perturbation of the dielectric constant of the medium. The band structure is determined using the plane wave method where the transmission spectra, field profile, and mode amplitudes are obtained by applying the finite difference time domain method. Due to the time-dependent perturbation of the refractive index of the medium that constitutes the dual negative refraction, asymmetric transmission mechanism is achieved for one of the desired modes, demonstrating optical isolation. Using the dual negative refraction effect in photonic crystal structure, the optical isolation is reported for only one of the desired optical modes. It is anticipated that the proposed mode conversion mechanism can be employed for designing ultrahigh-speed optical interconnections. The proposed optical isolator model is expected to have a significant impact on designing ultrahigh-speed integrated optical platforms.

Model

Abstract Optically detected magnetic resonance (ODMR) experiments are performed at room temperature on crystalline sexithiophene (6T) photoluminescence (PL). The observed spectra are interpreted in terms of microwave induced transitions between spin sublevels of triplet–triplet pairs states. These triplets are produced by intersystem crossing and their mutual annihilation which leads to delayed fluorescence (DF) is modulated by the high power microwave and enhance the PL process.

Mode Converter Optical Isolator Based on Dual Negative Refraction Photonic Crystal

Magnetoelectrical measurements were performed on a diode structure, based on an anthracene-containing poly(arylene-ethynylylene)-alt-poly(arylene-vinylene) denoted AnE-PVstat, to clarify the role of the recombination and dissociation of electron-hole (e-h) pairs in the magnetoconductance (MC). We report the observed MC under a weak magnetic field (<1 T) at room and low temperatures. Positive MC is observed and reaches up to 2% at a magnetic field of 450 mT at room temperature. It is found that with the increase of the voltage, the MC effect decreases. We also report the difference in MC between perpendicular (θ = 90°) and parallel (θ = 0°) alignment of magnetic field with respect to the current direction. The experimental data were analyzed in the context of the e-h pair model, based on the Stochastic Liouville Equation. To interpret the experimental results on magnetoconductance measurements, anisotropic hyperfine interaction has been introduced through an anisotropic hyperfine field. The dissociation ra...

Evidence of triplet–triplet interaction in crystalline sexithiophene

In this paper, we have used in-house the 3-D finite-difference time-domain method to analyze a novel design of metallic nanoparticles based on a sensing nanosystem. The proposed structure is composed of two gold-nanocylinders of finite height with varying radii separated by a nanogap. We have demonstrated that tunable plasmonic nanoparticles can be controlled by varying the size of the interparticles separation distance. By engineering the nanogaps, it is shown that a strong enhancement of the electric field is achieved. Our simulations show a pronounced wavelength shift for small nanogaps. In addition, the influence of the refractive index of the surrounding medium is presented.