Light Propagation In Waveguides Research Articles

Compact all-optical decoder design for optical integrated circuits.

This paper constructs and discusses a 1×2 decoder based on two-dimensional photonic crystals. The designed decoder is a priority decoder with one main input and one enabled input. This logic circuit's structure is very simple and compact, and it employs a photonic crystal structure with dimensions of 11×11 rods built of GaAs. The calculation results reveal that the output power values for logical mode 1 are extremely close to the power of the light source, whereas the power is very low and close to zero in logical mode 0. As a result, the difference between logical values 0 and 1 in the output will be adequate, and the circuit's accuracy will be good. The finite difference-time domain (FDTD) approach is used for time computations and light propagation in waveguides.

On the influence of Earth’s rotation on light propagation in waveguides

We analyse the influence of Earth’s rotation on the propagation of light in optical media. This is done using both geometrical optics and a perturbative calculation based on Maxwell’s equations in rotating coordinates in flat spacetime. Considering light propagation in cylindrical step-index waveguides in particular, the first order correction to electromagnetic modes is computed. The calculation shows that Earth’s spin causes a weak mode coupling, giving rise to sidebands, whose amplitudes are computed as well. The correction to the dispersion relation derived here allows to assess the anisotropy of light propagation due to Earth’s rotation. The linearisation of this result is found to agree numerically with a simple formula derived from geometrical optics.

Diffraction and Waveguide Propagation of Light in Tooth Enamel

Diffraction and Waveguide Propagation of Light in Tooth Enamel

Amplification of the Fluorescence Propagating in the Waveguide Regime in a Planar Layer of NLC

The amplification of spontaneous fluorescence in a planar layer of nematic liquid crystal doped with DCM dye in the mode of waveguide light propagation has been studied. The gain reaches the value α = 0.0014 μm–1 at a pump radiation intensity of 1.38 MW/cm2. Numerical simulation of the structure imitating the experimental cell showed qualitative agreement of the calculation results with the experimental data.

Waveguide Propagation of Light in Polymer Porous Films Filled with Nematic Liquid Crystals

We theoretically analyze the waveguide regime of light propagation in a cylindrical pore of a polymer matrix filled with liquid crystals assuming that the effective radial optical anisotropy is biaxial. From numerical analysis of the dispersion relations, the waveguide modes are found to be sensitive to the field-induced changes of the anisotropy. The electrooptic properties of the polymer porous polyethylene terephthalate (PET) films filled with the nematic liquid crystal 5CB are studied experimentally and the experimental results are compared with the results of the theoretical investigation.

Two-path self-interference in PTCDA active waveguides maps the dispersion and refraction of a single waveguide mode

Bound waveguide modes propagating along nanostructures are of high importance since they offer low-loss energy-/signal-transport for future integrated photonic circuits. Particularly, the dispersion relation of these modes is of fundamental interest for the understanding of light propagation in waveguides as well as of light-matter interactions. However, for a bound waveguide mode, it is experimentally very challenging to determine the dispersion relation. Here, we apply a two-path interference experiment on microstructured single-mode active organic waveguides that is able to directly visualize the dispersion of the waveguide mode in energy-momentum space. Furthermore, we are able to observe the refraction of this mode at a structure edge by detecting directional interference patterns in the back-focal plane.

Capillary array waveguide amplified fluorescence detector for mHealth

Mobile health (mHealth) analytical technologies are potentially useful for carrying out modern medical diagnostics in resource-poor settings. Effective mHealth devices for underserved populations need to be simple, low cost, and portable. Although cell phone cameras have been used for biodetection, their sensitivity is a limiting factor because currently it is too low to be effective for many mHealth applications, which depend on detection of weak fluorescent signals.To improve the sensitivity of portable phones, a capillary tube array was developed to amplify fluorescence signals using their waveguide properties. An array configured with 36 capillary tubes was demonstrated to have a ∼100× increase in sensitivity, lowering the limit of detection (LOD) of mobile phones from 1000nM to 10nM for fluorescein. To confirm that the amplification was due to waveguide behavior, we coated the external surfaces of the capillaries with silver. The silver coating interfered with the waveguide behavior and diminished the fluorescence signal, thereby proving that the waveguide behavior was the main mechanism for enhancing optical sensitivity.The optical configuration described here is novel in several ways. First, the use of capillaries waveguide properties to improve detection of weak florescence signal is new. Second we describe here a three dimensional illumination system, while conventional angular laser waveguide illumination is spot (or line), which is functionally one-dimensional illumination, can illuminate only a single capillary or a single column (when a line generator is used) of capillaries and thus inherently limits the multiplexing capability of detection. The planar illumination demonstrated in this work enables illumination of a two dimensional capillary array (e.g., x columns and y rows of capillaries). In addition, the waveguide light propagation via the capillary wall provides a third dimension for illumination along the axis of the capillaries. Such an array can potentially be used for sensitive analysis of multiple fluorescent detection assays simultaneously.The simple phone based capillary array approach presented in this paper is capable of amplifying weak fluorescent signals thereby improving the sensitivity of optical detectors based on mobile phones. This may allow sensitive biological assays to be measured with low sensitivity detectors and may make mHealth practical for many diagnostics applications, especially in resource-poor and global health settings.

Metal-Coated Waveguide Stretches Wavelengths to Infinity

A zero refractive index at optical frequencies, as demonstrated in a new nanoscale waveguide, enables opportunities for better control and enhancement of light propagation in waveguides, as well as development of photonic nanocircuits.

Negative refraction and lensing at visible wavelength: experimental results using a waveguide array

Experimental results showing "negative refraction" and some kind of "lensing" -in the microwave-infrared range- are often presented in the literature as undisputable evidence of the existence of composite left-handed materials. The purpose of this paper is to present experimental results on "negative refraction" and "lensing" at visible wavelengths involving a waveguide array formed by a tight-packed bundle of glass fibers. We will demonstrate that the observed phenomena are not necessarily evidence of the existence of left-handed materials and that they can be fully explained by classical optic concepts, e.g. light propagation in waveguides.

Bose–Einstein condensates in optical lattices: the cubic–quintic nonlinear Schrödinger equation with a periodic potential

The cubic–quintic nonlinear Schrödinger equation with a periodic potential, which is expressed in terms of the Jacobian function dn, is used to model a Bose–Einstein condensate trapped in an optical lattice (in most cases, the dn potential is very close to the ordinary sinusoidal one). The quintic term in the equation represents either effects of three-body collisions (which is relevant in the case when the ordinary two-body collisions are very weak), or an effective deviation of the trapped condensate from the one-dimensionality. The cases of both repulsive and attractive two-body interactions are considered. The same model governs the planar propagation of light in waveguides with the cubic–quintic optical nonlinearity, the periodic potential being induced by transverse modulation of the refractive index. In the case of the attractive quintic term (which is always the case if it accounts for the residual non-one-dimensionality of the tightly trapped condensate), a new family of exact periodic solutions is constructed in terms of Jacobian elliptic functions. Using semi-analytical and numerical methods, a stability region for these periodic states is identified. The effect of boundaries is shown to be very weak.E Kengne dedicates this work to Taa Bah Deffo Takotue Innocent, the Chairman of the Bandjoun Community in Douala (Cameroon).

Sub-diffraction light propagation in fibres with anisotropic dielectric cores

We present a detailed study of light propagation in waveguides with anisotropic metamaterial cores. We demonstrate that in contrast to conventional optical fibres, our structures support free-space-like propagating modes even when the waveguide radius is much smaller than the wavelength. We develop analytical formalism to describe mode structure and propagation in strongly anisotropic systems and study the effects related to waveguide boundaries and material composition.

Coupled-mode theory for periodic side-coupled microcavity and photonic crystal structures

We use a phenomenological Hamiltonian approach to derive a set of coupled mode equations that describe light propagation in waveguides that are periodically side-coupled to microcavities. The structure exhibits both Bragg gap and (polariton like) resonator gap in the dispersion relation. The origin and physical significance of the two types of gaps are discussed. The coupled-mode equations derived from the effective field formalism are valid deep within the Bragg gaps and resonator gaps.

Physical calculations aided with HPC cluster

A theoretical and numerical analysis of complicated physical models requires a large computing power. One of the ways to obtain sufficient computational power is to take advantage of the High Performance Computing (HPC) cluster environment. This paper shows the idea of using such an infrastructure in the modelling process of some physical phenomena. Three different issues embracing areas of acoustic field distributions, strip waveguide light propagation and modelling of planar interferometric structures are dealt with. Also the infrastructure of the HPC cluster created in the Department of Optoelectronics of our University is describer.

Nonreciprocal waveguides and lenses based on the Fresnel-Fizeau effect

The propagation of a radiation beam in a medium whose velocity varies in the direction transverse to the axis of the beam is considered. It is shown that, under these conditions, the Fresnel-Fizeau effect of partial entrainment of light leads to focusing of the beam and to the possibility of the waveguide propagation of light. The corresponding waveguides and lenses have the property of nonreciprocity; i.e., their characteristics change with the reversal of the direction of propagation. The estimates obtained show the feasibility of observing the effect for optical radiation.

Waveguide Propagation of Light in Cholesterics with Large Pitch

The Green's function and waveguide propagation of electromagnetic field in cholesteric liquid crystals with a pitch being large compared to the wavelength is considered. This function is constructed using the solution of the Maxwell equations. The behavior in the far zone is analysed in detail. The periodic system is distinguished from an anisotropic medium by a discontinuity of the wave vector surface and a break of the beam vector surface. Trajectories of beams in such a medium are not plane. The forbidden zone corresponds to capture of beams and formation of a wave channel. Within this wave channel the Green's function asymptotic differs from 1/r behavior.

Light propagation, optical modulation, and beam steering in waveguides with quantum well voltage tunable claddings

We present results on devices fabricated in a waveguide system utilizing a voltage tunable quantum well cladding layer. A (GaAs/AlGaAs) beam steering device produced an angular shift of 2.4° under an applied voltage of 20 V. It is shown numerically that electro-optic modulators fabricated in such a material configuration can have simultaneously improved contrast ratios and insertion losses if the ratio of light propagating in the cladding and in the core regions can be controlled. A proof of concept device is demonstrated in which an electric field is used to change the distribution of light propagating in the waveguide.

A gas sensor based on an integrated optical Mach-Zehnder interferometer

In this paper we demonstrate a sensor system for measuring gaseous compounds using an integrated optical Mach-Zehnder interferometer (IO-MZ chip). One of the surface waveguide arms of the IO device is covered with a polysiloxane layer, sensitive to organic solvents. The refractive index of the polymer layer changes continuously when exposed to the vapours of such solvents. The influence on the evanescent field of the guided mode causes a change in the optical pathlength in the covered arm. Incoupled light of a semiconductor laser diode results in an interference pattern at the output of the IO-MZ chip. The phase shift of the signal is dependent on the gas concentration and the solvent type. We have determined the values for some hydrocarbons, chlorohydrocarbons and aromatic compounds. The extremely short response time of the system allows it to be used like a gas chromatographic detector. The applicationn of Maxwell's equations for the propagation of light in waveguides offers a simulation of the interference signals. By this means, the experimental signal obtained can be correlated to changes in refractive index of the polymer layer. The dependence of the interference patterns on wavelength is explained. White light interference is obtained by use of a xenon lamp.

Propagation of light in a CdSxSe1–xplanar waveguide structure with a variable band gap along the surface

An investigation was made of the conditions of propagation of light in waveguides having different band gaps Eg formed by two-stage diffusion in the same cadmium sulfide substrate. The efficiency of mode matching at the junction of two waveguides was determined as a function of changes in Eg and the length of the transition zone. Zero-order modes were the most efficiently coupled and as the mode number increased, the matching efficiency decreased. When waveguides having values of Eg differing by 0.12 eV were coupled, the optical energy transfer efficiency was higher than 80%. The overlap integral method used to calculate the efficiency of matching of the waveguide fields ensured a satisfactory agreement with the experimental results.

Discrete paraxial approximation

Using a new numerical paraxial approximation to the scalar Helmholtz equation in optics, one obtains, with solutions of the type u(r)e-iK0S(r), first a discrete eikonal equation and second a discrete ray equation both valid for any arbitrary stepsize unlike the discrete equations deduced directly from the usual eikonal and ray equations which requires a very small step-size (about wavelength). The properties of these equations are discussed and some applications given to light propagation in waveguides.