Step-index profile

About: Step-index profile is a research topic. Over the lifetime, 3104 publications have been published within this topic receiving 53199 citations.

Approximate thermal emission models of a two-dimensional graded index semitransparent medium

Abstract: This study develops numerical models for thermal emission in a two-dimensional semitransparent graded-index medium. Two piecewise continuous refractive index models, the bar model and the slab model, are presented. The formal is a combination of rectangular bars each having its own unique refractive index. The latter is a combination of slabs, each of which has a linear refractive index distribution. Two interface hypotheses are discussed: the reflection/refraction hypothesis and the refraction/total reflection hypothesis. The backward ray tracing method and the backward Monte Carlo method are employed for calculation. The apparent directional emissivity of a semitransparent medium with linear and nonlinear refractive index distributions is calculated. The results show that piecewise continuous refractive index can be used for modeling semitransparent media with continuously variable refractive index. Emission from the medium is complex and quite different from a medium with a constant refractive index, when the absorption coefficient is small and/or the refractive index varies greatly in the medium. The refractive/totally reflective inner interface in the bar model gives a more precise emission distribution and can be extended to simulate emission from a medium with a complex three-dimensional refractive index distribution.

Preform with graded refractive index and method for construction of the same

Abstract: A preform with a graded refractive index of synthetic material, i.e. optically clean polymer compounds, constructed by means of a technique where monomers with additives are supplied to a rotating tube (1) with end pieces (2' and 2'') via a cannula (4) in a continuous or discontinuous flow and so that the monomer composition is changed from a lower refractive index toward a higher refractive index from the periphery of the preform toward its rotation axis. Monomered material which is deposited during the rotation of the tube (1) is caused to polymerize by means of radiation with UV beams and/or by means of radical polymerization.

Frequency Characterization of the Nonlinear Refractive Index in Optical Fiber

Abstract: The Kerr and the electrostrictive contributions to the intensity-dependent nonlinear refractive index in optical fibers are discussed on both theoretical and experimental bases. Particular attention is devoted to the electrostrictive contribution that under particular conditions is enhanced by resonances. The resonant behavior of the electrostrictive effect is calculated, measured, and discussed for standard single-mode fibers and dispersion shifted fibers. Experimental results are also reported. Measure ments have been carried out with a simple and effective technique based on the cross-phase modulation effect that also allows one to evaluate the nonlinear refractive index at any bit rate. Electrostriction contributes 20 % to the total nonlinear refractive index but in the resonant regime becomes comparable to the Kerr effect.

Iterative simplex-finite difference method for the characterization of optical waveguides

Abstract: A new method is presented for reconstructing smooth refractive index profiles of optical waveguides from measured effective indexes. It is based on the semivectorial finite difference method to solve the polarized wave equation for a given refractive index profile. An iterative simplex algorithm is used to find the best refractive index parameters that give, as a solution, effective indexes close to the measured ones. The method is applied successfully to Ag/sup +/-Na/sup +/ ion-exchanged glass slab waveguides and to diffused Mg/Ti:LiNbO/sub 3/ slab waveguides. Dopant concentration profiles are obtained by using secondary ion mass spectrometry. The relationship between the refractive index change and the dopant concentration is determined for both cases. The iterative simplex algorithm-finite difference method (ISA-FDM) is compared to other index profile reconstruction methods, and the advantages with respect to WKB-based methods are pointed out.

Novel bifunctional systems for measuring the refractive index profile and residual stress birefringence in optical fibers and preforms

Abstract: Two measuring systems are presented enabling determination of the refractive index profile and its anisotropy as well as principal stress components in optical fibers and preforms, respectively. The system for optical fibers is a scanning-type, differentiating interferometer used to measure directly the wavefront derivative, from which, after the inverse Abel transformation, the index profile is obtained. The required high sensitivity of measurement is achieved by applying the sinusoidal modulation of the input beam ellipticity and the homodyne detection of the first harmonic component of the output intensity. After removing the Wollaston prism, the system can be used to measure the retardation function that is related to the fiber residual birefringence. The dynamic spatial-filtering technique, used until now to measure the ray deflection function, has been modified for testing the preforms. An optionally applied linear modulator of ellipticity of the input beam was added, to enable the measurement of the retardation function also. The system can be easily switched from the measurement of the ray deflection function to the measurement of the retardation function by moving only a single element.