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.

Effective parameters of resonant negative refractive index metamaterials : interpretation and validity

Abstract: We present a numerical study of resonant negative refractive index (NRI) metamaterials in which their effective parameters are calculated. For a periodic media consisting of split-ring resonators and metallic wires the effective refractive index is compared by means of two different methods. The first one is an inversion procedure in which the effective refractive index is calculated from the reflection and transmission coefficients of a finite structure and the second one consists its calculation from the phase velocity issued from the dispersion diagram. A significant difference between the two cases is highlighted in the frequency interval of interest (NRI regime) and for the finite media, counterintuitive observations are made. These anomalous features are observed in a frequency range in which there is a non-negligible contribution of the higher-order modes to propagation inside the periodic metamaterial. Hence in this particular frequency interval, the media cannot be described by an effective refractive index in a Fresnel sense. In other frequency regions, both methods converge and it will be shown that the metamaterial exhibits a negative refractive index.

Achromatic fiber optic coupler

Abstract: An achromatic fiber optic coupler of the type wherein first and second single-mode optical fibers, each having a core and a cladding, are fused together along a portion of the lengths thereof to form a coupling region. A matrix glass of lower index than the fiber claddings surrounds the coupling region. The fiber diameters are smaller in the coupling region than in the the remainder of the fibers. The refractive index n2 of the cladding of the first fiber is different from the refractive index n~ of the cladding of the second fiber, the difference between the refractive indices n2 and n~ being such that the coupler exhibits very little change in coupling ratio with wavelength over a band of wavelengths.

Sensitivity Enhancement of Turn-Around-Point Long Period Gratings By Tuning Initial Coupling Condition

Abstract: Long period grating (LPG) at turn-around-point (TAP) has been studied with a view to enumerate the dependence of sensitivity of a particular resonant mode at the TAP to surrounding refractive index on the initial coupling strength. It has been shown theoretically and also validated experimentally that sensitivity can be enhanced significantly by tailoring the coupling strength of the cladding mode at the resonant wavelength near the TAP. Sensitivity characteristics have been studied for surrounding refractive index in the range 1.335-1.360, which is of interest in the field of biosensors, where the sensitivity of conventional LPGs is relatively small. We could attain a sensitivity of similar to 1850 nm/RIU using a TAP-LPG with similar to 3-dB attenuation at resonance.

Multimode Optical Fiber Having Improved Bending Losses

Abstract: The present invention embraces a multimode optical fiber that includes a central core having an alpha refractive index profile with respect to an outer optical cladding and a depressed trench positioned between the central core and the outer optical cladding. The central core's refractive index at its periphery is the same as the outer cladding's refractive index. Typically, an inner cladding is positioned between the central core and the depressed trench. The optical fiber achieves reduced bending losses without significantly increasing numerical aperture.

Diamond-like carbon optical waveguide

Abstract: An optical circuit device has a carbon optical waveguide structure which has a substrate. A first carbon layer is atop the substrate and has a first refractive index. A carbon optical waveguide core is positioned atop the first layer and has a second refractive index different than the first refractive index. A cladding layer of carbon is positioned atop the first layer and the waveguide core and has a third refractive index different than the refractive index of the waveguide core.