GRIN Materials Research Articles

Customized linear refractive index GRIN prepared by rapid sintering of multilayer chalcogenide glass powders

AbstractGradient refractive index (GRIN) lenses have recently become a hot topic in compact imaging and achromaticity. Current research focuses on exploiting GRIN materials and upgrading the preparation technology. In this study, infrared (IR) GRIN materials were successfully prepared by spark plasma sintering of multilayer chalcogenide glass (ChGs) powders. ChGs powders were derived from the Ge20Se80‐xTex series glasses (x = 0–28 mol%) with a maximum refractive index difference (Δn) of 0.25. The similar glass transition temperatures (ΔTg < 10°C) promote efficient sintering of multilayer powders. Six‐, eight‐, and ten‐layer powders of different compositions were rapidly sintered with a thickness of 600, 300, and 200 µm per layer, respectively. Such tiny layer thickness enables the GRIN materials to exhibit nearly linear refractive index variation. Energy dispersive spectroscopy line scans well characterized the gradient variation of GRIN. The maximum deviation of the refractive index gradient from the fitted target line was only ± 0.016 for the 10‐layer GRIN. The sintered GRIN shows excellent IR transparency, which is of great interest for mid‐wave and long‐wave infrared imaging.

Propagation of Gaussian Beams through Active GRIN Materials

We discussed light propagation through an active GRIN material that exhibits loss or gain. Effects of gain or loss in GRIN materials can be phenomenologically taken into account by using a complex refractive index in the wave equation. This work examines the implication of using a complex refractive index on light propagation in an active GRIN material illuminated by a non-uniform monochromatic wave described by a Gaussian beam. We analyze how a Gaussian beam is propagated through the active material in order to characterize it by the beam parameters and the transverse irradiance distribution.

Design of GRIN optical components for coupling and interconnects

AbstractThis paper reviews the design of some optical systems for coupling and interconnection by GRIN components. The optical systems designed with these components are based on imaging and transforming properties of such components to carry out specific functions. First of all, a brief description of light propagation through GRIN materials will be given. After that, a device to couple light by a GRIN fiber lens into fibers of different core sizes with low loss is described. The coupling efficiency as well as the coupling loss are studied versus variation of the GRIN fiber lens length and the refractive‐index profile of the coupler. The design of crossover and parallel interconnects by using a GRIN planar structure will be presented. The optical analysis includes the PSF for describing the performance of the device and the SBP for estimating the numbers of channels that can be handled. The dependence of the number of channels on the wavelength of light and the transverse aperture of the planar interconnect is shown.

Thermal emission characteristics of a graded index semitransparent medium

This paper develops a numerical model for thermal radiative transfer in a two-dimensional semitransparent graded index medium. A piecewise continuous refractive index model, the linear refractive index bar model, is presented. This model is established based on three hypotheses, and has a higher precision than the bar model used previously. This paper also studies the thermal emission from a two-dimensional graded index medium, which is scattering or non-scattering. We find that it can present an obvious pattern of directional distribution at times. The refractive index distribution and absorption coefficient are the two main influential factors. This finding differs from the common belief that thermal sources, such as the incandescent filament of a light bulb, emit a quasi-isotropic light. The finding also suggests that there maybe other important applications of artificial GRIN materials.

Analysis of large refractive index difference of GRIN-rod lenses caused by ion-exchanging

The GRIN-rod lenses are made by two steps ion-exchanging, and the refractive index distribution of the sample is measured by the YaMing interferometer. The results show large differences in the refractive index of the samples. The reason for the increase of the refractive index difference by two-step ion-exchanging is discussed. The results of this research may help to produce GRIN materials.