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.

Tunable two-dimensional liquid gradient refractive index (L-GRIN) lens for variable light focusing.

Abstract: We report a two-dimensional (2D) tunable liquid gradient refractive index (L-GRIN) lens for variable focusing of light in the out-of-plane direction. This lens focuses a light beam through a liquid medium with a 2D hyperbolic secant (HS) refractive index gradient. The refractive index gradient is established in a microfluidic chamber through the diffusion between two fluids with different refractive indices, i.e. CaCl2 solution and deionized (DI) water. The 2D HS refractive index profile and subsequently the focal length of the L-GRIN lens can be tuned by changing the ratio of the flow rates of the CaCl2 solution and DI water. The focusing effect is experimentally characterized through side-view and top-view image analysis, and the experimental data match well with the results from ray-tracing optical simulations. Advantages of the 2D L-GRIN lens include simple device fabrication procedure, low fluid consumption rate, convenient lens-tuning mechanism, and compatibility with existing microfluidic devices. We expect that with further optimizations, this 2D L-GRIN lens can be used in many optics-based lab-on-a-chip applications.

Wave propagation in a single-mode fibre with dip in the refractive index

Abstract: A theoretical study has been carried out on propagation in single-mode fibres having a dip in the refractive index at the centre of the core. The energy of the mode gradually spreads from the centre of the core with increase of the degree of the dip. Nevertheless the near- and far-field distributions of such single-mode fibres are very nearly Gaussian in shape. A simple method of estimating the limit of the single-mode region for any kind of index profile is presented. For a particular class of profiles, dip widths up to 30% have a negligible effect on the propagation characteristics.

Measurements of photoinduced transformations in amorphous As2S3 films by optical waveguiding

Abstract: Photoinduced changes in refractive index and thickness in evaporated As2S3 films have been measured by means of a prism‐coupling technique. The irreversible and reversible structural transformations are associated with increases in the refractive index of 0.133 and 0.029, respectively, at a wavelength of 633 nm. Additionally, a dynamical change in refractive index by 0.003 appears under the band‐gap illumination of about 10 mW/cm2. The origin of this change is attributable to a result from photoelectronic excitation. In the irreversible process, the films expand first and subsequently contract as the refractive index increases monotonically, whereas any change in thickness was not detected within an experimental error of ±10 A for the reversible process.

Overlap relation between free-space Laguerre Gaussian modes and step-index fiber modes.

Abstract: We investigated the overlap relation of the free-space Laguerre-Gaussian modes to the corresponding linearly polarized modes of a step-index fiber. To maximize the overlap for an efficient coupling of the free-space modes into a fiber, the scale-dependent overlap was theoretically and experimentally determined. The presented studies pave the way for further improvement of free-space to fiber optical connections.