A Liquid-core Liquid-cladding Optical Waveguide Based on Thermal Gradients across the Laminar Flow of Water in Capillary Tubing

: A liquid-core liquid-cladding optical waveguide based on thermal gradients across laminar flow was built with the laminar flow of water in a stainless capillary tube placed in a heat source. Its characteristics were studied with both experiments and a computational fluid dynamics simulation, firstly showing that it had the nature of a graded index optical fiber.