Convex Lens whose refractive index varies

Parallel light rays passing through a convex lens whose refractive index varies through time. At the start the refractive index is set at one and the light beams pass through the lens without changing course. As the animation proceeds, so the refractive index increases (indicated by the moving triangle and the increasing blueness of the lens) and the light beams are brought to a focus progressively closer to the lens.