What is GRIN lenses GRIN lenses are short cylindrical lengths of glass with a graded refractive index: the index decreases with the square of the distance from the axis of the lens GRIN lenses are very similar to graded index fibre and are sometimes called SElFoC lensesWhat is GRIN lenses • GRIN lenses are short cylindrical lengths of glass with a graded refractive index: the index decreases with the square of the distance from the axis of the lens. • GRIN lenses are very similar to graded index fibre and are sometimes called SELFOC lenses