Abstract: A waveguide assembly for guiding radiation along an optical path, the assembly comprising a first guide element, a second guide element and a coupling element for coupling radiation between the first element and the second element, the first element, second element and coupling element comprising a refractive index along the optical path which is greater than a refractive index of a medium surrounding the elements, wherein, the first and second elements are spaced from the coupling element along the optical path, such that the medium extends between the first element and the coupling element and second element and the coupling element, within the optical path and wherein the radiation is arranged to couple between the first and second guide elements by reflecting within the coupling element from an interface between the coupling element and the medium.