Integrated optical device with stray light control

An integrated optical device comprises at least one optical waveguide (1) formed on a substrate, the waveguide (1) being of elongate form with an optical axis extending along its length, at least one interceptor trench (3, 4, 5 or 6) being provided in the substrate adjacent at least one side of the waveguide (1), the trench (3, 4, 5, 6) presenting a surface to intercept stray light travelling in the substrate in a direction substantially parallel to the optical axis of the waveguide (1), said surface being angled with respect to the direction of travel of said stray light so as to alter the direction of travel of the stray light intercepted thereby. Also described is an integrated optical device comprising an array of two or more rib waveguides 10, each rib comprising a slab portion 10B and a rib 10A projecting from it, any optically conductive layer being removed from a selected region 11 between the slab portions. Substrate 13 is shown.