An opto-electronic device comprises a waveguide along which light may propagate and an electrode associated with the waveguide and arranged to apply a variable electric field thereto. The waveguide includes one or more active regions in which variations in the electric field applied by the electrode to the waveguide cause variations in absorption of the light, and one or more passive regions in which variations in the electric field applied by the electrode to the waveguide cause substantially no variations in any absorption of the light. Relative proportions of the waveguide that comprise the active and passive regions vary along at least part of the length of the waveguide.