A waveguide device and method of doping a waveguide device, the waveguide device comprising a rib waveguide region, the rib waveguide region having: a base, and a ridge extending from the base, wherein: the base includes a first slab region at a first side of the ridge and a second slab region at a second side of the ridge; a first doped slab region extends along the first slab region; a second doped slab region extends along the second slab region; a first doped sidewall region extends along a first sidewall of the ridge and along a portion of the first slab, the first doped sidewall region being in contact with the first doped slab region at a first slab interface; and a second doped sidewall region extends along a second sidewall of the ridge and along a portion of the second slab, the second doped sidewall region being in contact with the second doped slab region at a second slab interface; and wherein the separation between the first sidewall of the ridge and the first slab interface is no more than 10 μm; and wherein the separation between the second sidewall of the ridge and the second slab interface is no more than 10 μm.