A tunable filter device comprising a waveguide containing a Bragg grating, and a planar substrate, the planar substrate comprising a core, a first cladding on a first side of the core, and a second cladding on a second side of the core, the waveguide containing the Bragg grating being positioned in the core, the planar substrate being such that a part of the first cladding is replaced with a liquid crystal, and the tunable filter device being characterised in that the waveguide containing the Bragg grating is ultraviolet light written, the first cladding has a surface which is smooth, flat and uniform due to the waveguide containing the Bragg grating being ultraviolet light written, and the liquid crystal is in contact with the smooth, flat and uniform surface of the first cladding whereby director orientation of the liquid crystal is uniform, controlled and controllable.