A variable optical device for selectively controlling propagation of light within an optical waveguide. The optical device comprises: a relief modulation defining a grating disposed proximal the waveguide and having a respective grating index of refraction n_G; a matrix surrounding at least the relief modulation, the matrix having an index of refraction n_EO that is controllable, in response to a selected stimulus between a first value that is substantially equal to the grating index of refraction n_G, and a second value that is different from n_G; and at least one electrode for supplying the selected stimulus to the matrix-grating system.