Embodiments of the disclosed technique disclose an optical device generating light by luminescence comprising a substrate, a waveguide, a pump light source and a photoluminescent layer, wherein the waveguide is positioned between the substrate and the photoluminescent layer, or the photoluminescent layer is positioned between the substrate and the waveguide. The pump light source is provided opposite to the photoluminescent layer at the backside of the substrate. The pump light source is adapted to pump the photoluminescent layer to emit light; and at least some of the emitted light is evanescently coupled into the waveguide.