A sensor comprises: a thin structure, which is configured to receive a force for deforming a shape of the thin structure and which is arranged above a substrate; and a waveguide for guiding an electro-magnetic wave comprising: a first waveguide part; and a second waveguide part; wherein the second waveguide part has a larger width than the first waveguide part; and wherein the first and the second waveguide parts are spaced apart by a gap which is sufficiently small such that the first and second waveguide parts unitely form a single waveguide, wherein one of the first and the second waveguide part is arranged at least partly on the thin structure and another of the first and the second waveguide part is arranged on the substrate.