A silencer for an exhaust system of a combustion engine, more preferably of a motor vehicle, has two end face bottoms facing away from each other, a closed circumferential jacket, at least one silencer insert, at least one inlet pipe and at least one outlet pipe. For example, the present technology can be applied to an image processing apparatus. The filtration layer is defined by one or more filter mediums. A hard mask of a flowable oxide is deposited over the metallic material in the via to protect the metallic material in the via, A subsequent dry sputter etch removes the metallic meterial from the surface of the insulator and a portion of the hard mask. This condition provides greater vertical confinement of the E-field of an optical signal passing through the waveguide.