A method for manufacturing an optical waveguide, in which a waveguide structure including a waveguide layer of ZnS—SiO2 is deposited on a first layer, wherein a first refractive index of the first layer is lower than the refractive index of the waveguide layer. A sensor arrangement includes a planar optical waveguide, a light source, a sensor, an application unit for applying an analyte on top of the planar waveguide and a processor connected to the sensor.