a method for manufacturing an optical device with a defined total device stress , birefringence and optical polarization dependence is disclosed . the method comprises first providing a tower cladding layer of an amorphous material with a first refractive index and then providing above the lower cladding layer an upper cladding layer of an amorphous material with a second refractive index . an optical waveguide core comprising an amorphous material having a third refractive index is provided between the lower and the upper cladding layers . the upper cladding layer is thermally annealed by keeping the upper cladding layer at a first temperature , then raising the temperature to a second temperature , maintaining the second temperature for an annealing time period , and lowering the temperature to a third temperature , after which the temperature is lowered to a fourth temperature .