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 (larger than the first refractive index and the second 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.