Photonic substrate preparation method and photonic waveguide preparation or fabrication method

Method for fabricating a photonic integrated circuit optical waveguide device for reducing copper impurity optical loss in at least one of at least one optical waveguide and at least one optical waveguide structure of the photonic integrated circuit optical waveguide device, the at least one of the at least one optical waveguide (111) and the at least one optical waveguide structure comprising a waveguide core comprising silicon nitride, the method comprising:

• providing at least one substrate comprising silicon,
• depositing at least one copper gettering layer and/or material comprising silicon nitride on the at least one substrate comprising silicon,
• depositing at least one optical waveguide cladding layer and/or material on the at least one copper gettering layer and/or material comprising silicon nitride that is deposited on the at least one substrate comprising silicon,
• forming the at least one of the at least one optical waveguide and the at least one optical waveguide structure comprising at least one elongated waveguide core comprising silicon nitride provided on and supported by the at least one optical waveguide cladding layer and/or material that is deposited on the at least one copper gettering layer and/or material comprising silicon nitride which is deposited on the at least one substrate comprising silicon, the at least one elongated waveguide core comprising silicon nitride being supported by and/or being at least partially embedded by the at least one optical waveguide cladding layer and/or material;
• and
• thermally annealing the at least one substrate comprising silicon after the formation of the at least one of the at least one optical waveguide and the at least one optical waveguide structure on the at least one substrate comprising silicon to remove hydrogen impurities and/or hydrogen-related impurities from the at least one of the at least one optical waveguide and the at least one optical waveguide structure, and to capture or trap copper impurities of the at least one substrate comprising silicon in the at least one copper gettering layer and/or material comprising silicon nitride.