Integrated optical circuits have been fabricated using laser-written masks. Straight and curved channel waveguides have been made by ion exchange from a KNO3 melt of dimensions 10 to 30 pm in width and typically 4 to 5 cm in length. A mask made by a multiple exposure technique from a laser-written curved channel mask has been used to delineate a directional coupler in LiNbO3.
K. E. Wilson,
C. T. Mueller,
"Integrated Optical Circuits Fabricated With Laser-Written Masks", Proc. SPIE 0321, Integrated Optics II, (27 August 1982); doi: 10.1117/12.933215; https://doi.org/10.1117/12.933215