Лазерная модификация титановой пленки на поверхности оптических волноводов в ниобате лития

The availability of thin titanium film laser modification for precise loss control in lithium niobate optical waveguides was demonstrated. A simple ray model of the interaction between a nanosized metal cover on the top surface of a Ti-indiffused channel waveguide and orthogonal optical waveguide modes with changes in optical losses up to 0.95 and 1.05 dB/mm for TE- and TM-polarized modes respectively in case of 5 nm titanium film covering was suggested. The consistency between obtained theoretical losses and results of optical film modification by a 976 nm laser beam with the threshold intensity up to 1 kW/mm2 was demonstrated. The suggested method was applied for precise balance of optical field intensities in arms of Mach-Zehnder optical modulator; an associated increase of the extinction ratio from 30 to 48 dB was achieved.