Photosensitive phosphorus-doped boron-codoped silica planar waveguide for waveguide Bragg grating prepared by spin coating

Phosphorous doped silica layers are grown from tetraethylorthosilicate (TEOS), phosphoric acid and PBF polymer, with spin coating technique on silica glass. The phosphorus-doped and boron-codoped photosensitive silica waveguide samples show index modulation around 1×10^-4 for thickness between 3 μm to 8 μm. The refractive index range is between 1.51 to 1.54 which is dependent on the coating parameters and concentration of phosphoric acid. Photosensitivity test and treatment are performed using a 366 nm UV source, with 0.36 mW/cm² power at pulse rate of 50 Hz. All samples show a decrease in refractive indices under the UV exposure. They begin to saturate after first 30-60 minutes in treatment. Further UV exposure will slowly increase again the refractive index. It is estimated that, with a laser source power from ArF and KrF of about 10 mW, the Bragg grating writing duration will be in between 20 to 30 second. The samples were also thermally treated to increase the index modulation by the factor of 10.