Optical waveguide filter fabricated by excimer laser irradiation

Ge-SiO2 thin films highly photosensitive to excimer laser light were deposited by plasma enhanced chemical vapor deposition. In this paper, the following two studies are reported: (1) Direct writing of the channel waveguide was successfully confirmed only by irradiation with excimer laser through a Cr mask pattern, which was previously coated on the slab waveguide by sputtering method. Bragg gratings with high diffraction efficiency were also printed in the waveguide by another laser irradiation through the phase mask. (2) Channel waveguides with Bragg gratings were fabricated on the glass ceramic substrates with negative thermal expansion coefficient. Doping of the B2O3 to Ge-SiO2 glass film effectively suppressed the temperature drift of the stop band (dλ/dT) of the gratings. The dλ/dT attained in this study was 4 pm/◦C, which was one-third of those of commercially available waveguide gratings.