Photosensitive and athermal glasses for optical channel waveguides

Abstract

Ge–SiO2 thin glass films photosensitive to excimer laser irradiation were fabricated by plasma enhanced chemical vapor deposition. A channel waveguide was successfully fabricated by irradiation with only an excimer laser through a Cr mask pattern, which was previously coated on the slab-waveguide by the sputtering method. Bragg gratings with high diffraction efficiency were also fabricated in the waveguide by another KrF laser irradiation through the phase mask without hydrogen loading. Channel waveguides with Bragg gratings, on the other hand, 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 less than one-third of those reported for commercially available waveguide gratings. Although the grating printed in the Ge–B–SiO2 film was almost erased by annealing at a temperature lower than 500 °C, a new type of grating with much higher diffraction efficiency than that before annealing was formed after annealing at 600 °C. The diffraction efficiency of the new grating was unchanged after repeated heating between room temperature and 600 °C.