CO/sub 2/ Laser Annealing of Si/sub 3/N/sub 4/, Nb/sub 2/O/sub 5/, and Ta/sub 2/O/sub 5/ Thin-Film Optical Waveguides to Achieve Scattering Loss Reduction

Significant reductions in the optical scattering losses of Si ₃N ₄, Nb ₂O ₅, and Ta ₂O ₅ waveguides fabricated on SiO ₂ /Si substrates have been measured following CO ₂ laser annealing. The largest improvements were observed for Si ₃N ₄ waveguides, where waveguide attenuation values of about 6.0 dB/cm before laser annealing were reduced to as low as 0.1 dB/cm afterwards. An improvement of more than an order of magnitude was obtained for a Nb ₂O ₅ waveguide upon laser annealing, the attenuation coefficient decreasing from 7.4 to 0.6 dB/cm. In the case of one Nb ₂O ₅ waveguide no improvement was obtained upon laser annealing. The attenuation coefficient of a reactively sputtered Ta ₂O ₅ waveguide was found to decrease from 1.3 dB/cm before laser annealing to 0.4 dB/cm afterwards. In the case of a thermally oxidized Ta ₂O ₅ waveguide a small initial improvement in waveguide attenuation was followed by degradation upon further laser annealing.