CO2laser annealing of Si3N4, Nb2O5, and Ta2O5thin-film optical waveguides to achieve scattering loss reduction

Significant reductions in the optical scattering losses of Si
3
N
4
, Nb
2
O
5
, and Ta
2
O
5
waveguides fabricated on SiO
2
/Si substrates have been measured following CO
2
laser annealing. The largest improvements were observed for Si
3
N
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
2
O
5
waveguide upon laser annealing, the attenuation coefficient decreasing from 7.4 to 0.6 dB/cm. In the case of one Nb
2
O
5
waveguide no improvement was obtained upon laser annealing. The attenuation coefficient of a reactively sputtered Ta
2
O
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
2
O
5
waveguide a small initial improvement in waveguide attenuation was followed by degradation upon further laser annealing.