A novel and generic method for fabricating silica-on-silicon planar lightwave circuits with cores composed of two or more different types of glasses is described. The basic process technologies used are silane/germane/nitrous-oxide based plasma enhanced chemical vapor deposition and fluorine based reactive ion etching. Very high-quality interfaces between the different core glasses are obtained with interface losses as low as 0.022 +/- 0.012 dB and reflection levels below -80 dB. This technique adds flexibility and ease to the design of complex silica planar waveguide components, allowing, e.g., independent optimization of amplifying and passive sections in lossless devices based on erbium-doped planar waveguides.
I E E E Photonics Technology Letters, 1998, Vol 10, Issue 10, p. 1431-1433