Fabrication of low-temperature PECVD channel waveguides with significantly improved loss in the 1.50-1.55-μm wavelength range

By excluding nitrogen-containing gases from the deposition process, silica-based waveguides have been fabricated by PECVD at low temperature with a propagation loss less than 0.2 dB/cm in the 1.50-1.55-μm wavelength range. PECVD is performed in a high-plasma-density hollow cathode system from a mixture of oxygen and silane. Carbon tetrafluoride is used as a fluorine dopant to depress the refractive index in the buffer and cladding layers. A controllable refractive index change in the range 0.004-0.02 can be obtained.