Propagation losses of silicon nitride waveguides in the near-infrared range

Si3N4/SiO2 waveguides have been fabricated by low pressure chemical vapor deposition within a complementary metal-oxide-semiconductor fabrication pilot line. Propagation losses for different waveguide geometries (channel and rib loaded) have been measured in the near infrared as a function of polarization, waveguide width, and light wavelength. A maximum thickness of single Si3N4 of 250 nm is allowed by the large stress between Si3N4 and SiO2. This small thickness turns into significant propagation losses at 1544 nm of about 4.5 dB/cm because of the poor optical mode confinement factor. Strain release and control is possible by using multilayer waveguides by alternating Si3N4 and SiO2 layers. In this way, propagation losses of about 1.5 dB/cm have been demonstrated thanks to an improved optical mode confinement factor and the good quality of the interfaces in the waveguide