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

Si 3 N 4 ∕ SiO 2 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 Si 3 N 4 of 250 nm is allowed by the large stress between Si 3 N 4 and SiO 2 . 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 Si 3 N 4 and SiO 2 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.