Fabrication and characterization of non-doped SiO2 cladding layer for polarization-insensitive silica waveguide by using plasma enhanced chemical vapor deposition

We developed a technique for fabricating the cladding layers of silica waveguides and used this technique to fabricate an arrayed waveguide grating (AWG). The technique consists of two deposition process of non-doped SiO2. The first deposition process is a two-step deposition process combining plasma-enhanced chemical vapor deposition (PECVD) using tetraethylorthosilicate (TEOS) gas with an etching-back non-doped SiO2 by RF sputtering, and the second is a deposition process by means of PECVD using SiH4 gas. The non-doped SiO2 cladding layer must meet requirements of a thickness over 10 µm without cracking and a refractive index the same as that of fused silica. By using this fabrication technique, these requirements are satisfied and narrow core-to-core gaps are successfully filled with non-doped SiO2 without producing voids. The developed silica waveguide with non-doped SiO2 cladding has a propagation loss of 0.07 dB/cm and the developed AWG has a polarization sensitivity of 0.001 nm, which is one order of magnitude lower than that of existing AWGs.