Mitigating Water Absorption in Waveguides Made From Unannealed PECVD SiO₂

Water absorption was studied in two types of waveguides made from unannealed plasma enhanced chemical vapor deposition (PECVD) SiO2. Standard rib anti-resonant reflecting optical waveguides (ARROWs) were fabricated with thin films of different intrinsic stress and indices of refraction. Buried ARROWs (bARROWs) with low and high refractive index differences between the core and cladding regions were also fabricated from the same types of PECVD films. All waveguides were subjected to a heated, high humidity environment and their optical throughput was tested over time. Due to water absorption in the SiO2 films, the optical throughput of all of the ARROWs decreased with time spent in the wet environment. The ARROWs with the lowest stress SiO2 had the slowest rate of throughput change. High index difference bARROWs showed no decrease in optical throughput after 40 days in the wet environment and are presented as a solution for environmentally stable waveguides made from unannealed PECVD SiO2.