Direct Measurement of Total-Ionizing-Dose-Induced Phase Shifts in Commercially Available, Integrated Silicon-Photonic Waveguides

In this work, integrated silicon-photonic waveguides are exposed to ionizing radiation. A microbeam X-ray source was utilized to deliver an isolated dose to a waveguide that behaved as one branch of an integrated Mach–Zehnder interferometer (MZI) structure, such that any radiation-induced phase shifts can be directly measured. It is found that the silicon waveguides used in the present study exhibit a nonmonotonic change in the effective index of refraction,neff, for bothO- andC-band operation due to radiation exposure.nefffirst decreased with increasing dose, which is attributed to native SiO2 growth in the silicon core. At larger doses, this trend reverses and the observed net change inneffeventually becomes positive. This increase inneffcan most likely be attributed to radiation-induced densification of SiO2. Overall, it was found that these commercially available silicon waveguides are sensitive to doses above1× 10^9rad(Si), and the nonmonotonic trends suggest that competing simultaneous mechanisms affect the waveguides under high dose levels.