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,$n_{\text {eff}}$, for both$O$- and$C$-band operation due to radiation exposure.$n_{\text {eff}}$first 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 in$n_{\text {eff}}$eventually becomes positive. This increase in$n_{\text {eff}}$can most likely be attributed to radiation-induced densification of SiO2. Overall, it was found that these commercially available silicon waveguides are sensitive to doses above$1\times 10^{{9}}$rad(Si), and the nonmonotonic trends suggest that competing simultaneous mechanisms affect the waveguides under high dose levels.