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.