Optical Single-Event Transients Induced in Integrated Silicon-Photonic Waveguides by Two-Photon Absorption

Optical single-event transients (OSETs) were measured for the first time in integrated silicon-photonic waveguides. A custom test fixture and novel experimental setup were used at the U.S. Naval Research Laboratory to induce a dense cloud of electron-hole pairs (EHPs) in a waveguide by the two-photon absorption process. Experimental data showed that the fractional (or percent) extinction of the optical power in the waveguide due to an OSET is dependent on the number of injected EHPs. This fractional extinction was also shown to be constant regardless of the optical power level in the waveguide. These OSETs are a direct result of a reduction in the optical transmission ratio due to transient free-carrier absorption. The peak of the largest measured OSET degraded the transmission ratio by 15%, which, according to simulations, corresponds to roughly 9×10
¹⁹
cm
^-3
peak EHP generation. Simulation results suggest that the EHP density levels generated by heavy ions in space could potentially cause up to 100% fractional extinction of light in the waveguide, that is, total loss of the optical signal. A simulation technique to predict the OSET effects in any arbitrary photonic circuit is shown. Here, an electrooptic modulator was used as an example. The results of this study pose concerns for use of integrated silicon photonics for radiation-intensive applications.