Analysis of Optical Single-Event Transients in Integrated Silicon Photonics Mach-Zehnder Modulators for Space-based Optical Communications

Optical single-event transients (OSETs) were measured for the first time in integrated silicon-photonic phase shifters and Mach-Zehnder modulators (MZMs). A pulsed laser was utilized to induce a dense cloud of electron-hole pairs (EHPs) in one arm of the MZM by employing the two-photon absorption (TPA) process. Experimental data demonstrated the creation and propagation of transients in both the electrical and optical domains. It has been found that in the presence of an induced cloud of EHPs inside the phase shifter, two mechanisms work in parallel to generate OSETs: transient free-carrier absorption (TFCA), and transient phase change due to the dynamic alteration of the refractive index. In the case of a phase-sensitive component like the MZM, it has been observed that transient phase change dominates, leading to the largest transients at Quadrature (Quad) biasing points, where the MZM is most sensitive to phase changes. An analytical model has been developed to predict the effects of single-event transients (SETs) on MZMs, as well as a simulation methodology to validate the accuracy and reliability of the predictions. Finally, an analysis of the effects of radiation-induced optical transients over an optical communications link is also presented. The probability of symbol errors is shown to increase due to OSET-induced errors based on the chosen modulation schemes, representing a potential vulnerability for space systems.