Framework for tunable polarization state generation using Berry's phase in silicon waveguides

We present a framework for an arbitrary polarization state generator exploiting Berry's phase through a cascade of in-plane and out-of-plane silicon strip waveguides. We establish two criteria required for a passive device to achieve 90° polarization rotation, and derive explicit equations to satisfy the criteria. The results define regions within the parameter space where active tuning of the polarization state is possible over the entire Poincaré sphere. We use numerical modeling to show ±30 dB tuning of the polarization extinction ratio between the quasi-transverse electric and magnetic modes for a range of devices with deflection angles ranging from 5° to 45°, and modal birefringence from 0 to 0.05. We envision control of optical polarization on the chip-scale in integrated waveguides for communications, sensing, and computing applications.