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

Abstract

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.

Higher Order Mode Conversion From Berry's Phase in Silicon Optical Waveguides

“…To achieve additional mode conversion with our geometry, multiple out-of-plane waveguides can be cascaded together and connected by in-plane sections. When combined with active tuning via the thermo-optic or plasma dispersion effects, such an approach can enable electrically controlled generation of optical angular momentum at the output [7]. Furthermore, mode converters on the input can be added to convert fundamental modes to higher order modes such as the E 21 mode utilized in this work [37], [38].…”

“…Since then, Berry's phase has been observed in other optical platforms including bulk optics and integrated waveguides [2]- [5]. Polarization rotation via Berry's phase is inherently broadband due to topological origins and implementations can be realized in guided wave geometries without large changes in waveguide cross-section that can introduce undesirable impedance mismatches [5]- [7]. Berry's phase has been utilized to achieve on-chip mode conversion and dynamic polarization control between the fundamental quasi-TE and quasi-TM modes of silicon strip waveguides [5]- [7].…”

“…Polarization rotation via Berry's phase is inherently broadband due to topological origins and implementations can be realized in guided wave geometries without large changes in waveguide cross-section that can introduce undesirable impedance mismatches [5]- [7]. Berry's phase has been utilized to achieve on-chip mode conversion and dynamic polarization control between the fundamental quasi-TE and quasi-TM modes of silicon strip waveguides [5]- [7]. Manifestations of Berry's phase in the case of higher order modes propagating along a curved ray have been reported in the paraxial regime [8]- [10], however, higher order mode demonstrations in integrated waveguides with high index contrast have not been reported.…”

“…A waveguide deflected by angle will nominally rotate an input quasi-TE polarization by angle 2 such that the output is generally a weighted superposition of the quasi-TE and quasi-TM modes. We first describe TE to TM mode conversion with a Jones calculus formalism and then extend the description to higher order mode conversion [6], [7].…”