Topological Polarization Beam Splitter with Polarization-Selective Edge States

TL;DR

This paper demonstrates a topologically protected on-chip polarization beam splitter using a Floquet-engineered silicon nitride lattice, achieving robust polarization separation with high extinction ratios and inherent defect resilience.

Contribution

It introduces a novel topological polarization beam splitter based on Floquet engineering, enabling robust, scalable polarization control in integrated photonics.

Findings

Achieved extinction ratios of 16-20 dB for protected ports.

Demonstrated wavelength-dependent polarization behavior.

Identified spectral regions for polarization-independent edge transport.

Abstract

The realization of on-chip polarization beam splitters robust to fabrication imperfections remains a key challenge for polarization-sensitive photonic integration. We demonstrate a topologically protected polarization beam splitter based on a Floquet-engineered microring lattice implemented on a CMOS-compatible silicon nitride platform. By tailoring the dispersion of inter-ring coupling, the lattice supports complementary trivial and topological band gaps for orthogonal eigenpolarizations. At telecom wavelengths, TE modes propagate via a topological edge state while TM modes are suppressed by a trivial gap; this behavior reverses at shorter wavelengths. We measure extinction ratios of 16-20 dB for the protected port and 10-20 dB for the non-protected port, with insertion loss of 2 dB at long wavelengths. Reduced TM extinction at shorter wavelengths is attributed to suboptimal input coupling. We further identify spectral regions where both polarizations exhibit nontrivial band gaps, enabling polarization-independent edge transport and establishing a Floquet dual-polarization topological regime. Because operation is governed by band topology rather than geometric fine-tuning, the device shows intrinsic robustness to defects. These results establish polarization-tailored topological lattices as a scalable platform for robust beam splitting, routing, and interconnects in classical and quantum photonic systems.