Broadband Polarization Beam Splitter on a Silicon Nitride Platform for O-Band Operation

Wideband polarization beam splitters (PBS) are a key building block in polarization management circuits for wavelength division multiplexing applications. A broadband PBS on a 300-mm silicon nitride (SiN) photonic platform is reported based on phase-controlled directional coupler (DC). Unlike classical DC-based PBS made on silicon, the proposed configuration leverages the comparatively lower birefringence in SiN to yield wideband and efficient splitting. A semi-analytical approach, based on transfer matrix modeling and 3-D finite difference time domain, has been used to design and optimize the structure for O-band operation. The proposed PBS has been experimentally demonstrated showing insertion loss (IL) lower than 0.6 dB and extinction ratio (ER) as high as 10 dB over 95-nm bandwidth for both polarizations. Furthermore, this simplified architecture eases cascading, allowing the demonstration of IL below 1.1 dB and ER larger than 24 dB over 85-nm wavelength range in a dual-stage configuration.