Compact and high-performance polarization beam splitter based on triple-waveguide coupler

Abstract

Polarization beam splitter (PBS) is a fundamental component of integrated photonics to manipulate wave polarization state, and most PBS devices were designed on the popular SOI. As an alternative, a PBS may be implemented on the basis of thin-film LiNbO3-on-insulator (LNOI), a promising platform for developing various compact or ultra-compact photonic active and passive devices. However, smaller modal birefringence of the LNOI waveguide makes it not easy to implement a PBS of high-performance. Here, we propose a compact, high-performance PBS on the basis of a triple-waveguide coupler consisted of two LNOI ridge waveguides and an amorphous silicon (α-Si) nanostrip assisted waveguide. By making use of the α-Si nanostrip, the PBS works in the case that the TM polarization mode meets the phase matching condition while the TE polarization mode does not. Numerical results show that the PBS is compact with a length of only 31 μm. The device can achieve an ultra-high polarization extinction ratio (>29.4 dB) and an ultra-low insertion loss (<0.066 dB) in the operating wavelength range of 1500–1600 nm for the TE polarization mode, and a polarization extinction ratio of > 20 dB and an insertion loss of < 0.16 dB over a ∼ 60 nm bandwidth from 1527 nm to 1587 nm for the TM polarization mode. Moreover, the device has a larger feature size that facilitates fabrication. Overall, this device has the advantages of compact size, higher polarization extinction ratio, lower insertion loss, and larger feature size, which is suitable for on-chip applications.