Ultrahigh extinction ratio and ultralow insertion loss for polarization beam splitter based on two folded asymmetrical directional couplers with dual-stage etching

Abstract

We propose and experimentally demonstrate a polarization beam splitter (PBS) with excellent performance in terms of ultrahigh extinction ratio and ultralow insertion loss. The PBS consists of two dual-stage etched asymmetrical directional couplers, which are cascaded by a bend waveguide to form a folded structure. In the PBS, the fundamental transverse magnetic ( T M 0 ) mode is efficiently cross-coupled to the cross-port, while the fundamental transverse electric ( T E 0 ) mode outputs at the through-port. Thanks to the cascaded structure and dual-stage etching, a silicon-on-insulator-based PBS with ultrahigh extinction ratio and ultralow insertion loss is achieved. The measurement results reveal an extinction ratio beyond 25 dB and an insertion loss less than 0.7 dB within a wide bandwidth of 175 nm for the T E 0 and T M 0 modes.