Ultra-compact beam splitter based on hybrid slot waveguides enhanced by silicon nitride ALIG structure

A novel structure of polarization beam splitter (PBS) using hybrid slot structure (HSS) consisting of horizontal/vertical slot waveguide (H/VSW) is proposed and characterized. A silicon nitride augmented low index guiding (ALIG) is employed to improve the performances of PBS device. TE mode is well confined in VSW formed by bottom silicon layers, and is transmitted through bar port, while TM mode is strongly cross-coupled to the adjacent waveguide and is directed to cross port by an asymmetric directional coupler (ADC). The results demonstrate a compact device with 4.05 mu m coupling length, low insertion loss (IL) of 0.92 dB(0.55 dB), low crosstalk (XT) of -47.9 dB(-43.6 dB) for TM(TE) mode at 1.55 mu m. To keep XT < -35 dB, a 44 nm bandwidth is obtained for TM mode from 1.533 mu m to 1.577 mu m while XT of TE mode is below -35 only if lambda < 1.62 mu m.