Silicon nitride polarization beam splitter based on polarization-independent MMIs and apodized Bragg gratings

We present the design and experimental results of a novel polarization beam splitter (PBS) with a high polarization extinction ratio (PER) made on a Si₃N₄ platform. The PBS is composed of two identical polarization-independent multi-mode interferometers and two identical apodized Bragg gratings. The operating principle of this device is based on the fact that the TE and TM stopbands of the grating are centered at different wavelengths. The reflected and transmitted light from the gratings are routed to separate output ports by the two-MMI configuration. The experimental results show that a PER of > 30 dB is achieved over a bandwidth of 22 nm, with an insertion loss of ∼ 1.1 dB. The total length of the device is ∼ 820 µm.