Design of feasible Si-Si3N4 interlayer polarization beam splitter toward 3D optical interconnect

The 3D photonic integrated structure can increase the integration density of the device on a limited chip area, so that the chip has a higher optical interconnection capability. A polarization beam splitter (PBS) is one of the key components for manipulating different polarization states in the areas of optical interconnection and communication. In this paper, a novel interlayer PBS based on an asymmetrical directional coupler (DC) was proposed, which consists of a silicon rib waveguide (WG) and a silicon nitride (Si₃N₄) strip WG with a gap of 850 nm. By carefully adjusting the geometric parameters of the DC, the phase matching condition between these two WGs can be satisfied for the TM polarization, while the coupling efficiency of the TE polarization is frustrated due to the large phase mismatch. By adding a filter to the thru port the performance of the proposed PBS is improved. The device with a 220 nm Silicon-On-Insulator (SOI) WG and a 700 nm × 400 nm Si₃N₄ WG operates in a broadband width of 100 nm, with an extinction ratio (ER) <20 dB. The insertion losses (ILs) are <0.22 dB for both TE and TM polarizations at a wavelength of 1550 nm. At the same time, our design parameters conform to the Multi Project Wafer (MPW) process conditions, and the device is highly implementable. The device is potential to use for the on-chip 3D optical interconnect in the future.