Fabrication-tolerant integrated polarisation splitter based on cascaded Mach–Zehnder interferometers

We report a fabrication-tolerant polarisation splitter based on cascaded Mach–Zehnder interferometers. This configuration enables a factor of 2 – 3 increase (at the 20 dB level) in the tolerance to the phase difference in comparison with a single interferometer. As an example, we present numerical simulation of a splitter with a centre wavelength of 650 nm, based on a planar waveguide from Si₃N₄. The permissible channel waveguide width deviation from calculation results (20-dB extinction coefficient bandwidth) is ~8% (~30 nm) for the TE polarisation and ~30% (100 nm) for the TM polarisation.