Broad bandwidth and large fabrication tolerance polarization beam splitter based on multimode anti-symmetric Bragg sidewall gratings.

A novel polarization beam splitter based on an anti-symmetric sidewall Bragg grating in a multimode silicon-on-insulator strip waveguide is demonstrated. Anti-symmetric spatially periodic refractive-index perturbations are designed for strong coupling between the fundamental (TE0) and the first-order transverse electric modes (TE1), while not for transfer magnetic modes. An adiabatic coupler is cascaded at the input-port, so as to drop the TE1 reflection. The Bragg grating has a compact length of ∼20  μm (55 periods). The polarization isolations of the through- and drop-ports at the wavelength of 1557 nm are 34 and 31 dB, respectively. A broad bandwidth of 64 nm and a large fabrication tolerance of 80 nm for polarization isolation over 20 dB are also achieved.