Fabrication of low-loss and polarisation-insensitive 256 channel arrayed-waveguide grating with 25 GHz spacing using 1.5% Δ waveguides

A 256 channel arrayed waveguide grating with a 25 GHz spacing was fabricated on a 4 inch Si wafer using 1.5%Δ silica-based waveguides with a minimum bending radius of 2 mm. By improving the fabrication methods of 1.5%Δ waveguides, we have obtained an on-chip loss of 2.7-4.7 dB, a far-end crosstalk of <-40 dB and a polarisation-dependent wavelength shift of <0.025 nm