Polarisation insensitive and tuneable optical add and drop multiplexer utilising vertically stacked buried semiconductor waveguides

A polarisation insensitive and tuneable optical add and drop multiplexer has been realised by utilising vertically stacked buried semiconductor waveguides. The difference in peak wavelength of the dropped light between the two orthogonal polarisations was as small as 0.03 nm, which is much smaller than the 3 dB bandwidth of 0.4 nm. The difference in peak power was also as small as 0.7 dB. Furthermore, polarisation insensitivity was maintained even during wavelength tuning.