We report on an all-optical demultiplexer based on gain-transparent operation of a semiconductor optical amplifier (SOA) in an ultrafast-nonlinear interferometer (GT-UNI), The GT-UNI comprises a robust fiber-chip setup in a folded geometry. For switching window widths of 5.2 ps and 6.0 ps, error-free demultiplexing of 160-10 Gb/s is demonstrated.