Abstract: An optical transmission system including an interferometer and a source of optical signals. The interferometer comprises a four-pod optical coupler having first and second input ports and first and second output pods, a silica optical fiber coupling the first and second output pods which exhibits the Kerr optical non-linearity, and an erbium fiber optical amplifier situated asymmetrically between the output ports. The source of optical signals is coupled to the first input port of the interferometer. The system is operated in a regime in which the optical signals saturate the amplifier thereby suppressing any oscillatory output, and their power is sufficient to switch an input signal coupled to the first input pod to the second input pod. This provides pulse shaping and amplification characteristics which are relatively insensitive to the input power of the optical signals from the optical source.