Despite improvements in conventional semiconductor optical amplifier-based interferometric switches used for telecom applications such as demultiplexing and add/drop multiplexing, limitations remain. These switches suffer from poor linearity, distortion of transmitted data and excess noise. A group of researchers for the Heinrich-Hertz Institut f?r Nachrichtentechnik in Berlin says it has designed a switch with high linearity, high switching contrast and wide bandwidth. A gain-transparent semiconductor optical amplifier is the switch's essential component.