A low crosstalk high-speed polarisation-independent optical switch unit for fibre route protection in public telecommunication networks

The authors discuss the design of an exchange-rack compatible fibre route protection unit which will switch a receiver to a spare fibre within 150 ns of an alarm being asserted as a TTL signal. The configuration described allows single-ended control, with the switch adjacent to the receiver and associated alarms. At the present level of technological development, the 3 dB coupler also offers lower optical loss than would the equivalent optical switch. The optical interface is standard CCITT single mode fibre suitable for signals of arbitrary polarisation