Method for switching transmission route, and optical transmission device

A method for switching a transmission route for use in transmission from a transmission station to a receiver station in an optical network in which the transmission station and the receiver station are connected through a plurality of transmission routes with redundancy, comprising the steps of:

• (a) converting a main signal transmitted from the transmission station to a regenerator station arranged on a first one of the plurality of transmission routes, into an electric signal, and detecting an input level of the main signal, in the regenerator station;
• (b) converting the electric signal into an optical signal, inserting the optical signal, as the main signal, into the first one of the plurality of transmission routes from the regenerator station when the input level is equal to or higher than a predetermined level, and stopping output of the optical signal from the regenerator station when the input level is lower than the predetermined level;
• (c) transmitting a control signal indicating occurrence of a failure, from the regenerator station through a transmission route to the receiver station, when the input level is lower than the predetermined level;
• and
• (d) switching a transmission route from which the receiver station acquires the main signal, from the first one of the plurality of transmission routes to a second one of the plurality of transmission routes, when an input level of the main signal at the receiver station is lower than a predetermined level or when the receiver station receives the control signal.