Optical switches are provided in an optical transmission system having at
least two optical nodes in optical communication over a primary optical path and
a backup optical path. An optical switch is located in each of the optical nodes.
Each of the optical switches includes a switching element having an input port
and a plurality of output ports coupled to the primary and backup optical paths,
respectively. The switching element has a first state optically coupling an optical
signal from the input port to the primary path and a second state optically coupling
an optical signal from the input port to the backup path. First and second optical
taps are located in the primary optical path. Third and fourth optical taps are
located in the backup optical path. A first photodetector is optically coupled
to the second optical tap for receiving a portion of the optical signal traveling
in the primary optical path. A second photodetector is optically coupled to the
third optical tap for receiving a portion of the optical signal traveling in the
secondary optical path. A first optical path optically couples the first optical
tap to the fourth optical tap such that a portion of an optical signal traveling
in the secondary path is coupled onto the primary path. Finally, a controller is
electrically coupled to each of the optical switches. The controller is configured
so that when each of the switching elements are in the second state and the first
photodetector in each of the optical switches detects an optical signal, the controller
returns the switching elements to the first state.