Patent ID: 7620274

Claim:
An optical protection switch comprising: a loop mirror having a first port and a second port; a first circulator operable to couple a first optical signal from a first input port to the first port of the loop mirror and to couple an output optical signal from the first port of the loop mirror to an output port; a second circulator operable to couple a second optical signal from a second input port to the second port of the loop mirror and to couple a third optical signal from the second port of the loop mirror to a drop port; a direction-dependent phase shifter in the loop mirror operable in a first state and a second state; the protection switch operable to switch the first optical signal as the output optical signal and to switch the second optical signal as the third optical signal when the direction-dependent phase shifter is in the first state; the protection switch operable in a second state to switch the first optical signal as the third optical signal and to switch the second optical signal as the output optical signal when the direction-dependent phase shifter is in the second state; and a controller operable to switch the direction-dependent phase shifter between the first state and the second state based on a first power level of the first optical signal and a second power level of the second optical signal.