Abstract: An apparatus for determining a position of a disturbance to an optical fibre assembly comprises a detector system that receives concurrently, from the optical fibre system, a first digital optical signal having a first wavelength and a second digital optical signal having a second wavelength. The apparatus monitors a common parameter of the first and second signals over time and determines respective times at which a change occurs in said parameter in each signal, the change arising from a disturbance to the optical fibre assembly. The apparatus uses the first and second times to determine a position of the disturbance.

Abstract: An apparatus for determining a position of a disturbance to an optical fibre assembly comprises two monitoring units each comprising a respective light detector and a respective clock. The first monitoring unit receives a first digital optical signal from the optical fibre assembly. The second monitoring unit receives a second digital optical signal from the optical fibre assembly. The apparatus monitors the state of polarisation of the first and second digital optical signals and determines respective times at which a change occurs in the state of polarisation of each signal, the change arising from a disturbance to the optical fibre assembly. The apparatus uses said times to determine a position of the disturbance.

Abstract: An apparatus for determining a position of a disturbance to an optical fibre assembly comprises a detector system that receives concurrently, from the optical fibre system, a first digital optical signal having a first wavelength and a second digital optical signal having a second wavelength. The apparatus monitors a common parameter of the first and second signals over time and determines respective times at which a change occurs in said parameter in each signal, the change arising from a disturbance to the optical fibre assembly. The apparatus uses the first and second times to determine a position of the disturbance.

Abstract: An apparatus for determining a position of a disturbance to an optical fibre assembly comprises two monitoring units each comprising a respective light detector and a respective clock. The first monitoring unit receives a first digital optical signal from the optical fibre assembly. The second monitoring unit receives a second digital optical signal from the optical fibre assembly. The apparatus monitors the state of polarisation of the first and second digital optical signals and determines respective times at which a change occurs in the state of polarisation of each signal, the change arising from a disturbance to the optical fibre assembly. The apparatus uses said times to determine a position of the disturbance.