Abstract: An apparatus (1) for determining a position of a disturbance to an optical fibre assembly (2) comprises two monitoring units (6, 8), each comprising a respective light detector (12a, 12b) and a respective clock (24a, 24b). The first monitoring unit (6) receives a first digital optical signal from the optical fibre assembly (2). The second monitoring unit (8) receives a second digital optical signal from the optical fibre assembly (2). The apparatus (1) 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 (2). The apparatus (1) 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.

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.