Abstract: An apparatus for detecting and/or locating a fibre-optic cable (170) by applying a magnetic field with a component parallel to the cable (170) and detecting the cumulative rotation of polarisation of a polarised beam passing through the magnetic field multiple times. The beam is preferably input into the cable (170) multiple times, with the same polarisation and amplitude each cycle. In this case, a regeneration stage (800) is provided to recycle the beam with the correct amplitude and polarisation. A method of detecting a fibre-optic cable (170) is also disclosed.

Abstract: An apparatus and method are provided for detecting disturbances (changes in physical configuration) in optic communication or transmission media such as fibre-optic cables 180 has a source 110 of pulsed laser light, a circulator 150 for inputting the pulsed laser light into the fibre-optic cable and receiving backscattered radiation from the cable 180, and a detection stage 160 for detecting the amplitude of radiation backscattered from the cable 180 as a function of time, the backscattered radiation being caused by pulses of laser light input into the cable 180 at a first end. The results may be analysed and may be correlated to indicate the existence and/or location of a disturbance. A method of detecting such disturbances is also disclosed.