Optical waveguide cable contg. safety monitoring fibre - which exhibits pronounced increase in attenuation if unauthorised tapping of cable occurs

摘要

The cable contains one or more fibres (I) carrying data and protected against external influences causing damage or fracture; and in the cable is >=1 other fibre (II) carrying a monitoring signal and with an attenuation which is easily altered. Fibres (II) are pref. aligned parallel with fibres (I), or may be wound round fibres (I). Fibres (II) are pref. made of low strength glass and/or notched glass, esp. an alkali- or alkaline earth-silicone glass. Alternatively, fibres (II) are made of quartz with a polymethyl-siloxane sheath (IIA) contg. an agent which swells in the presence of water. Fibres (II) may alternatively be located in a loose, soft plastic sheath which is perforated.