| 摘要 |
In a optical cable comprising at least one separate optical fibre and/or optical bundle, the optical fibre or bundle (4) is loosely housed in, or surrounded by, an elongate compartment (11) bounded by a fluid-impermeable wall or fluid-impermeable walls (6, 8). The elongate compartment (11) extends throughout the cable length and contains a fluid, e. g. air above or below atmospheric pressure, at such a pressure that detection of a change in pressure of the fluid will serve to indicate that a fluid-impermeable wall (6, 8) has been ruptured, e. g. by someone illegally tapping the cable. The cable may also incorporate at least one electric conductor (5, 9) extending along the cable length radially outward of the optical fibre or bundle and, when a detectable current is flowing in the conductor (5, 9), constituting part of an electric alarm system. |
