Abstract: A method of installing a transmission line (such as an optical fibre telecommunications line) in the ground includes the steps of forming a tunnel in the ground using a mole constituted by a water-jetting head and piping for supplying pressurized water to the head, and positioning the transmission line in the tunnel. The head is guided along a pre-installed buried elongate member such as a twisted copper pair telecommunications line.

Abstract: A connector for connecting an optical fibre (25) to an optical device, comprises a holder (4) and gripping means (5). The holder (4) is formed with a through-bore (21) having first and second end portions (21a, 21b). The first end portion (21a) of the through-bore (21) is sized and shaped to be an interference fit around one end portion (8) of a standard fibre connector (1). The gripping means (5) is engageable with the holder (4) to constrict a portion (21d) of the through-bore (21), thereby to grip the optical fibre (25) which has been inserted into the through-bore via the second end portion (21b).

Abstract: A surveillance system in which a cyclically varying signal is launched into a data carrying optical fibre (3). The signal is reflected from the far end of the fibre and the returning signal compared with the launched signal. A change in the phase difference between the launched and returning signal is indicative of a change in length of the fibre. A microprocessor (8) is used to discount environmentally induced changes caused by temperature or traffic vibration. Alternatively the cyclically varying signal may also be transmitted to the far end of the fibre in digital form and after conversion used as the reference for comparison at the far end.