Abstract

During the past year a number of experimental monomode optical fibre links have been assembled at British Telecom Research Laboratories in order to aid transmission performance studies and to provide test bed links for system trials. These links include a 102 km laboratory link¹, a 31.6 km cabled laboratory link² (containing 15 splices), a separate 31.5 km cabled link³ (containing 30 splices) and a 61.3 km cabled link⁴ (containing 37 splices). The last 2 links have been installed in operational duct in the vicinity of the Research Laboratories to form a complex of cables linking Martlesham to telephone exchanges at the nearby towns of Woodbridge and Ipswich. The 31.5 km field installation, cable manufactured by Telephone Cables Limited (TCL), has been successfully operated at a bit rate of 650 Mbit/s³. Installation of the 61.3 km cabled link, manufactured for BT by Standard Telephone Laboratories⁴, has recently been completed at the time of writing. System trials⁵ have now been successfully conducted at 565 Mbit/s (1300 nm) over the full 61.3 km and at 140 Mbit/s (1550 nm) over an unrepeatered 90 km link formed by splicing the 2 installed cable routes together.