Laser welded metallic tubes with incorporated optical fibres has during the past years been used for a variety of cable designs. So far, fibres in metallic tubes are most frequently used in OPGW, submarine cables and special cable designs for military or industrial applications. The tubes however are adequate for an even wider range of cables, from standard terrestrial cables to complex umbilical constructions for dynamic applications. The tube properties determine the proper cable design for the application in question, and it is consequently necessary to know certain characteristics of the tube. The tube itself is a rugged construction, where in general the ratio between tube wall thickness and tube dimension determines the mechanical performance. Tubes may be manufactured in dimensions ranging from slightly below 1mm to more than 5mm diameter, and the maximum number of fibres per tube depends on design details such as fibre bend loss sensitivity, required fibre strain relief, fibre identification system, etc.
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