The loose tube is a semi-finished product, which is an essential ingredient in optical fiber cable. The loose tube process is one of the most commonly employed protection methods in the cabling process. Optical fibers must be protected from direct mechanical and environmental influences in order to make the cable suitable to function for the desired lifetime.
Several color coded optical fibers are placed loosely inside a plastic tube filled usually with jelly in a loose tube. Fibers are loose inside the tube and that is the reason behind its name Loose tube. Manufacturing loose tube is one of the critical and important processes in optical fiber cable manufacturing plans. People involved in the manufacturing and testing of optical fiber cables understand the importance of loose tube manufacturing.
Loose tube manufacturing needs precise technical skills. Though the process follows a set of procedures, rules, and mathematical formulas, a high degree of “Intuition” factor works practically in actual manufacturing situations. This is the point where the experience and skill of the operator come in to picture.
The selection of the diameter of the loose tube has its impact on mechanical and environmental characteristics and the cost of the cable. Hence it is the skill of a cable design engineer to find balance the cost impact and cable performance at the stage of cable design itself. When I started the career in optical fiber cable manufacturing, we used 3.0 mm outer diameter for a loose tube with 12 fibers. The inner diameter was 2.0 mm. I have heard from my seniors that the tube diameter was still bigger when they started their career, say in 1988.
Loose tube diameter has been reducing overall these past years. Over the past 21 years, I could see the loose tube drops its size and weight. Currently, a 12 fiber can be placed in a loose tube with an outer diameter of 1.4mm. More than outer diameter, inner diameter and thickness are the parameters of concern for a loose tube. I just want to focus on what we see outside, i.e., outside diameter.
From 3.0 mm outer diameter, the loose tube reduced its size to 2.8 mm. From 2.8 mm it was reduced to 2.5 mm. This was around in 1997. This diameter stayed for a quite long period. After the telecom recession, cable makers started experimenting with reducing the size of the loose tubes. It was then the diameters such as 2.3 mm, 2.1 mm, etc were being introduced. With the entry of many Chinese cable makers into the global cable supply market, traditional cable manufacturers again reduced the diameter to lower than 1.9 mm.
Microduct cables got popular in some markets after 2005. Cable makers could place 12 numbers of 250 micrometer diameter in a loose tube of 1.5mm. Of course, the mechanical performances of microduct cables were lower compared to that of conventional duct cables.
With the introduction of 200 micrometer fibers, loose tube diameter can further reduce to 1.3 mm. Though 200 micrometer optical fibers have been introduced, they are yet to make their roads to the telecom market on a massive scale.
In short, if we see the trend of reduction in the outer diameter of loose tubes, I can say, over the past 21 years, the loose tube diameter has come down from 3.0 mm to 1.3 mm. This means a reduction of more than 57 percent.