What are the Recent Trends in Optical Fiber Cable Designs?

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This might be an interesting topic of
discussion to a few engineers engaged in fiber optic cable design. We don’t
intend to provide any mathematical formula used in the
fiber optic cable design in this post, but this may show you the trend
in optical fiber cable design around the world.

 

Optical fiber cables with loose tubes
are dominant in the European market. Loose tube technology is sophisticated
compared to ribbon technology. Loose tubes need excess fiber length inside them
in order to withstand temperature and mechanical effects. Excess fiber length
or in short EFL is the key to loose tube technology. Controlling the excess
fiber length in a loose tube is a skillful job. The theoretical calculation can
guide the engineers to set the pay-off and take-up tensions, water trough
temperatures, etc, but the practical manufacturing conditions are important
factors to decide the excess fiber length. These may be different from factory
to factory and needs optimization. This optimization requires analytical
skills.

 

The inner diameter and therefore outer
diameter of the loose tube was depending on the control of excess fiber length.
Fiber cable manufacturing machine makers have come up with solutions to control
excess fiber length in a loose tube. The outer diameter of a loose tube
containing 12 fibers was around 3.0mm and the inner diameter was 2.0mm some
years back. It was brought down to 2.5mm and 1.7mm respectively in an attempt
to reduce the cable diameter and cable cost. For many years, 2.5mm was the
standard loose tube size in many parts of the world. The last 10 years record
shows that many cable manufacturers dared to experiment towards lower size
loose tubes. Due to these efforts, 12 fibers loose tube size was brought down
to around 2.2mm.

 

The development of microduct cables
encouraged fiber optic cable manufacturers to further experiment with the lower
sizes of loose tubes. In microduct cables, 12 fibers are put into a loose tube
having an outer diameter of approximately 1.5mm and the inner diameter of
approximately 1.1mm. Such a smaller size has been achievable with the support
of machine suppliers. What is required is a small capstan in a loose tube line
between the extruder and wheel capstan to control the excess fiber length.

 

Reduced size fiber optic cables become
practically possible with the help of a small capstan or any other device to
control the excess fiber length. The mechanical performances of the small size
cables will not be equal to that of the big size cables. Smaller size cables
require lesser force to install and therefore the required pulling strength
will also be less. The changes towards lower sizes save material,
manufacturing, and installation cost.

 

East Asian markets where ribbon
technology is dominant followed basically the concept of reduced sizes of fiber
optic cables. For example in Japan, NTT has driven research in fiber optic
cable manufacturing facilities to use underground ducts to accommodate a
maximum number of cables. The reduced slotted core diameter and development of
thin ribbons made it possible to achieve smaller sizes for ribbon slotted core
cables also. With NTT’s installation techniques a duct having 75mm outer
diameter can accommodate 3 ribbon cables of 1000 fibers. This means 3000
optical fibers in a 75mm duct!

 

Recent trends show the development of
smaller size cables around the world. If you have not still decided to develop
smaller size cables, it is not too late. Smaller size cables will present
severe competition in the tenders, where conventional cable makers will face
threats. Responsible cable design engineers must put their efforts towards
change in the design to reduce the cable cost.