Optical Fibre Construction Parameters

Detail Fibre Construction Parameters

“Even with the much more resilient and robust bend-insensitive varieties, optical fiber is still glass and requires both skill and knowledge to install.”

Construction-Optical Fibre Cable

Construction-Optical Fibre Cable

Fibre Geometric Parameters

  Fibre can either be single-mode (SM) or multimode (MM). Fibre sizes are expressed by using two numbers e.g. 9/125. The first number refers to the core size in microns and the second number refers to the core and cladding size combined in microns. It is impossible to differentiate between SM and MM fiber with the naked eye. There is no difference in the outward appearances; both are 125 microns in size – only the core size differs.

Fiber Geomtric parameters

Fiber Geomtric parameters

Fibre Construction:

Core: The optical core is the light-carrying element at the center and is usually made up of a combination of silica and germanium.

Cladding: Cannot be removed! The cladding surrounding the core is made of pure silica and has a slightly lower index of refraction (i.e. less dense) than the core. This lower refractive index causes the light in the core to reflect when encountering the cladding and remain trapped within the core.

Fiber core cladding and buffer coating

Fiber core cladding and buffer coating

Buffer coating: This is removed during stripping for splicing or connectorization and acts as a shock absorber to protect the core and cladding from damage.

Cable Jackets: Polyethylene (PE) is the material of choice for use as an Outside Plant (OSP) cable jacket. The performance of raw PE can degrade rapidly through exposure to sunlight. For this purpose, Carbon Black is combined with the PE and is used to absorb the UV light and subsequently dissipates. Jacket colors other than black are used for reasons of enhancing identification.

Cable jacket and buffer coating

Cable jacket and buffer coating

  Cable jackets shall be marked with manufacturer’s name, month and year of manufacture, sequential meter markings, fiber type, the number of fiber’s, along with a telecommunications handset symbol. Cables without these markings will not pass inspections and should not be installed.

Strength cable members

Cable GYTA53 _Not afraid of mice anymore

Cable GYTA53 _Not afraid of mice anymore

  Aramid fibers (Kevlar – a very strong, very light, synthetic compound developed by DuPont – is used when a cable is pulled into a duct, with the tension being applied to the Kevlar. The Kevlar is used as a draw string to pull the cable into the duct so as not to put stress on the fibers.
  The term is also used for the fiberglass or steel rod in some cables used to stiffen it. Impact resistance, flexing and bending are other mechanical factors affecting the choice of strength members.

Moisture/Water-blocking

  In a loose tube cable design, a filling compound, water swell-able yarns or gel (a soft, gooey, substance) are commonly incorporated in the cable. This minimizes the chance of water or moisture penetrating the length of the tube in the event that the tube is damaged. When water freezes it expands by approximately 9% – therefore, water in a cable can cause repeated freeze and thaw cycles.

Moisture/Water blocking

Moisture/Water blocking

Micro fiber cables technology

  Since SM fiber was first introduced in the early 1980s, not too much has changed in its basic geometric parameters. The SM core size has remained somewhere between 8 and 10 m – the core / cladding diameter has remained at 125 m. The outside plant (OSP) fiber coating is now either 200 or 250m. Most notably, standardizing these dimensions has greatly improved interoperability and consistency across optical networks.
Micro cables offers a great deal more density. Only a few years ago, a cable diameter of ± 12 mm was required for a 48-fiber cable design. Today, cables with only an 8 mm diameter has a capacity of 144-fibres. This is achieved by using 200m coated fibers. The 200 m coated fiber’s cross sectional area is ±46% smaller than that of the conventional 250 m coated fiber.

EIA/TIA-598B and Microduct colour code

EIA/TIA-598B and Microduct colour code

  The central tube micro cable design also provides the highest fiber density, yielding a relatively small cable OD. The individual fibers are bundled into groups of twelve within the cable’s central tube, and the bundles are easily identifiable with colored binders in accordance with EIA/TIA-598B, “Optical Fibre Cable Colour Coding”.

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