Multi-mode Optical Fiber in Telecommunication Network

Multi-mode optical fiber in telecommunication network : It is often asked where multi-mode optical fiber is used in telecommunication or used for which purpose in telecommunication network. Today we will discuss this issue in particular and we will specifically discuss where and how multi-mode fiber can be used in FTTH network.

This article will cover the minimum standards and requirements for the construction, properties, testing of Multi-mode Graded Index Optic Fiber cables to be used in the telecommunication network.Manufacturers of multi-mode optical fiber claims for longevity and performance of their cables internal plastic components (such as secondary coatings and conductor insulation) with due regard for the installation requirements of the telecom industries.

Multi-mode optical fiber

Multi-mode Optical Fiber in Telecommunication Network

Description of Multi-mode optical fiber 

Multi-mode optical fiber cable specified is for use underground or indoors network, as a transmission medium for carrying modulated Light signals on short to medium distance junction routes.

When purpose for the direct burial, the multi-mode fiber cables shall be protected with an outer sheath of high density polyethylene.

When purpose for indoor installation, the cable shall be provided with a halogen-free sheath. Multi-mode optical fiber design depend upon the purpose and network type.

Design of Multi-mode optical fiber

Multi-mode fiber cable shall withstand a minimum pulling force of 1kN. The minimum bending radius of the cable shall be 20 times the outer cable diameter during installation (Dynamic load). The minimum bending radius of the installed cable shall be 15 times the outer cable diameter. It is the intention to perform the cable splicing operation above ground where possible.

For the FTTH purpose multi-mode fiber cable shall be light, flexible, and easy to install. The optical fiber shall consist of a Multi-mode, graded index, glass core/glass cladded fiber. Multi-mode optical fiber shall be designed and manufactured on 50/125 μm diameter.

The nominal fiber core diameter shall be 50 μm . The maximum tolerance shall be ± 3 μm. The nominal fiber cladding diameter shall be 125 m. The maximum tolerance shall be ± 3 μm. Core and cladding non-circularity shall be less than 0.06. The core eccentricity shall be less than ± 3 μm.

Primary Coating of Multi-mode optical fiber

The primary coating shall consist of a heat or UV cured .acrylic material, or other similar substance. The primary coating shall be easy to remove. Any chemicals required to soften the coating for removal shall be readily available, safe to use and shall be a non-irritant to the user.

Secondary Containment of Multi-mode optical fiber

The secondary containment shall be designed so as to accommodate elongation of the cable or fibres due to temperature changes etc. without causing damage to the fiber, or increase in the loss of the fiber due to micro bending or tension. 

The containment shall consist of a plastic "loose" tubing. The secondary containment shall be removable without damage to the fiber, to permit access to the fiber itself for jointing purposes.

The loose tube secondary containment consist of Polybutylene terephthalate (PBTP), Polyamide, Polypropylene.

The primary coated fiber, or the secondary fiber containment and all fiber groups shall be numbered or color-coded to ensure ease of fiber identification.

Strength Members in Multi-mode optical fiber

The strength member shall normally be made from a single solid steel wire. For special purposes, the cable may be ordered as non-conductive. If the construction is not to contain any metallic elements, the strength member shall consist of a fiber reinforced plastic based on aramide cord or similar non-conductive, high tensile strength, low elongation material.

Polyethylene Sheath -PE or Halogen Free

The multi-mode fiber cable shall be supplied for with either- a polyethylene (PE) sheath for outdoor installation or a flame retarded halogen free polyethylene co-polymer sheath, for indoor installation.

The average thickness at any cross-section shall not be less than 90 % of the specified thickness. The minimum spot thickness shall not be less than 70% of the specified thickness.

You can also READ : Why multimode optical fiber commonly not used in telecom?

Multi-mode optical fiber Sheath Marking

Length Marking: Sequentially numbered length markers shall be placed at regular longitudinal intervals of not more than one meter on the out side sheath. Continuous sequential numbering shall be employed for any single length.

The numbers shall be not less than 3.0 millimeters in height and spaced to produce good legibility. The number shall be of a clearly distinguishable contrast marking.

The accuracy of the length marking shall be within 1 %. An occasional illegible marking is permissible if there is a legible reading on either side of it. The high count length marker shall be on the outer end of the cable when drummed.

PE sheathed cable : The word "DUCT" shall be permanently impressed at longitudinal intervals of not more than 500 mm on the PE sheath.

HDPE 'sheathed cable : The symbol of a telephone hand set shall be permanently impressed at longitudinal intervals of not more than 500 mm on the HDPE sheath.

Halogen free sheathed cable : The word "H FREE" shall be permanently impressed at longitudinal intervals of not more than 500mm on the Halogen free sheath.

Metal Free Cable : Should the cable not contain any metallic elements additional text shall be impressed as follows - "M-FREE".

Cable transmission mode : The letters 'MM' (abbreviation for multi-mode) shall also be impressed on the outer sheath.

Multi-mode optical fiber wavelength

Optical properties 

Multi-mode optical properties

The nominal value of the maximum theoretical numerical apperture shall be equal to or more than 0.19 and shall be stated by the manufacturer. The maximum deviation shall be no more than 0.02 from value specified by the supplier.

The nominal value of the theoretical refractive index shall be in the range of 1.4 to 1.5, it shall be stated by the manufacturer and shall provide the maximum coupling between cable and terminal equipment.

The tensile strength of the fibres shall be a minimum of 400 MPa. The primary coated fiber shall withstand at least 0.6 % elongation during 0.1 sec. at 20 ± 2°C and R.H of 70 % . Breakage shall be lower than 1% per kilometer fibre length.

Polyethylene Sheath  For Outdoor Installation

The sheath (s) shall provide the cable with a tough,, flexible, protective covering, able to withstand exposure to sunlight, temperature and stresses expected during storage, normal installation procedures and whilst in service, under the conditions to local area atmosphere.

The median of the measured values of the PE tensile strength shall not be less than 12.5 MPa. The median of the measured values of the HDPE tensile strength shall not be less than 15 MPa.

The polyethylene shall contain 2.5 ± 0.5 % of well dispersed carbon black. Compliance shall be checked.

Integrity Test of Multi-mode optical fiber

The force required to peel the aluminum foil from; the sheath shall not be less than 0.8 N/m. The water vapor permeation rate shall not exceed 0.13 x D expressed in g/100m/week. (where D is the internal diameter of the sheath in millimeters).

A 3m length of cable shall be supported horizontally and a 1 meter head of water, containing a sufficient quantity of water soluble fluorescent dye for the detection of seepage, shall be applied to the core for 24 hours at a temperature of 20°C + 5°C.

If water leakage is detected, one additional sample from the same reel of cable shall be tested. If this sample exhibits water leakage the entire reel of cable is to be rejected. If the sample exhibits no leakage, the entire reel of cable is considered acceptable.

Halogen Free” sheath integrity

The PE sheath shall withstand a spark test voltage of at least 8 kV r m s or 12 kV d.c. All cables shall be capable of holding pressure to determine that the sheath contains no holes or weak points.

Tensile Performance Test

The tensile force shall be applied to the test sample in 200 N increments, at a jaw speed of 40mm/min.The resultant plot shall include tensile force and elongation as the test parameters. (The test shall be halted at 3kN, or when a cable element fails).

Packing and Cable Drum of Multi-mode optical fiber

The cables shall be supplied on drums in lengths as specified at the time of tender. Each length of cable shall be wound on a separate drum unless otherwise specified or agreed to by the Telecom Company.

The diameter of the drum barrel shall be large enough to prevent damage to the cables during reeling or unreeling. In no event shall the diameter of the barrel be less than 40 times the outside diameter of the cable.

The drums shall be substantial and constructed so as to prevent damage to the cables during shipment and handling . Lags or other suitable means of protection shall be applied to the drums to prevent damage to the cables during shipment and storage. Nails and staples used in the construction of the drums must not be placed in a position where they can damage the cables. The drums shall be non-returnable.

The spindle hole shall allow use of a 75mm spindle without binding.The drum size, including lags, shall not exceed 2.72 meters in diameter and 1.5 meters in width.

Marking on Cable Drum of Multi-mode optical fiber

Details given below shall be distinctly marked in a weather proof material on both outer sides of the drum flanges-

➤Name of Telecom Company .
➤Arrow showing the direction the drum shall be rolled
➤Country of origin .
➤The label, "CAUTION-OPTICAL FIBER CABLE- NOT TO BE LAID FLAT".
➤Manufacturer's name or trademark
➤A mark indicating the location of the inner end of the cable.

Last Word

Friends, I have tried my best to provide complete information about multi-mode optical fiber. Full details of where multi-mode optical fiber can be used in telecommunications are given. Information about what will be the parameter and specification of multi-mode optical fiber is also given.

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