Fiber Optic Cables for Access and Last Mile Networks

The growth of Fiber to the home projects around the world demands a variety of optical fiber cable designs for the access network. Each design has its own specific application and features.

The FTTX cables employing the latest bend optimized fiber, BIF, has many requirements to be met in order to make them suitable for FTTx application. The Last mile connectivity to a home or an apartment can be generally divided into the following sections.

The feeder cable from a Central office’s OLT can reach the Fiber distribution hub or Main distribution frame at the building or premise through an underground duct or by aerial drop.

Aerial drop fiber optic cable constructions

From FDH or MDU installed at the building, the cables will run vertically to the floors. Such cables shall meet riser application characteristics, especially that related to fire resistance and low smoke properties of sheath apart from low bend characteristics.

The indoor cables that run horizontally to the customer premise shall be easy to install and connect to the Rosette or Connector box fit at the wall of the customer’s home. From Rosette to the Optical Network Unit, ONU, the communication signals will pass through special fiber optic cables having very low bending properties.

Corning has an excellent bending resistant cable called Corning Clearcurve for indoor wiring. Indoor wiring with fiber optic cable is a challenge to many network installers as the conventional fiber is extremely sensitive to bending. House wiring requires the cables to be bend at curves and stapled to the wall for easy installation. This extreme bend condition induces an attenuation increase in conventional single mode fiber. This problem called for a bend optimized fiber complying with requirements of ITU-T G.657 specifications.

The special environments demand different cable configurations. Some of the cable designs being employed in FTTx applications are shown below for reference. These designs are with single mode fiber, optical fiber ribbon, and tight-buffered single mode fiber, etc. The strength members used in these FTTX cables vary from steel wires to Fiber-reinforced plastics, FRP, or Kevlar FRP, KFRP.

Fiber to the home cable constructions

The core structure can be purely dry, loose tube structure or tight buffer design. Aramid yarns can be used to house the fibers at the core. The sheathing materials shall meet the fire resistance properties to make these cables suitable for Fiber to the building, fiber to the home, Fiber to the premise applications.

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