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Fiber Optic Construction

Optical fibers are circular dielectric wave-guides that can transport optical energy and information. they have a central core surrounded by a concentric cladding material. A protective coating is used to reduce cross talk between adjacent fibers and loss-increasing micro-bending that occurs when fibers are pressed against rough surfaces. To provide further protection, fibers are commonly incorporated into cables.

A fiber Optic cable consists therefore of the following components: Core, Cladding, Coating, Strength member, and Cable Jacket. As shown below.

cable-structure-ceo1

Core

This is the very center of the cable and is the medium of propagation of the light wave/optical signal. It is made up of silica glass/plastic with high index of refraction;typical core diameter ranges from 8 microns for single mode fiber up to 1000 microns for Plastic Optical Fiber (POF).

  • Hollow Core Optic fiber

In almost every fiber-optic network, light travels through plastic or glass fibers — in hollow core optic  fiber (which is the latest invention), light travels through an air gap, allowing for networks that are faster, have more bandwidth, and traverse greater distances.

In a vacuum, the speed of light is 2.99792458 x 108 m/s; approximately 3.00×108 m/s, approximately 186,282 miles/s. In air for visible light which has an index of refraction 1.003, it is about 299,700 kilometers (186,200 miles) /s while the  same light travelling through glass of index of refraction 1.5, will travel at a speed of 200,000 kilometers (120,000 miles) /s. This tells us that the light is fastest in a vacuum, faster through air and fast glass.

Therefore, the hollow-core optical fiber allows light to travel along its length at around 99.7% the speed of light in a vacuum, or a 30% improvement over conventional (silica glass) optic fibers. The light will travel through hollow tubes.

These hollow-core fibers have lower signal loss (allowing for longer distances between repeaters), and the increased speed of light through an air gap(about 30% faster than plastic/glass) reduces latency. 

Cladding

The cladding is made of a silica glass/plastic material just like the core but of a lower refractive index. The difference in index of refraction forms a mirror at the boundary of the core and the cladding; and because of it’s lower refractive index compared to that of the core, it reflects the light back into the center of the core.

This is the phenomenon of total internal reflection which occurs when a light wave is moving from a denser medium (high index of refraction, e.g water) to a less dense medium (lower index of refraction, e.g air); and the angle of incidence is greater than the critical angle.

The cladding together with the core form a single solid strand of fiber, either glass or plastic. Total internal reflection in the fiber, as a result of the properties of the core and cladding, thereby guiding the light wave down the fiber makes it a wave guide.

Buffer Coating

A buffer is something that reduces shock or forms a barrier between adversaries.

buffered-fiber

The buffer coating is a protective layer surrounding the cladding. Typically it made up of a thermoplastic material for Tight Buffer Fiber Cables and a Gel material for Loose Tube Fiber cables.

Loose tube cables are designed for harsh environment conditions in the outdoors. They protect the Fiber core, cladding, and Coating by enclosing everything within fairly rigid protective sleeves or tubes. Many loose tube cables contain a water resistant Gel surrounding the fibers. The gel helps protect the fibers from moisture, making the cables ideal for high humidity environments, where water or condensation may otherwise be problematic. The gel filled tubes can expand or contract with temperature changes, as well. Despite the benefits, gel filled loose tube cables are not the right choice if the Cable needs to be submerged in water, or routed around multiple bends. Excess Strain may cause the fibers to emerge from the gel.

On the other hand, Tight buffered cables are optimal for indoor applications. Being more robust than loose-tube cables, they are best suited for moderate length LAN or WAN connections, long indoor runs, direct burial, and for underwater use. Rather than using the gel Layer loose tube has, tight buffered cables have a two-layer coating. The first is plastic, and the other, waterproof acrylate. The Acrylate keeps moisture away from the cable. The Core is never exposed when bend or compressed underwater. Tight buffered cables may be easier to install, because there is no gel to clean up and it does not require a fan out kit for Splicing or termination.

Strength member

This further protects the fiber from over stretching during installation; also from expansion and contraction due to temperature changes.

In single and double fiber cables, the strength members are wrapped around the coating; while in multi strand cables, the strength member is in the center of the bundle

Cable Jacket

This is the last item on the construction. It provides the final protection from the environment in which the cable is installed. Of concern is the intended placement of the cable. Different jacket suite different environments/ solutions such as indoor, outdoor, aerial or buried installations.

Please thank you for reading, I hope it was worth it. This is the beginning of yet many articles on telecommunications. Add your views on the comments section.