The Wonder of Fiber Cable

 

the fiber            cable Wonder of Light

Abstract The optical fiber systems have low attenuation and high signal integrity hence allowing for longer signal transmission intervals than copper-based systems. Minhaj Alam CAD Engineer

What is Fiber Optic Cable?

An optical fiber is a flexible, transparent fiber made by drawing glass (silica) or plastic to a diameter slightly thicker than that of a human hair. Optical fibers are used most often as a means to transmit light between the two ends of the fiber and find wide usage in fiber-optic communications, where they permit transmission over longer distances and at higher bandwidths (data transfer rates) than electrical cables. Fibers are used instead of metal wires because signals travel along them with less loss; in addition, fibers are immune to electromagnetic interference, a problem from which metal wires suffer. Fibers are also used for illumination and imaging, and are often wrapped in bundles so they may be used to carry light into, or images out of confined spaces, as in the case of a fiberscope. Specially designed fibers are also used for a variety of other applications, some of them being fiber optic  sensors and fiber lasers.

 

The major benefits of fiber optic cabling are:

Easy Handling Some communication systems require tens or even hundreds of fibers (such as a metro backbone system). Put fibers in a cable make it very easy to install and maintain.

Protection from damaging forces Fiber optic cables have to be pulled into place through ducts (outdoor) or  conduits (indoor). Pulling eyes are attached to the strength members or cable outer jackets. This is critical for isolating the fibers from the applied pulling forces. Glass fibers cannot endure more than 0.1% to 0.2% elongation during installation.

Protection from harsh environment factors Cable structures protect fibers from moisture (outdoor cables), extreme temperature (aerial cables) and influx of hydrogen into the fiber.

 

Types of Fiber Optic Cable

There are two primary types of fibre – singlemode and multimode.

Singlemode fibre has a much smaller core size of 9 microns and has a single light path and can travel much longer distances of up to 100km. These require more expensive electronics which operate in the 1310 and 1550nm windows and are typically used in longer distance LAN’s, Cable TV and telephony applications.

 

Multimode fibre can carry multiple light rays (modes) at the same time by having varying optical properties at the core; essentially light travelling the shortest path (down the middle) travels the slowest.The larger core simplifies connections and takes advantage of the lower cost LED & VCSEL technologies which operate in the 850nm window. Due to dispersion the range is limited so it tends to be used as premises cabling when less than a kilometre. It comes in two core sizes, 62.5 and 50 microns.

 

Splice Losses of Fiber Cable

What is acceptable dB loss for fiber?

As per the Fiber Optic Association (FOA), the acceptable dB loss for fiber is determined on the basis of what kind of optical fiber cable it is: multimode fiber cable or single-mode fiber cable. The multimode fiber loss is defined around 3 dB per km for an 850 nm light source and 1 dB per km for a 1300 nm light source. Similarly, a single-mode fiber cable experiences acceptable fiber loss of around 0.5 dB per km for 1310 nm optical power source and 0.4 dB per km for 1550 nm optical power source.  

 

 

What is the acceptable loss of the mating of two splice on connectors?

When it comes to designing optical fiber, it is important to balance performance with optical loss. As optical loss is inevitable, there is always a minimum level of acceptable loss involved in various processes. When it comes to mating of two splices on connectors, the acceptable fiber splicing loss is calculated to be around 0.7 to 1.5 dB per connector. In fusion splicing, the acceptable loss is reduced to around 0.1 to 0.5 dB per splice. Hence, it is not surprising to see fusion splicing being preferred in the industry.

 

 

Colour Coding

t would seems that the colour coding, the colour of the jackets and buffers means the characteristics (Fire retardant, Mechanical, Single or Multi mode, Dielectric properties of the sheath…) of the cable. But not all manufacturers adhere to the same standards. The colour coding, the difference of the colour is used to identify the cables, to visual recognize each of them to connect in right order. Table shows the difference of used colours for cables 1-12 fiber strands. In case of more fibers they are indicated with same colours, but with lines or dotted lines.