How to choose your fiber optic Cable?

Table of content

Introduction - What is an optical fiber ?

In this article, we will try to guide you on how to choose your fiber optic cables properly. However, we first need to understand what exactly is a fiber optic cable.

Defintion

An optical fiber is a flexible, transparent fiber made by extruding 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. [1]

 

 

 

 

 

 

Fiber Optic Cable Composition

1- Core
Depending on the fiber, the core can be equal to 9µm (Single mode), 50µm (Multimode OM2/OM3/OM4/...) or 62.5µm (Multimode OM1).

2- Cladding
Providing a lower refractive index at the core interface in order to cause reflection within the core so that light waves are transmitted through the fiber. The cladding usually has a diameter of 125µm

3- Buffer
Offering the first layer of protection of the fiber (against bending and shock).

4- Jacket
Offering the second layer of protection and allowing, based on its colors to specify which type of fiber it is (OMx, OSx).

Single Mode or Multimode?

Many decisions come into play when installing fiber optic cabling. By far, one of the most important questions is whether to install single mode or multimode. This decision has huge implications for your network’s distance, bandwidth, and budget, so it’s vital to understand the differences between these two types of fiber optic glass.
For many of you, new to fiber, multimode fiber may seem appealing because the name implies that more can be sent over the cable. However, “multimode” refers to multiple rays of light simultaneously taking different tracks down the core of the fiber. This characteristic, enabled by multimode’s larger core, actually creates some limitations.

 

 

Indeed, in multimode fiber, light travels down the core, bouncing off the cladding as it goes. As each beam of light has an individual path, each will reach the end of the optical fiber at different times. This spread is called modal dispersion, and it creates limits on data as well as distance. As a matter of fact, the narrower the core, the bigger the bandwidth. This is because you will have less reflection,dispersion... and so received a narrowed impulse which will allow a higher bandwidth.

 

 

If you also want to improve your knowledge about the sources of attenuation in fiber optics, check out our guide dedicated to Fiber Transmission Loss.

For each mode, there are multiple types of fiber, which imply different characteristics. Below you will find a table that provides you with a resume of performance and how to distinguish the different constructions.

Why Use Multimode?

Why bother with multimode if it provides less bandwidth for a shorter distance? The answer is simply related to the cost of single mode.
Today, the total cost of a single mode installation ranges between 1,5 to 5 times the cost of a multimode installation.
This might be a bit surprising as multimode fiber is a tinny bit more expensive.

Indeed, the main source of expense for single mode installation are the transceivers. For single mode you must use an expensive powerful laser. This laser must send a concentrated beam into the 9um core, with enough power to travel long distance and must be able to follow the targeted bandwidth.

Plus, Multimode transceivers consume less power, which can be significant when you have a huge data center, for which you must take into account the cost of power consume by the equipment as well as the cost to cool down your data center.

 

 

Physical Contact

With physical contact, the connector's 2 ferrules are placed against each other, aligning the cores, enabling the wavelength to pass through both connectors.

There are multiple types of PC connectors: Flat, PC, UPC, APC.

• Where the FLAT connector are simply flat/perfectly vertical, leaving a small air gap between the 2 ferrules.
• Where the PC connector is similar to the Flat Fiber connector, but is polished with a slight spherical (cone) design to reduce the overall size of the end-face. Decreasing the air gap, resulting in lower Optical Return Loss (ORL).
• Where the UPC connector (Ultra PC) is a PC connector with an extended polishing method that creates an even finer fiber surface finish, decreasing again the ORL.
• Where the APC connector (Angle PC) is a PC connector with a small 8° angle, allowing an even tighter connections.