Working with fiber optics: not as scary as it seems.

Everyone has heard many times about the difficulties in the work, about the need for highly qualified specialists. Many believe that welding of fiber optics and installation of equipment using fiber optic cable is a risky process that requires expensive materials and highly paid employees, that it is not for them. But the market offers a large number of tools and equipment for cutting and installing cable, which greatly facilitates the work of installing fiber optic cable. This article is devoted to this issue.

We regularly hold seminars on fiber optic data transmission systems. And when communicating with listeners, we often encountered a situation when people are ready to use these systems: they have projects, the advantages of the solution prevail over the cost — that's it, set up and deliver the project, get money and confidence that the customer will not have any complaints about the quality of the work performed. But the fact that specialists have no experience working with such equipment stopped them. Everyone has repeatedly heard about the difficulties in the work, about the need for highly qualified specialists. Many believe that welding fiber optics and installing equipment using fiber optic cable is a risky process that requires expensive materials and highly paid employees, that this is not for them.

In fact, working with fiber optics, although it requires certain experience and skills, but developing them is not such a difficult task. Especially since the market now offers a large number of tools and equipment for cutting and installing cable. This article is devoted to this issue.

Introductory information
One of the main requirements when working with fiber optic cables is careful attention to all stages of the cable system installation process: laying, cutting, connecting and terminating. A mistake costs a lot — these are the costs of finding the damage site and replacing a section of the cable. Replacing a damaged section not only increases labor costs, but also reduces the quality of the entire system: each connecting element, each soldering introduces its own distortions into the transmitted signal, reduces the signal transmission distance, and requires an increase in the optical budget of the system.

For specialists who are just starting their work on fiber optic installation, it is recommended to purchase a ready-made set of basic tools and materials necessary for the work: containers, dispensers, distributors, consumables and protective equipment. After some time, when you get basic skills in working with fiber optic cable and form preferences in the variety of tools and materials used, you can combine the set «for yourself».

Cutting fiber optic cable
A fiber optic cable consists of several optical fibers, which together with reinforcing threads are enclosed in a protective polymer sheath. To protect against aggressive external influences, the cable is placed in armor protection made of corrugated aluminum or steel protective tape or steel wire. Due to the fact that optical fiber is quite sensitive to axial and radial deformations, inexpensive cable cutters used to work with copper cables are not suitable for cutting it. It is recommended to use a tool with blades designed for cutting steel.

The initial stage of cutting fiber-optic cables is the removal of the upper layer of protective and armor coatings, which is performed with the same tools as cutting conventional cables. Polymer insulation and foil are opened with cutters, and steel wire is cut off with side cutters. It is recommended to use cable knives: they allow you to remove the polymer coating from a cable with a diameter of 4 to 35 mm, and at the same time, the cable knife has a special attachment that limits the depth of the cut of the shell, which eliminates damage to the fiber optic cores.

But in further work, you still cannot do without special tools:
* scissors or nippers with ceramic blades are used to remove reinforcing threads from Kevlar. Conventional scissors do not cut these thin, flexible and strong fibers, but squeeze or bend them;
* strippers are designed to remove the buffer layer. Their use reduces the risk of damaging the optical fiber: first of all, because its working surfaces have a fixed setting;
* a fiber optic cleaver is used to cut off excess fiber at an angle of 90 degrees. Cleavers can be manual or automatic. When preparing fiber optics for subsequent welding or splicing, it is recommended to use automatic cleavers, which allow you to get a clean and smooth cleavage without defects at an angle of 90 ± 0.5 degrees. For example, a cleavage with an angle of more than 2 degrees can lead to an increase in connection losses of up to 1 dB, which, with an overall optical budget of the system of 15-25 dB, is often an unaffordable luxury;
* microscopes allow you to diagnose optical fiber connectors for the quality of core polishing, the presence of cracks, scratches;
* crimpers are designed to crimp tips, connectors and contacts.

Connecting fiber-optic cables
There are three widely used methods for installing fiber optics:
* welding of optical fibers;
* connection using mechanical connectors;
* connection using a splice.

Welding of optical fibers
Welding of fiber optics is carried out using special welding machines and is usually performed in three stages:
* preparation and stripping of cable, obtaining a high-quality end;
* welding with a welding machine;
* testing and evaluation of the quality of the connection.

The welding machine performs the connection of optical fiber with good parameters of the connection point simply and quickly. Modern welding machines allow to reduce losses at the connection point to 0.04 dB and less. The device automatically performs all necessary operations: aligns optical fibers, melts the ends of optical fibers, welds them. The most functional (but, unfortunately, more expensive) models also check the quality of the connection. After that, the welding point is protected, usually with a heat-shrinkable tube.

Connection using mechanical connectors
Optical fiber splicing is also used when terminating fiber with connectors. For these purposes, ready-made fiber-optic jumpers are used — pigtails (English: Pigtail — flexible conductor). A pigtail is usually manufactured in a factory, it is a section of fiber-optic cable that has an optical connector on one side. The fiber of the optical cable is spliced with the fiber of the pigtail, and then it is connected to the equipment using a connector.

Connection using a splice
A splice is a device for joining fiber-optic cables without welding. The prepared ends of optical fibers are inserted into the splice through special guides towards each other and fixed in it. To reduce insertion losses, the joint between the fibers is placed in a special (immersion) gel, which is often located inside the splice.

The technology of splicing includes several stages:
* cutting the fiber-optic cable;
* processing the ends;
* making the connection;
* testing and evaluating the quality of the connection;
* applying protective coatings, restoring the protective shell and armor.

The use of splices simplifies the process of splicing fiber optics, but working with them requires practical skills. The insertion loss with this method of connecting fibers is less than when using a pair of fiber optic plugs and an adapter, but can still be 0.1 dB or more. According to the requirements of the standards for SCS IS0 11801, TIA EIA 568B, the insertion loss in a splice should not exceed 0.3 dB. To achieve this, the position of the fibers relative to each other is adjusted during installation, and it is also necessary to constantly measure the losses at the connection site during the work.

In addition, it should be taken into account that over time, the losses at the connection site using a splice can increase due to the displacement of fibers in space or drying of the immersion gel.

Author of the article — Karachunsky S.A.,
Marketing Director of the company «B1 Electronics».
The company presents SF&T products — equipment for transmitting various types of signals via fiber optic cable.