To unite networks located in different buildings into a single information space, you cannot do without the construction of trunk cable lines. Depending on the required data or signal transmission speed, the distance between the ports of the active equipment for the trunk, various technologies and data transmission media can be used: coaxial cables, twisted pair cables, optical cables and wireless technologies.
From a functional point of view, when the distance between networks is more than 150 meters, and when it is required to transfer data over 10 Mbps, the best option today is the use of optical cables and the construction of fiber optic communication lines (FOCL). The data transmission medium in the FOCL is an optical fiber (optical fiber).
When constructing a trunk in SCS, standards allow the use of two types of optical fibers:
- Single-mode optical fiber
- Multimode optical fiber
The advantages of using optical cables are obvious, this is a wide bandwidth, currently limited exclusively by the capabilities of terminal equipment, a low attenuation level that allows you to use a communication line at a distance of several tens of kilometers without amplifying the optical signal, good information security that cannot be read from the line without violating its integrity, and much more.
But FOCL also has drawbacks, one of which is some difficulties in connecting individual sections of the cable. And one of the most important jobs after laying the cable, requiring the presence of highly qualified specialists at the company, is the connection of optical fibers.
Today, there are many technologies for connecting optical fibers. In this article we will consider two of them, this is arc welding, carried out using a welding machine and mechanical connection inside a special coupling, splice.
Optical Fiber Welding
A special welding machine is used to weld optical fibers. This is a complex device containing a microscope used to align the fibers, clamps with v-grooves for reliable fixation of the fibers and micro products used to automate the process, arc welding, a shrink chamber for heating the thermowell, a microprocessor used to control the device and the system quality control.
The process technology for welding optical fibers consists of the following steps:
- Removing the shells using a stripper of a buffer layer, a tool designed to work with fibers of various diameters.
- Fiber preparation for welding. First, a heat shrink sleeve is put on one of the ends, which is necessary to protect the welding site. Then the stripped ends of the optical fibers are degreased with a lint-free cloth soaked in alcohol. After degreasing, the fiber end is chipped off with a special device, a cleaver. The cleaving angle should be 90 ° ± 1.5 °, otherwise, inhomogeneity will form at the weld site, leading to large attenuation and back reflections. After cleavage, the optical fibers are placed in the welding machine.
- The fibers in the apparatus are aligned. If the apparatus is automatic, then it itself estimates the cleavage angle, aligns the fibers relative to each other and, after confirmation from the operator, conducts the welding process. If the device is non-automatic, then all these operations are carried out by a specialist manually. In the process of welding, the fibers are heated and melted by an electric arc, then combined, and the place of welding is additionally heated to eliminate internal stresses.
- Quality control of welding. An automatic welding machine analyzes the images obtained from the microscope and gives an approximate estimate of the level of losses. More accurately, the result can be estimated using an optical reflectometer, a device that allows detecting inhomogeneities and the degree of attenuation along the entire line.
- Welding point protection. A thermowell, clad at one end of the cable, moves to the weld point and is placed in a heat shrink oven for about a minute. After cooling, the sleeve is placed in the protective splice plate of the coupling or optical cross, where the technological stock of fiber is laid.
Mechanical Fiber Optic Splice
For the mechanical connection of optical fibers, a special device is used, a splice. The splice consists of housing through special channels and guides, the chipped ends of the fibers are introduced into. The guides serve for the precision joining of the ends in a chamber filled with immersion gel, which is necessary to minimize transient attenuation and tightness of the joint. The refractive index of the gel is close to that of the fiber core, which minimizes the back reflection. The top is closed by a lid.
The technology of the process of fibre optic splicing using mechanical splice consists of the following steps:
- The ends of the fibers are cleaned, degreased and the ends are chipped off. The tolerances on the chipping angles are also very tight. The difference between a mechanical splice and a welded splice is that it does not require the use of a heat-shrink sleeve since the mechanical splice performs the function of mechanical protection of optical fibers.
- The prepared ends of the fibers are introduced from different sides through the side channels of the splice into the chamber filled with immersion gel. The fibers are introduced before mutual contact. After insertion, the splice lid closes and securely fastens the joint.
- The assembled splice is installed on the splice plate of the coupling or cross, along with it the technological stock of fiber is laid. The fibre optic cable installation contractors are used in this.
- The quality of the mechanical connection can be checked with an optical tester or OTDR.
Comparison of the Use of Welding or Mechanical Bonding of Optical Fiber
Each of the two methods described has its advantages and disadvantages.
- The advantages of welded joints include low transient attenuation, high reliability and fast fiber bonding. The disadvantage is the high cost of equipment (welding machine), the presence of a qualified operator, the need for a larger area for work, and the power (or recharging) of the welding machine.
- The advantages of mechanical bonding are simplicity and low installation time, shorter fiber stock, the disadvantages are a higher level of transition attenuation.
Bottom Line
It makes sense to use a welded joint when building long sections of highways. In cases requiring high-quality lines, for example, when building high-speed fiber optic lines for data centers, where low attenuation and back reflection parameters are required. Splicing using a mechanical splice is most often applied for temporary connections, for example, for urgent repair of cable damage, for installation of low-budget lines and when working in hard-to-reach places.
