When installing fiber-optic communication lines, one of the main processes determining the degree of communication distribution and its effectiveness is the installation of optical fibers. During the work, the fibers are combined with each other and the cables are laid.
Reinforcement, which provides mechanical safety of the joint and fastens compatible fibers, called optical fiber connectors. The main conditions that the connectors must meet are:
- the triviality of the structure;
- reliability of fastening;
- minimal losses;
- resistance to environmental factors.
There are two types of losses that follow the combination of fibers: internal and external.
Internal losses relate to the characteristics of the fiber itself and are caused by differences in core diameter.
External losses are due to the connection method, as well as the processing of the ends of the optical fibers. The end spacing, the angle of inclination of the fiber end, the transversality of the core, the Fresnel reflections, and the axial inclinations are important.
Internal Fiber Loss
The consequence of combining different fibers, which, as a rule, have unequal numerical apertures and diameters, becomes internal losses.
Losses in the area of the docking boundary are of zero value subject to the rectilinear propagation of light energy. In the opposite case, the region of peripheral light rays is displaced into the sheath of the fiber having a smaller diameter, and then is lost.
In the framework of single-mode optical fibers, internal losses occur regardless of the direction of displacement and are caused solely by the difference in the diameters of the mode field of the connected fibers.
The non-concentric arrangement of the core in the reflective cladding zone is considered another source of loss. Thus, the core of the fiber changes its location with respect to the center of the fiber itself. Other losses may be caused by an imperfect cross-sectional shape of the fiber in the wire zone.
The difference in fiber cladding diameters is another cause of internal loss. This may occur with mechanized fiber alignment.
External fiber loss
There are 4 known reasons that provoke external losses:
- end zone quality;
- corner transition;
- radial transition;
- axial transition.
In the connecting zone, the fiber is located in the central axial part. In the case where the central axis of the fibers do not coincide, losses occur due to the radial transition. If the alignment diverges due to the gap (axial transition), the fiber is faced with other types of losses.
The exponent R is calculated by dividing the power of the reflected wave by the power of the input wave and describes the reflection at the interface of two media.
Chipped fibers must be located perpendicular to the axes and parallel to each other when combined. The degree of loss in the angular transition caused by the divergence of the fibers relative to each other is determined through the parameter of the numerical aperture.
Fiber optic mounting
During installation and connection of the optical trunk, a stationary combination of various sections of the wire is made. When installing a wok in a room, connectors are used that look like detachable connectors. The operation of combining fibers is carried out according to a certain algorithm. Initially, the end parts of the fibers are processed, then docking begins.
Before connecting the optical fibers, it is necessary to prepare the end parts of the optical fiber: the first protective layer is removed from the fibers, the flat end face is processed by grinding or chipping. To remove the first layer, it is necessary to apply not only chemical, but also mechanical methods of removal.
The preparation of the end portion of the optical fiber associated with a break is called spalling. The fiber cleavage should be perpendicular. Possible deviations cannot reach more than 2 degrees.
If there are discrepancies between the connecting fibers (having smooth and flat end parts), a certain amount of light rays returns to the original source and forms a return loss. Giving the ends of the fibers round in shape during grinding allows you to reduce return loss.
The connection is made by mechanical splicing, as well as welding. The main tool is an electric arc, which is formed between the electrodes. Welding machines differ in the way they work: they can be automatic, semi-automatic, or manual. The mechanical connection has two different forms: passive and active. The shape depends on whether the fiber is smoothed to reduce losses.
In the process of mechanical joining, 3 main techniques are used:
- rotatable splices from AT&T;
- guides (4-rod) firms TRW;
- GTE elastomeric splices.
The main method of combining a fiber optic line with an active network device is to use connectors, that is, connectors that are spliced by a special optical adapter inserted into the cross. Here the fiber is digested, the ends of which are equipped with pigtails and connectors.
A fiber optic connector is a mechanical device that is used for regular alignments. It allows you to quickly reconfigure devices, explore the fibers and connect them to the primary light sources. An optical connector for combining single fibers has two important details - the connector itself and the plug.