Some kind of transmission medium goes under a colloquial name of fiber-optics. They use luminous signal (not e.g. electromagnetic impulses) for sending information. Glass fibers from 0.4 to 150 micrometers thick, made of silicon dioxide and surrounded by intransparent plastic sheath replace classic copper wires. In a single fiber-optic cables there can be from one to a dozen or so or sometimes even several dozen fibers.
The rule of fiber-optic’s functioning is based on a phenomenon of transferring a light impulse generated by a laser source of light through a quartz fiber, with the use of wave phenomena such as reflection. Like every transmission medium, fiber-optic cabling has its advantages and disadvantages. The following ones can be mentioned as the most essential:
- Very low signal attenuation, amounting in first-class wires to about 0.2 dB/km. It allows sending data without lowering the line bandwidth on a distance to 100 kilometers in a single cabling segment, without a necessity of using additional reinforcing devices.
- Lack of energy emission to the environment, what will significantly reduce signal losses.
- Insensitivity to external conditions such as electromagnetic field, acoustic disruptions, excess voltage in energetic installation, etc.
- A very high bandwidth obtained on long distances, up to 100 Gb with a standard type of fiber-optic cabling. Wires made in xWDM technology, which uses redoubling of a signal sent in a single fiber can obtain a bandwidth up to 1 Tb/s.
- Safety – risk of interception or eavesdropping sent data is practically impossible to realize.
- Considerable sensitivity to mechanical damage.
- Little flexibility of a cable – in the thinnest wires a minimal bend radius cannot be smaller than a dozen or so centimeters. In multi-core cables this radius usually exceeds a value of one meter. It indicates that fiber-optic cabling does not work in applications requiring flexible elastic cables such as LAN, home and office cabling, etc.
- High unit cost of fiber-optic cabling and cooperating devices as well.
- A necessity of strict obeying the rules of constructing cabling segments, connecting wires, making plugs and connections. Any quality negligence has a significant influence on the correct functioning of cabling made this way.
Due to a functioning regulation, fiber-optics (strictly speaking a method of transmitting a luminous signal in a fiber) can be divided into two fundamental groups. These are:
- Single-mode optical fibers – in a single fiber of a fiber-optic there is a single transmitted beam. Its wave has a definite length – most often about 1560 nm. A fiber’s diameter comprises in a range between 0.4 and 10 micrometers (the most common are eight-micrometer fibers). The length of a single cabling segment can amount up to 100 kilometers. The advantage of a single mode fiber is lack of phenomena affecting the weakening or blurring a signal, apart from material dispersion – a phenomenon of different angles of deviation and different wave lengths. This phenomenon can be significantly limited using beams of a maximum monochrome (unfortunately, there is no technology which would enable to generate a perfectly monochromatic beam).
- Multi-mode optical fibers – in a single fiber there are many transmitted beams. Their waves’ lengths amount values from a range between 1545 and 1565 nm. This solution makes the appearance of a mode dispersion (which approximately means blurring of a beam). This phenomenon has a significant influence on obtaining a speed of data transmission and a maximum length of a single cabling segment. Mode dispersion is caused by a way of different length between a transmitter and a receiver, which a beam has to cover, as a result of different angle of beam reflection from a fiber-optic’s sheath and core. A typical fiber’s diameter comes to between 50 and 125 micrometers. In practice, a single segment’s length should not exceed two kilometers. The main advantage of multi-mode optical fibers is their considerably lower unit cost in comparison with the single-mode ones.