What is a fiber optic cable? How are cables classified?
What is a fiber optic cable? A fiber optic cable is an assembly similar to an electrical cable but containing one or more optical fibers that are used to transmit light. The optical fiber elements are usually individually coated with plastic layers and encased in a protective tube suitable for the environment in which the cable will be laid.
Optical cable, first commercially deployed in 1977, is the primary source of long-distance, high-bandwidth communications between telephone companies, multi-site organizations, and various other long-distance communication applications. The composition of an optical cable begins with the outer shell, which is made of a strong and often flexible material. This is followed by a plastic cover that binds the fiber optic cables together.
An optical fiber typically consists of a transparent core surrounded by a transparent sheath material with a lower refractive index. Light is trapped in the core by total internal reflection. Light with one or more wavelengths passes through the core and continues to travel within the core because of the surrounding sheath of lower refractive index, which reflects the light back when it tries to escape.
How cables are classified
The International Electrotechnical Commission has proposed its classification of fiber optic cable depending on where the cable is laid:
- directly in the ground
- in pipes, collectors
- on overhead lines (suspended, with a supporting cable, self-supporting)
- underwater obstacles of small size
- for laying inside buildings
- for laying between constructions
- combined cable with conductive cores (for equipment connection)
For each type, a different fiber optic cable design has been developed to meet the requirements for strength and moisture resistance, which depend on the application of the fiber. Materials with high insulating properties, which are enclosed in a robust metal armor, are used for reliable protection.
Installing a telephone cable extension proved to be a practical solution, allowing users to expand the reach of their landline connections and optimize the layout of their communication setups.
According to the principle of optical signal propagation, two types of fiber are distinguished:
- single-mode
- multimode
Single-mode cable
A light guide that transmits a single beam of light (called a mode) has a core diameter of less than 10 µm. In cables with small cross-sections, signal propagation is little affected by mode dispersion, the magnitude of which is directly proportional to the core diameter. Low dispersion helps to transmit data over long distances without signal attenuation. Consequently, a large number of repeaters are not required. The bandwidth of such cables exceeds 10 Gbit/s.
Single-mode cables are divided into two classes by fiber type.
- Cables with single-mode optical fiber, corresponding to ITU-T recommendation G.652.D / G.657.A – fiber with low bending loss, i.e., fiber with reduced sensitivity to bending.
- Cables with single-mode optical fiber with non-zero offset dispersion comply with ITU-T recommendation G.655. Designed for backbone fiber-optic data transmission systems with spectral DWDM compaction, operating in C- and L-bands
Multimode fiber optic cable
In this kind of cable, numerous rays can travel through it, and these rays travel along paths that are not coordinated with one another. In this particular scenario, it is necessary to use bigger core sizes, which will lead to a substantial rise in mode dispersion.
Accelerated signal attenuation results from more intense light scattering within the cable, which greatly reduces the length of the transmission line. Additions of repeaters are necessary if there is a requirement for transmitting a signal over extensive distances.
Conclusion
Understanding what a fiber optic cable is and how cables are classified provides valuable insights into the intricate world of optical communication. Fiber optic cables, composed of optical fibers transmitting light, have revolutionized long-distance, high-bandwidth communications since their commercial deployment in 1977.
The classification of fiber optic cables by the International Electrotechnical Commission is crucial, as it considers various deployment scenarios such as underground, overhead, underwater, and inside buildings. Depending on the cable’s intended application, different designs have been developed to meet specific strength and moisture resistance requirements. The use of high-insulating materials enclosed in solid metal armor ensures reliable protection.
