Optical-fiber Technology

Optical-fiber Technology - modes

Optical fibers are divided into single and multi-mode. This division results from the number of dispatched modes (rays of the light beam). Optical fiber modes are characteristic of the fiber and they determine layout of the field and the physical shape of the light beam settling in the optical fiber. The increased value of the light refractive index in core`s axis in relation to the surrounding coat makes the light beam, led through an optical fiber, has a tendency to remain directly in the core. Singlemode optical fiber operates in 1310nm and 1550nm transmission windows, while value of the dispersion is lowest for 1310nm window. Single mode optical fibers with displaced dispersion are optimized for operation in 1550nm transmission window and they provide a wider band for carrying a singlemode optical fiber in the same window. This allows for construction of longer sections of optical fiber lines without the necessity to use signal regeneration (100-150km). Singlemode optical fibers are used in far-reaching and local networks, especially for co-operation with transmission systems with high multiplicity, guaranteeing low signal suppression and broad industrial band.

The most often used optical fiber is the one with step refractive index in which only one mode can be propagated, the so-called basic mode.

The lower the V value, the less modes lead the optical fiber. The one-modity condition of the fiber is for the V to be V < 2,405. In order to retain this condition, a single-mode optical fiber has to have a sufficiently small ray of the core, small difference of the refractive indexes and a great length of the carried wave. As only one mode is propagated in a single-mode fiber, it is devoid of inter-mode dispersion. Only this type of fiber is currently used in far-reaching optical fiber communication.

When the FITL?

When various services are required, that is installation of only one integrated optical network instead of a few specialized ones. Moreover, at present investing only once in optical fiber cables, the devices and the service is legitimate. When the existing network contains copper wires, their change into an optical fiber is a safe investment for the moment and for the future. Due to economical reasons, it is not currently legitimate or profitable to use optical fiber connections in the whole area of the access network up to subscriber`s terminals themselves. However, the range of usage of optical transmission in access networks is constantly expanding.

Basic advantages to be obtained when using FITL technology:

- decrease of the total investment expenditure on subscriber`s network, as we deal with one integrated network for all of the services;
- decrease of network supervision and management costs - greater durability of the optical fiber cable in comparison to copper cables, easier maintenance and repairs of an integrated network, common network supervision system;
- thanks to high physical redundancy of optical fiber lines (from over a dozen to several dozens of fibers in one cable) interference of numerous services on offer is possible, as well as avoiding limitations in introduction of new broadband services in future;
- various capacities offered in particular solution options (FTTC/B/H), combined with reach of about to 20 kilometers, allow for application of FITL systems in areas with a varied level of subscriber`s concentration, as well as with a varied demand of the services.

See also: Optical-fiber Technology Optical-fiber Technology - Architecture