Characteristics and Application of Fiber Optical Communication System

Fiber optical communication is a communication method that uses light waves as an information carrier and fiber optic as a transmission medium. From a principle point of view, the basic material elements that constitute optical fiber communication are optical fiber, light source and photodetector. Optical fibers are usually classified according to manufacturing process, material composition and optical characteristics, in addition, optical fibers are also divided into optical fibers for communication and optical fibers for sensing according to their uses. Transmission media optical fiber is divided into general and special, and functional device optical fiber refers to the fiber used to complete the functions of light wave amplification, shaping, frequency division, frequency doubling, modulation, and optical oscillation.

 

 

1. Features of Fibre Optical

① The amount of information that can be transmitted in a unit time is large. In the early 1990s, the practical information rate of fibre optical communication was 2.488 Gbit / s, that is, a pair of single-mode optical fibers could open 35,000 phones at the same time, and it is still developing rapidly.

②Economy. The construction cost of optical fiber communication decreases with the increase in the number of uses.

③Small size, light weight, construction and maintenance are relatively convenient.

④Use less metal, strong anti-electromagnetic interference, strong anti-radiation, and good confidentiality.

 

 

2. Basic Composition of Fiber Optical

The main components of the conventional optical fiber communication system are optical fiber, light source and photodetector. Optical fibers include single-mode and multi-mode optical fibers, and light sources include semiconductor lasers and light-emitting diodes. Medium and long-distance systems use single-mode fiber and semiconductor lasers, newly developed high-speed system uses distributed feedback (DFB) laser, and short-range systems can use multimode fibers and light-emitting diodes.

The conventional optical fiber communication system refers to a system where the transmitting end performs intensity modulation on the light source, and the receiving end uses a photodetector to directly detect the received optical signal (IM / DD). It is also called intensity modulation direct wave optical fiber communication system. It was actually used in the early 1990s. Its basic structure takes the 2.488Gbit / s system as an example.

The time-division multiplexer at the transmitting end combines the input digital signal of 155Mbit / s into a signal of 2.488Gbit / s. The signal directly -modulates a distributed feedback laser, and then transmits the dimmed output to the single-mode fiber. At the other hand, photoelectric detector detects the dimmed light, and obtains a digital signal of 2.488Gbit / S, and then decomposes the multiplexer to obtain a set of digital signals of 155Mbit / s.

 

 

3. Application Scope

Optical fiber communication was first used between telephone office to form a local optical fiber network, and then as a long-distance communication to form a nationwide optical fiber network, which will become the backbone of a broadband communication network. Later, the submarine optical cable was developed.

The submarine optical fiber communication system is used for cross-ocean communication or short-distance cross-island and coastal communications. The well-known submarine optical fiber communication systems are those across the Atlantic and Pacific. For example, the earliest transatlantic system TAT-8, which began commercial use in December 1988, has 3 pairs of optical fibers in the optical cable, 2 pairs for use, and 1 pair for backup. Each pair of information rate is 280Mbit / s. The total length is 6700km, the average relay station spacing is 67knu and the wavelength is 1.3μm, and the conventional single-mode fiber is used.

Developed countries are planning to design and build fiber optical user networks, namely fiber to the home (FTTH) or fiber to the roadside (FTTC). Other applications are fiber optic local area networks used in various occasions, etc.