Classification of fiber optic communication systems

There are various classifications of optical fiber communication systems. Generally, they are classified in the following ways:

Can be divided into optical fiber analog communication systems and optical fiber digital communication systems.

Optical fiber digital communication systems have more advantages than optical fiber analog communication systems and can better meet the requirements for communication capacity and communication quality that exceed those of the past. The advantages of optical fiber digital communication systems are as follows:

Strong anti-interference capability, good transmission quality. In analog communication systems, noise accumulates along the signal path, and both are inseparable. As the transmission time and distance increase, it is impossible to separate the noise from the signal to restore the original signal. Optical fiber digital communication systems use regenerative repeaters, which do not include amplification of noise. As long as the signal-to-noise ratio is sufficiently high, the noise can be eliminated through a certain threshold, and the original signal can be regenerated.

Can use time division multiplexing with long transmission distance. Optical fiber digital communication systems can use different methods to regenerate transmission signals, eliminate noise during transmission, restore the original signal, and extend the transmission distance.

Suitable for transmission of various services with flexible flexibility. In optical fiber digital communication systems, various information such as voice and images can be converted into binary digital signals, which can combine transmission technology and switching technology to facilitate the realization of integrated services.

Easy to achieve encrypted high-speed confidential communication. Only those who understand the correspondence between密钥 (keys) and the decoding method can achieve this confidential communication. It is difficult to steal the confidential information that needs to be designed with encryption methods.

Optical fiber digital communication systems mostly use digital circuits, which are easy to integrate, small in size, and miniaturized, standardized, increasing equipment reliability and helping to reduce costs.

Optical fiber digital communication systems have the disadvantage of occupying a wide frequency band, the system's frequency utilization is not high, the equipment is complex, and the cost is relatively high.

Besides occupying a narrower bandwidth, fiber optic analog communication systems also have advantages such as simple circuitry, no need for analog-to-digital or digital-to-analog conversion, and lower cost. Fiber optic analog communication systems are mainly used for short-distance communication, while fiber optic digital communication systems are mainly used for long-distance communication.

Classification of fiber optic communication systems

Can be divided into short wavelength multimode optical fiber communication systems and long wavelength optical fiber communication systems.

Short wavelength multimode optical fiber communication systems generally operate at wavelengths around 0.85μm, with communication rates below 34Mbit/s and repeater distances within 10km.

Long wavelength optical fiber communication systems can be further subdivided into the following three types:

1.31μm multimode optical fiber communication system: Operating wavelength around 1.31μm, communication rate of 34Mbit/s and 140Mbit/s, repeater distance around 20km.

1.31μm single-mode optical fiber communication system: Operating wavelength around 1.31μm, communication rate of 140Mbit/s and 565Mbit/s, repeater distance of 30-50km (140Mbit/s).

1.55μm single-mode optical fiber communication system: Operating wavelength around 1.55μm, communication rate above 565Mbit/s, repeater distance around 70km.

Can be divided into Plesiochronous Digital Hierarchy (PDH) systems and Synchronous Digital Hierarchy (SDH) systems.

Large-capacity optical fiber digital transmission currently uses Time Division Multiplexing (TDM) technology. Multiplexing is divided into several levels, resulting in three transmission systems: Plesiochronous Digital Hierarchy (PDH) system and Synchronous Digital Hierarchy (SDH) system.

In PDH systems, the bit rates at each level cannot directly correspond to their standard values and have a specified tolerance, which is abnormal. Usually, positive justification methods are used to achieve quasi-synchronous multiplexing, with transmission rates generally below 565Mbit/s.

SDH systems are not only suitable for point-to-point transmission but also suitable for network transmission between multiple points. Currently, practical SDH series systems can achieve single-wavelength communication rates of 2.5Gbit/s and 10Gbit/s.

Can be divided into the following three types:

Low-speed optical fiber communication systems: This type has transmission rates of 2Mbit/s and 8Mbit/s.

Medium-speed optical fiber communication systems: This type has transmission rates of 34Mbit/s and 140Mbit/s.

High-speed optical fiber communication systems: This type has transmission rates higher than 565Mbit/s.

Can be divided into the following two types:

Direct intensity modulation optical fiber communication system: The digital electrical signal to be transmitted is directly modulated in the light-emitting process of the light source, also known as internal modulation optical fiber communication system. This system has relatively simple equipment, lower prices, and higher modulation efficiency, but it will broaden the spectrum and affect rate improvement.

Indirect modulation optical fiber communication system: After the light source emits light, a modulator is added to the light output path for modulation, also known as external modulation optical fiber communication system. This system has little effect on the light source spectral line and is suitable for high-speed communication.