Optical fiber application and system design

Human society has now developed into an information society, and the exchange of information such as voice, image and data is very large. The previous means of communication can no longer meet the current requirements, and optical fiber communication has been widely used due to its advantages of large information capacity, good confidentiality, light weight, small size, and long distance without hops. Its application fields cover communication, transportation, industry, medical, education, aerospace and computer industries, and are developing to a wider and deeper level. The application of light and optical fiber is bringing profound influence and change to human life.

Optical fiber network system design:

The design of an optical fiber system generally follows the following steps:

1) First of all, find out what kind of network is to be designed, what is its current situation, and why fiber optics are used.

2) According to the actual situation, select the appropriate optical fiber network equipment, optical cables, jumpers and other items for connection. Selection should be based on availability, and then based on performance, price, service, origin and brand.

3) Determine the route of the line according to the customer's requirements and network type, and draw the wiring diagram.

4) When the route is long, the attenuation margin of the system needs to be calculated. The calculation can be carried out according to the following formula:

Attenuation margin = transmitting optical power - receiving sensitivity - line attenuation - connection attenuation (dB) where line attenuation = cable length × unit attenuation;

The unit attenuation has a great relationship with the quality of the fiber. Generally, the single mode is 0.4~0.5dB/km; the multimode is 2~4dB/km.

Connection attenuation includes welding attenuation joint attenuation. Welding attenuation is related to welding methods and the quality of personnel. Generally, hot melting is 0.01~0.3dB/point; cold melting is 0.1~0.3dB/point; joint attenuation has a great relationship with the quality of the joint. Usually 1dB/point. The system attenuation margin is generally not less than 4dB.

5) If the calculation is unqualified, the design should be modified according to the situation, and then calculated. This situation may sometimes repeat several times.

Design example:

Transformation of a campus network:

According to the situation, a three-port repeater (twisted pair-optical fiber-slim cable) is used on one side of the existing thin cable network, and a twisted pair HUB with optical fiber backbone is used on the other side. In the middle, an overhead or buried 4-core outdoor multimode optical fiber cable of bundled tube type is used, and then it is spliced ​​into an indoor jumper with ST head (because the optical fiber interface of the equipment is ST type).

Attenuation calculation: (Generally, multi-mode equipment does not need to be calculated within 2km, here is just an example)

Transmit power: -16dBm

Receive sensitivity: -29.5dBm

Line attenuation: 1.5km×3.5dB/km=5.25dB

Connection attenuation: The attenuation of 2 connectors is: 2 points × 1dB/point = 2dB

The two points of welding are: 2 points×0.07dB/point=0.14dB

Attenuation margin=-16dBm-(-29.5dBm)-5.25dB-0.14dB-2dB=6.11(dB

After the above calculation, it can be seen that the system capacity is greater than 4dB, and the above options can meet the requirements.