Theoretical knowledge, components and laying points involved in optical fiber

Optical fiber has become the main means of long-distance wired signal transmission, and the installation and maintenance of optical fiber is also the basic skills of weak current people. There are many theoretical knowledge, components and laying points involved in the optical fiber, and we have made some combing here.

Three kinds of light

Not all light can be used for signal propagation in optical fibers. Three wavelengths of light are mainly used in the light: 850 nm, 1,300 nm, and 1,550 nm.

Where to use it?

The single-mode fiber uses 1310 nm or 1550 nm, and the multimode fiber uses 850 nm.

The difference between single mode and multimode

The central glass core of the multimode fiber is thicker (50 or 62.5 μ m) and transmits light in multiple modes. However, the dispersion between the modes is large, which limits the frequency of the transmission of digital signals, so the distance of the multi-mode optical fiber transmission is relatively close, generally only a few kilometers.

The single-mode optical fiber center glass core is very thin (the core diameter is generally 9 or 10 μ m), and can only transmit one mode of light. Therefore, its intermode dispersion is very small, and it is suitable for remote communication.

The color of the thread skin

A simpler way to distinguish is that the multimode fiber skin is orange and the single mode fiber skin is yellow.

Scattering and loss

In single-mode fibers, 1310 nm light has a minimum dispersion and 1550 nm light has a minimum loss.

So, what exactly is the loss?

1310 nm : 0.35~0.5 dB/km

1550 nm : 0.2~0.3 dB/km

850 nm : 2.3~3.4 dB/km

Light signals have too many enemies

Optical loss is one of the causes of optical fiber signal attenuation. In addition, scattering, absorption and so on can also cause optical fiber signal attenuation.光损耗的原因

• Natural loss of light

• Insertion loss of the inserted optical components in the optical transmission line

• Head loss during optical fiber connection

• The impedance mismatch in the cable makes the light produce a reflection, which is called the echo loss

• The bending, extrusion, impurity and impurity of fiber materials can cause loss

Fiber optic renewal

• Fixed connection, commonly known as the dead joint, generally using optical fiber welding machine, used for optical cable direct head.• Active connector, commonly known as live connector, is connected with a removable connector for optical fiber jumper, equipment connection and other positions.

Fixed joint tips

Secondary discharge fuse shall be used to installing fixing fitting. First, preheat and fire the end face of the optical fiber, shape the end surface, remove dust and debris, and make the optical fiber end surface pressure uniform through preheating.

Light also has noise

In addition to attenuation, the effect of optical fiber information conduction is affected by noise. Attenuation means less useful signals, and noise means more useless signals.

The cause of the resulting noise generation

• The extinction ratio is not qualified

• Random variation in light intensity

• Time jitter caused

• Point noise and thermal noise of the receiver

• Pattern noise of the optical fiber

• The dispersion leading to the pulse broadening

• Mous assigned noise for LD

• The frequency chirp of the LD

• reflect

And dispersion?

Dispersion is also an important factor affecting the transmission of light signals.

Dispersion: the optical pulse after a distance along the optical fiber. It is the major factor limiting the transmission rate.

The cause of the dispersion generation

• Intermode dispersion: It occurs only in multimode fibers, because different modes of light are transmitted along different paths.

• Material dispersion: light travels at different wavelengths.

• Waveguide dispersion: The reason is that the light energy travels at a slightly different speed. In single-mode fiber, it is very important to change the dispersion of the fiber by changing the internal structure of the fiber.Effect of fiber-optic materials on the propagation

• Glass fiber: fiber core and cladding are glass, small loss, long transmission distance, high cost;• Rubber silicon fiber: fiber core is glass, cladding for plastic, characteristics are similar to glass fiber, the cost is low;

• Plastic fiber: fiber core and cladding are plastic, large loss, transmission distance is very short, the price is very low. Used for home appliances, audio, and short-distance image transmission.