Analysis of the style and characteristics of optical fiber transmission

Optical fiber transmission method

The transmission interval of coaxial cable is 光纖線 limited due to the characteristics of the wire itself. In an application environment full of electromagnetic waves, the nuisance of electromagnetic waves further reduces the compliance of coaxial cable transmission. If the installation site is located in a minefield, the equipment at both ends is still Will be destroyed by lightning strikes. Optical fiber transmission has the incomparable advantages of coaxial cable and has become the first choice for long-distance video transmission.

1. The characteristics of optical fiber transmission

(1) Low transmission loss

Consumption is the primary characteristic of the transmission medium, it only determines the interval of relay required to transmit the signal. As the transmission medium of the optical signal, the optical fiber has the characteristics of low loss. For example, if a 62.5/125μm multimode fiber is used, the attenuation of 850nm wavelength is about 3.0dB/km, and the attenuation of 1300nm wavelength is lower, about 1.0ddB/km. If 9/25μm single-mode fiber is used, the attenuation of 1300nm wavelength is only 0.4dB/km, and the attenuation of 1550nm wavelength is 0.3dB/km, so ordinary LD light source can transmit 15 to 20km. At present, products that transmit 100 kilometers have emerged.

(2) Transmission frequency bandwidth

The bandwidth of the optical fiber can reach more than 1GHz. The bandwidth of the ordinary image is around 6MHz, so it is more than enough to transmit one channel of image with one core fiber. The advantage of optical fiber high bandwidth is not only capable of transmitting multi-channel images at the same time, but also capable of transmitting voice, manipulation signal or contact signal, and some can even use one core optical fiber to achieve bidirectional transmission function through special optical fiber passive components.

(3) Strong anti-interference

The carrier wave in optical fiber transmission is light wave, which is a very high frequency electromagnetic wave, which is much higher than the frequency used in ordinary electric wave communication, so it is free from nuisance, especially strong electric nuisance. At the same time, because the light waves are bundled within the optical fiber, there is no radiation, no pollution to the environment, no leakage of transmitted signals, and strong confidentiality.

(Iv) High safety performance

The glass material used in the optical fiber is non-conductive and anti-lightning; the optical fiber transmission is not like the traditional circuit that generates sparks due to short circuits or poor wars, so it is particularly suitable for use in flammable and explosive places. The optical fiber is helplessly eavesdropping like a cable. Once the optical cable is damaged, it will be discovered immediately, so it is more secure.

(5) Light weight, good mechanical performance

The optical fiber is as small as a silk, and the weight is extremely light. Even if it is a multi-core optical cable, the weight will not double due to the increase in the number of cores, and the weight of the cable is generally proportional to the outer diameter.

2. Optical fiber layout and transmission mechanism

An optical fiber is a medium for light wave transmission. It is a cylinder composed of medium materials and is divided into two parts: a core and a cladding. Light waves travel along the core. In practical engineering use, optical fiber refers to the core of the fiber drawn from the preform and simply coated. The core is then coated, reinforced and protected to become an optical cable that can be adapted to various engineering applications.

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