Optical fiber transmission advantages

Optical fiber transmission has many outstanding advantages:

Bandwidth

The width of the frequency band represents the size of the transmission capacity. The higher the carrier frequency, the greater the bandwidth of the signal that can be transmitted. In the VHF band, the carrier frequency is 48.5 MHz to 300 MHz. With a bandwidth of about 250MHz, it can only transmit 27 sets of TVs and dozens of sets of FM broadcasts. Visible light has a frequency of up to 100000 GHz, more than a million times higher than the VHF band. Although the bandwidth of the fiber is affected due to the different loss of the fiber to different frequencies, the bandwidth in the lowest loss region can reach 30000 GHz. At present, the bandwidth of a single light source only accounts for a small part of it (multi-mode fiber has a bandwidth of about several hundred megahertz, and good single-mode fiber can reach 10 GHz or more), and advanced coherent optical communication can arrange 2,000 lights in the 30000 GHz range. Carriers, wavelength division multiplexed, can accommodate millions of channels.

Low loss

In a coaxial cable system, the best cable has a loss of more than 40 dB per kilometer when transmitting 800 MHz signals. In contrast, the loss of the optical fiber is much smaller, and the transmission of light of 1.31 um is less than 0.35 dB per kilometer. If 1.55 um of light is transmitted, the loss per kilometer is even smaller, which is less than 0.2 dB. This is 100 million times smaller than the coaxial cable's power loss, allowing it to travel farther. In addition, there are two characteristics of optical fiber transmission loss, the first is that all cable television channels have the same loss, do not need to be equal to the cable trunk must be introduced to equalize the equalizer; second, the loss of almost no change with temperature, do not worry Changes in the ambient temperature cause fluctuations in the level of the mains.

Light weight

Because the fiber is very thin, single-mode fiber core diameter is generally 4um ~ 10um, the outer diameter is only 125um, plus waterproof layer, stiffeners, sheaths, etc., with 4 ~ 48 fiber optic cable diameter is less than 13mm, The diameter of the coaxial cable is much smaller than that of the standard coaxial cable, which is 47mm. With the glass fiber as the fiber, the specific gravity is small, so that it has the characteristics of small diameter and light weight, and the installation is very convenient.

Strong anti-interference ability

Because the basic component of the fiber is quartz, only light, not conductive, not affected by the electromagnetic field, the optical signal transmitted in it is not affected by the electromagnetic field, so the optical fiber transmission has a strong resistance to electromagnetic interference, industrial interference. Because of this, the signal transmitted in the optical fiber is not easy to be eavesdropped, which is advantageous for confidentiality.

High fidelity

Because fiber-optic transmissions generally do not require repeater amplification, they do not introduce new non-linear distortions due to amplification. As long as the linearity of the laser is good, the television signal can be transmitted with high fidelity. The actual test shows that the carrier frequency of the good AM fiber system is greater than 70dB for the C/CTB beat ratio and 60dB for the intermodulation index cM, which is much higher than the nonlinear distortion index of the general cable trunk system.

Reliable work performance

We know that the reliability of a system is related to the number of devices that make up the system. The more equipment, the greater the chance of failure. Because the fiber optic system contains a small number of devices (does not require as many tens of amplifiers as the cable system), the reliability is naturally high. In addition, the fiber optic equipment has a long life, and the time for failure-free operation is 500,000 to 750,000 hours. The shortest life among them is the laser in the optical transmitter, and the minimum lifetime is also more than 100,000 hours. Therefore, the performance of a well-designed, correctly installed and commissioned fiber optic system is very reliable.

The cost keeps falling

At present, some people have proposed the new Moore's Law, also known as the Optical Law. The law states that the bandwidth of optical fiber transmission information is increased by 1 time every 6 months while the price is reduced by 1 time. The development of optical communication technology has laid a very good foundation for the development of Internet broadband technology. This cleared up the last obstacle to the use of fiber optic transmission for large cable television systems. Since the source of the material (quartz) for producing the optical fiber is very abundant, as the technology advances, the cost will be further reduced; and the copper raw material required for the cable is limited, and the price will be higher and higher. Obviously, in the future, optical fiber transmission will have an absolute advantage and become the most important means of transmission for the establishment of a cable network in the province and even in the country.