Optical fiber action

Optical fiber can be used for optical fiber communication. Laser is an ideal light source for optical fiber communication because of its strong directivity and high frequency. Compared with radio communication, optical fiber communication can provide more communication channels to meet the needs of large-capacity communication systems.

Optical fiber generally consists of two layers, the inner layer is called the inner core, with a diameter of several tens of microns but a high refractive index; The outer layer is called cladding and has a low refractive index. The light incident from one end of the optical fiber is repeatedly refracted by the inner core and transmitted to the end. Due to the difference in refractive index between the two layers, the light entering the inner core always stays in the inner core for transmission. The transmission distance of light is related to the optical loss of optical fiber. If the optical loss is small, the transmission distance will be long, otherwise the attenuated signal will be amplified by a repeater. Optical fiber made of the latest fluorine glass can transmit optical signals to the other side of the Pacific Ocean without any relay station.

In practical use, thousands of optical fibers are often combined and strengthened, making optical cables like cables, which not only improves the strength of optical fibers, but also greatly increases the communication capacity.

Using optical cable instead of communication cable can save a lot of nonferrous metals, saving copper 1. 1 t and lead 2 ~ 3 t per kilometer. Optical cable has the advantages of light weight, small volume, compact structure, good insulation performance, long service life, long transmission distance, good confidentiality and low cost. Optical fiber communication, combined with digital technology and computer, can be used to transmit telephone, image and data, control electronic equipment and intelligent terminals, and play the role of replacing communication satellites.

Optical fiber with large optical loss can be used in short distance, and is especially suitable for making various human endoscopes, such as gastroscope, cystoscope, proctoscope, hysteroscope, etc. It is extremely beneficial to the diagnosis and treatment of various diseases.

Optical fiber is called optical fiber for short, and the "optical fiber communication" we often hear is the use of the principle of total reflection. In order to illustrate the transmission effect of optical fiber on light, we have done the following experiments.

The actual optical fiber is a very fine special glass fiber with a diameter of only a few microns to 100 microns, which is composed of an inner core and a sheath. The refractive index of the inner core is greater than that of the outer shell, and when light propagates, total reflection occurs at the interface between the inner core and the outer shell.

If the optical fibers are gathered into a bundle so that the relative positions of the optical fibers at both ends are the same, the image of light and dark colors can be transmitted from one end to the other. In medicine, endoscopes made of optical fibers are used to examine the insides of human stomach, intestine, trachea and other internal organs. The actual endoscope is equipped with two groups of optical fibers, one for transmitting light into the human body and the other for observation.

As we know, light is also an electromagnetic wave, which can be used as a carrier to transmit information like radio waves. When the laser carrying sound, image and various digital signals is input from one end of the optical fiber, it can be transmitted to the other end thousands of miles away along the optical fiber to realize optical fiber communication.

The main advantages of optical fiber communication are large capacity, small attenuation and strong anti-interference. For example, the theoretical transmission capacity of a pair of optical fibers is 2 billion telephones and10 million televisions; Today, the world's largest "Intelsat-6" can only transmit 33,000 telephone lines and 4 TV lines. Even the optical fiber communication with hundreds of thousands of telephone lines actually used now has a larger capacity than satellite communication.

Although the development of optical fiber communication has only a history of more than 20 years, the development speed is amazing. Some developed countries have not only established optical fiber communication networks across the seabed, but also established optical fiber communication networks between cities. The use prospect of optical fiber is very broad, not only optical fiber telephone has been widely used, but also optical fiber TV will soon enter the homes of ordinary people. In addition, since the emergence of phototransistors, high-capacity and high-speed optical computers are expected to be widely used at the beginning of the next century, which are inseparable.

China's optical fiber communication technology started earlier, and now it has become one of the more advanced countries in optical fiber communication technology. Since 1972, dozens of optical fiber communication lines have been opened, and the communication network between provincial capitals in China has basically been built. Beijing Cable TV will lay cable TV cable around Beijing 1999.

Optical fiber communication technology stands out from optical communication, becomes one of the main pillars of modern communication, and plays an important role in modern telecommunication network. As a new technology, the rapid development and wide application of optical fiber communication in recent years is rare in the history of communication, and it is also an important symbol of the world's new technological revolution and the main transmission tool of various information in the future information society.

Optical fiber communication is the main transmission means of modern communication network. Its development history is only one or two decades, and it has experienced three generations: short wavelength multimode fiber, long wavelength multimode fiber and long wavelength single mode fiber. The adoption of optical fiber communication is a major change in the history of communication. More than 20 countries, including the United States, Japan, Britain and France, have announced that they will no longer build wired communication lines and are committed to developing optical fiber communication. China optical fiber communication has entered the practical stage.

Optical fiber is short for optical fiber. Optical fiber communication is a communication mode with light wave as information carrier and optical fiber as transmission medium. In principle, the basic material elements of optical fiber communication are optical fiber, light source and optical detector. In addition to classifying optical fibers according to manufacturing process, material composition and optical characteristics, optical fibers are often classified according to their applications, which can be divided into optical fibers for communication and optical fibers for sensing. Transmission medium optical fiber can be divided into general purpose and special purpose, and functional device optical fiber refers to the optical fiber used to complete the functions of light wave amplification, shaping, frequency division, frequency doubling, modulation and optical oscillation, and often appears in the form of some functional device. The rapid development of optical fiber communication is mainly due to its following characteristics:

(1) has large communication capacity and long transmission distance;

(2) Small signal crosstalk and good safety performance;

(3) Anti-electromagnetic interference and good transmission quality;

(4) The optical fiber is small in size and light in weight, which is convenient for laying and transportation;

(5) Rich materials and good environmental protection;

(6) no radiation, not easy to eavesdrop;

(7) The optical cable has strong adaptability and long service life.

References:

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