Optical communication is a communication method that uses light waves as carriers. Perhaps you don't know exactly what optical communication is, but you are definitely using optical communication, such as when you make a phone call or when you open a browser to browse a webpage, you are already using optical communication. Optical communication has integrated into every corner of our lives.

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Beacon Tower, open the communication gate

The earliest communication should have belonged to over 3000 years ago, when slave countries had a political and military demand for communication, and beacon towers emerged. The most famous one is The story of "Making fun of Marquises by the Beacon Fire". The cruel King You of Zhou indulged in debauchery and corruption. With a smile from Bao Si, the concubine of Bo, he ordered a beacon to be lit. The neighboring lords thought that Xirong was coming and led troops to rescue them, but when they saw the brilliant lights and loud music, they realized that it was the absurd thing that King You of Zhou did with a smile from Bo Mei. The lords dared not speak out in anger and withdrew their troops back to camp. Bao Si saw this and indeed smiled calmly. Shortly after, Xirong did indeed attack, and although he reignited the beacon, no reinforcements arrived The lords thought that King You of Zhou had repeated his old tricks. As a result, Xirong destroyed the city and killed King You of Zhou, leading to the downfall of Western Zhou. The story of "The Beacon Fire Playing with Marquises" not only vividly depicts the use of beacon towers for communication at that time, but also warns future generations that communication is important and cannot be played lightly.

Visual optical communication

Visual optical communication refers to receiving information through both eyes, including semaphores, signal lights, telescopes, lantern language, and other historical trends. Although their manifestations are different, they all use the atmosphere to propagate visible light and the human eye to receive signals. These primitive communication methods, although not truly optical communication, are still widely used in our daily lives due to their convenience and reliability.

Optical telephone, the prototype of modern optical communication

In 1880, American telephone inventor Bell successfully developed the optical telephone. He uses sunlight as a light source to project a constant beam of arc light onto the sound film of the microphone, producing a reflected beam of varying intensity with the vibration of the sound. This process is called modulation. Then, using the atmosphere as the transmission medium and selenium crystal as the light receiving device, the modulated optical signal received by the receiving end is demodulated and restored to the original signal, thus achieving communication. The farthest call distance reaches 213 meters, which is the first step in the history of true optical communication and the prototype of modern optical communication. Bell invented the optical telephone, but the light that propagated in the air did not bend, which was a fatal flaw in atmospheric optical communication. Later, underground communication experiments such as reflective waveguides and lens waveguides appeared. Using specialized optical glass channels for light reflection/projection to transmit optical signals, although solving the problem of light turning, the construction cost of optical communication is too high, and the transmission loss of light is too large. By the mid-1960s, the loss of high-quality optical glass was still as high as 1000 dB/km, making it impossible to use it on a large scale. At that time, there was no reliable light source or stable transmission medium, so it could not develop to the practical stage.

The Beginning and Prosperity of Optical Communication

Since the invention of the first ruby laser by American scientist Theodore Harold Maiman in 1960, which solved the light source problem, humans have gradually unveiled the mystery of optical communication. Until Chinese scientist Kao K. C. proposed the feasibility of optical fiber as a transmission medium, and in 1970, Corning, USA, pulled out the first low loss quartz fiber with a attenuation of 20dB/km, marking a new chapter in world optical communication. At the same time, Bell Laboratories in the United States, NEC, a Japanese electrical company, and the Soviet Union have successively developed dual heterojunction semiconductor lasers that operate continuously at room temperature. The combination of fiber optics and lasers has propelled communication technology from laboratory research to the practical application of fiber optic communication. Therefore, 1970 is known as the "first year" of optical communication.

In the following decades, optical communication focused on improving transmission rate and increasing transmission distance, and vigorously promoted the development period of applications. With the reduction of fiber loss and the continuous development of new laser devices and optical communication devices such as photodetectors, fiber optic communication has explosive development, and various practical fiber optic communication systems have emerged one after another. The transmission capacity of fiber optic communication systems has increased by a million times, and the development speed is unprecedented.

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After 1986, with the goal of ultra large capacity and ultra long distance, comprehensive and in-depth research on new technologies was carried out. Many countries around the world have begun to apply optical communication technology on a large scale, with significant progress in transmission capacity and distance. Since 1991, China has stopped building long-distance cable communication systems and vigorously developed fiber optic communication. With the advancement of the broadband strategy in China, the three major telecommunications operators in China are accelerating the pace of optical network city construction. China's optical communication industry has shown a high-speed growth trend, which has penetrated into every corner of our lives to this day. From basic communication to the exciting online world, optical communication is indispensable.