What is optical communication?
| What is optical communication?
Optical communication is a technique that uses light to transmit information to the other party.
| The basic structure of optical communication
Computers and mobile phones around us send information via electrical signals "0 and 1". Optical communication is composed of a "transmitter" that converts an electrical signal into an optical signal, a "receiver" that converts an optical signal into an electrical signal, and a "fiber" that transmits light.
| The advantages of optical communication
1. Long transmission distance, economical and energy saving
2. One-time transmission of massive information
3. Communication speed is fast
1) Long transmission distance, economical and energy saving
Assume that 10Gb of information (10 billion signals) is transmitted in one second. If electrical communication is used, the signal is adjusted every 100 meters. In contrast, if optical communication is used, the adjustment interval needs to be 100 kilometers or more. The fewer the number of adjustment signals, the less the number of machines used, and therefore the economical and energy-saving effect.
For example, when talking to a foreign friend or chatting online, it feels no different from talking in the country. Unlike the past, the sound will lag behind. In the era of only electrical communication, the distance that can be transmitted at one time is short and the amount of information transmitted is small, and international communication is mainly transmitted as a relay through artificial satellites. However, when optical communication is used, the one-time transmission distance is long and the amount of information transmitted is large. Therefore, by using the optical fiber cable laid on the seabed, it is possible to realize natural communication with overseas. (The speed of the electric wave and the light are the same. However, since the transmission path becomes longer via the satellite, the signal arrives slowly. The distance of the submarine cable is much shorter, so the signal will be reached faster.)
2) One-time transmission of massive information
A large number of users can receive the required information (movies or news, etc.) at the same time. In one second, electrical communication can only transmit up to 10Gb (10 billion 0 and 1 signals). In contrast, optical communication can transmit up to 1Tb (1 trillion 0 and 1 signals).
3) Fast communication speed
The communication will be delayed due to electrical noise, resulting in a decrease in communication speed. However, optical communication is not affected by noise, so signals can be transmitted quickly.
Where is optical communication used?
| Optical communication exists around us and the world
Internet-based devices such as the Internet, mobile phones, and IP phones connect everyone to their region, to the entire country, and even to the global communications network. For example, signals from computers and mobile phones gather at the base stations and network providers of local communication carriers, and then transmitted to the world through optical fibers in submarine cables.
| A variety of devices connected to the network
The various devices we use today are networked. The emergence of the Internet has made our lives more comfortable and convenient.
Why do you need optical communication technology?
Our traffic is increasing every year. We use the mobile phone, SMS, receiving images, and network (virtual) stores to exchange information. Equipment performance has improved year by year and usage has changed. We can imagine that the traffic will continue to increase in the future. Optical communication technology is used in information exchange.
As the entire social traffic increases, so does the technology that only one fiber can transmit more information.
Unit indicating the amount of transmission
The unit is bps. That is, the abbreviation of bit per second indicates the number of bits that can be transmitted in one second. For example, 1 bps means that 1 bit of data can be transmitted in 1 second.
Device used in optical communication (optical transmission device)
| Optical transmission device is doing it
The key parts of the optical communication network are equipped with optical transmission devices. This device plays many roles.
1. Signal conversion (transmission signal): converts an electrical signal into an optical signal.
2. Signal multiplexing: Converging multiple narrow signals into one wide signal.
3. Signal relay: long-distance transmission, relay signal in the middle.
4. Signal steering: The transmission direction of the converted signal.
5. Signal Demultiplexing: Decompose the multiplexed signal into the original individual signal.
6. Signal conversion (received signal): converts an optical signal into an electrical signal.
| Optical transmission device
Various components are installed in the device.
1. convert (send signal)
The received electrical signal is converted into an optical signal.
Multiple signals are multiplexed and transmitted simultaneously.
During the transmission, the waveform and intensity of the signal are degraded. Therefore, it is necessary to restore the waveform to a waveform that is neat as the original signal, and increase the light intensity. If the waveform is seriously degraded, it is necessary to temporarily convert the optical signal into an electrical signal. After the waveform is corrected incorrectly, it is converted into an optical signal for transmission.
According to the direction of the signal, the optical switch switches the transmission direction of the optical signal.
The multiplexed signal is decomposed into the original individual signal.
6. Conversion (receiving signals)
The received optical signal is converted into an electrical signal.
Communication method (now and future)
The following describes the communication method by car and lane. Assume that the car represents the time of possession of the lane (1 zone), the amount of information (number of bits) that the cargo represents each time, and the wavelength of the lane represents light.
| Current communication speed: 10Gbps, 40Gbps per wavelength transmission
Time Division Multiplexing (TDM: Time Division Multiplexing)
Since the information that can be transmitted is limited each time, it is necessary to transmit in a time-phase. For example, when multiple users send information at the same time, there is only one lane for carrying information, so trucks loaded with different information packages need to be arranged in a row. When the lane is blocked, the transmission speed will be slower.
WDM: Wavelength Division Multiplexing
The amount of information that can be transmitted at one time is large. By changing the wavelength, information of multiple users can be transmitted at the same time. For example, even if multiple users send information at the same time, as long as a plurality of lanes are distributed, it is not easy to cause clogging, and the goods (bits) can be smoothly transported, and the transmission speed is relatively stable.
Multi-level modulation (MM: Multi-level Modulation)
A method of transmitting a plurality of signals in one interval of one wavelength. By changing the waveform of the light, multiple pieces of user information are transmitted on the same wavelength. A representative technique is four-phase differential phase shift keying modulation (DQPSK) Ifferential Quadrature Phase-Shift-Keying). Normally, each truck is loaded with 1 bit of cargo, but when using "DQPSK", each truck can carry 2 bits of cargo.
| Future communication speed: 100Gbps per wavelength transmission
100 Gbps is equivalent to a DVD transfer speed of about 0.4 seconds. (assuming conversion to a DVD with a capacity of 4.7GB)
The light advances while vibrating. The direction of vibration is called "polar wave", and it is divided into two types: light that advances vertically (vertical wave) and light that moves horizontally (horizontal wave). The information contained in the polarized waves does not interfere with each other and can transmit a large amount of information. For example, two trucks are driving at the same time on one lane, and the two trucks do not collide when transmitting information.
Wonderful vast optical network (example introduction)
With fiber optics all over the world, we have access to quality service in every situation. Next, introduce related examples.
Little story (why the sky is blue and the sunset is red)
| Why is the sky blue and the sunset red?
Have you ever wondered why the sky looks blue? There is a reason for the sky to appear blue. The wavelengths of light are different and the colors are different. When sunlight enters the Earth's air layer (atmosphere), it collides with dust (molecular molecules) in the air, thus changing the direction of light. That is to say, since light of a shorter wavelength (which is shorter than a red light blue wavelength) is more likely to collide with dust, light is easily spread everywhere. The reason why the sky looks blue is because the shorter wavelength blue light spreads across the sky.
| The wavelength of sunlight
The sun looks white, in fact, because of the mixed light from red to blue. That is to say, the wavelengths of light in sunlight are different.
| The reason why the sky is blue (sunlight collides with dust)
1) Sunlight enters the air layer. There is a lot of dust floating in the air layer.
2) The blue light with a short wavelength is easy to collide with dust, and the light spreads around.
In addition, red light with a longer wavelength is free to shuttle between dust.
3) The blue light spreads to the entire sky, and from a distance, the sky is blue.
| The reason why the sunset is red
Why does the blue sky appear red in the evening? This is related to the distance of sunlight passing through the air layer. When the sun goes down, the position of the sun moves horizontally from our upper direction. Thus, the distance of the sunlight passing through the air layer becomes longer in the horizontal direction than when it is directly above, and the long-wavelength red light that has previously passed through the dust gap starts to collide with the dust. Moreover, because the wavelength of blue light is short, it is impossible to reach the far side, and only the sky covered by red light is in our eyes, so the sunset looks red.
As shown in the above figure, the reason why the setting sun is red is that light having a longer wavelength does not easily scatter even after passing through a thick atmosphere, and has a property of being able to reach a distant place. Optical communication is the use of this principle, in order to reduce the scattering in the fiber, to achieve long-distance transmission, the use of light with a slightly longer wavelength.
Pre-knowledge (what is the wavelength)
| What is the wavelength?
Literally, "wavelength" is the "length of the wave." "Waves" include sound waves, electric waves, and light waves. Wavelength refers to the length of a "wave" between one wave and the next.
The difference in wavelengths can be seen everywhere. For example, the difference in color and the difference in sound level depend on the "length" of the wavelength.
| wave partner
The wavelengths are different and the types are different. The frequency used in optical communication is 1.3 micrometers or 1.55 micrometers, which is one type of infrared rays.
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