How much do you know about laser communication?

A relatively straightforward understanding of laser communication is the way in which information is transmitted using lasers. The technical principle is similar to the principle of radio communication, that is, the sound signal is first modulated onto the laser beam , and then the laser with the sound signal is sent out.

The laser itself has the characteristics of high brightness, strong directivity, good monochromaticity and strong coherence. In addition to the language information language, it can also transmit text, data, images and other information.

Advantages of laser communication

1. Large communication capacity. In theory, laser communication can simultaneously transmit 10 million TV programs and 10 billion road calls.

2. Strong confidentiality. The laser is not only extremely directional, but also invisible, so it is not easily intercepted by the enemy, and the security is good.

3. Lightweight structure and economical equipment. Since the laser beam divergence angle is small and the directivity is good, the transmitting antenna and the receiving antenna required for laser communication can be made very small. Generally, the antenna has a diameter of several tens of centimeters and a weight of several kilograms, while a similarly functioning microwave antenna has a weight. In terms of several tons, more than ten tons.

The weakness of laser communication

1. Communication distance is limited to line of sight (several kilometers to tens of kilometers), which is vulnerable to weather and may even cause communication interruption in severe weather conditions. Atmospheric molecules such as oxygen, nitrogen, carbon dioxide, and water vapor absorb light signals; the density of atmospheric molecules is uneven, and dust, smoke, ice crystals, salt particles, microorganisms, and tiny water droplets suspended in the atmosphere There is scattering. Clouds, rain, fog, snow, etc. cause the laser to be severely attenuated. Atmospheric turbulence caused by air convection on the Earth's surface can cause beam deflection, beam spread, beam flicker (random variation of bright and dark spots in the beam section), and image jitter (random jitter of beam convergence points).

2. Lasers of different wavelengths have different reductions in the atmosphere. The theory and practice prove that the laser with a wavelength of 0.4-0.7 μm and a wavelength of 0.9, 1.06, 2.3, 3.8, 10.6 μm has less attenuation, and the laser with a wavelength of 0.6 μm has a stronger ability to penetrate the laser. Atmospheric laser communication can be used for lakes and rivers, border, islands, mountains and canyons, etc. communication; can be used for the temporary replacement of a microwave communication device when communication is interrupted or coaxial cable repair. A blue-green laser with a wavelength of around 0.5 μm can be used for underwater communication or for submarine communication.

3. Targeting difficulties. The laser beam has a very high directivity, which makes it difficult to aim at the point between the transmitting and receiving points. In order to ensure the aiming between the transmitting and receiving points, not only the stability and accuracy of the equipment are required, but also the operation is complicated.

The main application of laser communication

1. Short-range communication between the ground;

2. Send fax and TV within a short distance;

3. Due to the large capacity of laser communication, it can be used for data transmission of missile range and multi-channel communication between the ground.

4. Global communications and interstellar communications through satellite total reflection, and communications between submarines.