The laser itself has the characteristics of high brightness, strong directivity, good monochromaticity and strong coherence. In addition to the language information language, the laser can transmit characters, data, images and other information.
Laser communication more intuitive understanding is the use of laser transmission of information communication. Its technical principle and the principle of radio communication is similar, that is, the first sound signal modulated onto the red laser beam, and then send the laser with the sound signal.
The advantages of laser communications: large communications capacity, in theory, laser communications can simultaneously send 10 million television programs and 100 million road phone. Confidentiality, the laser is not only extremely strong direction, and can be used invisible light, which is not easily intercepted by the enemy, the confidentiality is good. The structure is light and the equipment is economical. Since the divergence angle of the green laser pointer beam is small and the directivity is good, both the transmitting antenna and the receiving antenna required for laser communication can be very small. Generally, the diameter of an antenna is several tens of centimeters and the weight is only a few kilos, microwave antenna, the weight of a few tons, more than ten tons of dollars.
Communications distances are limited to line-of-sight (kilometers to tens of kilometers) and are subject to the effects of the weather and even disrupt communications in harsh climates. Atmospheric oxygen, nitrogen, carbon dioxide, water vapor and other atmospheric molecules on the optical signal absorption; atmospheric molecular density and suspended in the atmosphere of dust, smoke, ice, salt particles, microorganisms and tiny water droplets and other optical signals Scattering effect. Clouds, rain, fog, snow and other laser so severely attenuated. Atmospheric turbulence caused by air convection on the Earth's surface can have effects such as beam deflection, beam spread, beam flare (random variation of bright and dark spots within beam cross-section), and image jitter (random jump of beam convergence point).
Different laser wavelengths have different reduction in the atmosphere in the house. Theory and practice show that the laser attenuation of the wavelength is 0.4 ~ 0.7 m, and the wavelength is 0.9, 1.06, 2.3, 3.8, 10.6 m, respectively. The laser with 0.6 m wavelength has stronger fog penetration ability. Atmospheric most powerful lasercommunication can be used for communication of rivers, lakes, border areas, islands, mountains, canyons and other places. It can also be used in microwave communication or coaxial cable communication, temporary repair equipment when interrupted repair. Blue green laser with wavelength of 0.5 m can be used for underwater communication or submarine communication.
Aiming difficult. The laser beam has a very high directivity, which brings with it many difficulties in aiming at the transmitting and receiving points. In order to ensure the aiming between transmitting and receiving points, not only the high stability and precision of the equipment are put forward, but also the operation is complicated.
The main application of laser communications: short-range communication between the ground; short distance transmission of fax and television; due to the large burning laser pointer communication capacity, for missile range data transmission and multi-channel communication between the ground. Global and satellite communications through satellite total reflection, and underwater submarine communications.