ºnew IR laser night vision systems theory and applications (1)

The most basic ºnew IR laser night vision system, from high-power Semiconductor Laser LD, drive controller, optical enlargement beam collimation lenses, cameras and long focal length lens, transmission systems and monitors, etc.

High-power Semiconductor Laser LD, through larger current drive and control, launching out people invisible infrared light line to illuminate the target object photographed. But as the laser beam thin, high-brightness, so it must be based on the monitoring of the long range target distance and scope through expanding collimating optics lens will illuminate infrared beam spread beam to the monitoring of the target scenario. Infrared reflection by the objects into the camera after long focal length lens to the photosensitive surface imaging. At this point we can see from the infrared reflectance image instead of the visible light reflection, that is, at this point the image ultra low Lux camera can shoot to dark environment invisible images. This image, and then through the transmission system to the monitoring center to record and display.

Infrared transfer of technology issues and solutions

Because it is more than 1km ºnew IR wave transmission, there are several technical issues.

1, in the air transmission quality is subject to weather.

2, in any link of air transport, there are several factors to be considered (i.e. cause transmission signal attenuation of reason).

Molecular absorption in the atmosphere

LED and LD luminous atmospheric transport system of signal loss, mainly by the transmission medium — caused by atmospheric absorption.

Because the beam from the gases pass through, there will always be a degree of molecular absorption. Also, the air on certain wavelengths of light absorption so badly, the wavelength is not available for signal transmission. Caused by atmospheric absorption of attenuation is acceptable band known as atmospheric transmission window (atmospheric windows). This atmospheric transmission window-band data in the various literature can be found, so all LED and LD system must be in this atmospheric transmission window wavelength.

Air particles absorb

Air particles such as dust and smoke, is another cause optical signal absorption factor.

Clearly, the atmosphere is always more or less contains such particles, especially in the water nearby, such particles content sometimes very high. In these places, always try to have the optical device installation, high above the ground to improve the optical transmission of results.

Vapour absorption and scattering

Fog is causing serious infrared absorption factor, and mist may also make the light before, backscatter.

Therefore, the area in the misty, must be based on local climate to select optical transceiver device working hours because of fog when the system will not work properly.

Effect of atmospheric disturbances

The atmosphere has a certain degree of disorder, it can cause signal loss, but also to signals mixed into noise.

The wind will cause atmospheric turbulence and Atmospheric Turbulence will cause the signal path on the refractive index of air. This phenomenon and sun exposure areas produce heat waves, the phenomena caused by a mirage. This impact is ultimately reflected in the infrared beam to the other direction cannot be determined, allowing the camera to capture the desired monitoring goals.

So, thanks to the infrared light transmission technology is in the air media, so the transmission quality is subject to weather.

Generally, sunny on transmission quality impact, rain, snow and fog effects on transmission quality. Tested, infrared light transmission affected by attenuation experience values are: sunny 5 ~ 15dB/Km; rainy day 20 ~ 50dB/Km; or snow 50 ~ 150dB/Km; fog 50 ~ 300dB/Km. The current solution to this problem, generally use the higher power of LD pipe, advanced optics and beam.

In fact, on ºnew IR laser night vision system, mainly affected by the air particles, mist, absorption and scattering of synchronization Pulse range-gated technology better solve the problem.

Sync pulse range-gated technology

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