Optical fogging technology and its development

Natural light is composed of light waves with different wavelengths. The visible range of the human eye is approximately 390 nm to 780 nm. Wavelengths from long to short correspond to seven colors of red orange blue green orange violet, and wavelengths less than 390 nm are called ultraviolet light, and the wavelength is greater than 780nm is called infrared. Different wavelengths of light have different characteristics because of different wavelengths. Fog and smoke affect the cause of visible light imaging. Infrared rays, because they have longer wavelengths, are less affected by aerosol during propagation, and can penetrate certain concentrations of haze and dust. To achieve accurate focus, this is the basis for optical fogging.

1, the lens

It is known from the principle that the focus of optical fogging is the interception and accurate focusing of light in a specific near-infrared band. Most of this work is done by the lens. In 2005, the Qinghai-Tibet Railway project began to have corresponding fog demand, and the market was of high quality. Fujinon lens can choose different wavelengths through the built-in processor, so began to consider the use of interception of different specific wavelengths of light to achieve through fog, and ultimately developed a series of tests after the fog lens and fog camera finished product, and put into production in 2006 In the following 07, patent approvals were obtained, and the concept of fogging lenses began to appear on the market.

It can be said that the quality of the lens determines the effect of optical fogging. The difficulty of the lens design lies in the optical design, including the grasp of the optical path and the selection of the filter. Secondly, the selection of materials and technology also determine the effect of the finished product. The biggest difference of the fog lens is that it can bear the width of the infrared band, that is, the latitude of the focal plane. In principle, the wider the available near-infrared wavelength band, the better, but it is limited by the difficulty of designing the optical path of the lens and the CCD's photosensitivity. Currently, the longest infrared band available in the security industry is known to be 1100 nm.

2. Filter

People who know how to convert cameras day and night are familiar with filters. Generally, this type of camera is equipped with two filters. One is responsible for filtering out light waves other than visible light during the day to make the image clearer and brighter. One application is at night and is responsible for Release the infrared band that the CCD can carry to achieve infrared monitoring at night.

The professional fog lens incorporates highly targeted filters. The function is to precisely intercept the light in the desired wavelength band. In order to adapt to specific environmental conditions, multiple filters for different bands are often loaded and linked to the camera via the 485 interface. To achieve switching. Normally, a camera with a fog lens can only have the day and night conversion function in the basic imaging performance. However, considering the high cost of the fog lens, some camera manufacturers are also looking for a more economical optical fog mode. Shenzhen Optoelectronics Technology (Shenzhen) Co., Ltd. took the lead in the use of a four-filter wavelength switching device. Unlike the previous day and night conversion cameras of two filters, we have innovatively added four filters to the inside of the camera, in addition to day and night conversion. The addition of a filter that selectively filters light in the 400-nm to 400-nm wavelength band enables strong light suppression. Of course, in order to more accurately capture the near-infrared band for imaging, a fog filter is also added to achieve more economical optical fogging. . This mechanical device can be automatically controlled by the camera or manually switched. The combination of optical penetrating fog and electro-permeating fog is a four-filter color photoelectric combined with intelligent fogging camera, which can achieve twice the visibility of fog.

3, bottlenecks and development

Because the direct use of light that can penetrate through the haze of near-infrared wavebands can be used for imaging. Although optical fogging can only obtain black-and-white surveillance images, its imaging effect is outstanding, and it has also been used in maritime and oceanography. On the other hand, it is affected by the lens. High cost restrictions, although in recent years, large projects such as safe cities and even civilian markets have also seen certain fog demand, but the actual number is still limited.

At the same time, because the technology is already mature, relying on the lens or optics to achieve better fogging requires an alternative approach. In the short-term, the tolerance of the lens to the wavelength is difficult to extend beyond 1100 nm, but if you do not take into account the visible light, it can be extended in the near-infrared band; so you can consider loading two sets of lenses in a device, under normal circumstances The visible light lens and the foggy day use a special fog lens, which not only preserves the visible color picture, but also makes the tolerance of the fog lens more comfortable and enables multi-image contrast monitoring.