[æ–‡|蔺ç¦åˆ] Abstract: Active infrared monitoring is an important means of security monitoring. At present, active infrared cameras on the market mainly include LED infrared and laser infrared. LED infrared light intensity and technical level limit, it is difficult to achieve night vision monitoring above 80m, it is also difficult to achieve clear lighting above 50m; in recent years, domestic laser infrared technology is developing rapidly, monitoring distance and illumination brightness are far more than LED infrared light And superior performance. Based on the research experience of Inspur Huaguang, this paper summarizes the research situation of domestic laser night vision, introduces the system composition of laser infrared monitoring and the advantages and development status of laser infrared technology, and provides suitable infrared monitoring equipment for customers and engineering companies. Learn from.
1. INTRODUCTION <br> <br> night vision monitor camera means clearer target screen presentation at night or in low light environment, which by means of optical imaging technology to monitor the target device's nighttime observation [1]. Night vision technology is mainly divided into active infrared technology, passive infrared technology, low light level night vision technology, among which the most widely used in the civilian field is active infrared night vision technology. Since the development of the active infrared technology in the 1960s by the American Bell Labs, the technical level has experienced rapid development, from the infrared light bulb with photoelectric conversion efficiency of only 5%, to the laser infrared illumination module with luminous efficiency of more than 60%. Today's active infrared night vision field mainly includes LED infrared technology and laser infrared technology. LED infrared technology mainly uses LED infrared light with wavelength near 850nm as the illumination source of surveillance camera, and the luminous efficiency is up to 30%. Laser infrared technology mainly uses lasers with wavelengths of 810nm, 860nm and 940nm as the illumination source of surveillance cameras.
After years of development, LED infrared technology currently dominates the civilian security lighting market. However, due to the limitations of LED infrared technology and the limitation of LED luminous efficiency, night vision monitoring of more than 80m cannot be achieved, and imaging above 50m is not clear enough. These problems need to be solved by the promotion of laser night vision technology.
In recent years, with the continuous development of the domestic laser infrared technology research and development speed and the continuous strengthening of the promotion, the use of laser infrared illumination technology can achieve monitoring requirements of tens of meters or even several kilometers. This paper summarizes the development achievements of domestic laser night vision in the fields of illumination distance, light source life and lens matching.
2. Laser night vision surveillance system composed of <br> <br> laser night vision surveillance system consists of laser lighting modules, surveillance cameras, machinery lines and display components.
2.1 Laser Lighting Module The laser lighting module is the illumination component of laser night vision. The semiconductor laser has the advantages of high power and good collimation. Therefore, the laser illumination distance is long, and the night vision monitoring illumination of 100 meters to several kilometers can be easily realized. The laser illumination module uses a semiconductor laser, but the high-power semiconductor laser often adopts a wide strip structure, and has a problem that the beam divergence angle is large and the light intensity distribution is asymmetric [2], so the semiconductor laser needs to be homogenized by the spot. Figure 1 shows the laser spot of the Inspur Huaguang laser after homogenization.
After the spot is homogenized, it is also necessary to use an optical beam expander to achieve laser illumination. Fixed focus illumination and zoom illumination are available for different environmental requirements. Our lasers can achieve fixed-focus illumination at different distances of 30m, 50m, 100m, etc., and can also achieve zoom illumination from 20m to 200m or more.
2.2 Laser night vision camera selection There are two main types of photosensitive elements used in cameras: CCD (Charge Coupled Device) and CMOS (Complementary Metal-Oxide Semiconductor). Both types of light-sensitive elements have a wide spectrum of induction, Figure 2 shows the spectrum of the Si-based CMOS, and Figure 3 shows the spectrum of the black-and-white CCD. It can be seen that in the near-infrared region of the two photosensors, the photosensitivity decreases as the wavelength increases. Nowadays, the wavelength of the domestic laser illumination source is generally 810 nm, and the infrared wavelength of the LED is 850 nm. That is to say, under the same light intensity, a suitable camera is more sensitive to the detection of the laser wavelength, and the imaging is clearer.
In order to ensure the image quality and avoid mutual interference between infrared light and visible light, the photosensitive element of the camera generally has a filter in front of it. When selecting a laser night vision camera, the filter must pass light near the wavelength of 810 nm.
3. Advantages of laser night vision and domestic research 3.1 Illumination distance Far laser device has high optical power and low beam divergence, which is conducive to laser beam shaping and can realize night vision illumination farther than LED dot matrix and LED array. In general, the distance of laser night vision monitoring is directly related to laser emission power, illumination angle, atmospheric environment, target reflectivity, imaging system characteristics, etc.:
Among them, Ed is the illuminance threshold for imaging the photosensitive element, P is the laser power without other light conditions, R is the illumination distance, θ is the illumination angle, ε is the illumination system transmittance, Ï is the target diffuse reflection coefficient, and μ is the atmospheric attenuation. The coefficient, Ï„ is the transmission rate of the imaging system, D is the transmission aperture of the imaging system, and f is the focal length of the imaging system [3].
For example, using a laser high-speed ball designed by our company's laser, the illumination angle is set to 0.07 rad at 200 meters. The estimation conditions are as follows: the transmittance of the transmitting and receiving optical system is related to the number of glass elements used, whether or not the antireflection coating is applied, and after the optical coating treatment, it can be around 0.9. Take ε=0.9, τ=0.9. The SONY camera has an F value of 3.0, a nominal CCD minimum illumination of 0.01 Lux, a signal-to-noise ratio greater than 50, and an illuminance threshold of less than 0.0002. It is said that the diffuse reflection coefficient of the white paper is about 0.75, and the air attenuation coefficient of the emptying is 0.0002/m. After calculation, it is necessary to see the white cardboard at 200m, and the laser power should be above 2W. Considering the air attenuation in different environments, we use 4W laser to meet the requirements of various application environments. At present, the domestically produced cloud-based laser monitoring equipment uses laser illuminator to output more than 15W, and the night monitoring distance can reach 3-5. Kilometers.
3.2 Long laser life The photoelectric conversion efficiency of the semiconductor laser is above 60%, and the heat is less than 40% of the total power. In addition, the thermal conductivity of the metal heat sink is high. At the same time, the temperature control circuit can ensure that the working temperature of the laser does not exceed 50 degrees Celsius. However, the photoelectric conversion efficiency of LEDs is up to about 25%, and more than 75% of the electric power is converted into heat. The lifetime of a semiconductor device is closely related to temperature, and the empirical formula for the lifetime of an optoelectronic device:
L(T) is the lifetime of the device at a temperature of T, Ea is the activation energy, K is the Boltzmann constant, and A is a constant [4]. It can be seen from this formula that the higher the temperature, the shorter the life, so the lifetime of the semiconductor laser can be much larger than that of the LED infrared lamp.
In addition, the study found that the failure of semiconductor lasers is mainly due to early failure and late life end failure, and the probability of occurrence of medium-term failure is small. After aging, the semiconductor laser basically eliminates the early failure products and ensures that the laser infrared lamp has a long enough service life.
The following figure shows the aging of the 2W semiconductor laser produced by 5 sets of Inspur Huaguang. The aging current is 3A. It can be seen that the optical power is basically stable after 1000 hours of aging.
The semiconductor laser is mainly caused by the non-radiative transition of the electron-hole pair in the active region and the high power density of the cavity surface. The high current, high temperature and high humidity environment will reduce the service life of the laser. In addition, the electric surge and static electricity will cause the semiconductor laser to fail. [4]. Our laser lighting module has advanced packaging form and circuit design, which improves the product's ability to resist high temperature, high humidity and antistatic, and reduces the failure probability of the device. The theoretical life is above 30,000h.
3.3 Synchronous Zoom Technology The laser night vision synchronous zoom technology is a technology in which the laser beam angle changes synchronously with the camera's shooting distance, ensuring that the shooting area is effectively illuminated. Some domestic laser night vision device manufacturers claim that their products have synchronous zoom technology, but the results are uneven. Many products have flashlight effects or insufficient beam utilization, which affects the monitoring effect. We use advanced electromechanical control methods to make the product with zoom laser light and integrated machine synchronous zoom with power-off memory function, effectively solve the phenomenon of vignetting, flashlight and lighting unclear.
4. Conclusion <br> <br> as active infrared technology, infrared laser technology has matured, and significantly higher than the infrared LED technology advantages: shoot the picture clearer, monitoring a wider range, longer life, more energy efficient, more cost-effective . At this stage, the civilian market is still mainly occupied by LED infrared lamps, and laser infrared is currently only used in special fields. With its superior performance advantages, laser night vision will surely achieve large-scale application in the civilian field.
Inspur Huaguang is working hard to promote the popularization of laser night vision. The "Tension" series of laser lighting products will change the pattern of the infrared monitoring market with superior performance and high cost performance. (This article is submitted by Inspur Huaguang)
References [1] Zhao Juan, Zhang Bohu, Xu Bo. Research on laser infrared night vision system[J].Science and Technology Information,2007,21:225-226.
[2] Li Zongyang. Research on beam characteristics of high power semiconductor lasers [D]. Changchun: Changchun University of Science and Technology: 2010.
[3] Shan Xiaonan. Design of active infrared night vision monitoring system for semiconductor lasers [J]. Opto-mechanical information, 2011, 12: 5-8.
[4] Lei Zhifeng, Yang Shaohua, Huang Yun. Reliability and Lifetime Evaluation of High Power Semiconductor Lasers[J]. Applied Optics, 2008, 1:90-95.
1. INTRODUCTION <br> <br> night vision monitor camera means clearer target screen presentation at night or in low light environment, which by means of optical imaging technology to monitor the target device's nighttime observation [1]. Night vision technology is mainly divided into active infrared technology, passive infrared technology, low light level night vision technology, among which the most widely used in the civilian field is active infrared night vision technology. Since the development of the active infrared technology in the 1960s by the American Bell Labs, the technical level has experienced rapid development, from the infrared light bulb with photoelectric conversion efficiency of only 5%, to the laser infrared illumination module with luminous efficiency of more than 60%. Today's active infrared night vision field mainly includes LED infrared technology and laser infrared technology. LED infrared technology mainly uses LED infrared light with wavelength near 850nm as the illumination source of surveillance camera, and the luminous efficiency is up to 30%. Laser infrared technology mainly uses lasers with wavelengths of 810nm, 860nm and 940nm as the illumination source of surveillance cameras.
After years of development, LED infrared technology currently dominates the civilian security lighting market. However, due to the limitations of LED infrared technology and the limitation of LED luminous efficiency, night vision monitoring of more than 80m cannot be achieved, and imaging above 50m is not clear enough. These problems need to be solved by the promotion of laser night vision technology.
In recent years, with the continuous development of the domestic laser infrared technology research and development speed and the continuous strengthening of the promotion, the use of laser infrared illumination technology can achieve monitoring requirements of tens of meters or even several kilometers. This paper summarizes the development achievements of domestic laser night vision in the fields of illumination distance, light source life and lens matching.
2. Laser night vision surveillance system composed of <br> <br> laser night vision surveillance system consists of laser lighting modules, surveillance cameras, machinery lines and display components.
2.1 Laser Lighting Module The laser lighting module is the illumination component of laser night vision. The semiconductor laser has the advantages of high power and good collimation. Therefore, the laser illumination distance is long, and the night vision monitoring illumination of 100 meters to several kilometers can be easily realized. The laser illumination module uses a semiconductor laser, but the high-power semiconductor laser often adopts a wide strip structure, and has a problem that the beam divergence angle is large and the light intensity distribution is asymmetric [2], so the semiconductor laser needs to be homogenized by the spot. Figure 1 shows the laser spot of the Inspur Huaguang laser after homogenization.
Figure 1 Laser spot after homogenization of wave
After the spot is homogenized, it is also necessary to use an optical beam expander to achieve laser illumination. Fixed focus illumination and zoom illumination are available for different environmental requirements. Our lasers can achieve fixed-focus illumination at different distances of 30m, 50m, 100m, etc., and can also achieve zoom illumination from 20m to 200m or more.
2.2 Laser night vision camera selection There are two main types of photosensitive elements used in cameras: CCD (Charge Coupled Device) and CMOS (Complementary Metal-Oxide Semiconductor). Both types of light-sensitive elements have a wide spectrum of induction, Figure 2 shows the spectrum of the Si-based CMOS, and Figure 3 shows the spectrum of the black-and-white CCD. It can be seen that in the near-infrared region of the two photosensors, the photosensitivity decreases as the wavelength increases. Nowadays, the wavelength of the domestic laser illumination source is generally 810 nm, and the infrared wavelength of the LED is 850 nm. That is to say, under the same light intensity, a suitable camera is more sensitive to the detection of the laser wavelength, and the imaging is clearer.
In order to ensure the image quality and avoid mutual interference between infrared light and visible light, the photosensitive element of the camera generally has a filter in front of it. When selecting a laser night vision camera, the filter must pass light near the wavelength of 810 nm.
3. Advantages of laser night vision and domestic research 3.1 Illumination distance Far laser device has high optical power and low beam divergence, which is conducive to laser beam shaping and can realize night vision illumination farther than LED dot matrix and LED array. In general, the distance of laser night vision monitoring is directly related to laser emission power, illumination angle, atmospheric environment, target reflectivity, imaging system characteristics, etc.:
Among them, Ed is the illuminance threshold for imaging the photosensitive element, P is the laser power without other light conditions, R is the illumination distance, θ is the illumination angle, ε is the illumination system transmittance, Ï is the target diffuse reflection coefficient, and μ is the atmospheric attenuation. The coefficient, Ï„ is the transmission rate of the imaging system, D is the transmission aperture of the imaging system, and f is the focal length of the imaging system [3].
For example, using a laser high-speed ball designed by our company's laser, the illumination angle is set to 0.07 rad at 200 meters. The estimation conditions are as follows: the transmittance of the transmitting and receiving optical system is related to the number of glass elements used, whether or not the antireflection coating is applied, and after the optical coating treatment, it can be around 0.9. Take ε=0.9, τ=0.9. The SONY camera has an F value of 3.0, a nominal CCD minimum illumination of 0.01 Lux, a signal-to-noise ratio greater than 50, and an illuminance threshold of less than 0.0002. It is said that the diffuse reflection coefficient of the white paper is about 0.75, and the air attenuation coefficient of the emptying is 0.0002/m. After calculation, it is necessary to see the white cardboard at 200m, and the laser power should be above 2W. Considering the air attenuation in different environments, we use 4W laser to meet the requirements of various application environments. At present, the domestically produced cloud-based laser monitoring equipment uses laser illuminator to output more than 15W, and the night monitoring distance can reach 3-5. Kilometers.
3.2 Long laser life The photoelectric conversion efficiency of the semiconductor laser is above 60%, and the heat is less than 40% of the total power. In addition, the thermal conductivity of the metal heat sink is high. At the same time, the temperature control circuit can ensure that the working temperature of the laser does not exceed 50 degrees Celsius. However, the photoelectric conversion efficiency of LEDs is up to about 25%, and more than 75% of the electric power is converted into heat. The lifetime of a semiconductor device is closely related to temperature, and the empirical formula for the lifetime of an optoelectronic device:
L(T) is the lifetime of the device at a temperature of T, Ea is the activation energy, K is the Boltzmann constant, and A is a constant [4]. It can be seen from this formula that the higher the temperature, the shorter the life, so the lifetime of the semiconductor laser can be much larger than that of the LED infrared lamp.
In addition, the study found that the failure of semiconductor lasers is mainly due to early failure and late life end failure, and the probability of occurrence of medium-term failure is small. After aging, the semiconductor laser basically eliminates the early failure products and ensures that the laser infrared lamp has a long enough service life.
The following figure shows the aging of the 2W semiconductor laser produced by 5 sets of Inspur Huaguang. The aging current is 3A. It can be seen that the optical power is basically stable after 1000 hours of aging.
Figure 5 Semiconductor laser high current aging light failure
The semiconductor laser is mainly caused by the non-radiative transition of the electron-hole pair in the active region and the high power density of the cavity surface. The high current, high temperature and high humidity environment will reduce the service life of the laser. In addition, the electric surge and static electricity will cause the semiconductor laser to fail. [4]. Our laser lighting module has advanced packaging form and circuit design, which improves the product's ability to resist high temperature, high humidity and antistatic, and reduces the failure probability of the device. The theoretical life is above 30,000h.
3.3 Synchronous Zoom Technology The laser night vision synchronous zoom technology is a technology in which the laser beam angle changes synchronously with the camera's shooting distance, ensuring that the shooting area is effectively illuminated. Some domestic laser night vision device manufacturers claim that their products have synchronous zoom technology, but the results are uneven. Many products have flashlight effects or insufficient beam utilization, which affects the monitoring effect. We use advanced electromechanical control methods to make the product with zoom laser light and integrated machine synchronous zoom with power-off memory function, effectively solve the phenomenon of vignetting, flashlight and lighting unclear.
4. Conclusion <br> <br> as active infrared technology, infrared laser technology has matured, and significantly higher than the infrared LED technology advantages: shoot the picture clearer, monitoring a wider range, longer life, more energy efficient, more cost-effective . At this stage, the civilian market is still mainly occupied by LED infrared lamps, and laser infrared is currently only used in special fields. With its superior performance advantages, laser night vision will surely achieve large-scale application in the civilian field.
Inspur Huaguang is working hard to promote the popularization of laser night vision. The "Tension" series of laser lighting products will change the pattern of the infrared monitoring market with superior performance and high cost performance. (This article is submitted by Inspur Huaguang)
References [1] Zhao Juan, Zhang Bohu, Xu Bo. Research on laser infrared night vision system[J].Science and Technology Information,2007,21:225-226.
[2] Li Zongyang. Research on beam characteristics of high power semiconductor lasers [D]. Changchun: Changchun University of Science and Technology: 2010.
[3] Shan Xiaonan. Design of active infrared night vision monitoring system for semiconductor lasers [J]. Opto-mechanical information, 2011, 12: 5-8.
[4] Lei Zhifeng, Yang Shaohua, Huang Yun. Reliability and Lifetime Evaluation of High Power Semiconductor Lasers[J]. Applied Optics, 2008, 1:90-95.
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