Development of photoelectric detection technology

Photoelectric detection technology is a kind of technology that detects and identifies the object according to the light wave's characteristics radiated or reflected by the detected object. This technology endows the photoelectric technology with four advantages in a military application: to see more clearly, fight more accurately, respond faster and survive better.

Photoelectric detection technology is the core technology widely used in modern war, including photoelectric reconnaissance, night vision, navigation, guidance, homing, search, tracking, and identification. Photoelectric detection includes the detection of optical signals from ultraviolet (0.2-0.4 μ m), visible (0.4-0.7 μ m), infrared (1-3 μ m, 3-5 μ m, 8-12 μ m), etc.

The new generation of photoelectric detection technology and its intellectualization will enable the related weapons to obtain longer working distances, more robust single target / multi-target detection. And recognition ability, achieve more accurate strike and rapid response, and receive the initiative in minimal casualties. Simultaneously, the weapon equipment has a robust independent decision-making ability, which enhances the ability of confrontation, counter confrontation, and their survival. Advanced photoelectric detection technology has become an important symbol of a country's military strength.

The prominent feature of modern high-tech war is an information war, and the first task of information war is how to obtain information. Who gets more information, who receives the data first, who has the initiative of information war. Photoelectric detection is an essential means to obtain information. Microwave radar and optoelectronic imaging equipment are often used to learn from each other and complement each other. They can get more information and contact information earlier. The former has a long operating distance and can work all-weather; the latter has a high resolution, strong recognition ability, and anti-interference ability. No matter reconnaissance satellite, early warning satellite, early warning aircraft, or uncrewed reconnaissance aircraft, they are often equipped with synthetic aperture radar, CCD camera, infrared thermal imager, or multispectral camera at the same time. To improve ballistic missiles' early warning capability, the space-based infrared system (SBIRS), being developed in the United States, plans to use a dual-sensor scheme. A broad field scanning short wave infrared capture sensor and a narrow field staring multi-color tracking sensor can capture and track ballistic missiles' whole process from launch to re-entry into the atmosphere. The cr-135s Cobra ball early warning aircraft has been equipped and improved in the United States. Uses visible light and medium wave infrared camera to accurately measure the missile launch at a distance of 420km, determine the engine flameout point, and calculate its trajectory and collision point. Recently, a long-range laser rangefinder has been added to it, with an operating distance of 400km. The U.S. Navy is also developing an airborne photoelectric sensor system for active/passive surveillance of the theater ballistic missile defense system known as the "guard" system. It includes an infrared search tracker (IRST), a dual-band six × 960 HgCdTe detector array with a detection distance of 800km, a range finder/tracker (LR / T), a 128 × 128 InSb focal plane array to precise track (about five μ RAD) targets, and a laser to target range (100-1000km), to obtain real-time three-dimensional information of long-distance targets and win sufficient early warning Time.

In other photoelectric technology applications, such as precision guidance, navigation, fire control, counter weapons, communication, display, and so on, all play an essential role.

Photoelectric detection technology

1. Visible light detection

Visible light CCD and CMOS imagers are widely used in military remote sensing, reconnaissance, aircraft navigation, missile and bomb guidance, and other modern military equipment because of their small size, lightweight, low power consumption, long life, reliability, and impact resistance. It is also widely used in civil applications, such as security, monitoring, a video doorbell, video e-mail, video phone, video conference, digital camera, medical and Bioscience experimental records, etc. CCD and CMOS imagers are used.

    The modern visible light imager has been digitized, saved in the floppy disk, hard disk, and CD, and then read, displayed, and printed out by computer. This kind of image can also be patched, cut and pasted, and transmitted over a long distance, which is also one of modern communication's main contents.

    The necessary indexes of the advanced image sensor are definition (photosensitive element number), sensitivity (quantum efficiency), dynamic range (full well charge number). Therefore, modern advanced technology improves these bases further This indicator and efforts to improve the above image properties.

2. Infrared acquisition

Because any object whose temperature is higher than absolute zero will radiate infrared rays. That can detect the existence of the thing even in the absence of light at night by using a proper detector sensitive enough to infrared rays what shape image can also be obtained. The temperature and radiation peak wavelength of some familiar objects are shown in Table 1.

Table 1 temperature of typical objects and wavelength of infrared radiation

Photoelectronic can see that the infrared radiation of the objects encountered in the war is mostly between 1 and 12 μ M.

However, not all the signals in this band can travel far in the atmosphere. The practice shows that only three band signals can travel far in the atmosphere. They are respectively called short wave infrared (SWIR, 1-3 μ m), mediumwave infrared (MWIR, 3-5 μ m), and longwave infrared (LWIR, 8-12 μ m). Generally speaking, military infrared technology is mainly aimed at these three infrared bands, and the emphasis is still on medium wave and long wave infrared.

   The core of infrared detection equipment is the infrared detector. In a sense, the level of the infrared sensor determines the performance of infrared photoelectric detection equipment. Generally speaking, the unit and multi-element devices are called the first generation infrared devices. The focal plane line array and array are called the second generation devices, and the dual (multi) band and intelligent focal plane devices are called the third-generation devices. Accordingly, they have evolved into infrared devices—the generation of photoelectric detection equipment.

2.1 PtSi Infrared Detector

This is the early infrared detector, which works in the medium and short wave. Its relatively simple manufacturing process, good original uniformity, and relatively low cost have obtained early military applications. For example, the early rattlesnake missile's infrared guidance is the use of the PtSi detector. Still, because of its low quantum efficiency and quiet performance, it affects weapons and equipment's performance. After InSb, the HgCdTe detector was replaced.

2.2 InSb infrared detector

InSb working band is currently the most widely used and researched in a medium wave. The military is often used as a 128 × 128 yuan staring array for the seeker. Because of its better performance/price ratio, new air-to-air missiles developed by the United States, Britain, Germany, and Israel all use this specification. 256 × 256640 × 480 or 512 × 512insb detectors are required for precise and high-speed images or use on high-value occasions. The "sniper" pod produced by Lockheed Martin company in the United States, the affair pod developed by Raytheon company, the listening pod developed by Northrop Grumman company in cooperation with Rafael company in Israel, and an / aaq-22 saf developed by forward-looking infrared system company in the United States The world's most advanced forward-looking, navigation and aiming equipment, such as ire thermal imager, use 640 × 480 yuan or similar InSb array. 2000 × 2000 InSb combined with visible light into a low frame rate, a two-color camera has been reported for the battlefield and environmental monitoring.

2.3 HgCdTe infrared detector

Due to the HgCdTe infrared detector's invention, it is possible to detect low-temperature targets (requiring longwave detection). the former two types of infrared detectors can be replaced in principle, so advanced western countries develop this kind of detector. It is still focused on the second generation and the third generation of infrared detectors. This detector is divided into 4 (6) × n-line array focal plane and array focal plane. The former is mainly more mature than the latter, adopting parallel scanning technology. It can achieve higher performance of array focal plane with the same number of elements, and the price is lower than that of array focal plane. Therefore, western countries are also developing typical 4 × 288, 4 (6) × 576, 6 × 960, etc.; typical types of array focal plane are 128 × 128256 × 256 (or 320 × 256), 512 × 512 (or 640 × 480), 1024 × 1024, etc.

2.4 GaAs/AlGaAs Quantum well-infrared detector（QWIP）

The quantum well infrared focal plane detector has application value in the large array and bicolor focal plane with the scale of 384 × 288640 × 512. At present, it is mainly used in industry and medical treatment. There are also applications in the military field where long-time integration is allowed. For example, the German tank driver observation thermal imager uses a 640 × 512 longwave quantum well infrared focal plane detector with a spectral response range of 8-9 μ MUncooled infrared focal plane detector. The most potential development direction of a quantum well infrared focal plane detector in the future is military space application, such as polychrome (4-color), ultra-long wave (14-16 μ m) large area array.

2.5 Uncooled infrared focal plane detector

Because of the disadvantages of a refrigerated infrared focal plane detector, such as high power consumption, high cost, and inconvenient operation, many countries are looking for new technology to manufacture uncooled infrared focal plane. At present, the technology is developing rapidly. An uncooled infrared focal plane detector has been designed to 320 × 240640 × 480 scales. Uncooled infrared sensors can be divided into two types: ferroelectric type and thermal resistance type. The development of uncooled infrared detectors based on vox and x-si thermal resistance is fast. The main technical focus is to improve the array's size to reach the order of 640 × 480 yuan and reduce the size of photosensitive elements to get the center distance of 25 μ m. further improve the noise equivalent temperature difference, dynamic range, and other essential performance indicators, also reduce the cost and convenient use. It is mainly used in industry, security, individual weapon observation and aiming, etc. Its price is relatively low, and it is also used in the guidance of short-range missiles with low-performance requirements.

2.6 Third-generation infrared detector

The United States has begun to develop the third generation of infrared sensors and put forward the concept of the third generation of infrared thermal imagers. Mainly two-color or three-color high-performance, high-resolution, refrigerated thermal imagers and intelligent focal plane array detectors. The U.S. night vision and electronic sensor administration believe that the development of the third generation of infrared sensors is the key to maintaining the United States' advantages in the night war. Therefore, the long-term development trend of infrared detection technology is to develop the third generation of infrared detectors. The main parameters of the third generation of infrared focal plane detectors are shown in Table 2.

Table 2 required performance parameters of the third generation infrared detector

Due to the continuous improvement of foreign infrared detector technology, it is quite difficult to upgrade the technology on the detector chip. In order to further improve the performance of infrared detector, people are now turning their attention to the signal readout integrated circuit (ROIC) of infrared detector. With the development of computer technology and integrated circuit, ROIC has made great progress. Medium scale infrared focal plane array and corresponding readout circuit have formed production scale in 1990s. Now advanced countries are developing ROIC and intelligent focal plane array for large-scale focal plane array (third generation device) and its multiple functions.

Smart focal plane array is also called on-chip system. On-chip signal processing means to imitate the function of vertebrate retina on the chip of photosensitive element or in the area closest to photosensitive element, to process the signal after light electricity conversion in the early stage, and then output the subsequent data processing. Although this process does not belong to the process of receiving optical signal directly, it has a great influence on the comprehensive performance of photodetector.

3.UV detection technology

UV detection technology has many applications in national defense, national economy and scientific research fields, such as missile threat warning, interstellar communication, chemical and biological warfare agent detection and spectral measurement, engine and nuclear reactor monitoring, plant growth, radiation dose measurement, water purification, pollution monitoring (such as ozone) flame detection, gas (generator) furnace monitoring and UV astronomy.
In the past 20 years, there are mainly three types of UV detectors, namely photomultiplier, imaging UV sensor and AlGaN / GaN photodiode imaging array, which are called the first, second and third generation UV imaging sensors.
In many of the above applications, we hope to detect only ultraviolet light rather than visible light and infrared radiation, especially sunlight, so as to reduce false detection and background flux. So in recent years, the research in the field of short wave ultraviolet detector focuses on the realization of "solar blind" detector, that is, the detector insensitive to photons above ~ 280nm, which is called the third generation ultraviolet detector.
The military applications of ultraviolet detection mainly include missile guidance, incoming missile warning, biochemical agent detection, military meteorology and military short-range communication, etc.

4.Micro imaging sensor

The main feature of micro imaging sensor is that its size is significantly reduced, the spatial resolution is high and the power consumption is low. The main application fields of micro imaging sensors are robots, micro vehicles, micro aircraft, micro spacecraft, unattended sensors and monitoring networks, as well as alert and law enforcement. Its application prospects are as follows:
·Network sensing points supporting NCW
·Portable surveillance and unattended networked surveillance for battlefield intelligence
·Video control of UAV and ground UAV
·Automatic monitoring for facility alert
·Target recognition of smart weapons
·Precise aiming system for armored vehicles and missiles
·Robot vision
·Public security, border patrol, law enforcement and traffic surveillance
·In the next few years, the overall goal of videoconference in terms of micro sensors is:
·Small scale integrated network demonstrating micro sensors for acoustic, seismic and infrared imaging;
·Verify the application of ultra light, low cost and small volume 3D integrated package in the affordable compact design;
·A self-organizing network is developed to support the secure communication of processed information. The tactical communication distance between the network area of microsensor and the warfighter is up to 10km.

5. Imaging polarization detection

The purpose of imaging polarization detection technology is to improve the contrast of the target, suppress the background clutter, provide the information of the target surface material, and distinguish the natural object and the artificial object. Therefore, imaging polarization detection can improve the detection and recognition ability of targets, and it is possible to detect camouflaged targets in isothermal objects.
At present, there are short wave, medium wave, long wave and multispectral, hyperspectral imaging polarization detection experiments. The main experiments are mine detection, cloud measurement and the detection of sea surface temperature, emissivity and sea wind vector on the earth's ocean surface. It should be said that they are still in the early stage of research.

6. Multispectral / hyperspectral imaging technology

Optical remote sensing is an effective method to collect target and background data. However, due to the limited optical spatial resolution, the spatial information based on the radiation intensity does not always provide enough target information, such as small targets in a long distance or targets hidden in a brighter background interference, which can not be distinguished only according to their radiation intensity characteristics. Therefore, it is more and more important to use multi-dimensional discrimination methods such as spectral characteristics, polarization characteristics and time characteristics to identify the target and background in remote sensing. Spectral imaging is developed under this concept. Spectral imaging technology can be roughly divided into three categories according to the number and resolution of wavebands: multispectral imaging, with 10-50 wavebands and 0.1 spectral resolution (Δλ / λ); hyperspectral imaging, with 50-1000 wavebands and 0.01 spectral resolution; Polarographic imaging, with 10-100 wavebands and 0.001 spectral resolution. At present, a variety of multispectral or hyperspectral imaging systems have been equipped with remote sensing satellites, such as IKONOS satellite and reconnaissance aircraft such as U-2 high altitude reconnaissance aircraft, except polar spectral imaging technology is not used for military remote sensing. The key civilian applications are environmental monitoring and resource management.
The analysis of multispectral / hyperspectral imaging data shows that the value of this unique data lies not in whether it can produce beautiful images, but in the information inherent in the unique spectral characteristics obtained by the multispectral / hyperspectral imager, such as the information of vehicles hidden under trees and buried mines.

Visible CCD and infrared HgCdTe focal plane arrays are the most widely used focal plane arrays in multispectral imagers. In the future, CCD and polychromatic infrared focal plane arrays will still be the main trend.
The technical characteristics of its development are: to improve the spectral resolution as much as possible; to make full use of all kinds of electromagnetic spectrum that can pass through the atmosphere; to expand to infrared, far infrared and microwave; to divide the spectral segments into more detailed. For example, the U.S. land satellite thematic mapper has 7 spectral segments; AVIRIS airborne visible and infrared multispectral imager is divided into 224 bands in visible and infrared spectral segments; China's airborne spectral imager has 72 bands, including 32 visible bands, 32 short wave infrared bands and 8 long wave infrared bands.
Therefore, in the future, remote sensing technology will be integrated with multispectral / hyperspectral imager, interference radar, passive radar, synthetic aperture radar and other multisensors, which can collect multi-dimensional data at the same time. Through advanced data fusion technology, sufficient target information can be obtained, so that remote sensing technology will be multi-scale, multi band, all-weather, high-precision, efficient and fast Goal development.

7. Lidar imaging technology

It is the target of lidar to identify, classify, detect and aim military targets precisely. Lidar has become the key development of high sensitivity detection radar because of its strong anti-jamming and imaging ability.
In many image processing, automatic target recognition (ATR) is needed, which promotes the development of lidar. For example, in the detection of static targets in terrain background, Doppler radar and visible or infrared thermal imaging system have their own difficulties. The advantage of lidar is that each pixel has not only high angular resolution, but also accurate range data, with stable target and background characteristics, so it can accurately model in ATR system. Of course, in some applications, due to the narrow beam and limited scanning speed, lidar needs to work together with infrared, visible and millimeter wave radars, and then improve the system performance through data fusion. At present, laser imaging technology mainly includes scanning imaging, laser illumination range gated imaging, laser illumination single imaging and coherent lidar.
The principle of lidar is the same as that of radio radar, but the difference is that the optical band laser transmitter and the corresponding laser receiver are used. In the early stage, CO2 laser has been used as the transmitter of lidar, and a variety of ground-based and airborne prototypes have been developed. However, due to the large volume of CO2 laser, the large optical aperture, and the need for refrigeration of detector and other factors, its mobile environment, especially the competitiveness of Airborne tactical application, has been restricted. With the development of laser diode pumping technology (DPSSL) and new solid-state laser materials, small solid-state lidar with high efficiency, all solid and eye safety is developing, which has been used in heterodyne Doppler lidar, range imaging and obstacle avoidance. Due to its small size, light weight, solid reliability, high efficiency and low cost, semiconductor laser diode has great potential in the application of lidar due to its rapid development in recent years. It is typically used in helicopter obstacle avoidance and ground object detection. The biggest application advantages in front of it are robot vision system and laser underwater target imaging detection.
It is precisely the focal plane array detector array that is suitable for laser detection that has become the key to the development of floodlighting single imaging.

8. Multisensor data fusion technology

Modern detection technologies are all working towards the direction of multi-sensor fusion to make up for some defects of single detection technology, so that the detected target information can be as rich as possible, accurate, rapid and real-time, so that in wartime, the priority and initiative of information can be grasped, and the precious time of first mover can be won, so as to win the victory of the war. Because multi-sensor fusion is bound to adopt data fusion technology; at present, due to the emergence of new advanced sensors and advanced processing technology, as well as the improvement of software and hardware, real-time data fusion is more and more possible to achieve and get rapid development.
The sensor types of single platform equipment may include: radar, laser rangefinder / target indicator / tracker, forward looking infrared system, TV (including laser TV), IFF, radar warning machine, missile approach warning receiver, laser warning receiver and other different types of sensor fusion.
Multiple platforms equipped with different types of sensors can significantly expand the space, frequency and time domain of sensor detection by means of increasingly mature data link technology.
To sum up, the actual optoelectronic technology is the expansion and extension of the radio band, and provides a wider new field for the highly developed electronic technology. Therefore, the photoelectric detection technology is one of the important technologies in the detection technology field. The important, rather than the only one, is the discussion of the photoelectric detection using its detection characteristics and other detection technologies. It is complementary rather than alternative. The purpose is to acquire information as rich, accurate, rapid and real-time as possible, so as to grasp the information priority and initiative in wartime, and win precious first mover time, so as to win the victory of the war. Therefore, photoelectric detection technology needs to attract the general attention of the industry and occupy a certain position in equipment development.

Author brief introduction

Zhang Weizhong (1941 -), graduated from Shanghai Jiaotong University in 1964, engaged in laser technology research after graduation, professor level senior engineer.

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