Special image sensors

Special image sensors 

   The development of modern science and technology, especially the development of high-tech undertakings in the fields of national security, public security and criminal investigation, medical imaging, materials science, aerospace, aviation, astronomical observation and forest fire prevention, has put forward higher requirements for some outstanding performance of image sensors. In order to meet the needs of modern science and technology development, it is no longer possible to improve the performance of image sensors alone. To this end, some processes that can improve the special performance of image sensors are combined with other devices and other image sensors to form image sensor devices with special functions, referred to as special image sensors.    There are many special image sensors, which should include smaller, ultra-high-speed and ultra-large image sensors, but due to space limitations, this chapter only discusses the following very special special image sensors, including low-light image sensors, infrared image sensors, ultraviolet image sensors and X-ray image sensors. Low-light image sensor The low-light night vision technology developed in the early 60s of the 20th century has already appeared low-light image sensors. Low-light night vision technology greatly improves the night vision ability of the human eye, allowing people to see distant scenery and targets through night vision instruments in the dark night when they cannot see their fingers. At present, many types of low-light night vision image sensors have been developed in the world, which are widely used in various departments such as national defense, public security, medical imaging and astronomical observation. Among them, the low-light CCD image sensor is the most widely used and promising low-light night vision image sensor device. This section mainly introduces the basic working principle, basic structure, characteristics and applications of low-light CCD night vision image sensors. Overview of the development of low-light image sensors Image sensors were produced in the 40s of the 20th century, when the photoelectric sensitivity of image sensors was still very low and could not meet the requirements of night vision. Later, people used electronic enhancement technology to make cascading image intensifiers, through which the image intensifier can observe scenery with a degree of less than 0.1lx. This instrument composed of image intensifiers that can directly observe low-light scenery images through fluorescent screens is called direct-view night vision devices. Direct vision night vision devices play an important role in improving the combat capability of troops at night and the rapid response ability of troops. The gall is that the fluorescent screen of the direct-looking night vision device is only enough for one or two people to see, and the image cannot be technically processed, sent over a long distance, and the image cannot be retained. In order to meet the needs of modern warfare, night vision instruments should be able to transmit images to the rear command system in real time, and can store and retain images. In the early 60s of the 20th century, the image intensifier and vacuum electron beam camera tube were organically combined to develop the first generation of low-light image sensor, also known as low-light TV camera tube. Compared with the direct-view night vision device, the low-light TV camera tube has the following characteristics: 1. It is convenient to use image processing technology to improve the quality of the displayed image; 2. It can realize long-distance transmission of images or long-distance remote control camera; 3. It is convenient to form a TV tracking device with the optoelectronic automatic control system, which is directly used in the fields of weapon guidance, command and shooting, and has the characteristics of strong anti-interference ability and rapid response; 4. It can be observed by more people in a wider range of places at the same time; 5. It can be recorded and stored for a long time. Although the low-light TV camera tube is not as good as the direct-view night vision device in terms of volume, importance, energy consumption, cost, use and maintenance, due to the advantages of the above five aspects, it has received more and more attention and is widely used in national defense, public security, medical imaging and astronomical observation.    The low-light TV camera tube is widely used in military equipment, thus further promoting its development, different cascading methods, different structures, different observation distances of low-light TV camera systems continue to improve, CCD camera devices are also used to make low-light TV camera tubes. Due to the continuous improvement and performance of CCD camera devices, CCD camera devices are also used to make low-light TV camera tubes. Due to the many unique characteristics that CCDs have in solid-state cameras, CCD low-light TV cameras are the latest and most promising class of products.     Models and performance of low-light television camera systems used in some military equipment. These products can be summarized into five types, and the main area of each type is the difference in the image sensor device.     The first type of product is a low-light TV camera tube composed of a cascading image intensifier coupled with an optical guide camera tube. The second category of products is the low-light television camera tube (MCPI-V) composed of an image-enhanced coupled optical guide camera using a microchannel board, and the low-light camera tube (TGI-HJC) composed of a third-generation image-enhanced coupled light guide tube. The third type of product is a low-light camera tube (I-SEC) that uses a camera-coupled secondary electron conductance camera. The fourth type of product is a low-light camera tube (I-EBS, I-SIT, I-SEM) composed of an image intensifier coupled with an electron bombardment silicon target camera tube. The fifth category is the low-light camera tube (EB-CCD) composed of electron bombardment CCD, and the low-light camera tube (I-CCD) composed of gallium arsenide (CaAs) semiconductor photocathode material coupled with CCD. In addition, there is a low-light CCD camera tube (TDI-CCD) with electron accumulation method. This type of low-light camera tube is the most promising class.   At present, there are two types of low-light CCD cameras, namely enhanced (I-CCD) and cumulative TDI-CCD cameras. They have reached a minimum illuminance of 10-6Lx and a resolution better than 510TVL. For example, the SIM-CCD launched by SIM Security & Electronic Systems in Germany works at 10-6lx and has a wide dynamic range and can operate in the illuminance range of 10-5~10-8lx. The device is constructed with a CCD and a microchannel board image intensifier with a resolution of up to 510TVL. Xybion Electronic Systems of California, USA, has recently launched a TDL-CCD low-light camera with gallium arsenide image intensifier that can operate at illuminances below 10-6lx. The cooling temperature developed by B&M Spectrum can be as high as 10-11lx at a low temperature of -75~-150°C.