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 criminal investigation, medical imaging, material science, aerospace, aviation, astronomical observation and forest fire prevention, puts forward higher requirements for some outstanding performance of image sensors. In order to meet the needs of the development of modern science and technology, it is not enough to rely on the improvement of the performance of the image sensor itself. To this end, some processes that can improve the special performance of image sensors are combined with image sensors such as other devices to form an image sensor device 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 limited by space, this chapter only discusses the following very special image sensors, including low-light image sensors, infrared image sensors, ultraviolet image sensors and X-ray image sensors.
Low-light image sensor
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 objects through night vision instruments in the dark night when they cannot see five fingers. At present, many types of low-light night view 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 currently the most widely used and promising low-light night view image sensor device. This section mainly introduces the basic working principle, basic structure, characteristics and application of low-light CCD night view image sensor.
Overview of the development of low-light image sensors
Image sensors were born 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 cascaded image intensifiers, through which the observation degree of less than 0.1lx can be achieved. This kind of instrument composed of image intensifiers that can directly observe low-light scene images through the phosphor screen is called a direct-vision night vision device. Direct night vision devices play an important role in improving the combat capability of troops at night and the rapid reaction ability of troops. The guts are that the fluorescent screen of the direct night vision device is only enough for one or two people to watch, and the image cannot be technically processed, sent over a long distance, and cannot retain the image. 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 sensors, also known as low-light TV camera tubes. Compared with the direct vision 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 the long-distance transmission of the image or remote control camera; 3. It is convenient to form a TV tracking device with the photoelectric automatic control system, which is directly used in weapons guidance, command shooting and other fields, 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 night vision device in terms of volume, importance, energy consumption, cost, use and maintenance, etc., due to the advantages of the above 5 aspects, it has received more and more attention, and is widely used in national defense, public security, medical imaging and astronomical observation.
Low-light TV camera tube is widely used in military equipment, which further promotes its development, different cascade methods, different structures, different observation distances of low-light TV camera system continues to improve, CCD camera devices are also used to make low-light TV camera tube. Due to the continuous improvement and performance of CCD camera devices, CCD camera devices are also used to make low-light TV camera tubes. Because CCDs have many unique characteristics of solid cameras, CCD low-light TV camera tubes have become the latest and most promising category of products.
The model and performance of low-light television camera systems used on some military equipment. These products can be summarized into 5 types, and the main difference of each type is the image sensor device.
The first category of products is a low-light television camera tube composed of a cascaded image intensifier coupled with a light guide camera tube. The second category of products is the low-light television camera tube (MCPI-V) composed of microchannel plate image enhancement coupling light guide camera tube, and the low-light camera tube (TGI-HJC) composed of the third generation image enhancement coupling guide tube. The third category of products is a low-light camera tube (I-SEC) composed of a secondary electronic conductivity camera tube coupled with an image. The fourth category of products 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 a low-light camera tube (EB-CCD) composed of electron bombardment CCD, and a low-light camera tube (I-CCD) composed of an image intensifier composed of gallium arsenide (CaAs) semiconductor photocathode material coupled with CCD. In addition, there are low-light CCD camera tubes (TDI-CCDs) with electron accumulation methods. This type of low-light camera tube is the most promising category.
At present, there are two types of low-light CCD camera tubes, namely enhanced (I-CCD) and cumulative TDI-CCD camera tubes. Their minimum illumination has reached 10-6Lx, and the resolution is better than 510TVL. For example, the SIM-CCD launched by the German SIM Security and Electronic Systems Company works at 10-6lx, has a wide dynamic range, and can work in the illuminance range of 10-5~10-8lx. It consists of a CCD and a microchannel plate image intensifier with a resolution of up to 510TVL. Xybion Electronic Systems in California, California, USA, recently launched a TDL-CCD low-light camera, which uses arsenic gallium image intensifier and can operate in illumination below 10-6lx. The refrigeration temperature developed by B&M Spectroscopy can be as high as 10-11lx at a low temperature of -75~-150°C.