What are SWIR Sensors?
Short-Wave Infrared (SWIR) sensors are sensors that are designed to detect and capture electromagnetic radiation in the short-wave infrared region, wavelength typically ranging from 1000 nm to 2500 nm. Unlike visible light sensors that operate within the visible spectrum of 400 nm - 700 nm, SWIR sensors exploit the longer wavelengths that fall just outside this range. The SWIR region provides unique advantages, including the ability to penetrate fog, smoke, and certain materials, making it an ideal solution for challenging imaging conditions. The SWIR wavelengths are beyond the perception of human eyes, allowing SWIR imaging to frequently produce superior images compared to those captured using visible light.
Working of SWIR Sensors
SWIR sensors utilize a combination of technology, including indium gallium arsenide (InGaAs) or mercury cadmium telluride (MCT) detectors, to capture and convert SWIR radiation into visible images or data. These detectors are highly sensitive to the SWIR spectrum, allowing them to detect even the faintest signals. The captured data can then be processed and displayed, providing valuable insights that are often invisible to the naked eye.
InGaAs Sensors
Several manufacturers produce SWIR imagers and Focal Plane Arrays (FPAs) that can detect different segments of the electromagnetic spectrum. SWIR imagers refer to short-wave infrared imagers, which are devices used to capture images in the short-wave infrared range of the electromagnetic spectrum. They are capable of detecting wavelengths typically ranging from 1.4 to 3 micrometers. Whereas focal plane arrays are sensor arrays that are used in imaging systems to convert incoming light into electrical signals. They are composed of a grid of individual light-sensitive pixels, each capable of detecting and measuring the intensity of light.
One important type is the InGaAs sensor, which sets itself apart by not requiring cryogenic cooling. In certain types of sensors, such as infrared sensors, cryogenic cooling is required to improve their performance and sensitivity. But InGaAs sensors exhibit good performance even at higher temperatures.
InGaAs is a semiconductor fabricated with a specific combination of Indium, Gallium, and Arsenic, which grants it a spectral response ranging from 0.9 to 1.7 µm. They can detect both Near Infrared (NIR) and SWIR. InGaAs generates approximately 80, 90, or even more photoelectrons per 100 incident photons.
An InGaAs sensor possesses a hybrid structure that merges a CMOS readout circuit made of silicon with an InGaAs photosensitive array. The process of integrating the InGaAs array with the readout circuit is a comparatively intricate and time consuming one, involving numerous manufacturing steps. Moreover, the production yield is relatively low, resulting in higher costs for these sensor types compared to CCD or CMOS sensors. A drawback of these sensors lies in their inability to detect shorter wavelengths corresponding to visible colors, primarily due to the constraints of the manufacturing process. Some of these constraints are sensors' composition, structure, or materials used in their fabrication that is not optimized for detecting visible colors or shorter wavelengths of light.
Achieving 100 percent accuracy and uniformity in combining the readout circuit with the photosensitive area is currently technically impossible. As a result, these sensors unavoidably exhibit a small percentage of defective pixels (less than 1 %) and each pixel displays slightly different behavior compared to CCD or CMOS sensors. Without any image preprocessing within the camera, the raw image appears noisy. Camera manufacturers employ diverse techniques to enhance the image quality before it is transmitted to the image-processing system. These techniques include image processing algorithms, optical image stabilization, high dynamic range, noise reduction techniques, image sensor advancements, and Optical design & lens quality.
Mercury Cadmium Telluride Sensors
Mercury Cadmium Telluride (MCT) sensors are highly sensitive devices used for detecting and measuring infrared radiation. These sensors are constructed using a compound semiconductor material made from a combination of mercury, cadmium, and tellurium.
Due to their unique composition, MCT sensors exhibit exceptional sensitivity to infrared radiation, enabling them to detect even weak infrared signals with remarkable accuracy. This sensitivity makes them ideal for various applications such as thermal imaging, surveillance, remote sensing, and scientific research. Additionally, MCT sensors can be tailored to cover specific wavelength ranges by adjusting the composition of the material, allowing for precise detection and analysis of infrared radiation.
Applications of SWIR Sensors
SWIR sensors have revolutionized surveillance systems by enabling night vision capabilities and the ability to see through atmospheric obscurants. They can detect concealed objects, identify individuals in low-light conditions, and aid in perimeter security, making them invaluable tools for law enforcement and military operations.
They are instrumental in assessing crop health, monitoring irrigation, and identifying potential plant diseases. By analyzing the reflected SWIR radiation from plants, these sensors can detect stress levels, optimize water usage, and facilitate early intervention to prevent crop losses.
SWIR sensors play a critical role in manufacturing and quality control processes. They can identify material composition, inspect product integrity, and detect defects that are not visible under visible light. This helps in ensuring product quality, reducing waste, and enhancing overall efficiency.
They have shown promise in various medical applications. They can penetrate tissue deeper than visible light, enabling non-invasive imaging techniques such as blood vessel visualization, tumor detection, and monitoring oxygen saturation levels. SWIR imaging can aid in early disease diagnosis and improve patient outcomes.
SWIR sensors contribute to environmental research by capturing valuable data about vegetation, water quality, and pollution levels. Their ability to penetrate water and measure unique spectral signatures allows scientists to monitor ecosystems, study climate change impacts, and make informed conservation decisions.
