Introducing SWIR Sensing Applications
We recently started a series of blog posts to explore short wave infrared (SWIR) imaging with a particular focus on emerging quantum dot (QD)-CMOS technology. The first post provided an introduction and established some of the fundamentals of why SWIR is an exciting part of the electromagnetic spectrum (1.0 – 3.0 µm) that holds a lot of potential for wider technology adoption, sharing some exciting SWIR images that were taken with a QD-CMOS camera built by Emberion, using Nanoco’s HEATWAVE® QD materials.
In this second post, we want to provide an overview of established applications of SWIR imaging, as well as highlight fascinating use cases that QD-CMOS SWIR imaging technologies can help to unlock. Before getting deeper into individual applications, it is worth pointing out that due to specific atmospheric absorptions, the SWIR range offers some unique imaging opportunities with minimal solar background radiation (~1100 nm, ~1400 nm, ~1900 nm). This is of particular interest in applications that target improving visibility in challenging weather conditions, since broad solar background can negatively impact contrast through scattering and glare. Operating in these atmospheric absorption regions with an active light source maximises signal-to-noise ratio and improves the robustness of imaging systems.
Reference solar irradiance spectrum (AM1.5 at earth surface) showing irradiance across the visible, NIR and SWIR region with indicated atmospheric absorption gaps. Adapted from [1].
Apart from the absence of background light, these bands are of particular interest due to the strong light absorption of water in these regions, which causes the atmospheric absorption in the first place. These specific absorption features can be used in a large number of existing and prospective commercial applications, ranging from skin detection, as demonstrated in Apple’s Airpods (3rd generation) to industrial and consumer-based food safety monitoring, since water-rich areas can indicate early degeneration.[2] On a larger scale, water absorption can be used in hyperspectral imaging applications targeting crop monitoring with unmanned aerial vehicles (UAVs), helping with early disease detection or water stress assessment – as shown in the image below for a vineyard (based on 1485 nm reflectance). Similar concepts also apply to mining operations where a wider adoption of high-resolution hyperspectral imaging can enable more frequent geological assessments (different minerals show varying spectral responses, here around 2200 nm), thus directing operations to areas of high value.
(Left to right) Hyperspectral image showing a water stress map of a vineyard, recorded using a UAV mounted SWIR camera.[3] Hyperspectral image exhibiting the difference in mineral distribution in an open pit mine.[4] Visible and SWIR image of food packaging, demonstrating enhanced vision at SWIR wavelengths.[5]
While these applications are based on specific molecular interactions and strong absorption of SWIR light, the other family of applications is based around transparency and reduced interactions of SWIR radiation, for example with certain types of plastics. As shown in the image above, utilising SWIR provides visibility of features that are hidden in the visible and can enhance quality control processes in manufacturing and packaging lines.
Also, due to the longer wavelengths compared to NIR and visible light, SWIR experiences less scattering by fine airborne particles, thus enabling longer range sensing/imaging in environmentally challenging conditions, caused by smog, fog or smoke. This finds use in a wide array of important areas, such as firefighting, search and rescue missions, as well as several defence applications. Based on the above, SWIR also enables improved vision capabilities in automotive applications, such as advanced driver assistance systems (ADAS), which currently rely on shorter wavelength technologies. An important wavelength for these applications is 1550 nm, as it balances longer detection ranges with improved eye safety, low solar background, as well as specific materials interactions. From a systems perspective, applications operating at 1550 nm also benefit from the widespread adoption of fibre optic communications and the established commercialisation of various optical components. While this is beyond the scope of this article, systems considerations are a driver for the success of specific applications, in particular for those requiring active illumination.
While SWIR technology has found adoption in several niche markets beyond the reach of NIR, its high cost remains a barrier to broader use. As a result, cost-effective CMOS-based NIR solutions continue to dominate many IR sensing applications. Looking ahead, significant cost reductions in SWIR sensors are expected to drive wider adoption across a range of markets. In a world driven by data, the production of low cost sensors capable of recording a wide range of spectral data could unlock a wave of exciting new applications and innovations, particularly in the consumer space. Areas of high interest include personal healthcare and cosmetics, where sensors could transform mobile devices into powerful, non-invasive diagnostic tools. In our next post, we’ll examine the working principles of QD-CMOS technology and highlight Nanoco’s key capabilities in this space. We’ll also compare QD-CMOS with established SWIR imaging technologies, such as InGaAs and Silicon-Germanium, to showcase the unique advantages QD-CMOS brings to the market. In the meantime, we will be at the International Image Sensor Workshop in Hyogo, Japan, happening from the 2nd – 5th June 2025. We look forward to discussing the latest trends and connecting with experts from the image sensor industry.
References:
[1] https://www.nrel.gov/grid/solar-resource/spectra-am1.5. Disclaimer: https://www.nrel.gov/disclaimer
[3] J. M. Meyer, R. F. Kokaly, E. Holley, Remote Sens. Environ., 2022, 275, 113000. This work is licensed under a Creative Commons Attribution 4.0 International License (CC BY 4.0). Material can be accessed at https://doi.org/10.1016/j.rse.2022.113000
[4] Z. Kandylakis et al., Remote Sens., 2020, 12, 2499. This work is licensed under a Creative Commons Attribution 4.0 International License (CC BY 4.0). Material can be accessed at https://doi.org/10.3390/rs12152499
[5] Image was recorded by Emberion using a proprietary SWIR camera, built with Nanoco HEATWAVE® QDs