Quantum Tech

The quantum revolution in SWIR sensing

5th June 2023
Paige West

Short-wave infrared (SWIR) detection is heralding a new age of sensing and imaging technology. Compared with other wavelengths used in sensing, SWIR suffers less from parasitic ambient light and enables powerful active illumination, which improves the signal-to-noise ratio, expanding the functionality of various applications.

This article originally appeared in the May'23 magazine issue of Electronic Specifier Design – see ES's Magazine Archives for more featured publications.

However, the proliferation of SWIR technology has been hampered by a lack of sufficiently powerful or affordable systems. To bring SWIR into wider markets, a mass technology disruption will be needed.

That disruption will be provided by quantum dots (QDs).

QDs are nanoscale semiconductors capable of absorbing and emitting light across the infrared spectrum, including SWIR. Unlike other SWIR sensing technology, QDs are powerful enough to capture the detailed visual data required by electronics manufacturers while costing around a tenth of the price and matching the high performance of other solutions such as InGaAs sensors.

As a result, QDs provide the best of both worlds, making unified sensing and imaging available and affordable to everyone by providing widespread access to this essential invisible data. Adopting this technology will be key to taking SWIR sensing from niche applications to the mass market.

Consumer applications

Existing applications for SWIR imaging are limited by the price (often a few thousand dollars per chip) and the resulting availability of the technology. This has so far restricted its use to medical, defence, and industrial purposes, such as semiconductor defect inspection or optical sorting. While SWIR sensing is sometimes used in consumer markets (e.g. skin detection in headphones and proximity sensing in smartphones), improving the quality of data accessible with high-performance QD sensors will expand the range of applications massively.

For example, QD SWIR sensors will literally change the face of smartphones. Front-facing cameras not only take up valuable display space on phone screens when the industry is trending towards edge-to-edge design, their silicon-based composition means they can be imprecise and unreliable. In contrast, SWIR sensors can be made thinner than ever, and can be placed behind the OLED screen which is transparent in this wavelength range.

SWIR sensing also provides a solution to barriers that have prevented the wholesale adoption of virtual reality headsets and limited them to use in gaming. When worn for long periods, VR headsets can become uncomfortable due to their potential for eye damage caused by near-infrared light. They can also struggle to operate in bright conditions.

QD sensors are small and light enough to fit on a headset while possessing the advanced sensing capabilities to accurately map spaces at increased distances. These sensors can also track the movement of fine features like fingers, removing the need for separate controllers, suffer less from solar illumination, and even offer extended battery life. They can also be finely tuned to only emit and absorb non-damaging wavelengths, allowing the headsets to be safely worn for extended periods.

Fitness trackers are already common sights in the consumer electronics market, but by using QD sensors, SWIR detection will make these devices more accurate and unlock exciting new features. Current trackers use LED light to detect blood flow and monitor users' heart rates, or ECG technology to track the electrical impulses that cause the heart to pump.

In contrast, SWIR sensors can peer beneath the skin to detect important changes in melanin or haemoglobin levels. This enables real-time health monitoring, transmitting data to the cloud for analysis and immediate action if required. This could also provide a non-intrusive way for people with diabetes to monitor their glucose levels and blood sugar levels by looking at their watch.

In security and surveillance cameras, SWIR detectors replace reliance on near-infrared technology that has reduced performance over long range and inclement weather conditions particularly in foggy or rainy weather. SWIR cameras demonstrate upgraded visual quality, capability, and overall performance, seeing much further even in low light. They can see through obscurants like smoke and dust to ensure accuracy in all conditions.

This ability also benefits the automotive sector; with current vehicle LiDAR (Light Detection and Ranging) systems often limited on wet or snowy roads due to light reflection, QD-based SWIR sensors will enable enhanced performance and take the LiDAR effective range from 200m to 500m. As a result of this increased range and sensing power, QDs could even help make truly autonomous vehicles a reality.

Industrial applications

That is not to mention the improvements that QDs offer to existing uses of SWIR sensing technology. With factories increasingly using SWIR to sort products or conduct quality checks, the superior sensing and imaging capability of QDs, with sensitivity to wavelengths of 1,700nm or longer, offer revolutionary benefits.

For example, these devices could scan through silicon wafers to identify microscopic defects or enable machines to examine fruit for bruises hidden beneath the surface. From plastic sorting to solar panel inspection and pharmaceutical quality monitoring, there are many ways that SWIR light can help identify whether products have been contaminated with another substance.

At wavelengths of 2,000nm, QDs unlock hyperspectral imaging capabilities far beyond what is currently available. Using previously hidden data, these devices allow us to see beneath the surface of the earth, objects, or even people, to identify contaminants in the soil or subdermal health issues that would otherwise be much harder to detect. This could allow farmers to significantly boost their crop yields and help doctors treat health conditions before progressing to a more serious stage.

Upscaling supply

Supplying these emerging markets will require vast increases in sensor production. For SWIR to truly penetrate consumer devices, QD developers will need to be able to create millions of units at a minimal cost.

Most QD production processes experience low throughput and a high risk of defect formation. Attempts to commercialise this technology utilise spin-coating, depositing up to 10 thin QD layers sequentially and washing them with chemical treatments. This protracted process is wasteful and inefficient, resulting in low QD yield.

However, nanomaterials developer Quantum Science has overcome this problem with an innovative approach to QD synthesis. Quantum Science has formulated stable colloidal QD inks that can be deposited in a single step by conducting the ligand exchange process in solution. This removes the need for further chemical processes, minimising waste and the chance of defects forming.

This efficient process facilitates the mass production of high-performance optoelectronic devices, helping to bring evolutionary sensing technology to market more quickly than ever. Quantum Science's INFIQ QD solutions can capture wavelengths from 800nm to 2,400nm, and boast high optical performance, uniformity, and stability. By the middle of 2024, they will enter existing product lines to serve the market's needs. The company has also already launched its non-toxic QD solutions for sampling customers with widespread release anticipated soon, offering an alternative suitable for a wider range of applications.

The potential of SWIR sensing to overhaul technology as we know it is world-changing. The ability to supply QDs at scale will be critical to meeting market demand in the coming years and ensuring everyone can benefit from this invisible data.

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