Short-wave infrared (SWIR) imaging and sensing is coming to consumer electronics. This technology, that has previously been limited to defence and machine vision applications, enables the capture and use of vast quantities of ‘invisible’ data, and its proliferation in this new market sector will drastically improve the performance of existing sensors, ushering in a revolution in what consumer devices can do.
From wearable electronics that can track health conditions in real time, to household appliances that can detect food freshness, SWIR sensing capability will be essential for bringing specialist applications to high street devices.
In fact, in the SWIR market, the consumer electronics segment is growing more quickly than any other. By 2027, analysts predict the market for SWIR-capable consumer devices alone will have expanded from almost nothing to $2.07 billion, with the wider SWIR technology market valued at $2.9 billion. In just four years, this technology is expected to appear in everything from affordable smartphones to augmented or virtual reality headsets.
But for SWIR capability to truly enter the consumer sector, the technology it relies on must rapidly advance. With incumbent solutions constrained by performance and cost issues, quantum dots (QDs) could offer the answer to making SWIR functionality cost effective and accessible for a wider market.
The quantum realm
SWIR light encompasses wavelengths from 1,000nm to around 3,000nm. Compared with other wavelengths, it is better at penetrating through otherwise impermeable materials and environmental conditions and is safe for the eye. For imaging and sensing, this means SWIR capability enables increased detection range and accuracy of depth measurements.
QDs are nanoscale semiconductors that can absorb and emit wavelengths of light, including SWIR. These materials are already widely used for display purposes by tuning them to respond to visible wavelengths; for example, in some television screens. However, by selecting a different type of QD materials, and controlling the size of QDs during synthesis, developers can change the wavelengths that they respond to.
Crucially, QDs offer a cost-effective, compact SWIR-sensitive technology for consumer markets that unlocks a host of new enhancements and functionalities. With the proliferation of QDs in the consumer sector, the industry will benefit from significant advancements in facial recognition, augmented reality, distance measurements, and more, enabling brands to create exciting, unique selling points that differentiate them from competitors.
SWIR applications for consumer markets
For example, biometrics sensors are already used in some modern smartphones for recognising things like fingerprints and users’ faces. These sensors, and others like them, are based on near-infrared (NIR) technology.
Both NIR and SWIR signals can suffer from reduced signals in consumer devices due to the low transmittance of display panels and the dense metal routing in screens. However, SWIR signals can suffer less from ambient light disturbance, meaning the sensors can receive more useful information and less noise.
SWIR light is also capable of passing through silicon, which is commonly used in display panels. In contrast, NIR light can be absorbed by silicon, and may lead to unintentional activation of some illuminated R/G/B pixels, which creates a white dot on the screen and causes a poor user experience. The only solution to this involves complex synchronisation of the screen and sensor operation – whereas SWIR is naturally immune. As a result, SWIR light is preferable for under-display optical sensing in the majority of cases.
SWIR-equipped devices will be able to automatically adjust their brightness depending on ambient conditions or detect incoming movement and switch off to prevent accidental touches. Wearable devices will also benefit from SWIR sensing through improvements to health monitoring functionality. Although many smartwatches can already track everything from heart rates to sleep patterns, their reliance on silicon-based visible or NIR light sensors is holding back their potential.
For example, smartwatches equipped with QDs will be able to use SWIR light to detect otherwise invisible biomarkers like alcohol levels and glucose, meaning the devices will be able to accurately monitor a far broader range of conditions. This is because SWIR sensors are powerful enough to ‘see’ beneath the skin, removing the need for invasive monitoring procedures.
As a result, fitness trackers will be able to provide their users with detailed, real-time information about their health, transmitted to the cloud and analysed immediately so users can quickly receive any support that they need.
These are just a couple of examples of how SWIR capability will benefit consumer devices. SWIR sensors can detect signs of spoilage in food before it becomes visible, meaning smart fridges could notify their owners that food is approaching its true use-by date. Virtual and augmented reality headsets equipped with SWIR technology will gain enhanced eye-tracking capabilities, enabling them to be worn for longer periods without the risk of eye strain. Earbuds can use minute proximity sensors to accurately detect when they are inserted into the ear rather than when stored into a pocket or case.
These benefits will extend into automotive applications. Light detection and ranging (LiDAR) systems are already used for external 3D mapping in cars, but equipping eye-safe SWIR technology to LiDAR systems means the laser power can be increased, improving detection ranges from 200m with NIR light to 500m. SWIR LiDAR systems are also uniquely capable of detecting reflections from road surface hazards such as ice or oil, enabling the vehicle to automatically adjust its grip for safer driving.
Changing the game
SWIR sensors are primarily limited by the cost and performance of the most common technologies today.
The most mature SWIR sensing technology is based on indium gallium arsenide (InGaAs), but these systems are expensive to produce, costing up to $10,000 per unit. InGaAs systems also suffer from limited wavelength ranges and big pixel size, while requiring bulky cooling systems that complicates making them small enough for consumer device applications.
Meanwhile, alternative silicon-based sensors are limited to NIR wavelengths and are incapable of detecting SWIR, because they become transparent in the SWIR range.
QDs offer a solution to all these problems: compared with InGaAs, QD technology has lower manufacturing costs by orders of magnitude, often costing just a tenth the price of the larger devices. QDs enable image designs with smaller pixel pitch than InGaAs, leading to improved resolution, and also benefit from extended spectral absorption range. This makes QDs the first viable SWIR technology for consumer markets.
However, the inherent toxicity of the best performing QDs has so far limited their proliferation in consumer devices. Most QDs are formulated using lead or other toxic heavy metals, limiting their use for consumer applications due to the restrictions that many markets have placed on lead. Although heavy metal-free alternatives do exist, they have so far been held back by inherent performance issues, preventing them from reaching above 1,400nm.
These performance issues are due to how QD growth changes with particle size. As the peak wavelength that QDs are sensitive to approaches the 1,100-1,200nm range, their growth becomes harder to control, because the chemical reactions involved in their production are difficult to scale and regulate.
However, thanks to a recent breakthrough in lead-free QD synthesis, these semiconducting nanocrystals will soon become available for consumer SWIR applications. Quantum Science, an expert in infrared QD technology, has recently created lead-free QDs responsive to 1,550nm. No longer limited by low performance, these INFIQ QDs are suitable for highly demanded functions like advanced face ID, 3D sensing, eye-safety tracking, and many more.
INFIQ lead-free QD technology is the key to bringing SWIR imaging and sensing to consumer markets and makes vital infrared data available for consumer device applications, heralding a revolution in the consumer electronics market.
Author details: Dr Hao Pang, CEO and Founder, Quantum Science
