A sulfur-based polymer lens could replace expensive germanium optics in thermal cameras
Thermal imaging cameras detect infrared radiation emitted by warm objects - a technology with applications spanning fire detection, wildlife monitoring, autonomous vehicle pedestrian sensing, medical diagnostics, and defense surveillance. The optics at the heart of these cameras must transmit infrared wavelengths rather than visible light, which means standard glass lenses are useless: glass absorbs the infrared spectrum. Conventional high-performance infrared lenses use germanium, a rare element that is difficult to source, expensive to process, and completely irreparable if cracked or scratched.
A germanium lens in a thermal imaging camera can cost hundreds to thousands of dollars. When dropped and damaged, the lens must be replaced entirely. As demand for thermal imaging grows in consumer products - from smartphone cameras to smart home appliances to driver-assist systems in cars - this cost and fragility profile creates a significant market barrier. Research published in Nature Communications by scientists at Flinders University in Australia describes a potential alternative built from one of the most abundant waste materials on Earth.
From petroleum byproduct to infrared optic
Elemental sulfur is produced in massive quantities as a byproduct of petroleum refining. Millions of tonnes are generated annually worldwide, and demand for sulfur in industrial applications does not keep pace with production, leaving substantial stockpiles with limited current use. Professor Justin Chalker and colleagues at Flinders University have spent years exploring how this abundant, low-cost material can be converted into useful polymers.
The new lens is made from elemental sulfur combined with an organic co-monomer material. The resulting polymer can be molded like a conventional plastic - a critical capability for mass production, since current infrared lens manufacturing relies on time-consuming milling processes. It transmits infrared wavelengths efficiently enough to produce high-quality thermal images, as the team demonstrated by mounting prototypes on thermal cameras and capturing images.
"As demand for thermal imaging in consumer products rises, there is an increasing need for lower cost optics. Our polymer lens provides a more sustainable alternative to more expensive inorganic materials such as germanium, silicon or chalcogenide glass," explained Professor Chalker. "In fact, the raw materials used to make this lens can cost less than 1 cent per unit, so it represents an extremely cost effective, competitive alternative for the thermal camera and sensor market."
Repair and recycling as core design features
The lifecycle properties may be as commercially important as the performance. Germanium lenses are effectively single-use: if damaged, they are discarded. The sulfur polymer lens can be repaired - damaged surfaces can be remolded - and the material can be recycled back into its raw components at end of life. In a market where devices are frequently dropped, particularly in field applications like wildlife monitoring or construction site inspection, repairability has real economic value.
"Some of the traditional lenses made from germanium cost hundreds or thousands of dollars and cannot be repaired if damaged. In contrast, our polymer lens is made from materials that are significantly cheaper. Even more, our polymer lenses can be molded rapidly like a plastic for mass production, and they can be repaired and recycled," said Professor Chalker.
First author Dr. Samuel Tonkin expects initial applications in smartphone IR cameras, fire detectors, driver-assist systems, and energy-saving air conditioners. Co-author Dr. Harshal Patel noted that once imaging systems reach consumer-level prices, they could become commonplace in fire detection systems and smart appliances - and that he personally plans to use them for wildlife surveys.
NASA collaboration for planetary science
The research team is working with collaborators at NASA - including co-author Dr. Tilak Hewagama - to evaluate the lens for imaging applications relevant to planetary science. Thermal imaging characterizes surface temperatures, detects geological features, and studies atmospheric properties of planets and moons. A low-cost, lightweight, robust infrared optic could expand thermal imaging capabilities on future planetary missions.
The study demonstrates proof-of-concept performance, but the detailed optical characterization data required to specify the lens for precision applications - resolution, transmission efficiency, thermal stability, and full spectral range coverage compared to state-of-the-art germanium optics - will be important for establishing where the polymer lens can directly substitute and where performance gaps remain. The research was funded by the Australian Research Council and Australia Economic Accelerator.