Welcome Physics World  June 2021

Keeping an eye on optical innovation

Welcome to this Physics World Optics & Photonics Briefing, which highlights the latest developments in areas including lasers and detectors, solar power, medical imaging and high-resolution displays.

Detection of light is fundamental to many photonics-based applications. To improve this light-sensing task, researchers have turned to the natural world for inspiration – and where better to start than the eye itself? A team headed up at Oregon State University in the US has devised a new type of sensor that mimics how the human eye responds to changing visual stimuli (“Perovskite sensor sees more like the human eye”). Rather than detecting the intensity of the input light, the new “retinomorphic” device is sensitive to changes in levels of illumination. This means that it inherently filters out static images, providing a voltage solely in response to movement. Such a sensor could potentially act as a building block for neuromorphic computers, as well as finding use in fields such as image recognition, autonomous vehicles and robotics.

And it’s not just human eyes that give rise to new devices. Researchers in the US and Korea have created a novel optical sensor inspired by the mantis shrimp, which is thought to have the most complex eyes in the animal kingdom. As well as detecting 12 different spectral channels, the mantis shrimp can also analyse the polarization of light. To achieve similar functionality, the researchers stacked polarization-sensitive organic photovoltaics and folded polymer retarders to create a compact sensor that can detect four spectral and three polarization channels, and could ultimately be designed to sense 15 spectral channels over a 350 nm bandwidth (“Mantis shrimp inspires dual action light sensor”).

In parallel to eyes motivating the invention of new light detectors, optical imaging also plays a central role in keeping the eye healthy, by providing non-invasive diagnosis of eye disease. Researchers at the Medical University of Vienna are developing an optical coherence tomography method that measures the diffusion of tracer particles to image vascular leakage – an important biomarker of vision-threatening retinal diseases such as age-related macular degeneration and diabetic retinopathy. In experiments in mice, the technique could clearly visualize leaky blood vessels and track leakage over time.

Elsewhere, a team at the National Eye Institute in the US has combined two imaging methods – annular pupil illumination and sub-Airy disc confocal detection – to visualize photoreceptors at the back of the eye in greater detail than ever before. The new sub-diffraction imaging technique could enable earlier detection of eye disease and help develop and assess new therapies.