All-Optical Near-Infrared Imaging via Semiconductor Nanocrystals - Renewal

This project is developing a new technology for Near Infrared (NIR) light imaging that is ultra-compact and multi-colour. Human eyes only see 0.0035% (visible light) of the electromagnetic spectrum around us. Among all invisible spectra, the NIR range is of particular interest because of its broad application, for example for medical diagnosis, food quality control, autonomous vehicles, and night-vision.

In conventional NIR-imaging technology, the NIR light gets converted to electrons and the resultant image is projected onto a display, where electrons get converted to light again to be viewed by the eye. Therefore, the converted images are monochrome. Moreover, this display blocks the perception of visible light, therefore disrupting normal vision.

Also, such cameras are either only operational in a short wavelength band (e.g. Ge or InGaAs, converting up to 1800nm) or require cooling (e.g. InAs or InSb detectors operating at -200 C). Moreover, NIR cameras must be bulky to accommodate all components for light/electron conversions.

The detectors used in today's technology mean that the aforementioned limitations cannot be avoided. This project is developing a new technology for NIR-imaging that is all-optical, i.e. no longer requires optical and electric signals to be converted to each other. This technology employs engineered nanocrystals, embedded within a thin and transparent layer, that capture the infrared light and re-emit it in the visible range. This approach offers new functionalities as a result of:

i. being ultra-compact; ii. forming colour images from invisible objects; iii. being transparent in both visible and NIR ranges; iv. capturing the visual information in the range of 400-4000nm, that is 10 times wider than the visible spectrum.

Such a revolutionary technology will be provided as a transparent thin and flexible layer that can upgrade any glass surface e.g. goggles and windows, to an NIR-imaging device, enabling a view over both visible and infrared frequencies concurrently. Therefore, information that is currently invisible to the naked eye will become visible - the ripeness of fruits and species health.

This technology will also enable us to see invisible objects in the dark. Imagine no light pollution and a massive reduction in greenhouse gases associated with a world where the lighting was not required to see at night.

To develop this technology, engineered arrays of nano-crystals, called metasurfaces, are being exploited. These metasurfaces are often a few hundred times smaller than a human hair. In the first phase of the project, we have managed to comprehensively study the ability of nano-crystals and metasurfaces for NIR imaging.

Subsequently, we have proposed an approach to enhance the capacity of metasurfaces for colour conversion by mixing NIR light with an extra laser beam and employing sum-frequency generation. As a result, we have demonstrated and patented the first prototype of nonlinear metasurfaces that can be used for NIR imaging. In the renewal stage of this project, we first demonstrate an innovative approach to generate colourful images by multi-resonant metasurfaces.

Consequently, we will exploit engineered metasurfaces for quantum imaging, as the final step for delivering the overarching aim: A novel NIR imaging technology at the nanoscale with low noise, high resolution, low power consumption, and the ability to work at room temperature.