Taming the spiderweb-like laser

Scientists have found a way to precisely control a network laser – a laser system based on a network resembling a spider’s web – to produce only specific colours or colour combinations at a time. The system could find new applications in sensing, computing and machine learning.

Published in the journal ‘Nature Communications’, the research was led by Imperial College London and successively supported by the EU-funded projects EPNRL and CORAL. The achievements of EPNRL – stemming from the successful collaboration between experts in network theory, photonics and semiconductor devices – resulted in the launch of CORAL.How do network lasers differ from traditional lasers? As described in a news item posted on the Imperial College London website, in traditional lasers, light is generated in narrow beams that remain stable over long distances. However, the laser light is usually only emitted in one frequency and therefore has a single colour. In contrast, network lasers “are made from a mesh of nanoscale optical fibres that are fused together to form a web-like network.” As light travels along the fibres, it interferes in a manner that creates hundreds of colours at the same time. “However, the colours are mixed in a complex fashion and emitted at random in all directions.”

The research team developed a method to control a network laser with precision so that it can produce different light colours. They shone unique “illumination patterns” on the laser and found that each pattern generates a different laser colour or colour combination. The illumination patterns were created using a digital micromirror device, or DMD, that is a computer-controlled device with several hundred thousand microscopic mirrors arranged in a rectangular array on its surface. “The DMD is optimised by an algorithm that selects the best pattern for a particular laser colour,” the news item reports.

“We have combined the mathematics of network theory with laser science to tame these complex lasers. We believe this will be at the heart of light processing on chips and we are testing it now as a machine learning hardware,” states study co-author Prof. Riccardo Sapienza from the Department of Physics at Imperial College London in the same news item.

Co-author Prof. Mauricio Barahona, from Imperial College London’s Department of Mathematics, remarks: “This is an example where we saw maths and physics coming together, showing how the properties of a network can affect and help control the lasing process. The next big challenge is to design networks and illumination patterns to control the temporal profile of the laser light and encode information in it.”

The 2-year EPNRL (Electrically pumped network random lasers) project ended in July 2020. CORAL (COntrolling network RAndom Lasers on chip) was launched in March of the same year and ends in 2024.

For more information, please see:

CORAL project web page

EPNRL project