Octopus-inspired sensor detects colours like humans

Scientists have for the first time developed a light detector that responds to red, green and blue light like the human eye does.
The device CMOS-compatible, bio-mimetic colour photodetector was created by researchers at Rice University's Laboratory for Nanophotonics (LANP).
It uses an aluminium grating that can be added to silicon photodetectors with the silicon microchip industry's mainstay technology, "complementary metal-oxide semiconductor," or CMOS.
Conventional photodetectors convert light into electrical signals but have no inherent colour-sensitivity. To capture colour images, photodetector makers must add colour filters that can separate a scene into red, green and blue colour components.
This colour filtering is commonly done using off-chip dielectric or dye colour filters, which degrade under exposure to sunlight and can also be difficult to align with imaging sensors.

"Today's colour filtering mechanisms often involve materials that are not CMOS-compatible, but this new approach has advantages beyond on-chip integration," said LANP Director Naomi Halas, the lead scientist on the study.

"It's also more compact and simple and more closely mimics the way living organisms 'see' colours," said Halas.
Cephalopods like octopus and squid are masters of camouflage, but they are also colour-blind.
Halas said the research team, which includes biologists Roger Hanlon of the Marine Biological Laboratory, and Thomas Cronin of the University of Maryland, Baltimore, suspect that cephalopods may detect colour directly through their skin.
Based on that hypothesis, LANP graduate student Bob Zheng, the lead author of the study, set out to design a photonic system that could detect coloured light.

"Bob has created a biomimetic detector that emulates what we are hypothesising the squid skin 'sees,'" Halas said.
Zheng's colour photodetector uses a combination of band engineering and plasmonic gratings, comb-like aluminium structures with rows of parallel slits.
Using electron-beam evaporation, which is a common technique in CMOS processing, Zheng deposited a thin layer of aluminium onto a silicon photodetector topped with an ultra-thin oxide coating.
Colour selection is performed by utilising interference effects between the plasmonic grating and the photodetector's surface.
The study was published in the journal Advanced Materials.