Filter uses nano-antennas to precisely control colour output

Whereas a conventional colour filter can only produce one fixed colour, a single active filter under exposure to different types of light can produce a range of colours.

According to a statement, the advance has the potential for application in televisions and biological imaging and could even be used to create invisible security tags to mark currency. The findings appear in the February issue of Nano Letters.

Kenneth Crozier, associate professor of electrical engineering at the Harvard School of Engineering and Applied Sciences (SEAS), and colleagues have engineered the size and shape of metal nanoparticles so that the colour they appear strongly depends on the polarisation of the light illuminating them. The nanoparticles can be regarded as antennas — similar to antennas used for wireless communications — but much smaller in scale and operating at visible frequencies.

‘With the advances in nanotechnology, we can precisely control the shape of the optical nano-antennas, so we can tune them to react differently with light of different colours and different polarisations,’ said co-author Tal Ellenbogen, a postdoctoral fellow at SEAS. ‘By doing so, we designed a new sort of controllable colour filter.’