A University of Michigan professor has developed a new type of colour filter made of nano-thin sheets of metal with precisely spaced gratings.
The filter might eventually enable higher-definition display screens to be made more efficient, smaller and at a higher definition.
The gratings, sliced into metal-dielectric-metal stacks, act as resonators that trap and transmit light of a particular colour, or wavelength, said Jay Guo, associate professor in the Department of Electrical Engineering and Computer Science. Simply by changing the space between the slits, different colours can be generated.
His team used this technique to make what they believe is the smallest colour logo of the university. At about 12 x 9 microns, it is about one-sixth the width of a human hair.
Conventional liquid-crystal displays are inefficient and manufacturing-intensive to produce. Only about five per cent of their back-light travels through them. They contain two layers of polarisers, a colour filter sheet and two layers of electrode-laced glass in addition to a liquid-crystal layer. Chemical colourants for red, green and blue pixel components must be patterned in different regions on the screen in separate steps.
Because displays based on Guo’s filters would eliminate the need for additional polariser layers, they would be simpler to manufacture. The new colour filters contain just three layers: two metal sheets sandwiching a dielectric. Red, green and blue pixel components could be made in one step by cutting arrays of slits in the stack.
Red light emanates from slits set around 360 nanometres apart, green from those about 270 nanometres apart and blue from those approximately 225 nanometres apart. The differently spaced gratings essentially catch different wavelengths of light and resonantly transmit them through the stacks.
’Amazingly, we found that even a few slits can already produce well-defined colour, which shows its potential for extremely high-resolution display and spectral imaging,’ said Guo.