Bilayer gratings based Surface Plasmon Resonance display device
Theory
SPR is an electromagnetic excitation existing on the interface of dielectric and metal. This picture is about the corresponding dispersion curve.
​
​​L
It is obviously that the two line have no intersection, which means the SPR cannot be excited with conventional illumination from the adjacent dielectric. So we need some special structure in order to excite the SPR, here we use the bi-layer gratings to excite the SPR.
To satisfy the equation, wavelength of coupling is specific, and could be tuned under different pitches.
Demos
The samples below are 300 nm pitch gratings. Diffraction colors are switchable when giving variety in incidence and ambient refraction.
​
​​L
RGB test shows the transmission spectra of three different gratings with pitch of 420 nm, 520 nm and 650 nm in air. [figure on the left]
​​L
And the photos of the transmission light are inset above the corresponding curves. The wavelength of peak in the blue, green and red curves is 470 nm, 542 nm and 675 nm, close to the simulated ones. The transmission efficiency is approximately of 17%, higher than the commercial liquid crystal displays and there is still much room for improvement by optimising the process of fabrication.
The contrast of on and off could reach 150:1. [figure on the right]
One more word
The fabrication of the device relates to nanofabrication, which I haven't tried before in classes. Quite excited!
