Polarization is widely used in optical technologies. The disadvantage of many components that use polarization in one form or another is that they require complex optical trains. Metasurfaces, arrays of optical components which are thinner than the wavelength of light, can offer a solution to this problem.
Federico Capasso, Harvard University, Cambridge, MA, USA, and colleagues have created a compact metasurface lens element which can create an image by separating light of opposite circular polarization states, and thus, focus light on two different points at the same time. The researchers used an off-axis lens to focus the light on two off-axis positions.
Such an off-axis lens is analogous to a superposition of the phase profiles of a “normal” refractive lens and a wedge. By using a combination of geometric and propagation phases together, the researchers were able to impart independent phase profiles on the two polarizations states, which recreates the effect of “flipping” the wedge for each state and separates the left- and right-hand circularly polarized light.
This type of chiral lens overcomes the issues of many other prototypes, as most focus on both circular polarizations and lose 50 % of their efficiency. The developed meta-lens can create images with a contrast of more than 20 dB and efficiencies of up to 70 %.
- High-efficiency chiral meta-lens,
Benedikt Groever, Noah A. Rubin, J. P. Balthasar Mueller, Robert C. Devlin, Federico Capasso,
Sci. Rep. 2018.