Abstract
Metasurfaces have revolutionized photonics due to their ability to shape phase fronts as requested and to tune beam directionality using nanoscale metallic or dielectric scatterers. Here we reveal inverse metasurfaces showing superior properties compared to their positive counterparts if transmission mode operation is considered. The key advantage of such slot-type metasurfaces is the strong reduction of light in the parallel-polarization state, making the crossed-polarization, being essential for metasurface operation, dominant and highly visible. In the experiment, we show an up to four times improvement in polarization extinction for the individual metasurface element geometry consisting of deep subwavelength nanoboomerangs with feature sizes of the order of 100 nm. As confirmed by simulations, strong plasmonic hybridization yields two spectrally separated plasmonic resonances, ultimately allowing for the desired phase and scattering engineering in transmission. Due to the design flexibility of inverse metasurfaces, a large number of highly integrated ultra-flat photonic elements can be envisioned, examples of which include monolithic lenses for telecommunications and spectroscopy, beam shaper or generator for particle trapping or acceleration or sophisticated polarization control for microscopy.
Highlights
The demand for creating desired states of light using fully integrated nanostructures has led to the development of metasurfaces (MSs), which rely on the interference of light from engineered scatterers and are composed of ultra-flat planar metallic nanostructures.[1,2] These structures have nanoscale dimensions and allow engineering of the direction and the relative phase of the scattered light to an unprecedented degree
We show the superior properties of inverse metasurfaces compared to their positive counterparts in case the transmission mode operation is considered
The key advantage of such slottype nanostructures is the strong suppression of transmitted light in the parallel-polarization state, making the crossed-polarization state, which is the relevant state for metasurface operation, highly visible
Summary
The demand for creating desired states of light using fully integrated nanostructures has led to the development of metasurfaces (MSs), which rely on the interference of light from engineered scatterers and are composed of ultra-flat planar metallic nanostructures.[1,2] These structures have nanoscale dimensions and allow engineering of the direction and the relative phase of the scattered light to an unprecedented degree. For a MS to operate in reflection, the mentioned conditions are typically achieved using bar-type MSs (here referred as positive MS, meaning pMS), isolated scattering elements forming a MS with comparably low metal filling fraction. If transmission mode operation is demanded, the low metal filling fraction leads to dominant scattering amplitudes of the parallel polarization state which are stronger than those of the crossed state due to the contribution of the light passing through the non-patterned regions We show that the individual elements of iMS geometry being composed of slot-type nanoboomerangs with feature sizes of about 100 nm and a high metal filling fraction fulfill the abovementioned conditions for the case of transmission mode operation (Fig. 1(a)). By conducting a straightforward designing procedure, we show that iMSs being composed of inverse nanoboomerangs allow accessing the entire phase space of 2π, providing identical functionalities as the pMS with substantially improved polarization extinction
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