Gap plasmon-based metasurfaces for total control of reflected light

Abstract

In the quest to miniaturise photonics, it is of paramount importance to control light at the nanoscale. We reveal the main physical mechanism responsible for operation of gap plasmon-based gradient metasurfaces, comprising a periodic arrangement of metal nanobricks, and suggest that two degrees of freedom in the nanobrick geometry allow one to independently control the reflection phases of orthogonal light polarisations. We demonstrate, both theoretically and experimentally, how orthogonal linear polarisations of light at wavelengths close to 800 nm can be manipulated independently, efficiently and in a broad wavelength range by realising polarisation beam splitters and polarisation-independent beam steering, showing at the same time the robustness of metasurface designs towards fabrication tolerances. The presented approach establishes a new class of compact optical components, viz., plasmonic metasurfaces with controlled gradient birefringence, with no dielectric counterparts. It can straightforwardly be adapted to realise new optical components with hitherto inaccessible functionalities.

Analog Computing Using Reflective Plasmonic Metasurfaces

“…Moreover, it is clear that the two contour lines of the reflection phase, with a π-phase difference, intersect a large span of the reflection amplitude variation due to a weakening of the GSP-resonance for increasing nanobrick size in the direction perpendicular to excitation (i.e., increase in L y ). Accordingly, by the assumption that the interaction between neighboring nanobricks is weak, a fact that has been verified in previous studies of GSP-based metasurfaces, 27 we can design inhomogeneous calculus metasurfaces, defined It is worth noting that despite the seemingly continuous reflection profiles in Figure 2b, the reflection is only controlled along the x-direction in integer steps of Λ, corresponding to the positions of the nanobricks. Additionally, as already mentioned, the integrator metasurfaces only approximate the operation for small k x -values.…”

“…25 Note that the latter two functionalities are obtained by varying the reflection phase linearly along the metasurface (keeping the reflection amplitude close to one and constant), whereas flat focusing mirrors require a parabolic phase profile. More importantly, GSP-based birefringent metasurfaces may be used to independently manipulate orthogonal polarizations, that being either in the context of polarization beam-splitters, 26,27 surface wave excitation, 28 or holography. 29 In the above mentioned applications of gradient (i.e., inhomogeneous) metasurfaces the considered functionalities are based on either position-dependent reflection amplitude or phase.…”

“…The configuration is based on GSP-based metasurfaces, [16][17][18][19][20][21][22][23][24][25][26][27][28][29] thus working in a reflection setup, which results in relatively simple designs, realizable in one step of electron beam lithography. Proof-of-concept experiments have been conducted on differentiator and integrator metasurfaces, demonstrating in both cases features of the designed functionality.…”

Efficient unidirectional polarization-controlled excitation of surface plasmon polaritons

“…The design procedure is somewhat similar to that described in our previous work on total control of reflected light with GSP-based metasurfaces, 21 but also substantially different, because the structure period is, in the present case, determined by the corresponding SPP wavelength rather than by the angle of diffraction into free space. Let us first consider the problem of efficient unidirectional SPP excitation with one-dimensional (1D) GSP-based metasurfaces, which create the appropriate phase gradient only in one direction.…”

“…[17][18][19] The presence of a continuous metal support in this configuration makes it also naturally compatible and, thereby, very attractive for implementing efficient SPP excitation. 20 Here, we realize efficient unidirectional polarization-controlled SPP excitation by applying our approach of independently manipulating orthogonal polarizations of reflected light with GSP-based gradient metasurfaces 21 to the SPP excitation. In particular, we design arrays of GSP resonators that would produce upon reflection two orthogonal phase gradients in two respective linear polarizations of incident radiation, so that the incident radiation (with arbitrary polarization) can efficiently (numerically estimated up to 40%) be converted into SPPs propagating in orthogonal directions dictated by the phase gradients.…”