Biomedical Engineering Reference
In-Depth Information
In our model, we fully take into account the dynamic interaction
withinthearrayandthecross-polarizationcoupling.Wevalidatethe
accuracy of our approach and its limitations by comparing the ho-
mogenizedmetasurfacemodelwithfull-wavenumericalsimulations
based on the finite integration technique (CST Microwave Studio
TM
2011), in order to outline the conditions under which the averaged
optical surface impedance may accurately describe the complex
wave interaction of planar plasmonic metasurfaces. Then, we apply
this analytical model to explore various technological approaches
to achieve strong chiral effects using metasurfaces, such as the
realization of lithographic periodic arrays of nanoparticles and
stacks of plasmonic metasurfaces to form twisted metamaterials,
a concept that we have recently introduced to provide strong,
broadband optical activity based on a lattice effect [58].
3.2 Wave Interaction with Planar Metasurfaces:
Theoretical Basis
One of the major advantages of metasurfaces is the relaxation of
complicated fabrication processes required in three-dimensional
metamaterials, which is especially challenging at optical frequen-
cies. Recent works based on a three-dimensional lithographic
method, direct laser writing (DLW), have demonstrated the re-
alization of three-dimensional metamaterials that exhibit strong,
broadband chirality in the near-infrared to mid-infrared regime
[26, 47]. DLW is an emerging microfabrication technique based
on two-photon absorption to initiate polymerization; the limitation
of this method resides in the minimum feature dimensions that
may be achieved in the fabricated structure, which is ultimately
dominated by the diffraction limit [48-50]. This is due to the fact
that light sources commonly utilized in this fabrication method
are Ti: Sapphire lasers with an emitting wavelength centered at
800 nm; therefore, the voxel size is severely limited by this length
scale. So far, the smallest feature achieved with this method is
in the micro-meter range. Planar lithographic methods, such as
electron beam lithography, on the contrary, utilize electron beams,
