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All-optical tuning of EIT-like dielectric metasurfaces by means of chalcogenide phase change materials
Full text linkElectromagnetically induced transparency (EIT) is a pump-induced narrowband
transparency window within an absorption lin
e of the probe beam sp
ectrum in an atomic
system. In this paper we propose a way to bring together the all-dielectric metamaterials to
have EIT-like effects and to optically tune the
response by hybridizing them with a layer of a
phase change material. We propose a design of the metamaterial based on Si nanoresonators
that can support an EIT-like resonant response. On the top of the resonators we consider a
thin layer of a chalcogenide phase change material, which we will use to tune the optical
response. Our choice is Ge
2
Sb
2
Te
5
(GST), since it has two stable phases at room temperature,
namely amorphous and crystalline, between which it can be switched quickly, nonvolatively
and reversibly, sustaining a large number of
switching cycles. They differ in optical
properties, while still having moderately low losses in telecom range. Since such dielectric
resonators do not have non-radiative losses of metals around 1550nm, they can lead to a high-
Q factor of the EIT-like response in this range
. Firstly, we optimize the starting structure so
that it gives an EIT-like response at 1550 nm wh
en the GST layer is in the amorphous state.
Our starting design uses glass as a substrate, but we also consider implementation in SOI
technology. If we then switch the thin layer of
GST to its crystalline phase, which has higher
losses, the EIT-like response is red shifted, pr
oviding around 10:1 contrast at 1550nm. This
reversible tuning can be done with an ns visible pulsed laser. We discuss the results of the
simulation of the dielectric metasurface for differe
nt configurations and
the tuning possibilit
Evaluation of the negative refractive index by beam deviation measurements
No full textHere we present an easy experimental method that allows the characterization of the negative refractive index of a isotropic metamaterial in the visible spectral region. The method is based on the measurement of the deviation of a light beam passing through the metamaterial as a function of the incident angle. The theoretical expression was derived in the case of negative refraction. It was shown that such a method can be used also in the realistic case of a thin metamaterial deposited on a thick substrate
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