Biomedical Engineering Reference
In-Depth Information
7.3 Dependence of Chirality on the Bent Angle of a
Gammadion Metal Slit
Gammadionshapesareoneoftherepresentativechiralpatternsthat
havebeenstudiedbyseveralresearchers ininvestigatingplasmonic
chirality: for example, see [19, 20, 23]. In a gammadion shape, there
are four bent wings that are bent in the same rotational direction.
This rotational arrangement of the bent wings confers chirality to
thegammadion.Ifwedefinethebentangle
θ
r
inagammadionasthe
angle between the inner and the outer segments of a wing as in Fig.
7.3(a),thereareseveralpossiblevariationsintheshapeasshownin
Fig. 7.3(b-e). When the bent angle is
180
◦
as in Fig. 7.3(b), the
shape becomes a cross-pattern that has no chiral property.
Toexaminethechirality,weconductednumericalsimulationsfor
the apertures in Fig. 7.3(b-e) with a Fourier modal method (FMM)
basedtechniqueinvolvingarigorouscoupledwaveanalysis(RCWA)
[27, 28].
Throughout this chapter, we assumed that light with a wave-
lengthof750nmisincidentfromthebackside(
z
<
0)ofthemetallic
θ
r
=
(
a
)
(
b
)
(
c
)
θ =
180
o
θ =
120
o
r
r
θ
r
o
(
d
)
θ =
90
(
e
)
θ =
30
o
r
r
y
x
z
Figure 7.3
(a)Schematicdiagramofagammadionwiththedefinitionofthe
bent angle
θ
r
and the convention of coordinate axis. Several examples of a
gammadion depending on the bent angle are presented in (b-e). The bent
angles in (b-e) are shown at the upper sides of each figure.
