Biomedical Engineering Reference
In-Depth Information
(black),showingthatrobusttransportbehaviorsdoexistwithinthe
polarization gap.
For the purpose of comparison, we also measured the trans-
mission spectra in the blocked/unblocked NC channel, as shown in
Fig. 5.16. Low transmissions were observed for either the dielectric
or PEC blocks, consistent with our FDTD simulations illustrated in
Fig. 1.14(c) and (d). In the simulation, the PEC obstacle is the same
as that in Fig. 5.14(b) and the working frequency is 10.2 GHz. The
FDTD results in Fig. 5.14(c) show that linear polarized EM wave
propagatesfrombottomtotopinthechannelandthefluxisblocked
once the PEC slab blocks the channel, as shown in Fig. 5.14(d).
Figure 5.16(b) shows that the relative phases between S
x
and S
y
have much larger fluctuations, and thus the polarizations of the
output wave do change when the obstacleis present.
5.4 Summary
In this review, we considered the optical properties of a PC
composing of a metallic helix array and the transport property of
a chiral channel drilled inside a dielectric PC. A semi-analytical
method is developed for solving the band dispersion of the metallic
helix array. Along the axis of helices, the band dispersion has
exoticfeatures,includingcircularlypolarizedandquasi-longitudinal
eigenmodes, giant polarization gap, and negative refraction bands
both above and below the gap. A metallic helix array can also serve
asahighlytransparentbroadbandwaveplateforwavepropagating
perpendicular to helix axis. We also showed that a chiral channel
in a 3D dielectric PC supports robust transport without breaking
time-reversal symmetry. A chiral channel mode is robust against
scattering of obstacles that reflect LH waves into RH waves. The
advantage of robust transport in a dielectric PC is that it does not
require magnetic materials and external magnetic field to break
time-reversal symmetry. These examples highlight the unusual
properties of helical and chiral photonic systems and some of these
properties may find useful applications.
