posted on 2016-11-16, 00:00authored byRuonan Ji, Shao-Wei Wang, Xingxing Liu, Huijie Guo, Wei Lu
Circular polarization-resolved imaging
and spectroscopy have versatile
applications ranging from astronomy and biological and biomedical
studies to remote sensing. To achieve real-time imagery with high
contrast and rich information, integratable circular polarizers with
high extinction ratios, broad operation bandwidths, and low insertion
loss are urgently desired, while to our knowledge no structures proposed
previously can balance these three vital parameters. In this paper,
a concept of a hybrid helix metamaterial has been proposed to achieve
ultrawide and giant circular dichroism with low insertion loss simultaneously.
By coupling the localized and delocalized resonant modes, a broad
and strong blocking band for unselected polarization can be realized
with a pencil-like configuration. A giant extinction ratio of 5.9
× 105 can be obtained with a six-pitch hybrid single-helix
array, which is almost 7 times larger than the best result reported
by Behera et al. in 2015. A very high average extinction ratio of
8.5 × 103 is achieved in the operation band of 3.5–9.5
μm, which is due to an average transmittance as low as 0.2%
for the unselected polarizations. More importantly, the top tapered
part well-matches the impedance and contributes to a high average
transmittance of 72% in the whole range. On the basis of the general
scalablility, the validity of such a concept is demonstrated experimentally
in the microwave range. The experimental results agree well with theoretical
ones. The proposed concept can also be broadly extended to other chiral
metamaterial systems for the design of novel high-performance circular
polarizers.