Image of a peacock mantis shrimp. Image: Silke Baron |
The eye of the peacock mantis
shrimp has led an international team of researchers to develop a two-part
waveplate that could improve CD, DVD, blu-ray, and holographic technology,
creating even higher definition and larger storage density.
Peacock mantis shrimp are one of
only a few animal species that can see circularly polarized light—like the
light used to create 3D movies. Some researchers believe the mantis shrimp’s
eyes are better over the entire visual spectrum than any man-made waveplates.
A waveplate is a transparent slab
that can alter the polarization of light because it is birefringent. The
mineral calcite, which sometimes is used as a waveplate, is birefringent. This
print viewed through a calcite lens appears as doubled and slightly offset
letters.
“We want to change the
polarization without affecting the amount of light that gets through,”
said Akhlesh Lakhtakia, Charles Godfrey Binder Professor of Engineering Science
and Mechanics at Penn
State. “We want both
transmittance and changing polarization to occur quite independent of
frequency. In other words, we do not want to affect the color.”
Waveplates restore polarization
in devices that require only one polarization of light, but lose polarization
within the process. They can also separate light into separate polarizations to
carry specific information and can filter light for optical devices.
Typically, waveplates are made
from minerals like quartz, calcite, or birefringent polymers. In some cases, to
create the range and transparency required, two different materials are stacked
or joined, but this type of construction sometimes delaminates, coming apart at
the seams.
A team of engineers from the
National Taipei Univ. of Technology and Lakhtakia developed a method to produce
periodically multilayered materials, similar to the lens in the peacock mantis
shrimp, that are suitable for waveplates in the visual light spectrum and
cannot delaminate because they are manufactured as one piece. The researchers
report their work online in Nature
Communications.
The research team’s waveplate is
made of two layers of nanorods that are structurally similar to those in the
eye of the peacock mantis shrimp. The researchers begin with tantalum
pentoxide, but deposit the two layers using different deposition processes
creating a multilayered thin film. One method produces a layer of needle-like
nanorods that are all parallel to each other and all slanted in the same
direction. The second method produces nanorods that also are parallel to each
other but are upright.
“The two separate layers are
needed so that we can play off one against the other to achieve the desired
polarization without significantly reducing transmittance over a broad range of
frequencies,” said Lakhtakia.
The waveplates consist of a layer
of slanted nanorods sandwiched between two layers of upright nanorods. Multiple
sandwiches are then stacked to make the required waveplate. Because the size of
the nanorods is much less than the wavelengths of visible light, the waveplate
is birefringent. Because of the two materials, the waveplate can polarize or
repolarize light over the visual spectrum.
The researchers report that
“the fabrication technique of the periodically multilayered structures is
a workhorse technique in the thin-film industry, does not require expensive
lithography equipment and is compatible with … technology commonplace in
electronics and optoelectronics industries.”
