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HD Tech Could Get Big Boost from Little Shrimp

Photonics.com
Jun 2011
PHILADELPHIA, June 28, 2011 — A two-part man-made waveplate inspired by the eye of the peacock mantis shrimp could improve CD, DVD, Blu-ray and holographic technology, creating even higher definition and larger storage density.


A peacock mantis shrimp in the ocean. (Image: Jenny Huang)


Peacock mantis shrimp are one of only a few animal species that can see circularly polarized light — like the light used to create 3-D movies. (See: Shrimp Eyes That Polarize) Some researchers believe the mantis shrimp's eyes are better over the entire visual spectrum than any man-made wave plate.

A wave plate is a transparent slab that can alter the polarization of light because it is birefringent — exhibits double refraction. The mineral calcite, which is sometimes used as a wave plate, 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 Pennsylvania State University and a member of the international team that conducted the research. "We want both transmittance and changing polarization to occur quite independent of frequency. In other words, we do not want to affect the color."

Wave plates restore polarization in devices that require only one polarization of light but that lose polarization within the process. They can also divide light into separate polarizations to carry specific information and can filter light for optical devices.

Typically, wave plates are made from minerals like quartz or calcite, or from 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.


(Image: Silke Baron)


A team of engineers from the National Taipei University 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 wave plates in the visual light spectrum and cannot delaminate because they are manufactured as one piece.

The research team's wave plate 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 are also 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 wave plates consist of a layer of slanted nanorods sandwiched between two layers of upright nanorods. Multiple sandwiches are then stacked to make the required wave plate. Because the size of the nanorods is much less than the wavelengths of visible light, the wave plate is birefringent. Because of the two materials, the wave plate can polarize or repolarize light over the visual spectrum.


This schematic of tantalum pentoxide wave plate material shows the multiple layers created from individual sandwiches consisting of two layers of upright nanorods sandwiching a layer of slanted nanorods. (Image: Akhlesh Lakhtakia, Penn State)

"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," the researchers said in their paper. 

For more information, visit: www.upenn.edu  


GLOSSARY
optoelectronics
A sub-field of photonics that pertains to an electronic device that responds to optical power, emits or modifies optical radiation, or utilizes optical radiation for its internal operation. Any device that functions as an electrical-to-optical or optical-to-electrical transducer. Electro-optic often is used erroneously as a synonym.
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