By focusing an ultrashort laser beam onto the graphene oxide polymer, the researchers created a 10-100 times increase in the refractive-index of the graphene oxide along with a decrease in its fluorescence. (The refractive index is the measure of the bending of light as it passes through a medium.)
“The unique feature of the giant refractive-index modulation together with the fluorescent property of the graphene oxide polymer offers a new mechanism for multimode optical recording,” Professor Gu said.
To demonstrate the feasibility of the mechanism, the researchers encoded the image of a kangaroo in a computer generated hologram. The hologram was then rendered as a three-dimensional recording to the graphene oxide polymer. The encrypted patterns in the hologram could not be seen as a normal microscope image, but could be retrieved in the diffracted mode.
“The giant refractive index of this material shows promise for merging data storage with holography for security coding,” Professor Gu said.
“This exciting feature not only boosts the level of storage security, but also helps to reduce the operation costs of big data centres that rely on multiple physical duplicates to avoid data loss.”
The researchers say it could also revolutionise flat screen TV and solar cell technology.
“The giant refractive index we discovered shows the promise of graphene to merge electronics and photonics for the platform of the next generation information technologies.”
The researchers say they’ve reached a density of around 0.2 terabits per cubic centimeter, or 3.2 terabits per cubic inch. It’s hard to compare holographic to non-holographic storage, but hard drives are slowly creeping towards 1 terabit per square inch, while Blu-ray discs are a few orders of magnitude less, in the gigabits-per-square-inch range.
The lead researcher, Min Gu, claims that these GO-polymer discs aren’t just good for storing lots of data. “Conventionally, information is recorded as binary data in a disc. If the disc is broken, the information cannot be retrieved.. the new material allows the development of super-discs, which will enable information to be retrieved – even from broken pieces.” Gu doesn’t say how the data would be retrieved, but presumably it has something to do with its holographic nature.
Abstract
Graphene oxides (GOs) have emerged as precursors offering the potential of a cost-effective and large-scale production of graphene-based materials. Despite that their intrinsic fluorescence property has already brought interest of researchers for optical applications, to date, refractive-index modulation as one of the fundamental aspects of optical properties of GOs has received less attention. Here we reported on a giant refractive-index modulation on the order of 10^−2 to 10^−1, accompanied by a fluorescence intensity change, through the two-photon reduction of GOs. These features enabled a mechanism for multimode optical recording with the fluorescence contrast and the hologram-encoded refractive-index modulation in GO-dispersed polymers for security-enhanced high-capacity information technologies. Our results show that GO-polymer composites may provide a new material platform enabling flexible micro-/nano-photonic information devices.
SOURCES – Swinburne University of Technology, Extremetech, Nature Scientific Reports
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