Optical vortex generated using a radial polarization converter. Credit: Altechna; Kazansky et al., University of Southampton.
Back in May, University of Southampton researchers published a short paper in Applied Physics Letters regarding how they used novel microscopy-based optical polarization techniques to turn nanostructured silica glass into a new type of relatively inexpensive, data-dense, stable computer memory. Now, the group says it has extended five-dimensional memory capabilities to their system, adding even more data storage possibilities, and the potential applications seem to be mounting.
Let’s back up a little bit. The research group, led by Peter Kazansky at the university’s Optoelectronics Research Center, describes in the initial paper how they are able—if I understand this correctly—to use a femtosecond laser combined with a space variant polarization converter to “write” self-assembled nanostructures in silica glass. The vortices can either be “left handed” or “right handed” depending on whether the converter is used to induce radial or azimuthal polarization. In other words, on a nanoscale, information can be stored by switching from radial to azimuthal polarization (or vice versa) by controlling the “handedness” of the incident circular polarization.
Put even more simply, this approach uses microscopy tools and ultra-short laser pulses to create tiny voxels (volumetric pixels) in glass.
The authors acknowledge that somewhat similar techniques have been used with liquid crystals and photolithography/subwavelength gratings. However, they point out that a problem with the former is that the liquid crystals have a low damage threshhold, and a problem with the latter is that there are limits to the resolution.
Besides resilience and resolution, several other immediate advantages to nanostructured glass approach jump out, particularly in regard to costs and permanence.
For example, the investigators claim the use of microscopy tools makes the approach 20-times cheaper and it is more compact. In a university news release, Kazansky says, “Before this we had to use a spatial light modulator based on liquid crystal which cost about £20,000. Instead we have just put a tiny device into the optical beam and we get the same result.”
However, since publication of the paper, the researchers have developed this technology even further and adapted it for a five-dimensional optical recording. “We have improved the quality and fabrication time and we have developed this five-dimensional memory, which means that data can be stored on the glass and last forever,” said Martynas Beresna, lead researcher for the project. “No one has ever done this before.”
When Beresna says, “No one has ever done this before,” I think he is mainly referring to the use of glass plus the combination of five-dimensional memory. Five-dimensional memory (think of this as two polarization orientation options, plus three wavelength options) isn’t novel by itself. In 2009, for example, Nature carried a widely covered paper about a team led by Min Gu, which was doing 5D memory work with gold nanorods in a polymer on a glass substrate.
In an interview with the London Telegraph, Beresna says their rewritable approach can, “currently store the equivalent of a whole Blu-ray Disc – up to 50GB of data – on a piece of glass no bigger than a mobile phone screen.”
The researchers say the stability of the glass they studied, its resistance to temperature, moisture, etc., gives it an obvious edge compared to existing archival media. On this issue, Beresna also says in the Telegraph piece, “Data can be stored on the glass and last forever. It could become a very stable and safe form of portable memory. It could be very useful for organizations with big archives. At the moment companies have to back up their archives every five to ten years because hard-drive memory has a relatively short lifespan. Museums who want to preserve information or places like the National Archives where they have huge numbers of documents, would really benefit.”
Regarding the mention of table-top particle accelerators in the headline—something I’ve always wanted for my coffee table at home—the authors don’t directly mention this, but the university’s press release does speak of particle accelerators as another possible application for the radial polarization converters, along with high-resolution medical imaging and laser processing of materials.
The university and the researchers have already partnered with a Lithuanian company, Altechna, to transfer the technology to various markets. The Altechna website does not specifically discuss a memory device, but does suggest uses related to laser machining, optical tweezers and Raman spectroscopy systems.