Inside the Optical Storage Improvement Plan

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Purdue University researchers are looking to improve optical storage with higher densities and faster reads. Success in technology development could replace Blu-ray disc for storage.

Through the generation of plasmonic colors, in conjunction with metallic nanoparticles and ultrathin metasurfaces, the storage medium operates at the nanoscale. According to the researchers, they have already reached a read speed of 18.3 Gbps, which is 143 times faster than the state-of-the-art Blu-ray disc. They were also able to store 5% more data than a Blu-ray disc.

Why colored numeric characters

Plasmonics – or nanoplasmonics – is a young field that deals with the interaction between light waves and metallic nanoparticles. Plasmonics works with nanoscale structures to harness the oscillations of electrons that occur when photons strike a metal surface. Researchers believe they can use this phenomenon for data storage that offers higher densities and faster reads than conventional optical discs.

To store data at this scale, scientists use plasmonic nanostructures that vary in their relative positioning. The nanostructures serve as tiny antennae that enhance light interactions. When light hits the nanostructures, they reflect different colors depending on their positioning. Changing these positions changes the reflected color spectrum. In other words, the researchers vary the orientation states of the nanoantennas to produce different reflected colors, which they can then translate into binary information.

In conjunction with the positioning of the nanostructure, the researchers use a surface-relief metasurface made of aluminum nanoantenna elements. The metasurface offers wider color variability and higher spatial resolution than other materials, which are often based on composite metal resonators. According to the researchers, the aluminum metasurface is free from anti-reflective complexities and supports lower thickness. It is also more compatible with commercial nanoimprinting processes.

The researchers proposed a frame-based storage structure in which each frame is composed of 16 nanopixels. Each nanopixel has four-unit cells, or nanoantennae. Each nanoantenna orientation has a unique color. In this way, an imaging system can retrieve the corresponding color sequence from each image. These colors can then be translated into binary data.

In their prototype, the researchers stored 3 bits of data per nanopixel, which allows for higher densities and read speeds than a Blu-ray disc. Based on their early simulations, the researchers believe they could store 4 bits of data in each nanopixel, which translates to 40% higher density than Blu-ray and achieves 191x faster read speeds. .

Uses of Enhanced Optical Storage

By repositioning the nanoantennas, plasmonic storage can generate a wide range of distinct colors, so there is more data storage in a finite space. An optical analyzer can then capture the unique color sequences as the disk spins, then translate those readings into binary data. Multiple scanners can simultaneously read multiple storage units, allowing for much faster read operations.

Storage administrators could potentially use the new technology to replace today’s pre-recorded audio and video optical discs, especially Blu-rays. These discs are read-only, non-recordable and mass-produced on a large scale, with the data burned onto the underlying medium. Plasmonic disks can be made in much the same way, in part because of the aluminum metasurface, the researchers say. The higher playback capacities and speeds could prove especially beneficial for increasing densities of video content.

In its current form, the plasmonic disk is a write-once-read-many (WORM) medium that promises higher read performance than other optical storage. It still offers the great durability and archival capabilities of traditional optical discs. This makes plasmonic storage well suited for read-intensive workloads that rely on cold or archived storage, such as analytical applications that incorporate machine learning, predictive analytics, and other advanced technologies.

Plasmon disks, in general, could be a good choice for archiving an assortment of structured and unstructured data, whether or not organizations are mining the data for advanced analytics. Media with quick read access can save an organization a lot of time when trying to find specific information. For example, IT may need access to archived data to resolve a compliance issue or in the event of a cyberattack.

Purdue researchers clearly have the optical storage market in mind, particularly as a replacement for Blu-ray disc.

Differences with traditional optical storage

Purdue researchers clearly have the optical storage market in mind, particularly as a replacement for Blu-ray disc. The medium they used for their demonstration was the same size as a standard optical disc – 120 millimeters in diameter. It spun at 5,000 rpm, a speed comparable to a Blu-ray disc.

Today’s optical discs are flat and circular. Data is stored as microscopic pits and patches, with the pits etched into a reflective layer of recording material. Data is written in radial patterns starting near the center of the disk. The lasers then read the discs as they spin. The differences in reflectivity determine which bits 0 and 1 represent the data. A CD can store up to 700MB of data, a DVD can store up to 8.5GB, and a Blu-ray Disc can store up to 128GB.

Data recording hardware depends on disk usage. Pre-recorded discs, such as those used to distribute feature films, may use less expensive materials, such as aluminum foil, to store the data. However, a disk for WORM data storage often includes an additional organic dye layer for writing the data. A rewritable disc uses phase change material that can be erased and rewritten many times.

The plasmonic disk developed by Purdue scientists is still in the early stages of research and has a single material for storing WORM data. The plasmonic disk includes a passive aluminum metasurface that reflects tunable plasmonic colors by bias. The metasurface consists of periodic arrangements of rectangular nanoantennae attached to an optically thick aluminum film. Researchers have estimated that this configuration can support storage densities up to 40% higher than conventional Blu-ray discs.

To record the data in the plasmonic prototype, the researchers used electron beam lithography to etch the information into the metasurface, but they believe more commercially viable means can record the data. Using plasmonics rather than a pit-and-land architecture enables improved optical storage, higher densities, and faster read performance.

Challenges of colorful digital storage

There appears to have been little progress towards commercializing the technology since Purdue scientists published their research. Undoubtedly, they face an uphill battle to meet the challenges of implementing a new type of data storage medium in today’s market.

Plasmonic storage is limited to pre-recorded and WORM storage, with no support for rewritable storage. The technology is also challenged by continued advances in Blu-ray storage. Although Blu-ray may not achieve the playback densities and performance promised by plasmonic storage, it is a well-established medium that organizations can use for prerecorded, WORM, and rewritable storage.

Even though plasmonic storage research is making significant progress, manufacturers can’t just start churning out drives. The manufacturing process might resemble that of Blu-ray discs, but manufacturers would need to adjust their operations to accommodate the new production-scale format. Equipment refitting and modification operations are no small task, and a technology must be able to demonstrate a lot of promise to attract industry attention.

Plasmonic disks face some of the same capacity limitations as other optical disks. Although they promise to deliver greater densities than Blu-ray, the medium itself still has to cope with the upper limits of a single spinning disc. However, other storage media can be grouped into much larger systems and come together as a single repository.

The plasmonic disk also faces significant advances in solid-state storage, which continues to improve in terms of capacity, performance and cost. Vendors are investing a lot of time and energy in researching more powerful SSDs, which pushes other forms of storage to the back burner. On-premises storage systems have gradually given way to cloud storage and streaming services.

The plan to improve optical storage through plasmonic disks must also compete with other efforts that meet future needs. For example, Microsoft’s Project Silica is investigating the feasibility of using superfast laser optics to store data in quartz crystal, which promises higher densities and resilience than anything currently archiving data. IBM has been working on a concept called racetrack memory, which applies electric current to nanowires to create opposing magnetic regions that can store large amounts of data. Scientists are also actively pursuing DNA memory, a storage approach that encodes data in genetic material.

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