Say goodbye to the dots and dashes to enhance optical storage media

The proposed anisotropic metasurface from Purdue University innovators has significant potential for high-density optical data storage, dynamic color image display, and encryption. (Image provided)

WEST LAFAYETTE, Ind. – Purdue University innovators have created technology aimed at replacing Morse code with colored “digital characters” to modernize optical storage. They are confident the advancement will help with the explosion of remote data storage during and after the COVID-19 pandemic.

Morse code has been around since the 1830s. The familiar dots and dashes system may seem antiquated given the amount of information needed to be acquired, digitally archived and rapidly accessed every day. But those same basic dots and dashes are still used in many optical media to aid in storage.

A new technology developed at Purdue is aimed at modernizing the optical digital storage technology. This advancement allows for more data to be stored and for that data to be read at a quicker rate. The research is published in Laser & Photonics Reviews.

Rather than using the traditional dots and dashes as commonly used in these technologies, the Purdue innovators encode information in the angular position of tiny antennas, allowing them to store more data per unit area.

"The storage capacity greatly increases because it is only defined by the resolution of the sensor by which you can determine the angular positions of antennas," said Alexander Kildishev, an associate professor of electrical and computer engineering in Purdue's College of Engineering. "We map the antenna angles into colors, and the colors are decoded."

Technology has aided in increasing storage space availability in optical digital storage technologies. Not all optical data storage media needs to be laser-writable or rewritable.

The majority of CDs, DVDs, and Blu-Ray discs are “stamped” and not recordable at all. This class of optical media is an essential part of disposable cold storage with a rapid access rate, long-lasting shelf life, and excellent archival capabilities.

The making of a Blu-Ray disc is based on the pressing process, where the silicon stamper replicates the same dot-and-dashes format the final disc is getting. A thin nickel coating is then added to get a negative stamp. The Blu-Rays, as well as DVDs and CDs, are just mass-produced.

"Our metasurface-based 'optical storage' is just like that," said Di Wang, a former Ph.D. student who fabricated the prototype structure. “Whereas in our demo prototype, the information is ‘burnt in’ by electron-beam lithography, it could be replicated by a more scalable manufacturing process in the final product."

This new development not only allows for more information to be stored but also increases the readout rate.

"You can put four sensors nearby, and each sensor would read its own polarization of light," Kildishev said. "This helps increase the speed of readout of information compared to the use of a single sensor with dots and dashes."

Future applications for this technology include security tagging and cryptography. To continue developing these capabilities, the team is looking to partner with interested parties in the industry.

Kildishev and his team work with the Purdue Research Foundation Office of Technology Commercialization to patent and license their technologies. For more information, contact Will Buchanan of OTC at wdbuchanan@prf.org.

About Purdue Research Foundation Office of Technology Commercialization

The Purdue Research Foundation Office of Technology Commercialization operates one of the most comprehensive technology transfer programs among leading research universities in the U.S. Services provided by this office support the economic development initiatives of Purdue University and benefit the university's academic activities through commercializing, licensing and protecting Purdue intellectual property. The office is located in the Convergence Center for Innovation and Collaboration in Discovery Park District, adjacent to the Purdue campus. In fiscal year 2020, the office reported 148 deals finalized with 225 technologies signed, 408 disclosures received and 180 issued U.S. patents. The office is managed by the Purdue Research Foundation, which received the 2019 Innovation and Economic Prosperity Universities Award for Place from the Association of Public and Land-grant Universities. In 2020, IPWatchdog Institute ranked Purdue third nationally in startup creation and in the top 20 for patents. The Purdue Research Foundation is a private, nonprofit foundation created to advance the mission of Purdue University. Contact otcip@prf.org for more information.

About Purdue University

Purdue University is a top public research institution developing practical solutions to today's toughest challenges. Ranked the No. 5 Most Innovative University in the United States by U.S. News & World Report, Purdue delivers world-changing research and out-of-this-world discovery. Committed to hands-on and online, real-world learning, Purdue offers a transformative education to all. Committed to affordability and accessibility, Purdue has frozen tuition and most fees at 2012-13 levels, enabling more students than ever to graduate debt-free. See how Purdue never stops in the persistent pursuit of the next giant leap at purdue.edu.

Writer: Chris Adam, cladam@prf.org 

Source: Alexander Kildishev, kildishev@purdue.edu

ABSTRACT

Enabling optical steganography, data storage, and encryption with plasmonic colors

Maowen Song, Di Wang, Zhaxylyk A. Kudyshev, Yi Xuan, Zhuoxian Wang,
Alexandra Boltasseva, Vladimir M. Shalaev and Alexander V. Kildishev

Plasmonic color generation utilizing ultra-thin metasurfaces as well as metallic nanoparticles hold a great promise for a wide range of applications, including color displays, data storage, and information encryption due to its high spatial resolution and mechanical/chemical stability. Most of the recently demonstrated systems generate static colors; however, more advanced applications such as data storage require fast and flexible means to tune the plasmonic colors, while keeping them vibrant and stable. Here, a surface-relief aluminum metasurface that reflects polarization-tunable plasmonic colors is designed and experimentally demonstrated. Excitation of localized surface plasmons encodes discrete combinations of the incident and reflected polarized light into diverse colors. A single storage unit - a nanopixel - stores a multiple-bit piece of information in the orientation of its constituent nanoantennae. This information is then reliably retrieved by inspecting the reflected color sequence with two linear polarizers. It is the broad color variability and high spatial resolution of the proposed encoding approach that supports a strong promise for rapid parallel read-out and encryption of high-density optical data. Our method also enables the robust generation of dynamic kaleidoscopic images with no detrimental "cross-talk" effect. The approach opens up a new route for advanced dynamic steganography, high-density parallel-access optical data storage, and optical information encryption.