holographic storage (holostorage)

What is holographic data storage?

Holographic storage is computer storage that uses lasers to store computer-generated data in three dimensions.

Holographic storage -- also called holostorage, three-dimensional (3D) storage or a holographic data storage system (HDSS) -- is a volumetric storage system. Where other optical storage mediums like CDs, DVDs or hard disks only store data on their surface, holographic data storage goes beneath the surface to use the entire recording medium, creating a holographic image of the data.

According to statista, the amount of global information created in 2020 was an estimated 64.2 zettabytes (ZB), and by 2025 the amount is estimated to be more than 180 ZB. To keep up with the inevitable need for storage, enterprises and cloud service providers must find a way to store all this data. Holographic storage is one method to do this, since its goal is to store a large amount of data in a small amount of space while meeting high performance, availability and durability requirements.

Once slated as the next generation of optical storage, the concept for holographic storage was first proposed in the early 1960s, shortly after lasers were invented. Research teams both in academia and industry continued to make progress in demonstrating the technology's potential into the early 2000s.

Although no one has yet to mass-commercialize this technology, many vendors, including IBM and Lucent, and organizations such as the Defense Advanced Research Projects Agency, are working on prototypes.

In 2020, Microsoft revisited this storage technology with Project Holographic Storage Device (HSD), a collaboration between Microsoft Research Cambridge and Microsoft Azure. The project's goal is to adapt holographic technology to cloud-scale storage for data centers.

How does holographic data storage work?

Prototypes of HDSS differ in operation, but most holographic data storage systems are based around the same concept. Basic holographic storage components include a blue-green laser, beam splitters, mirrors, LCD panels, lenses, a crystal and a camera.

An example of the basic operation behind an HDSS starts with the firing of a blue-green argon laser. A beam splitter then separates the laser into two beams -- the signal beam and the reference beam. The signal beam travels straight until it bounces off a mirror and into a spatial light modulator, which is an LCD that shows pages of raw data. The data is carried to a light-sensitive crystal. The reference beam emanates from the side of the beam splitter, taking a different path to the crystal. When the two beams meet, a pattern is created on the crystal that stores data in the volume of the crystal. Data can be stored in different areas in the crystal.

To retrieve data stored in the crystal, the reference beam shines into the crystal at exactly the same angle the data was originally stored. Data can then be reconstructed and projected onto a charge-coupled device (CCD) camera. The camera interprets and forwards the data to a computer. Whole pages of data can be retrieved quickly at one time using this storage method.

In launching Project HSD, Microsoft may be one of the vendors closest to having a successful holographic storage device. Its method of implementing the technology differs from traditional attempts at making a holographic storage device. The project achieves a data storage density that is 1.8 times higher than earlier volumetric holographic data storage prototypes.

Project HSD uses components such as high-resolution cameras and display screens in today's smartphones. The project also uses machine learning and deep learning to further improve precision and performance. As a result, the team at Microsoft has reduced optical distortions and manufacturing tolerance requirements.

Project HSD stores the holograms in electro-optic crystalline materials, unlike other holographic storage systems that are made out of lithium-niobate or photopolymer materials. This means Project HSD is not limited to write once, read many operation. The stored hologram is erased by exposing the crystalline material to ultraviolet light, enabling the hologram to be used again.

Despite Microsoft's departure from traditional holographic storage in its use of different material for the crystal, the basic approach to reading and writing data is much the same as other holographic storage systems.

Holographic storage applications and use cases

Holographic storage systems are a rewritable, high-density, high-speed optical information storage medium. Holographic storage is capable of recording and reading data from the storage medium in parallel, which results in higher overall throughput. It also requires fewer mechanical parts, such as those found in hard disk drives.

Holographic storage could benefit warm data as well. Warm data is typically accessed and updated less frequently than data that supports important business applications -- rarely maintained in real time. It is a relatively cost-effective way to address specific business needs in an efficient and timely manner. Its fast read performance and ability to update data make it well-suited for many applications.

For example, holographic storage could benefit the following:

• applications that incorporate advanced technologies such as predictive analytics or artificial intelligence;
• big data analytics;
• cloud storage providers;
• data warehousing;
• enterprise data centers; and
• archival of warm data and less critical operations.

Advantages and disadvantages of holographic storage

The benefits of holographic storage include the following:

• Durability. Holographic media can last for about 50 years.
• High transfer rates. Holographic memory devices offer up to 1 gigabyte per second.
• High capacities. Holographic storage devices have a potential storage capacity of about 1 terabyte of data per square inch.
• Quick access to data. Access to data is quick compared to traditional magnetic drives.

But there are drawbacks to holographic storage as well.

• Data storage technologies currently on the market such as hard disk drives, can already compete with the projected capacities of holographic storage.
• Data must be retrieved at exactly the same angle it was written. Even with only a difference of a thousandth of a millimeter, the crystal will fail to retrieve data.
• The strength of a hologram is diminished if too many pages are stored in a single crystal.

Future of holographic data storage

Holographic storage has a long way to go from the research phase to the point where enterprises can readily purchase commercial products. Manufacturers have to set up entirely new environments for building the storage devices, which require a high degree of precision to ensure proper alignment of components.

Microsoft has breathed new life into holographic storage with Project HSD; however, most of the research on this project has focused on writing to and reading from a single zone -- a zone being a small area, or volume, inside the crystal. Multiple pages can be recorded in one zone. The team still faces challenges including delivering the same level of performance across multiple zones. Another worry is ensuring that inadvertent exposure to UV light does not erase data.