Storing data in holograms

Our every-day life is based on storing data. The card you use to open different doors around college, your phone and your laptop are all devices that store data inside them, allowing them to fulfil their functions. For decades now, data storing technology has been based on  magnetic data storage and conventional optical data storage. Holographic data storage is a newly introduced technology that has the potential to increase the speed, size and efficacy of data storing. In order to understand why it could prove to be so useful in the future, it is important that we look at the way we have been storing data to this day.

Magnetic and optical storage

Magnetic storage devices work by magnetising a material in different patterns. It is a form on non-volatile memory, meaning it keeps the data even after being power cycled (turned off and on again). Optical storage devices save data as patterns of dots that can be read using light. A laser beam is the usual light source. What they have in common is that they both rely on individual bits being stored in two-dimensional surfaces of a medium.

On the other hand, holographic data storage records data in the volume of a crystal medium, so in the same area as other forms of storage, it can record and read more information, by using light at different angles. To make this concept more tangible, the data that could be kept in more than 1000 CDs (optical storage) can be stored in only a sugar-cube sized crystal used for holographic memory.

How it works

The process starts with the information being stored as binary data in the SLM. The opaque areas represent 0 and the transparent ones represent 1. This is also referred to as the page of data.

A laser beam is split into two rays, one of which, that is called the information beam, goes through the page of data. The opaque parts don’t let light go through whereas the transparent parts do and so the laser beam now carries information in the form of an image. When it meets with the other ray, that was initially directed away from the SLM and is usually called the reference beam, they both create a pattern of light interference, also known as the holography data. This pattern created is stored as a hologram in the crystal or the photopolymer disc. One of the most important factors in the data storing process is the angle at which the reference beam hits the crystal. Each angle will produce a different page of data. A difference of just a thousandth of a millimetre will result in failure to retrieve the desired page of data.

Benefits

There are many benefits that the usage of HDS (Holographic Data Storage) would bring. One of its main advantages is that for the same amount of material used in other types of data storing devices, it could have a much higher capacity than them. IBMs test platforms can store up to 390 bits per square micron, whereas everyday DVDs have a storage of about 5 bits per square micron. If we put HDS into use, we would be able to store all the books in the US Library of Congress in only 6 disks.

When discs are read by machines, they are read bit by bit whereas when the reference ray hits the photosensitive material of the HDS it is able to read about one million bits in parallel, making media transferring an extremely fast process

Drawbacks

Holographic data storage seems quite impressive and it has a lot to offer. However, it does have a few drawbacks that have stopped it from becoming the main way of storing information.

The materials needed for the creation of a holographic data storage have been inaccessible and expensive for decades, for example it was hard to make lasers of the required size and the first LCDs were very expensive. Even though now, finding the materials to make a HDS is relatively easy, there are a few technical problems that reduce the efficacy of the product. The hologram can be diminished if too much data is stored in one crystal and in order to get the data required the rays need to be shined at precisely the angle they were shined when the data was recorded.

Holographic data storage is also a new and untested technology so scientist are not completely sure how long lasting it is, especially if it is unrecorded, and how it behaves to light exposure.

There is no doubt that there is so much potential to using holograms for storing information. Regardless of the many obstacles arising when trying to build a holographic data storage, a lot of progress has been done and it seems like in the near future we will be able to use photosensitive discs to store our data.

 

Sources

https://computer.howstuffworks.com/holographic-memory.htm 

https://www.ukessays.com/essays/computer-science/understanding-how-magnetic-storage-devices-work-computer-science-essay.php

https://www.igcseict.info/theory/3/mag/index.html

https://www.computerweekly.com/feature/Holographic-data-storage-the-next-big-thing

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