Nanostructures are usable for optical storage

Feb

7

2019

Nanostructures are usable for optical storage thanks to deep learning

Scientists propose deep learning for error correction when reading optical storage based on silicon nanostructures. This method enables optical storage with considerably higher density.

Researchers have been working on successors for DVD and Blu-ray with a higher storage density. With those existing optical media, bits are stored on a surface with a size related to the diffraction limit. That is the distance between two adjacent points that the laser can distinguish.

Many initiatives to increase the storage density have drawbacks, write researchers from the University of Toulouse. They offer or do not offer much improvement over the existing optical storage techniques or are complex with regard to the storage medium or readout system.

cd dvd blu-ray

Photonic nanostructures are promising, according to the researchers, as an instrument to control light on the nanoscale. This technique also has disadvantages, they acknowledge, because noise and small deviations in geometry, such as defects, can lead to errors in optical detection. Moreover, the material used, often gold, does not make production scalable.

The researchers therefore propose using silicon nanostructures. These support optical resonance with little loss and are tunable for the entire visible spectrum. In addition, the production has been tested and cheap thanks to CMOS technology.

The geometry of the structures concerns a layout of two blocks and two ‘holes’ that represent four bits, although variants of 2, 3 or 5 bits are possible. The structure is delimited by an L-shaped wall and the blocks have a size of 120x120nm with a height of 90nm.

Nanostructures machine learning

With the aid of dark field microscopy , the spectrum can be mapped from the light that diffuses the different structures. In order to obtain the bit-sequences representing the structures, the French scientists trained a neural network on a dataset of obtained spectra. They used an architecture optimized for recognizing patterns.

Nanostructures machine learning 2

The results were ‘quasi-error free’ and measuring a few wavelengths instead of the entire spectrum was already sufficient to read the information. The technique can be simplified by focusing on measuring rgb values ​​with which thousands of structures can be read out on a large surface with a single measurement, according to the scientists.

The researchers report nothing about the speed of reading or writing and it is not clear how much elongation there is to further increase the storage density. However, they point to the advantage of massively being able to read in parallel and the possibility of reading with simple and inexpensive systems, with which the research could be seen as a starting point for a new storage technique.

They published their research in an article called Pushing the limits of optical information storage using deep learning in Nature Nanotechnology . The entire article is only available for a fee, but a previous publication can be freely viewed .

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