{'fraction_non_alphanumeric': 0.013927576601671309, 'fraction_numerical': 0.005571030640668524, 'mean_word_length': 5.267441860465116, 'pattern_counts': {'":': 0, '<': 0, '<?xml version=': 0, '>': 0, 'https://': 0, 'lorem ipsum': 0, 'www.': 0, 'xml': 0}, 'pii_count': 0, 'substrings_counts': 0, 'word_list_counts': {'cursed_substrings.json': 0, 'profanity_word_list.json': 0, 'sexual_word_list.json': 0, 'zh_pornsignals.json': 0}}
High-density multilayer recording of microgratings for optical data storage

A novel approach to 3D optical information storage based on writing and reading of microscopic holographic gratings in a photopolymer layer is presented. Strongly localized reflection gratings created by two highly focused laser beams are used to replace the pit and land structure of the CD/DVD technology. The holographic recording method presented here allows employing various multiplexing methods. A combination of wavelength multiplexing and multilayer storage is proposed to achieve storage densities similar to page-oriented holographic data storage. In this paper we report on recording and readout of submicron-sized gratings using diffraction limited laser beams. The transversal extent of a micrograting corresponds to the optical resolution limit. Track spacing and bit-to-bit separation are about 500 nm. The interlayer spacing through the depth of the photopolymer is less than 8 micron. This way a 3D structure is realized that even refines the surface data structure of current DVDs.