Scholars from Zhejiang University have realized pixel-level three-dimensional programmable structural colors inside lithium niobate crystals

Recently, Professor Qiu Jianrong and Dr. Zhang Bo of Zhejiang University and researcher Tan Dezhi of Zhijiang Laboratory proposed a multi-dimensional optical storage strategy based on ultrafast laser-induced microphase transformation of lithium niobate crystal vitrification. Using the intrinsic birefringence effect of lithium niobate crystal, the ultrafast laser pulse is excited to couple the material modification in the crystal, and the pixel-level programmable three-dimensional structural color is constructed inside the crystal, which realizes the efficient and low-cost permanent preservation of large-scale data.

The results were published in the international authoritative journal Advanced Materials, and were selected as “Editor’s Choice” and cover paper.

Data is a factor of production in the new era and an important strategic resource of the country. With the development of big data, artificial intelligence and other technologies, the total amount of data generated by human society has exploded. In the face of large-scale data preservation, the existing storage technology has problems such as poor reliability, short lifespan, and low storage density, and the resulting energy consumption is quite huge. Faced with these problems, ultrafast laser engraving inorganic transparent media optical storage offers an attractive solution for preserving massive amounts of information in a simple process, extremely stable and long lifetime. However, due to the limitation of the inherent high damage threshold of inorganic transparent media, this kind of storage technology generally has problems such as high write energy consumption, slow read and write speed, and data extraction relies on complex optical systems, and the problems of insufficient uniformity and low standardization of storage media also seriously restrict the popularization and large-scale application of this technology.

Facing the national “Overall Layout Plan for the Construction of Digital China” and the “14th Five-Year Plan” for the Development of Big Data Industry, in response to the development needs of low-energy, high-efficiency and long-life optical storage, Qiu Jianrong’s team developed an optical storage based on ultrafast laser selectively inducing lithium niobate single-crystal microphase transition, and proposed a crystal birefringence effect to excite the intra-pulse coupling material modification mechanism, so that a single nJ-level ultrafast pulse can induce micro-amorphous phase transformation in the crystal matrix, combined with the color polarization effect. Pixel-level programmable structural colors are generated in the laser-modified region (Figure 1).

Fig.1 Ultrafast laser-induced microphase change optical storage mechanism

Due to the high flexibility of ultrafast laser direct writing, micro-phase transition regions can be manipulated anywhere in 3D space to achieve customized pattern and tonal style control (Figure 2). Ultrafast laser selectively induced single crystal microphase change optical storage has excellent comprehensive performance. The local phase modulation of the glass phase transition and the transparency of the lithium niobate crystal medium support the multi-channel extraction of information, and the written information can be compatible with a variety of mature data reading systems. The data point diameter can be reduced to 500 nm, and the data can be efficiently written with a single ultrafast pulse of 30 nJ, which is comparable to the laser modification energy of organic media. The microphase change structure has extremely high stability, and the stored information can withstand a variety of extreme environments such as strong magnetic field (42 T), high temperature (700 °C), strong acid (60% HNO3), and X-ray (50 kGy). Accelerated aging experiments show that the data storage life is as long as trillions of years at room temperature, which can truly achieve low energy consumption permanent storage of massive data.

It is worth noting that the data signal based on pixel-level structural color can be read at high speed through image recognition, which solves the problem of low information extraction efficiency and dependence on complex and expensive optical systems in multi-dimensional optical storage technology. By writing parameter codes to the laser, the wavelength and intensity signal of the structural color can be flexibly manipulated, and it can be used as a new information reuse channel to achieve multi-dimensional data storage.

Fig.2 Programmable color pixels are printed across dimensions

This work discovers a new mechanism of the interaction between ultrafast laser and matter, improves people’s understanding of the interaction between light and matter in the dielectric environment, proposes an intrapulse-coupled material modification strategy for ultrafast laser in inorganic crystal media, and establishes a new optical storage method-ultrafast laser selectively induced microphase change optical storage of lithium niobate crystals, following the three cutting-edge data storage technologies in the world: holographic storage, DNA storage, and glass storage. It provides a new technical route for the permanent storage of ultra-large-scale data in the future.

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