(a) Traditional optical data storage method – Optical disc (Note: Image source from the internet); (b) Schematic diagram of multidimensional data storage: Each data recording voxel can be decoded into a series of binary data; (c) Schematic diagram of super-resolution data storage: Each data recording voxel is decoded into a single binary digit but with higher spatial resolution.

Optical Data Storage:

In the current digital era, driven by the Internet of Things, big data analytics, artificial intelligence, and industry digitization, there is an exponential growth in global data. Traditional storage methods such as hard disk drives and magnetic tapes are currently confronted with significant limitations, especially in terms of storage lifetime and energy consumption. Optical data storage, recognized for its offline storage capability and features of high capacity and extended lifetime, has emerged as a promising approach for archiving "cold" data. However, traditional optical storage technologies like DVDs and Blu-ray discs are limited in capacity. Even with the introduction of multilayer recording in Blu-ray discs technology, there are still constraints on the number of layers. Advanced multidimensional and super-resolution optical data storage technologies have provided opportunities in the field of data storage. However, these technologies also bring significant challenges that research groups and technology companies worldwide urgently need to address.

Multidimensional Optical Data Storage:

In contrast to two-dimensional (2D) optical storage methods like DVDs and Blu-rays, three-dimensional (3D) optical data storage fully utilizes the volume of isotropic materials, allowing data storage at any position within the material. To surpass capacity limitations further, researchers are exploring dimensions beyond traditional 3D, involving methods based on optical properties of birefringence, plasmon resonance, and fluorescence. The multidimensional optical data storage solution enables a single recording voxel to store multiple bits of data by multiplexing parameters, such as intensity, frequency, polarization, and phase of the writing laser. These open up new possibilities for advancing optical data storage.

Super-Resolution Optical Data Storage:

The storage capacity of optical storage is also limited by the size of a single recording voxel due to the existence of the optical diffraction limit. The optical diffraction limit depends on the wavelength of the writing laser beam and the numerical aperture (NA) of objective lens. Shortening the wavelength of the writing laser and using higher NA objective lens are the conventional methods to increase storage capacity. However, further increasing the NA of objective lens is restricted by technological bottlenecks, and using shorter-wavelength laser sources increases system complexity and costs. Therefore, developing super-resolution optical storage technology that breaks the optical diffraction limit is essential to meet the demands for efficient and high-density optical storage.

Challenges in Next-Generation Optical Data Storage:

Although these novel approaches in multidimensional and super-resolution optical data storage showcase substantial advantages in storage capacity, several challenges need to be addressed before successful implementation in industrial applications. Key challenges include the time required to induce data, raw error rate, storage lifetime, system development, algorithm evolution, cost and industrial viability. Encouragingly, research groups and technology companies are actively addressing these practical challenges, exploring optimal solutions within these approaches, and are poised to smoothly transition them from research to industrial applications.

The research team led by Professor Zhang Jingyu, Professor Gan Zongsong and Professor Cao Qiang from Wuhan National laboratory for Optoelectronics, Huazhong University of Science and Technology, has provided a comprehensive overview of the latest advancements in next-generation optical data storage. The team provides comprehensive insights into various technological pathways, summarizing the substantial opportunities these methods present and outlining the challenges they may encounter during the transition to industrial applications. The relevant work has been published in Chinese Optics Letters 2023, Volume 21, Issue 12 (Zhi Yan, Jingqi Hu, Zhexiang Xiao, Dale Xie, Qiang Cao, Zongsong Gan, Jingyu Zhang. Decoding the future: opportunities and challenges in next-generation optical data storage [Invited][J]. Chinese Optics Letters, 2023, 21(12): 120051) and has been selected as the cover story for the current issue.

The cover reflects two approaches to next-generation optical data storage, with the right side representing multidimensional optical data storage and the left side representing super-resolution optical data storage. Both approaches aim to achieve higher-density data storage capacity. The multidimensional optical data storage route involves multiplexing parameters, including intensity, frequency, polarization, and phase of the writing laser, to enable a single recording voxel to store multiple bits of data. The super-resolution optical data storage route achieves higher storage density by reducing the size of data recording voxels.

The next-generation optical data storage technologies for increasing storage capacity includes two main promising approaches: multidimensional and super-resolution methods. Multidimensional optical data storage involves the multiplexing of laser intensity, wavelength, polarization, and phase to achieve multi-bit data storage in a single recording voxel. Super-resolution optical data storage aims to enhance spatial resolution by reducing the size of the recording voxel.