Optical storage devices, such as compact disk (CD) and digital versatile disc (DVD), provide us a platform for cheap and compact information storage media. Nowadays, information we obtain every day keeps increasing, and therefore how to increase the storage capacity becomes an important issue. In this paper, we reported a method for the increase of the capacity of optical storage devices using metallic nano-structures. Metallic nano-structures exhibit strong variations in their reflectance and/or transmittance spectra accompanied with dramatic optical phase modulation due to localized surface plasmon polariton resonances. Two samples were fabricated for the demonstration of storage capacity enhancement through amplitude modulation and phase modulation, respectively. This work is promising for high-density optical storage.

The use of optics for data storage could trace back to 40 years ago when the researchers explored the possibilities of optical technology to record and playback audio signals. Optical storage devices have great advantages in low cost, high reliability and good compatibility, which make them suitable for data backup, digital publications, audio & visual products, and so on. To meet with the increasing demand for information storage in the era of big data, optical storage technologies are actively involved in continuous improvement of ultra-high densities and data transfer rates. Several promising technologies have grained growing interest, such as holographic data storage (HDS), multi-layer optical storage, multi-dimensional optical storage and super-resolution near-field structure (super-RENS) optical storage, they are with great expectations because they utilize the volume of optical materials to store information and show great potentials in capacity, density and speed. These technologies, emerging with the revival of optical storage, are now providing a platform for people from both academic and industrial fields to overcome the challenges and realize the practical applications for next generation optical data storage in near future. In this “Special Issue on Optical Storage”, 5 review articles and 3 research articles are specially presented, which covers the research frontiers in relevant subjects.

Fundamental requirements for optical system design for volume recording system is identified. Anastigmatic objective lens design is required for conventional page-based system, whereas for multi-layer volume recording systems, an Aplanatic and zoom optical design is needed with an afocal sub-optical system including a high numerical aperture (NA) objective element. An NA 0.4 and four element design is feasible by only using offthe-shelf components. Recording depth ranges of 0.4 mm for wavelength 532 nm and 0.2 mm for 405 nm. The design demonstrates sufficiently small as-built wavefront error, less than 0.1 waves while implementing focusing and tracking capabilities to the design.

A novel multi-dimensional (MD) optical storage was presented, which was realized by utilizing the space between tracks. Based on scalar diffraction theory, the channel bits parameters of the multi-dimensional optical storage were optimized, and the linear and nonlinear signals were analyzed accurately. Therefore, the format of the multi-dimensional optical disc was obtained, which makes the detection of readout signal easier. With respect to servo, coding and readout physics parameter of channel, the multi-dimensional optical disc is compatible with traditional disc such as Blu-ray disc (BD). Also, the novel multi-dimensional optical storage is able to achieve a doubled density and a ten-fold readout data rate compared with traditional optical discs.

Pilot data aided feed forward (PAFF) carrier recovery is essential for phase noise tracking in coherent optical receivers. This paper describes a new PAFF system based on new pilot arrangement and maximum likelihood (ML) to estimate the phase jitter in coherent receiverinduced by local oscillator’s lasers and sampling clock errors. Square M-ary quadrature amplitude modulation (M-QAM) (4, 16, 64, and 256) schemes were used. A detailed mathematical description of the method was presented. The system performance was evaluated through numerical simulations and compared to those with noisefree receiver (ideal receiver) and feed forward without ML. The simulation results show that PAFF performs near the expected ideal phase recovery. Results clearly suggest that ML significantly improves the tolerance of phase error variance. From bit error rate (BER) sensibility evaluation, it was clearly observed that the new estimation method performs better with a 4-QAM (or quadrature phase shift keying (QPSK)) format compared to three others square QAM schemes. Analog to digital converter (ADC) resolution effect on the system performance was analyzed in terms of Q-factor. Finite resolution effect on 4-QAM is negligible while it negatively affects the system performance when M increases.

In the present work, we measured the forward bias current-voltage (I-V) characteristics of Si-doped n type gallium arsenide (GaAs) heterostructures infrared emitter over a wide temperature range from 350 to 77 K. Results showed that the slopes of the exponential curve changed slowly with temperature. The analysis of the various tunneling mechanisms indicated that the tunneling current varied approximately as a function of ~ exp( – αEg +βeV) where the parameters α and β varied indistinctively with temperature and voltage. The dependence of forward tunneling current on the temperature and bias can be explained by thermally induced band gap shrinkage and bias induced route change respectively. These results will be helpful for application of the optoelectronics device in both high and low temperature ambiences.

This paper reports a synthesis of zinc oxide (ZnO) nanosheets by hydrothermal method. ZnO nanosheets on Al substrate were generated by hydrothermal synthesis with zinc nitrate hexahydrate (Zn(NO3)2$6H2O) and hexamethylenetetramine (HMT) as a research system, which were controlled conditions of the reaction. The energy dispersive spectroscopy (EDS), scanning electron microscope (SEM) and transmission electron microscopy (TEM) images were achieved to determine the characterization of ZnO nanosheets. The diameter of ZnO nanofilm was from 0.5 to 1 μm, and its thickness ranged from 30 to 50 nm.

This paper gives an overview of the research and development progress on Blu-Ray DiscTM (BD) rewritable/recordable media for more than 20 years. The writable BD media had been developed for consumer use like video-recording/personal computer (PC) buck-up and professional use like broadcasting with increasing storage capacity and data rate. The key technology in each innovation was explained according to referenced papers.

Holographic data storage system (HDSS) has been a good candidate for a volumetric recording technology, due to their large storage capacities and high transfer rates, and have been researched for tens of years after the principle of holography was first proposed. However, these systems, called conventional 2-axis holography, still have essential issues for commercialization of products. Collinear HDSS, in which the information and reference beams are modulated co-axially by the same spatial light modulator (SLM), as a new read/write method for HDSS are very promising. With this unique configuration, the optical pickup can be designed as small as DVDs, and can be placed on one side of the recording media (disc). In the disc structure, the preformatted reflective layer is used for the focus/tracking servo and reading address information, and a dichroic mirror layer is used for detecting holographic recording information without interfering with the preformatted information. A 2-dimensional digital page data format is used and the shift-multiplexing method is employed to increase recording density. As servo technologies are being introduced to control the objective lens to be maintained precisely to the disc in the recording and reconstructing process, a vibration isolator is no longer necessary. Collinear holography can produce a small, practical HDSS more easily than conventional 2-axis holography. In this paper, we introduced the principle of the collinear holography and its media structure of disc. Some results of experimental and theoretical studies suggest that it is a very effective method. We also discussed some methods to increase the recording density and data transfer rates of collinear holography.

Nowadays, big-data centers still rely on hard drives. However, there is strong evidence that these surface-storage technologies are approaching fundamental limits that may be difficult to overcome, as ever-smaller bits become less thermally stable and harder to access. An intriguing approach for next generation data-storage is to use light to store information throughout the threedimensional (3D) volume of a material. Holographic data storage (HDS) is poised to change the way we write and retrieve data forever. After many years of developing appropriate recording media and optical read–write architectures, this promising technology is now moving industriously to the market. In this paper, a review of the major achievements of HDS in the past ten years is presented and the key technique details are discussed. The author concludes that HDS technology is an attractive candidate for big data centers in the future. On the other hand, there are many challenges ahead for HDS technology to overcome in the years to come.

The era of big data has necessitated the use of ultra-high density optical storage devices. Super-resolution near-field structure (super-RENS), which has successfully surpassed the fundamental optical diffraction limit, is one of the promising next generation high-density optical storage technologies. This technology combines the traditional super-resolution optical disk with a near-field structure, and has the advantages of structural simplicity, strong practicability, and, more importantly, compatibility with the current optical storage pickup. The mask layer in super-RENS functions as the key to realizing superresolution. Development of suitable materials and stack designs has greatly been improved in the last decade. This paper described several types of super-RENS, such as aperture-type, light scattering center-type, bubble-type, and other types (e.g., WOx and ZnO), particularly the newly proposed super-RENS technology and research achievements. The paper also reviews the applications of super-RENS in high-density optical data storage in recent years. After analyzing and comparing various types of super-RENS technology, the paper proposes the aperturetype based on the mechanism of nonlinear optics as the most suitable candidate for practical applications in the near future.

Long-term digital preservation is an important issue in data storage area. For years, magnetic media based solutions, such as tape and hard disk drive (HDD) based archive systems, monopolize the data archiving market due to their high capacity and low cost. However, in the era of big data, rapidly increasing volume, velocity, and variety of data set bring numerous challenges to the archive systems in various aspects, such as capacity, cost, performance, reliability, power consumption, and so on. In recent years, high capacity optical media, such as bluray discs (BDs) and holographic discs, emerge with the revival of optical storage. Due to the natural simple construction of the optical media, the archive systems based on those optical media, e.g., BD library, demonstrate attractive properties, such as cost per bit, reliability, power consumption, and so on, thus become feasible options in long-term digital preservation. In this paper, we reviewed and compared both the magnetic and optical media based solutions for long-term digital preservation, followed by a summarization on techniques to improve the optical media based archive system.