We report on the demonstration of holographic data storage (HDS) at a raw areal bit density of 2.2 Tbit/in2. The demonstration was performed on a platform incorporating several new technical innovations. One key innovation – the coherent data channel – was successfully introduced ahead of schedule following encouraging early results. Issues of media recording efficiency and carrier wavefront demodulation for homodyne detection are discussed.
A multilayer recording using a varifocal lens generated with a phase-only spatial light modulator (SLM) is proposed. A phase-only SLM is used for not only improving interference efficiency between signal and reference beams but also shifting a focus plane along an optical axis. A focus plane can be shifted by adding a spherical phase to a phase modulation pattern displayed on a phase-only SLM. A focal shift with adding a spherical phase was numerically confirmed. In addition, shift selectivity and recording performance of the proposed multilayer recording method were numerically evaluated in coaxial holographic data storage.
This paper proposes a method to increase the recording density of binary data pages in holographic memory. The recording density is increased by decreasing the rectangular aperture size on a Fourier plane. To extract the original data page from the low quality image, a four-step phase mask is designed. The principle of the proposed method is numerically verified.
In this research, we investigate the influence of Seidel aberrations on the point spread function and the probability density function of holographic data storage systems, and thus the storage capacity and bit error rate of storage system can be obtained. The aberrations tolerances of storage systems with different numerical aperture are obtained. Optimization on BER and SC of holographic data storage systems by reducing Seidel aberrations will be demonstrated numerically.
For holographic photopolymer media, the “formula limit” concept enables facile calculation of the fraction of writing chemistry that is usefully patterned, and the fraction that is wasted. This provides a quantitative context to compare the performance of a diverse range of media formulations from the literature, using only information already reported in the original works. Finally, this analysis is extended to estimate the scope of achievable future performance improvements.
Holographic data storage (HDS) employs the physics of holography to record digital data in three dimensions in a highly stable photopolymer medium. The photopolymer medium must provide the essential characteristics of low scatter and high dynamic range while maintaining low recording induced physical shrinkage and long archival lifetimes. In this article, we report on media advancements employing Akonia’s DREDTM technology which provide a 5x increase in media dynamic range with unchanged media shrinkage. We also discuss the implications of these results for photopolymer media mechanistic models.
Microholographic recording is promising for realizing next-generation optical data storage systems because of its affinity with conventional optical disk systems. One of the problems of the microholographic recording is that two beams are necessary for recording. This paper proposes a novel microholographic recording using only one beam for recording. In the recording process, a radially polarized light beam is used. A microhologram whose grating vector is perpendicular to the optical axis is formed in the recording medium, in contrast to the conventional microholographic recording in which the grating vector of the microhologram is parallel to the optical axis. In the readout process, a circularly polarized vortex light beam is used. A diffracted beam is generated in the transmission direction, in contrast to the conventional microholographic recording in which it is generated in the reflection direction. The diffracted beam is detected and discriminated from a non-diffracted beam. A readout signal simulation using a vectorial coupled wave theory has demonstrated the validity of this technology.
Multi-photon (MP) optical data storage systems (ODS) have been discussed for many years. A differentiating advantage for MP systems is the ability to interrogate through the depth of a multiple-layer substrate without significant influence from out-of-focus layers. Until recently, these systems have been impractical due to the cost, size and complexity of the lasers used for writing and reading. This presentation discusses a brief overview of MP physics for ODS, writing and readout techniques, MP-ODS systems published to date, potential storage densities, new compact MP laser sources appropriate for ODS, and a new MP enhancement effect for readout signal enhancement.
Optical data storage has been widely used in certain consumer applications owing to its passive and robust nature, but has failed to keep with larger industry data storage needs due to the lack of capacity. Many alternatives have been proposed and developed, such as 3D data storage using two-photon absorption that require complex and dangerous laser systems to localize the bits. In this paper, we present a method for localizing bits using a CW 405nm laser diode, in a multilayered polymer film. Data is stored by photobleaching a fluorescent dye, and the response of the material is nonlinear, despite the CW laser and absorption in the visible region. This is achieved using sub-μs pulses from the laser initiating a photothermal effect. This writing method, along with the inexpensive roll-to-roll method for making the disc, will allow for terabyte-scale optical discs using conventional commercial optics and lasers.
An optimized six-dimensional storage system has been investigated theoretically. The system uses multiple beams to create overlapped micro gratings as each storage cell. The cell capacity depends exponentially on the beam wavelength number. With two-photon absorption writing, coherence tomography reading and superresolving beam focusing, this system has extra-large capacity of >1 Pbyte per DVD sized disk (potential ~60 Pbytes per disk), extra-fast reading speed of >117 Gbits/s with high signal-to-noise ratio of >66 dB, large cell sizes (~0.3μm × 6μm) which greatly reduce data addressing difficulties and a standard drive like structure compatible with the CD and DVD disks.
Holographic Data Storage System (HDSS) is one of promising candidates for future high density Optical Data Storage (ODS) system. Modern HDSS using angularly multiplexed recording employs a complicated opt-mechanical system for controlling angle of the reference beam or disk positioning precisely and quickly to achieve high density and fast recording. However, mechanical instabilities during recording and involved degradation of signal quality in HDSS is one of the obstacles to prevent the technology from being a robust system. We analytically formulated effects of mechanical instabilities of a Galvano mirror and spindle motor on the HDSS by incorporating the concept of time averaged holography. Mechanical parameters such as amplitude and frequency of mechanical oscillation are related to optical parameters such as amplitude and phase of reference and signal beams. Through comparison of simulation results with experimental results, we confirmed that the developed optical model was able to predict signal level of a degraded holographic image due to mechanical instabilities. Then, the analytical formulation led to a new method of optical and post recovery for mechanical instability during recording hologram. The optical post recovery method enables a robust implementation of HDSS against mechanical instabilities.
To satisfy the growing need for faster archival data storage and retrieval, we proposed an improvement to the read and write data transfer rates of Holographic Data Storage Systems (HDSS). Conventionally, reading and writing of data utilize only a fraction of the available light. Our techniques apply a resonator cavity to the readout and recording of holograms so that more of the available light is used. Functionally, more power is used than what is provided without violating energy conservation. Thus, data rates and/or capacities can be increased due to enhanced power. These improvements are also inversely related to the diffraction efficiency of a hologram, which makes these cavity enhanced techniques well suited to HDSS where large numbers of multiplexed holograms require low diffraction efficiencies.
Previously, we presented the theory of cavity enhanced HDSS, the experimental effect of enhancement on readout, and the lack of effects on Bragg Selectivity. We have now formalized the enhancement in writing power and experimentally evaluated the improvement in writing speed over conventional means for writing a single plane wave hologram in Fe:LiNbO3 with a 532 nm wavelength, CW, single mode, DPSS, Nd:YAG, laser with a cavity on one of the writing arms. The diffraction efficiency was read during the recording by using a 632.8 nm wavelength HeNe Laser. We found that the enhancement of recording power for this configuration asymptotically approaches a factor of two, while the use of cavities in both writing arms provides a power enhancement which is limited only by the losses in the cavities.
We report volume holographic recording and reconstruction of plane waves using Bessel-like reference beams. A photorefractive lithium niobate crystal (0.05% Fe:LiNbO3) is employed as the holographic medium in a two-wave mixing set-up. The reconstructed plane wave has the same appearance as a Bessel beam, displaying a central maximum and concentric rings. Over a propagation range of 10 to 50 cm, the central intensity is observed to oscillate between maximum and zero intensity. The holographic reconstruction is capable of self-healing and propagation properties are preserved even with the use of a partially blocked readout beam. A theoretical framework based on the interference of a plane wave and a Bessel beam simultaneously reconstructed from a volume hologram is able to describe our experimental results.