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.
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.
The onslaught of big data continues even as growth in data storage density tapers off. Meanwhile, the physics of holography continues to suggest the possibility of digital data storage at densities far exceeding those of today’s technologies. We report on recent results achieved with a demonstrator platform incorporating several new secondgeneration techniques for increasing holographic data storage (HDS) recording density and speed.
Since the highest reported areal densities for hard disk drive products currently hover in the 1 Tbit/in2 range, we have adopted 2 Tbit/in2 as a milestone likely to generate interest in the technology. The demonstrator is based on an advanced pre-production prototype, and so inherits highly functional electronic, mechanical, and optical subsystems. It employs a high-NA monocular architecture with proven angle-polytopic multiplexing.
The demonstrator design includes several second-generation innovations. The first, dynamic aperture multiplexing, greatly increases the number of multiplexed holograms. The second, the DREDTM medium formulation, provides dramatically higher dynamic range to record these holograms. These two features alone theoretically allow the demonstrator to exceed 2 Tbit/in2. Additionally, it is equipped with the capability of quadrature homodyne detection, permitting phase quadrature multiplexing (QPSK modulation), and the potential to further increase user capacity by a factor of four or more. The demonstrator has thus been designed to achieve densities supporting the multi-terabyte storage capacities required for competitive products, and to demonstrate the potential for Moore’s-Law growth for years to come.
We present a homodyne detection system implemented for a page-wise holographic memory architecture. Homodyne
detection by holographic memory systems enables phase quadrature multiplexing (doubling address space), and lower
exposure times (increasing read transfer rates). It also enables phase modulation, which improves signal-to-noise ratio
(SNR) to further increase data capacity. We believe this is the first experimental demonstration of homodyne detection
for a page-wise holographic memory system suitable for a commercial design.
To compete in the archive and backup industries, holographic data storage must be highly competitive in four critical
areas: total cost of ownership (TCO), cost/TB, capacity/footprint, and transfer rate. New holographic technology
advancements by Akonia Holographics have enabled the potential for ultra-high capacity holographic storage devices
that are capable of world record bit densities of over 2-4Tbit/in2, up to 200MB/s transfer rates, and media costs less than
$10/TB in the next few years. Additional advantages include more than a 3x lower TCO than LTO, a 3.5x decrease in
volumetric footprint, 30ms random access times, and 50 year archive life. At these bit densities, 4.5 Petabytes of
uncompressed user data could be stored in a 19” rack system. A demonstration platform based on these new advances
has been designed and built by Akonia to progressively demonstrate bit densities of 2Tb/in2, 4Tb/in2, and 8Tb/in2 over
the next year.
Holographic data storage (HDS) remains an attractive technology for big data. We report on recent results achieved with
a demonstrator platform incorporating several new second-generation techniques for increasing HDS recording density
and speed. This demonstrator has been designed to achieve densities that support the multi-terabyte storage capacities
required for a competitive product. It leverages technology from an existing state-of-the-art pre-production prototype,
while incorporating a new optical head designed to demonstrate several new technical advances.
The demonstrator employs the new technique of dynamic aperture multiplexing in a monocular architecture. In a
previous report, a monocular system employing angle-polytopic multiplexing achieved a recording density over 700
Gbit/in2, exceeding that of contemporaneously shipping hard drives . Dynamic aperture multiplexing represents an
evolutionary improvement with the potential to increase this figure by over 200%, while still using proven anglepolytopic
multiplexing in a monocular architecture.
Additionally, the demonstrator is capable of two revolutionary advances in HDS technology. The first, quadrature
homodyne detection, enables the use of phase shift keying (PSK) for signal encoding, which dramatically improves
recording intensity homogeneity and increases SNR. The second, phase quadrature holographic multiplexing, further
doubles density by recording pairs of holograms in quadrature (QPSK encoding).
We report on the design and construction of the demonstrator, and on the results of current recording experiments.
The realization of a commercial holographic data storage device has remained elusive for many decades. The most recent efforts were by InPhase Technologies between 2001 and 2009 resulting in 52 functioning prototypes capable of 300GB/disk and 20MB/s transfer rates. Despite being the world’s first fully functional holographic drives, the primary competitor to holographic archive storage at that time, LTO, had already achieved 800GB and 120MB/in 2008; and by 2010, LTO had achieved 1.5TB and 140MB/s. This left InPhase at a competitive disadvantage to LTO archive solutions despite other strengths such as robustness, random access, and longer-term archive lifetime.
Looking into the future, holographic data storage must be highly competitive with tape in three critical areas: cost/TB, capacity/footprint, and transfer rate. If this can be achieved, holographic data storage would become a superior solution given the low latencies and overall robustness to propel it into being the archive storage front-runner. New technology advancements by Akonia Holographics have enabled the potential for ultra-high capacity holographic storage devices that are capable of world record bit densities of over 2Tbit/in2, 200-300MB/s transfer rates, and a media cost less than $10/TB in the next 5 years. A demonstration platform based on these new advances has been designed and is currently being built by Akonia to progressively demonstrate bit densities of 2Tb/in2, 4Tb/in2, and 8Tb/in2 over the next year.
The number of layers of a micro-holographic disk is limited by wavefront aberration which is strongly dependent on the
photopolymer initiation, termination and inhibition kinetics. 3D metrology is used to validate predicted index profiles.
Studies of development kinetics in volume photopolymers typically use transmission holography to quantify the
index distribution. This method has advantages including simplicity, quantitative index data and natural mapping
onto theories using harmonic expansion of the material response. A particular disadvantage is that the low spatialfrequency
response corresponding to the intensity of the writing beams can never be Bragg matched and thus
In configurations where the exposure is not primarily sinusoidal, the holographic method is not applicable.
Important examples include bit-oriented data storage, direct-write lithography, and the object beam of page-based
holography. In these cases the exposure intensity is essentially arbitrary and there is a need for metrology tools that
can quantitatively measure the real and imaginary parts of the weak 3D index perturbation. Images produced by
bright-field and phase-contrast microscopes are generally not quantitative and are corrupted by objects out of the
We have developed two methods, a form of optical diffraction tomography and a scanning transmission microscope,
that are specifically designed to measure the 3D index response of holographic materials. Both are optimized to
measure the extremely weak absorption and phase structures typical of photopolymers and have passbands that
match the expected spatial frequencies.
An overview of the InPhase Technologies holographic demonstration platform is presented. This compact, mobile system is a fully functional holographic recordable drive complete with custom optics and custom control and channel electronics. The development of this device paves the way for the commercialization of this technology.