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Securely storing large amounts of information over relatively short timescales of 100 years, comparable to the span of the human memory, is a challenging problem. Conventional optical data storage technology used in CDs and DVDs has reached capacities of hundreds of gigabits per square inch, but its lifetime is limited to a decade. DNA based data storage can hold hundreds of terabytes per gram, but the durability is limited. The major challenge is the lack of appropriate combination of storage technology and medium possessing the advantages of both high capacity and long lifetime. The recording and retrieval of the digital data with a nearly unlimited lifetime was implemented by femtosecond laser nanostructuring of fused quartz. The storage allows unprecedented properties including hundreds of terabytes per disc data capacity, thermal stability up to 1000 °C, and virtually unlimited lifetime at room temperature opening a new era of eternal data archiving.
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10.1117/2.1201603.006365
Eternal 5D data storage via
ultrafast-laser writing in glass
Peter Kazansky, Ausra Cerkauskaite, Martynas Beresna,
Rokas Drevinskas, Aabid Patel, Jingyu Zhang, and
Mindaugas Gecevicius
Information storage based on the introduction of nanostructures into
fused quartz using a femtosecond laser could ensure all that we have
learned will not be forgotten.
Compared with paper or clay, digital data storage is not very
durable. As such, securely storing large amounts of informa-
tion over even the relatively short timescale of 100 years—
comparable to the human memory span—is a challenging
problem.1Conventional optical-data-storage technology of the
type employed in CDs and DVDs has reached capacities of hun-
dreds of gigabits per square inch. However, the lifetime of this
media is limited to a decade as a result of unavoidable degrada-
tion suffered by the data layer. More futuristic DNA-based data
storage is capable of holding hundreds of terabytes (Tb) of data
per gram, but its durability is limited.2
The concept of storing data optically in the bulk of non-
photosensitive transparent materials (such as fused quartz,
which is renowned for its high chemical stability and resis-
tance) via femtosecond-laser (fs-laser) writing was first pro-
posed and demonstrated in 1996.3, 4 This method allows for
high-capacity optical recording by multiplexing new degrees of
freedom (e.g., intensity, polarization, and wavelength). This de-
velopment in data storage is based on the introduction of gold or
silver nanoparticles, which are embedded within the material.5
The plasmonic properties of these nanoparticles can then
be exploited.6, 7 More recently, polarization-multiplexed writ-
ing has been demonstrated by using self-assembled nanograt-
ings, which are produced via ultrafast-laser writing in fused
quartz.8, 9 These nanogratings, which comprise 20nm-thick lam-
ina structures embedded within the material,10–12 are resistant
to high temperatures.13 Despite several attempts to explain the
physics of this peculiar self-organization process, the formation
of the nanostructures remains a mystery.14,15
Based on this behavior, we have developed a method of
data storage that makes use of three spatial and two optical
Figure 1. 5D optical data storage, written in fused quartz using a fem-
tosecond laser. Three spatial dimensions and two optical ones (the slow-
axis orientation and the retardance) are exploited. Each voxel contains
a self-assembled nanograting that is oriented in a direction perpendic-
ular to the light polarization. The distance between two adjacent spots
is 3.7m and the distance between each layer is 20m. E: Electric field
of light wave. Arrow: Polarization direction.
dimensions.16 On the macroscopic scale, the self-assembled
nanostructures behave as uniaxial optical crystals with negative
birefringence. The alignment of the nanogratings gives rise to
optical anisotropy (a form of birefringence) of the same order of
magnitude as positive birefringence in crystalline quartz.
In conventional optical storage such as DVDs, data is stored
by burning tiny pits in one or more layers of the plastic disc,
thereby making use of three spatial dimensions. We have also
exploited two additional (optical) dimensions. When the data-
recording femtosecond laser marks the glass, it makes a pit with
a nanograting. This nanograting produces birefringence that is
characterized by two additional parameters. The slow-axis ori-
entation introduces a fourth dimension, and the strength of
retardance—defined as a product of the birefringence and the
length of the structure—forms a fifth dimension. These two pa-
rameters are controlled during recording by the polarization and
light intensity, respectively. By adding these additional optical
dimensions to the three spatial coordinates, we achieve 5D opti-
cal data storage: see Figure 1.
Continued on next page
10.1117/2.1201603.006365 Page 2/3
We have recorded the first digital documents (including
copies of the Universal Declaration of Human Rights, New-
ton’s Opticks, the Magna Carta, and the King James Bible) across
up to 18 layers using optimized parameters (light pulses with
energies of 0.2J and a duration of 600fs at a repetition rate
of 500kHz): see Figure 2. To test the durability of this data-
storage mechanism, we used accelerated aging measurements
(see Figure 3). These tests reveal that the decay time of the
nanogratings is 31020˙1years at room temperature (303K),
showing the unprecedentedly high stability of nanostructures
imprinted in fused quartz. Even at elevated temperatures of
462K, the extrapolated decay time is comparable to the age of
the Universe (13.8 billion years). Based on the tests, we believe
that these copies could survive the human race.9
The addition of more states of polarization and intensities—
currently limited by the resolutions of the slow axis orientation
(4:7) and the retardance (5nm)—could enable more than one
byte (8 bits, or 256 possible combinations) per modification spot
using the same birefringence measurement system. By recording
data with a 1.4NA (numerical aperture) objective and a shorter
wavelength (250–350nm), recording a disc with a 360Tb capacity
(more than 7000 times today’s 50Gb double-layer Blu-ray capac-
ity) could be made possible.
We have developed an extremely durable 5D data-storage
technique based on the imprinting of nanostructures in silica
glass via femtosecond-laser writing. This technology, which we
have coined ‘Superman memory crystal,’ could be produced on
a commercial scale for organizations with large archives (e.g., na-
tional archives, museums, libraries, and private organizations).
We believe that our method will also prove attractive for the
consumer market if the cost of hardware (particularly the ex-
pensive femtosecond laser) is reduced.17 Additionally, a number
of projects (such as Time Capsule to Mars, MoonMail, and the
Google Lunar XPRIZE)18–20 could benefit from the technique’s
extreme durability, which fulfills a crucial requirement for stor-
Figure 2. Copies of (a) the King James Bible and (b) the Magna Carta
imprinted in glass.
Figure 3. Arrhenius plot of the nanograting decay rate. The black dots
indicate measured values and the red dots are calculated based on fit-
ting results, showing the extrapolated lifetime of the stored data. The
gray shaded zone indicates the tolerance of extrapolated values. Based
on these results, the nanogratings would last for the current lifetime of
the Universe (D13:8 billion years) at a temperature (T) of 462K. The
inset shows the decay of the retardance strength over time at different
annealing temperatures (900, 1000, and 1100C).
age on the Moon or Mars. With this technology, we may have
finally achieved information immortality.21 In our future work,
we plan to improve write speeds and to develop a microscope-
free disc drive for data readout.
Author Information
Peter Kazansky, Ausra Cerkauskaite, Martynas Beresna,
Rokas Drevinskas, Aabid Patel, Jingyu Zhang, and
Mindaugas Gecevicius
Optoelectronics Research Centre
University of Southampton
Southampton, United Kingdom
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Eternal 5D data storage by ultrafast laser writing in glass
Presented at SPIE Photonics West, 2016.
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c
2016 SPIE
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