Multilayer optical bit-oriented memory

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Multilayer optical bit-oriented memory

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Multilayer optical bit-oriented memory

• Abstract
• The advent of blue-laser (405nm) optical
  storage in the form of BD, HD DVD, holographic
  memories, and UDO would seem to signal the end of
  optical storage's technology life. But, in fact,
  the future of optical storage is still very
  bright. Once theoretical methods of capacity
  growth, such as multilayer, multi-level,
  near-field, and holographic are ready to enter
  the product mainstream. The engineering
  challenges of these advanced recording methods on
  lasers, media, optical pickups, servos, and
  read/write channels will be significant, but
  achievable. One can confidently predict the
  future of optical storage will be 120-130mm disc
  media with capacities in the 100 GB to 1 TB range.

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Multilayer optical bit-oriented memory
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Multilayer optical bit-oriented memory

• Classical Optical Storage Classical Optical
  Storage - I
• Is the end of the technology line in sight? Is
  the end of the technology line in sight?
• Laser diode (LD) wavelengths (l) have reached
  the
• end of the visible spectrum at 405nm.
• Conventional objective lens have reached the
  limit
• of usable numerical apertures (NAs).
• Spot size is a function of l/NA shorter ls and
• bigger NAs yield smaller spot diameters and
  higher areal densities.
• The technology life appears ended - but wait!
  This
• is only true for linear thinking and design.

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Multilayer optical bit-oriented memory

• Classical Optical Storage - 2
• Is the end of the technology line in sight? Is
  the end of the technology line in sight?
• For l fixed at 405nm, classical optical storage
  can increase capacity in several ways, alone or
  in combination.
• Architecture Examples
• Multilayer Discs (MLD) 2-N surfaces.
• MultiLevel Recording (MLR) replicated, phase
  change.
• Near-Field Recording (NFR) read-only and
  write/read.
• Fluorescent Multilayer Disc (FMD) read and
  record.
• Attractive Combinations
• MLD MLR (25-50 GB/surface x 2.5 ML gain x N
  surfaces or 250-500 GB/120mm disc).
• NFR MLR MLD (50-200 GB/surface x 2.5 ML
  gain x 1-2 surfaces or 125 GB - 1 TB/120mm disc).

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3D optical memory conception
Multilayer optical bit-oriented memory
Femtosecond lasers Two-photon absorption Single-be
am recording Two-beam recording Fluorescent
readout Refraction readout Reflection
readout Polarization readout
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3D optical memory conception
Multilayer optical bit-oriented memory

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• 1-laser,
• 2-frequency converter,
• 3- beam splitter,
• 4-prism,
• 5-mirrors,
• 6-delay line,
• 7-lenses,
• 8-photochromic
• recording media,
• 9-filters,
• 10-irradiation detector

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Photochromic compounds
Multilayer optical bit-oriented memory
Many organic compounds exhibit reversible
photochromic transformations between two forms
hv
A B

hv To develop 3D bitwise working
optical memory photochromic compounds must
satisfy to the conditions of their application.
The concrete requirements are - large
cross-section of light absorption -high
efficiency of photochemical transformations
- thermal stability of forms A and B
-high stability of both forms to
irreversible phototransformations -non-destruc
tive and efficient readout of recorded
information by the certain method (fluorescent,
refractive, reflective, polarization
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Photochromic recording media
Multilayer optical bit-oriented memory

• In accordance with the present invention the
  medium material having the
• above improved properties comprises a light
  sensitive photochromic
• polymeric compositions based polycarbonate or
  polystyrene and one of new fulgimides.

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Photochromic recording media
Multilayer optical bit-oriented memory

• The main parameters
• -spectral characteristics of recording media
  provide application of laser radiation with 1064,
  532 and 266 nm
• -recorded information is retained at room
  temperature more 10 years
• -photoinduced change of refraction index may be
  over 10-2 at
• acceptable laser radiation power
• -a number of cycles for photoinduced recording-
  erasure processes may achieve 106.
• Therefore, it was unexpectedly revealed
  that above polymer materials based on
  polycarbonate or polystyrene and photochromic
  compound from a new fulgimide class undergo
  photochromic reaction accompanied with
  photoinduced changes of absorption and refraction
  which makes them suitable for the purposes of a
  2D or 3D working optical memory system.
• The new fulgimide class was patented.

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Multilayer optical bit-oriented memory
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Multilayer optical bit-oriented memoryDiode
pumping solid-state laser l 1064, 532, 266 nm

• Laser parameters
• Pulse duration 5 ns
• power (532) 50 mW
• Power (266) 5 mW
• frequency 20 kHz

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Multilayer optical bit-oriented memory Low
voltage multi-channel electro-optical modulators
Control voltage 5-10 V control frequency up
to 1 MHz
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Multilayer optical bit-oriented memory
Two-photon media

• Advantage
• - Altering of the medium state only in the focal
  volume
• Disadvantage
• High threshold
• Complicated of the light source miniaturization

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Multilayer optical bit-oriented
memoryOne-photon media

• Advantage
• - low threshold
• simplicity of the light source miniaturization
• Disadvantage
• darkness of the entire medium volume

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Multilayer optical bit-oriented memory
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Multilayer optical bit-oriented memory
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Multilayer optical bit-oriented memory
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Numerical model
Multilayer optical bit-oriented memory

• Eout(x.y)F-1H(fx,fy) ?FEin(x,y)
• where
• transfer function is
• is considered of the influence of the evanscente
  modes

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Transverse structure of the gaussian light beam
(w025 mm) ) near boundary of the two dielectrics
Multilayer optical bit-oriented memory
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Transverse structure of the gaussian light beam
(w012.5 mm) ) near boundary of the two
dielectrics
Multilayer optical bit-oriented memory
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Dependence of the reflection coefficient for
Gaussian beam from mediums refraction
coefficients
Multilayer optical bit-oriented memory

• 1 - w0 25 mm
• 2 - w0 12.5 mm
• 3 - w0 ? (plane wave).

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Diode pumping solid-state laser l 1064, 532,
355 nm
Multilayer optical bit-oriented memory
Beam quality TEM00 Tripled efficiency 20
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Multilayer optical bit-oriented memory Diode
pumping pig-tail laser with focusing lens
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Multilayer optical bit-oriented memory
Experimental setup
X-Y 20x20mm, step 5 mm, Z 5 mm, step 10
mm, repeatability 1 mm
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Multilayer optical bit-oriented memory

• System for the fine filtering of the
  monomers.
• Filtering particles with sizes up to 0,1 mm with
  next polimerization
• in clean conditions in closed volume of the
  special forming setup.

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Multilayer optical bit-oriented memory

• Optical scheme of the experimental setup

spatial resolution 1 mm, depth of field 10
mm, media thickness up to 1,5 mm
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Multilayer optical bit-oriented memory

• New photochromic recording media with the best
  properties providing their application in one-
  and two-photon 3D bitwise working optical memory
  have been worked out.
• Method for nondestructive readout based on
  photoinduced changes of refraction index have
  been developed for working optical memory.
• Prototype of the device for one-photon working
  optical memory based on photochromic recording
  media has been produced.
• Developed media were tested with positive
  results for application
• It was demonstrated that number of photochromic
  layers up to 30 is possible
• It was demonstrated that number of
  writing-erasing-reading circles is more than 106