1 Multilayer optical bit-oriented memory. 2 Abstract The advent of blue-laser (405nm) optical...

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Multilayer optical Multilayer optical bit-oriented memorybit-oriented memory

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Multilayer optical bit-oriented memoryMultilayer optical bit-oriented memory

AbstractAbstract

The advent of blue-laser (405nm) optical storage in the form of BD,The advent of blue-laser (405nm) optical storage in the form of BD, HD DVD,HD DVD,

holographic memories, and UDO would seem to signaholographic memories, and UDO would seem to signal l the end of opticalthe end of optical

storage's technology life. But, in fact, the future of optical storage is stillstorage's technology life. But, in fact, the future of optical storage is still very very

bright. Once theoretical methods of capacity growth, such as multilayer,bright. Once theoretical methods of capacity growth, such as multilayer, multi-multi-

level, near-field, and holographic are ready to enter the productlevel, near-field, and holographic are ready to enter the product mainstream. mainstream.

The engineering challenges of these advanced recordingThe engineering challenges of these advanced recording methods on lasers, methods on lasers,

media, optical pickups, servos, and read/write channelsmedia, optical pickups, servos, and read/write channels will be significant, but will be significant, but

achievable. One can confidently predict the future ofachievable. One can confidently predict the future of optical storage will be 120-optical storage will be 120-

130mm disc media with capacities in the 100 GB130mm disc media with capacities in the 100 GB to 1 TB rangeto 1 TB range..

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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 () 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 /NA; shorter s 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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Classical Optical Storage - 2Is the end of the technology line in sight? Is the end of the

technology line in sight?For 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: conception3D optical memory: conception

Femtosecond lasers

Two-photon absorption

Single-beam recording

Two-beam recording

Fluorescent readout

Refraction readout

Reflection readout

Polarization readout


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3D optical memory: conception3D optical memory: conception

1-laser, 1-laser, 2-frequency converter, 2-frequency converter, 3- beam splitter,3- beam splitter,4-prism, 4-prism, 5-mirrors, 5-mirrors, 6-delay line, 6-delay line, 7-lenses,7-lenses,8-photochromic 8-photochromic recording media, recording media, 9-filters, 9-filters, 10-irradiation detector10-irradiation detector


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Photochromic compoundsPhotochromic compoundsMany 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-destructive and efficient readout of recorded information

by the certain method (fluorescent, refractive, reflective,

polarization


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Photochromic recording mediaPhotochromic recording mediaIn 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 mediaPhotochromic recording media

The main parameters:The main parameters:-spectral characteristics of recording media provide application of laser -spectral characteristics of recording media provide application of laser

radiation with 1064, 532 and 266 nm;radiation with 1064, 532 and 266 nm;-recorded information is retained at room temperature more 10 years;-recorded information is retained at room temperature more 10 years;-photoinduced change of refraction index may be over 10-photoinduced change of refraction index may be over 10-2-2 at at acceptable laser radiation power;acceptable laser radiation power;-a number of cycles for photoinduced recording- erasure processes may -a number of cycles for photoinduced recording- erasure processes may

achieve 10achieve 1066..

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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Diode pumping solid-state laser Diode pumping solid-state laser = 1064, 532, 266 nm= 1064, 532, 266 nm

Laser parameters:Laser parameters:

Pulse duration – 5 nsPulse duration – 5 ns

power (532) – 50 mWpower (532) – 50 mW

Power (266) – 5 mWPower (266) – 5 mW

frequency – 20 kHzfrequency – 20 kHz

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Low voltage multi-channel electro-optical Low voltage multi-channel electro-optical modulatorsmodulators

Control voltage – 5-10 V; control frequency – up to 1 MHz

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Two-photon mediaTwo-photon media

Advantage:Advantage:

- Altering of the medium - Altering of the medium state only in the focal state only in the focal volumevolume

DisadvantageDisadvantage- High thresholdHigh threshold- Complicated of the Complicated of the

light source light source miniaturizationminiaturization

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One-photon media

AdvantageAdvantage::

- low threshold- low threshold- simplicity of the light simplicity of the light

source miniaturizationsource miniaturization

DisadvantageDisadvantage- darkness of the entire darkness of the entire

medium volumemedium volume

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Numerical modelNumerical model

EEoutout(x.y)=F(x.y)=F-1-1{H(f{H(fxx,f,fyy) ) F[EF[Einin(x,y)]}(x,y)]}

wherewhere::transfer functiontransfer function is is

is consideredis considered of the influence of the evanscente modes of the influence of the evanscente modes

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12exp, yxyx ffziffH


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Transverse structure of the gaussian light beam (0=25 m) ) near boundary of the two dielectrics


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Transverse structure of the gaussian light beam (0=12.5 m) ) near boundary of the two dielectrics


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Dependence of the reflection coefficient for Gaussian beam from medium’s refraction coefficients

1 - 1 - 0 0 =25 =25 mm;;2 - 2 - 0 0 =12.5 =12.5 mm;;3 - 3 - 0 0 = = (plane wave). (plane wave).


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Diode pumping solid-state laser Diode pumping solid-state laser = 1064, 532, 355 nm= 1064, 532, 355 nm


Beam quality – TEM00Tripled efficiency – 20%

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Diode pumping pig-tail laser with focusing lensDiode pumping pig-tail laser with focusing lens

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Experimental setupExperimental setup

X-Y – 20x20mm, step – 5 mm, Z – 5 mm, step – 10 mm, repeatability – 1 mm

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System for the fine filtering of the monomers.System for the fine filtering of the monomers.

Filtering particles with sizes up to 0,1 Filtering particles with sizes up to 0,1 m with next polimerizationm with next polimerizationin clean conditions in closed volume of the special forming setup.in clean conditions in closed volume of the special forming setup.

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Optical scheme of the experimental setupOptical scheme of the experimental setup

spatial resolution – 1 m, depth of field – 10 m, media thickness – up to 1,5 mm

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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

1 Multilayer optical bit-oriented memory. 2 Abstract The advent of blue-laser (405nm) optical...

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