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WO2003049097A1 - Support d'enregistrement holographique - Google Patents

Support d'enregistrement holographique Download PDF

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Publication number
WO2003049097A1
WO2003049097A1 PCT/GB2002/005298 GB0205298W WO03049097A1 WO 2003049097 A1 WO2003049097 A1 WO 2003049097A1 GB 0205298 W GB0205298 W GB 0205298W WO 03049097 A1 WO03049097 A1 WO 03049097A1
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WIPO (PCT)
Prior art keywords
holographic recording
recording medium
chalcogenide
medium according
filler material
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PCT/GB2002/005298
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English (en)
Inventor
Pavel Krecmer
Stephen Elliott
Jiri Prokop
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Polight Technologies Ltd.
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Priority claimed from GBGB0128904.0A external-priority patent/GB0128904D0/en
Priority claimed from GBGB0213109.2A external-priority patent/GB0213109D0/en
Application filed by Polight Technologies Ltd. filed Critical Polight Technologies Ltd.
Priority to AU2002343084A priority Critical patent/AU2002343084A1/en
Publication of WO2003049097A1 publication Critical patent/WO2003049097A1/fr

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    • G—PHYSICS
    • G11—INFORMATION STORAGE
    • G11C—STATIC STORES
    • G11C13/00—Digital stores characterised by the use of storage elements not covered by groups G11C11/00, G11C23/00, or G11C25/00
    • G11C13/04—Digital stores characterised by the use of storage elements not covered by groups G11C11/00, G11C23/00, or G11C25/00 using optical elements ; using other beam accessed elements, e.g. electron or ion beam
    • G11C13/042—Digital stores characterised by the use of storage elements not covered by groups G11C11/00, G11C23/00, or G11C25/00 using optical elements ; using other beam accessed elements, e.g. electron or ion beam using information stored in the form of interference pattern
    • G—PHYSICS
    • G11—INFORMATION STORAGE
    • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
    • G11B7/00—Recording or reproducing by optical means, e.g. recording using a thermal beam of optical radiation by modifying optical properties or the physical structure, reproducing using an optical beam at lower power by sensing optical properties; Record carriers therefor
    • G11B7/24—Record carriers characterised by shape, structure or physical properties, or by the selection of the material
    • G11B7/2403—Layers; Shape, structure or physical properties thereof
    • G11B7/24035—Recording layers
    • G11B7/24044—Recording layers for storing optical interference patterns, e.g. holograms; for storing data in three dimensions, e.g. volume storage
    • G—PHYSICS
    • G11—INFORMATION STORAGE
    • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
    • G11B7/00—Recording or reproducing by optical means, e.g. recording using a thermal beam of optical radiation by modifying optical properties or the physical structure, reproducing using an optical beam at lower power by sensing optical properties; Record carriers therefor
    • G11B7/24—Record carriers characterised by shape, structure or physical properties, or by the selection of the material
    • G11B7/241—Record carriers characterised by shape, structure or physical properties, or by the selection of the material characterised by the selection of the material
    • G11B7/242—Record carriers characterised by shape, structure or physical properties, or by the selection of the material characterised by the selection of the material of recording layers
    • G11B7/243—Record carriers characterised by shape, structure or physical properties, or by the selection of the material characterised by the selection of the material of recording layers comprising inorganic materials only, e.g. ablative layers
    • G—PHYSICS
    • G11—INFORMATION STORAGE
    • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
    • G11B7/00—Recording or reproducing by optical means, e.g. recording using a thermal beam of optical radiation by modifying optical properties or the physical structure, reproducing using an optical beam at lower power by sensing optical properties; Record carriers therefor
    • G11B7/24—Record carriers characterised by shape, structure or physical properties, or by the selection of the material
    • G11B7/26—Apparatus or processes specially adapted for the manufacture of record carriers
    • G—PHYSICS
    • G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
    • G03H—HOLOGRAPHIC PROCESSES OR APPARATUS
    • G03H1/00—Holographic processes or apparatus using light, infrared or ultraviolet waves for obtaining holograms or for obtaining an image from them; Details peculiar thereto
    • G03H1/02—Details of features involved during the holographic process; Replication of holograms without interference recording
    • G03H2001/026—Recording materials or recording processes
    • G03H2001/0264—Organic recording material
    • G—PHYSICS
    • G11—INFORMATION STORAGE
    • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
    • G11B7/00—Recording or reproducing by optical means, e.g. recording using a thermal beam of optical radiation by modifying optical properties or the physical structure, reproducing using an optical beam at lower power by sensing optical properties; Record carriers therefor
    • G11B7/24—Record carriers characterised by shape, structure or physical properties, or by the selection of the material
    • G11B7/241—Record carriers characterised by shape, structure or physical properties, or by the selection of the material characterised by the selection of the material
    • G11B7/242—Record carriers characterised by shape, structure or physical properties, or by the selection of the material characterised by the selection of the material of recording layers
    • G11B7/243—Record carriers characterised by shape, structure or physical properties, or by the selection of the material characterised by the selection of the material of recording layers comprising inorganic materials only, e.g. ablative layers
    • G11B2007/24302—Metals or metalloids
    • G11B2007/24314—Metals or metalloids group 15 elements (e.g. Sb, Bi)
    • G—PHYSICS
    • G11—INFORMATION STORAGE
    • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
    • G11B7/00—Recording or reproducing by optical means, e.g. recording using a thermal beam of optical radiation by modifying optical properties or the physical structure, reproducing using an optical beam at lower power by sensing optical properties; Record carriers therefor
    • G11B7/24—Record carriers characterised by shape, structure or physical properties, or by the selection of the material
    • G11B7/241—Record carriers characterised by shape, structure or physical properties, or by the selection of the material characterised by the selection of the material
    • G11B7/242—Record carriers characterised by shape, structure or physical properties, or by the selection of the material characterised by the selection of the material of recording layers
    • G11B7/243—Record carriers characterised by shape, structure or physical properties, or by the selection of the material characterised by the selection of the material of recording layers comprising inorganic materials only, e.g. ablative layers
    • G11B2007/24302—Metals or metalloids
    • G11B2007/24316—Metals or metalloids group 16 elements (i.e. chalcogenides, Se, Te)
    • G—PHYSICS
    • G11—INFORMATION STORAGE
    • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
    • G11B7/00—Recording or reproducing by optical means, e.g. recording using a thermal beam of optical radiation by modifying optical properties or the physical structure, reproducing using an optical beam at lower power by sensing optical properties; Record carriers therefor
    • G11B7/24—Record carriers characterised by shape, structure or physical properties, or by the selection of the material
    • G11B7/241—Record carriers characterised by shape, structure or physical properties, or by the selection of the material characterised by the selection of the material
    • G11B7/242—Record carriers characterised by shape, structure or physical properties, or by the selection of the material characterised by the selection of the material of recording layers
    • G11B7/243—Record carriers characterised by shape, structure or physical properties, or by the selection of the material characterised by the selection of the material of recording layers comprising inorganic materials only, e.g. ablative layers
    • G11B2007/24318—Non-metallic elements
    • G11B2007/24324—Sulfur

Definitions

  • the present invention relates generally to materials used for forming photorefractive holographic recording media.
  • the invention relates in particular to a method for producing a photorefractive holographic media which has good sensitivity and good transparency to enable thick samples to be used for multiplexing multiple pages of data.
  • the second technical solution to the increasing demands for data-storage systems is being developed on the basis of three-dimensional optical writing of pits and grooves into a series of multi-layers.
  • multi-layer disks are being considered using, for example, photorefractive polymers as discussed by D. Day, M. Gu and A. Smallridge (Use of two-photon excitation for erasable-rewritable three-dimensional bit optical data storage in a photorefractive polymer, Optics Letters 24 (1999) 948) or fluorescent materials.
  • This technical solution to the data-storage problem also has severe disadvantages such as the limited number of sensitive layers due to overlapping problems (noise due to interference and scattering) and still, most importantly, slow serial data processing.
  • holographic data recording and retrieval The third category of technical approach to data-storage systems for future recording media is in holographic data recording and retrieval.
  • holography Used for storage of digital information, holography is now regarded as a realistic contender for functions now served by opto-magnetic materials or optically written phase-change CD-ROMs and DVD-ROMs.
  • Much research has been carried out to find a suitable and commercially viable recording medium.
  • any photo-sensitive material can be used for holographic recording; however, long-time data storage, sensitivity, cost, speed of recording and developing of the holograms are only some of the issues which limit the available materials to a few which are potentially useful in the field of holographic data storage.
  • Typical materials extensively used in, for example, art holography, such as silver- halide materials, dichromated gelatin, bacteriorhodopsin etc. are generally unsuitable for data storage, as they typically require additional processing steps such as wet development.
  • Ion-doped inorganic photorefractive crystals such as lithium niobate, have served for laboratory use for many years.
  • Interfering light beams of suitable wavelength generate bright and dark regions in the electro-optic crystal and charge carriers- usually electrons- are excited in the bright regions and become mobile. They migrate in the crystal and are subsequently trapped at new sites.
  • electronic space-charge fields are set up that give rise to a modulation of refractive index via the electro-optic effect.
  • Photopolymers or photoaddressable polymers react to light with a refractive index change caused by a change in their molecular configuration resulting from polymerisation.
  • Photorefractive polymers utilise the same electro-optic effect as described above in the case of photorefractive crystals.
  • the major disadvantage of the monomer-polymer type material is the significant distortions of the holograms due to polymer shrinkage during polymerisation.
  • Photoaddressable - photochromic and photodichroic polymers that undergo a change in isomer state after two-photon absorption are the subject of extensive study. These materials are reversible and relatively fast (msec); however, disadvantages typically include relatively fast dark relaxation, short dark storage time and the requirement of coherent UV light sources.
  • Photorefractive polymers exhibit quite a high dynamical range with low intensity illumination, but still suffer from disadvantages like problematic preparation of thick samples, need for development of non-destructive readout and the necessity to apply a high electrical field for the transport and charge separation.
  • Organic polymers are generally also limited in having relatively low light intensity thresholds due to possible overheating (resulting in chemical decomposition).
  • the final class of materials that can be used for holographic data storage are chalcogenide glasses, and these form the subject of this application.
  • phase change photocrystallisation
  • the first group consists of optical recording media, which exhibit a phase- change (amorphous-to-crystal, or vice versa) upon illumination or heating. It is well known that some kinds of Te-based alloy film undergo comparatively easily a reversible phase transition on irradiation by a laser beam.
  • compositions rich in Te-component makes it possible to obtain an amorphous state by illumination with a relatively low laser power
  • their application as a recording medium has been proposed.
  • S. R. Ovshinsky et al. had first disclosed in U.S. Pat. No. 3,530,441 that thin films such as Te 85 Ge 15 and Te 81 Ge 15 S 2 Sb 2 produce a reversible phase-transition when exposed to light with a high energy density such as a laser beam.
  • the resulting image can either be used as such, utilizing the absolute contrast between fully opaque (non- irradiated) and transparent areas (illuminated) of the sample (amplitude image), or make use of the diffusion implicated differences in the solubility of the exposed and non-exposed areas in suitable solvents.
  • WORM write- once-read-many
  • Another disadvantage of these materials is firstly the high mobility of the small metal-ions (mostly Ag) in the host material, which causes a relatively fast degradation of the optical properties of the sample.
  • the non-dissolved metal at the non-illuminated areas of the sample has to be removed in an additional process step [C.W. Slinger, A. Zakery, P.J.S. Ewen and A.E. Owen, Photodoped chalcogenides as potential infrared holographic media, Applied Optics 31 (1992) 2490].
  • the photoinduced expansion/contraction of the glassy matrix can be used for the formation of relief holographic gratings in thin chalcogenide films. Though it might play an important role in fundamental understanding of photostrucural changes, it is rather a negative effect affecting the process of holographic recording in chalcogenide glasses. Fortunately it requires high exposure energies (200-300 J/mm 2 ) to significantly affect the surface relief of the sample. [V. Paylok, Appl. Phys. A 68 (1999) 489, S. Ramachandran, IEEE Photonics Tech. Lett.,8, 1996]. Wet etching of photo-induced holograms in chalcogenide glasses is another approach - T. Sakai and Y. Utsugi [Opt.
  • optically induced birefringence and dichroism are the next group of optical properties in chalcogenide glasses that can be used for hologram writing.
  • a change of refractive index of about ⁇ 3.10 '3 in an amorphous As 2 S 3 film was first observed in 1977 by Zhdanov and Malinovsky [V.G. Zhdanov and V.K. Malinovsky, Pisma Zh. Tehn. Fiz.3 (1977) 943], and nearly 100 research papers have been published on the subject since.
  • the structural changes associated with photoinduced anisotropy are the subject of speculations; however, it is generally accepted that the structural origin of the photoinduced anisotropy is different in nature from that of scalar photodarkening.
  • a photoinduced change in optical properties independent of the polarization of the inducing light is believed in the related art to be caused by one or more combinations of the following processes: atomic bond scission, change in atomic distances or bond-angle distribution, or photoinduced chemical reactions such as
  • the method comprises exposing a chalcogenide layer to a pattern of light having wavelengths less than that corresponding to the bandgap of the material whereby the optical density of the material is increased or decreased in the areas exposed to light to form a visible image.
  • the changes in absorption coefficient are mainly accompanied by a change in refractive index. This is typically greater than that in photorefractive crystals or polymers and can reach up to ⁇ n ⁇ 0.2-0.3 (for comparison Fe-doped LiNbO 3 ferroelectric crystals have ⁇ n ⁇ 10 "4 ).
  • reversible photoinduced shifts of the optical absorption of vitreous As 2 S 3 films were reported and used for hologram storage in these materials [US Patent 3,923,512, Ohmachi, Appl. Phys. Lett, 20 1972, J.S.,Berkes JJAppl.Phys, 42, 5908, K. Tanaka, Solid St. Commun., 11,1311].
  • the effective areal storage density can be significantly increased by recording of multiple, independent pages of data in the same recording volume.
  • This process in which the holographic structure for one page is intermixed with the recorded structure of each of the other pages, is referred to as multiplexing.
  • Retrieval of an individual page with minimum crosstalk from the other pages is a consequence of the volume nature of the recording and its behavior as a highly tuned diffracting structure.
  • This so called Bragg effect is the cause of a decrease in diffraction intensity by changing the angle or wavelength between different recording and playback beams.
  • the point at which the diffraction efficiency becomes zero depends on the recording angles, initial wavelength and optical thickness of the recording material. For a given recording configuration, altering the thickness plays the central role. As the thickness increases, the recorded structure becomes more highly tuned such that smaller mismatches among individual holograms can be tolerated.
  • chalcogenide glasses were to be used in a commercial holographic drive ("holodrive") they would require the use of very expensive tunable pulsed lasers emitting light having a relatively low energy (ie longer wavelength). This is due to these materials having relatively small values of energy band gaps, thereby exhibiting high optical absorption of the output of higher energy, shorter wavelength lasers.
  • the laser system would need to be tuned to bandgap or near the bandgap of the chalcogenide material, while at the same time retaining a high value of optical transmission- two conditions which are in principle contradictory and almost impossible to achieve in optically thick media (above 100 ⁇ m thick).
  • the low value of optical absorption is due to the material having a larger bandgap than previously used chalcogenide glasses, and moreover the bandgap can be tuned to a slightly shorter wavelength than 532nm to decrease the absorption of Nd:YAG laser light without substantially affecting the sensitivity.
  • Nd:YAG lasers are relatively cheap and can be pulsed.
  • WO01/45111 discloses a rewriteable chalcogenide based holographic recording medium which particularly utilises an As-Se based chalcogenide material.
  • the object of this invention is the utilization of a highly photosensitive composition of an amorphous chalcogenide material in the form of a relatively thick film (d >100 ⁇ m) for the preparation of a volume holographic recording medium with high diffraction efficiency, which allows multiple holograms to be stored, the material having a high level of optical transmission at the wavelength of interest.
  • a holographic recording medium comprises an amorphous mixture of a chalcogenide glass dispersed in a filler material, the filler material being substantially transparent to visible light, wherein the chalcogenide glass undergoes a photostructural change in response to illumination resulting in a change of refractive index of the chalcogenide glass.
  • a method of producing a holographic recording medium comprises the step of:- co-depositing a chalcogenide material and a filler material onto a substrate to form an amorphous film comprising an amorphous mixture of a chalcogenide glass and a filler material, the filler material being substantially transparent to visible light.
  • a method of holographic recording comprises the steps of:- providing a holographic recording medium comprising an amorphous mixture of a chalcogenide glass and a filler material, the filler material being substantially transparent to visible light; selectively illuminating the holographic recording medium thereby inducing a photostructural change resulting in a change of refractive index of the chalcogenide glass.
  • the combination of a transparent filler material which is optically inert with the chalcogenide material has the effect of diluting the active chalcogenide material, and thus reducing the overall optical absorption of the mixture to allow a high degree of multiplexing in thick films. This does, of course, reduce the overall sensitivity, but not enough to affect the function of the material as a holographic recording medium.
  • the filler material is optically inert in that it does not exhibit the photostructural effect in response to illumination. For instance, with the type of large bandgap phosphorus and sulphur based chalcogenide glass disclosed in our above-referenced co-pending
  • the transparency is already good at 532 nm (for 100 ⁇ m thick films), and the sensitivity is very high.
  • the amount of dilution required to obtain thicker samples does not critically affect the sensitivity.
  • This material when diluted according to the present invention, can achieve sample thicknesses of the order of 0.5 mm with approximately 50% transmissivity at 532 nm.
  • the dilution of the chalcogenide material leading to a reduction of the overall optical absorption can enable the use of smaller bandgap chalcogenides such as As 2 S 3 or materials as described in WO01/45111 such as As-Se glasses enabling the use of higher frequency light which would otherwise be practically impossible (due to very high absorption).
  • This enables the use of frequency doubled Nd:YAG lasers with these materials and at the same time potentially significantly increases the sensitivity of the holographic material.
  • the 532nm light can penetrate more deeply, allowing the multiplexing of more pages of data stored holographically.
  • the step of codepositing comprises coevaporating the chalcogenide material and the filler material from separate receptacles and condensing the vapour on the substrate to form the amorphous mixture.
  • the chalcogenide material and the filler are evaporated from separate receptacles, such as crucibles. This prevents chemical reactions taking place in the melt.
  • the filler material comprises a glass. More preferably an oxide, fluoride or chalcogenide glass and most preferably ZnS, YF 3 , B 2 O 3 or GeO 2 .
  • the glass filler must be transparent to visible light, and preferably has a band gap of at least 2.6 eV.
  • the amorphous chalcogenide mixture contains molecules of A 4 B 3 and/or A 4 B 4 where A is either phosphorus or arsenic and B is either sulphur, selenium or tellurium. These molecules can be particularly responsible for the photorefractive effect, either by being reoriented in response to illumination by polarised light or by being broken up.
  • the chalcogenide glass consists of sulphur, phosphorus and arsenic.
  • the illuminating light causes a breakdown of P 4 S 4 and/or P 4 S 3 molecules in the glass, producing an irreversible change.
  • This material is useful to produce a WORM (write once read many) type recording medium.
  • molecules of As 4 Se 3 are reorientated in response to illumination by polarised light when the medium is heated above the temperature at which a phase change of the molecular units takes place. Cooling sets the reorientated molecule.
  • the recorded data can be erased by heating the recording medium or by using the polarised light with an electric field vector in the orthogonal direction to that used for recording.
  • Figure 1 shows a ternary diagram of As-P-S compositions
  • Figure 2 illustrates diffraction efficiency of a sample of As 28 S 6 ⁇ P 6 ;
  • Figure 3a shows an x-ray diffraction pattern of a thin film of As 4 Se 3 ;
  • Figure 3b shows a Raman spectra of a thin film of As 4 Se 3 ;
  • Figure 4 shows a holographic recording medium in accordance with the present invention
  • Figure 5 shows a holographic image of the US Air Force military resolution target recorded in a thin film of As 2 S 3 diluted with ZnS;
  • Figure 6 shows an apparatus used for recording the holographic image of Figure 5.
  • Figure 7A illustrates the absorption profile, chalcogenide content and refractive index change for a homogeously diluted film
  • Figure 7B illustrates the Bragg selectivity of a homogeneously diluted film
  • Figure 7C illustrates the absorption profile, chalcogenide content and refractive index change for a inhomogeously diluted film
  • Figure 7D illustrates the Bragg selectivity of a inhomogeneously diluted film.
  • Figure 1 is a ternary diagram of an As-P-S system, on which approximate boundaries of the glass-forming region are marked.
  • Six example compositions are illustrated, As 12 S 72 P.
  • As 2 S 3 is also illustrated. All the example compositions which include a component of phosphorus were found to have higher bandgaps and increased sensitivity to a
  • Nd:YAG laser compared to the known and well studied As 2 S 3 glass. All the examples also had good transparency at 532nm.
  • Figure 2 illustrates the diffraction efficiency of one example, As 28 S 66 P 6 for three different exposure times of 20s, 40s and 60s using a Nd. ⁇ AG laser of intensity 80mW/cm 2 .
  • the maximum diffraction efficiency reaches a value of about 15% at an exposure of 4.8J/cm 2 .
  • the maximum diffraction efficiency obtained with As 2 S 3 is typically 0.2% with an Ar-ion laser beam (514 nm) and 50mW/cm 2 light intensity, in an exposure time of the order of tens of seconds.
  • the sensitivity S' of a sample can be calculated as: where I is the intensity of the light source, t is the exposure time, and ⁇ is the maximum diffraction efficiency. Sensitivities of about 0.1 cm 2 /J were obtained for the P containing materials. Typical sensitivity values for As 2 S 3 samples are in the range 0.02-0.03 cm 2 /J.
  • thermodynamically stable P 4 S 4 and P 4 S 3 molecules in the glass Each of these molecules, due to their inherent atomic structure, possesses a strong dipole moment (inherent or photo-induced). At first, these dipole moments are randomly oriented in the amorphous network. However, it is believed that during the illumination with light, those dipole moments (or molecules) being favorably oriented would couple with interacting photons and the coupling would lead to breakage or reorientation of the molecules. Atoms of these broken molecules would subsequently integrate into the amorphous structure and would then not contribute to a strong overall dipole moment (being the sum of all dipole moments of all molecules and atoms in the amorphous network). During the course of illumination, preferential depletion of the molecules in one direction, would thus result in strong inhomogeneity in the refractive index, the refractive index being strongly linked to dipoles.
  • phosphorus and sulphur based chalcogenide materials are suitable for use in a WORM type recording medium, as the photo-induced change in refractive index is substantially irreversible.
  • the raw material has good transparency to an Nd-YAG laser, for samples above 100 ⁇ m in thickness, it would be preferable to obtain even thicker samples of the order of 0.5 mm for improved multiplexing purposes and with further improved transparency.
  • a type of chalcogenide material suitable for a re-writeable holographic data storage medium is discussed in WO 01/45111.
  • Evaporation of the melt onto an amorphous silica substrate in high vacuum with an evaporation rate of 1-3 nanometers per second produces a thin film material consisting of an amorphous network with embedded molecular units of As 4 Se 3 .
  • concentration of the molecular unit phase is dependent on conditions such as temperature of the melt, temperature of the substrate, molar ratio of the elements in the melt, rate of evaporation, subsequent thermal treatment of the treated film etc. .
  • Figure 3a shows an x-ray diffraction pattern of a thin film prepared by very slow evaporation ( «1 nm/sec) of As 4 Se 3 bulk material. Compared with the result of Blachnik and Wickel, (1984 Thermochimica acta 81, 185), it is found that the major substance in the prepared film are the ⁇ -As 4 Se 3 molecules.
  • Figure 3b shows corresponding Raman spectra of the As 4 Se 3 film prepared with a very slow evaporation rate. Also, comparison with literature values shows that the major substance in the prepared films are the As 4 Se 3 molecular crystals (Bues W., Somer M. and Brockner W. 1980 Zeitschrift fur Naturforschung, 35b, 1063-1069).
  • this medium can be used as a rewritable holographic recording medium.
  • He-Ne laser light (633 nm) is generally required to achieve the necessary optical penetration in this material in order to multiplex multiple pages of data. This is because the As-Se material has a much lower bandgap than the above described phosphorous and sulphur-based material.
  • absorption of 532 nm light from a Nd:YAG laser is very high and writing with such a laser is not practicable unless the medium is effectively diluted.
  • Figure 4 illustrates the construction of a holographic recording medium according to the present invention having a substrate 1 which may be any suitable transparent material such as a polymer (eg. polycarbonate) or optical glass and an amorphous layer 2 of a chalcogenide material, which may be any of the above examples diluted with a filler material.
  • the present invention concerns the dilution of the above mentioned compositions to achieve optically thick amorphous layers which are sufficiently transparent to light from a frequency doubled Nd:YAG laser to allow multiplexing of multiple pages of data. It is by no means straightforward to dilute active chalcogenide film.
  • the inert matrix must have a similar physical and chemical characteristic to the chalcogenide film.
  • substantially different thermal expansion coefficients could cause cracking in the film.
  • the matrix would also need to adapt to potential products of the photoinduced reaction of the chalcogenide atoms. Also, isolated regions of chalcogenide material randomly distributed in the matrix of the inert material might even be prohibited from undergoing a photoinduced structural change if the matrix is a very rigid material.
  • the codeposition method can be used to maximise the particular chalcogenide entities within the material which are optically active. These include the A 4 B 3 and A 4 B 4 molecules.
  • Possible filler materials include YF 3 , ZnS, GeO 2 and B 2 O 3 .
  • Another example can be a chalcogenide glass having a larger bandgap (and hence different composition) than that of the molecular species.
  • the preferred method of preparation is by co-evaporation of the chalcogenide bulk material and a filler in two separate crucibles, and depositing the mixture as an amorphous layer onto the substrate.
  • the means of evaporation may be thermal evaporation, chemical vapour deposition electron beam evaporation, or laser ablation, or a combination such as e-beam for the filler and thermal for the chalcogenide.
  • the principle is to evaporate both entities from separate crucibles to prevent chemical reaction in the melt.
  • a holographic recording medium was prepared using YF 3 and As 4 Se 3 using a ratio between 1:10 to 1:100 (As 4 Se 3 :YF 3 ). Both substances were evaporated from molybdenem boats in vacuum of approximately 3 x 10 "4 Pa at evaporation rates of about 1 nm/sec. The mixture was condensed onto a silica substrate.
  • ratios of 1:1 or 1:2 are not possible as the stresses in the material are too great due to differences in thermal expansion coefficients. Also, such ratios seem to lead crystallisation of the molecular units. Ratios of 1:4 or 1:5 and less appear generally to work well.
  • a possible method is to use in sputtering two (or more) separate targets or a target wherein the two substances are mixed in powders and sputtered.
  • Figure 5 is a hologram recorded in a film comprising active As 2 S 3 glass diluted with ZnS filler.
  • Figure 6 illustrates the apparatus used to record the hologram of Figure 5.
  • a beam from an Nd:YAG laser 3 is split by beam splitter 4 into object beam 5 and reference beam 6, which are reflected by mirrors 7a, 7b.
  • the object beam 5 passes through the image plate 9, in this case being the US Air Force military resolution target. Both beams are focused by lenses 10a, 10b and the interference pattern of the two intersecting light beams is recorded in the medium 8.
  • Lens 11 focuses the read-out image onto a CCD camera 12 to record the image.
  • Figures 7A to 7D illustrate a further improved holographic recording medium.
  • the principle behind the nonhomogenous dilution is illustrated in Figures 7A to 7D.
  • Figures 7A and 7B illustrate a homogenously diluted film.
  • the x axis shows the thickness of the material (in this case 100 micrometers) and the y axis is normalised to the appropriate curves.
  • Curve (a) shows the exponential absorption losses of the incident light intensity throughout the thickness of the material.
  • Curve (b) shows a concentration profile of the chalcogenide glass through the thickness of the material, which in this case is constant.
  • Curve (c) shows the resulting exponential refractive index modulation throughout the thickness. If a diffraction grating (a 5 hologram) is written in the homogenously diluted film, the angular diffraction efficiency shown in Figure 7B is recorded.
  • Figures 7C and 7D show equivalent results for an inhomogenously diluted film.
  • Curve (b) shows that the chalcogenide content of the film substantially hyperbolically increases throughout the thickness of the film. The result is that the refractive index o change upon illumination within incident light remains substantially constant through the thickness of the film (c).
  • Figure 7D shows the resulting angular diffraction efficiency of a diffraction grating written in such a film. It should be noted that the total concentration of absorbing species (chalcogenide glass) in both the homogenously and inhomogenously diluted films are the same i.e. the average absorption coefficient 5 is the same.
  • the concentration profile can be achieved by varying the evaporation rates of chalcogenide material and filler material during deposition of the film. As deposition begins, the rate of evaporation of chalcogenide material is high, and the rate is decreased as the films thickness increases. Conversely, the rate of evaporation of filler starts low and increases as the rate of evaporation of chalcogenide material decreases.

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  • Chemical & Material Sciences (AREA)
  • Inorganic Chemistry (AREA)
  • Engineering & Computer Science (AREA)
  • Manufacturing & Machinery (AREA)
  • Holo Graphy (AREA)

Abstract

L'invention concerne un support d'enregistrement holographique comprenant un mélange amorphe de verre de chalcogénure dispersé dans un matériau de remplissage, ledit matériau de remplissage étant sensiblement transparent à la lumière visible, ledit verre de chalcogénure subissant un changement photostructurel en réponse à un éclairage, ce qui entraîne un changement d'indice de réfraction du verre de chalcogénure. Dans un procédé de production dudit support d'enregistrement holographique, un matériau à base de chalcogénure et un matériau de remplissage sont co-déposés sur un substrat de manière à former une couche amorphe comprenant un mélange amorphe d'un verre de chalcogénure et d'un matériau de remplissage, ledit matériau de remplissage étant sensiblement transparent à la lumière visible. La combinaison d'un matériau de remplissage transparent optiquement inerte avec le matériau à base de chalcogénure a pour effet de diluer le matériau à base de chalcogénure actif, et ensuite de réduire l'absorption optique globale du mélange pour permettre d'obtenir un degré élevé de multiplexage dans des couches minces. Cette opération réduit évidemment la sensibilité globale, mais pas assez pour affecter la fonction du matériau en tant que support d'enregistrement holographique. Le matériau de remplissage est optiquement inerte en ce qu'il ne présente pas d'effet photostructurel en réponse à un éclairage.
PCT/GB2002/005298 2001-12-03 2002-11-25 Support d'enregistrement holographique WO2003049097A1 (fr)

Priority Applications (1)

Application Number Priority Date Filing Date Title
AU2002343084A AU2002343084A1 (en) 2001-12-03 2002-11-25 Holographic recording medium

Applications Claiming Priority (4)

Application Number Priority Date Filing Date Title
GB0128904.0 2001-12-03
GBGB0128904.0A GB0128904D0 (en) 2001-12-03 2001-12-03 Holographic recording medium
GB0213109.2 2002-06-07
GBGB0213109.2A GB0213109D0 (en) 2002-06-07 2002-06-07 Holographic recording medium

Publications (1)

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WO2003049097A1 true WO2003049097A1 (fr) 2003-06-12

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Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN110462734A (zh) * 2017-12-08 2019-11-15 株式会社Lg化学 光聚合物组合物

Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
SU775760A1 (ru) * 1978-06-27 1980-10-30 Ужгородский Государственный Университет Способ изготовлени регистрирующей среды на основе халькогенидного стекла
WO1999047983A1 (fr) * 1998-03-13 1999-09-23 Ovd Kinegram Ag Elements de diffraction transparents et semi-transparents, notamment hologrammes, et procede de fabrication correspondant
WO2001045111A1 (fr) * 1999-12-17 2001-06-21 Polight Technologies Ltd. Support d'enregistrement holographique photoréfractif

Patent Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
SU775760A1 (ru) * 1978-06-27 1980-10-30 Ужгородский Государственный Университет Способ изготовлени регистрирующей среды на основе халькогенидного стекла
WO1999047983A1 (fr) * 1998-03-13 1999-09-23 Ovd Kinegram Ag Elements de diffraction transparents et semi-transparents, notamment hologrammes, et procede de fabrication correspondant
WO2001045111A1 (fr) * 1999-12-17 2001-06-21 Polight Technologies Ltd. Support d'enregistrement holographique photoréfractif

Non-Patent Citations (1)

* Cited by examiner, † Cited by third party
Title
DATABASE WPI Section Ch Week 198134, Derwent World Patents Index; Class L03, AN 1981-61646d, XP002233333 *

Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN110462734A (zh) * 2017-12-08 2019-11-15 株式会社Lg化学 光聚合物组合物
CN110462734B (zh) * 2017-12-08 2021-09-07 株式会社Lg化学 全息图记录介质、光学元件以及全息记录方法
US11226557B2 (en) 2017-12-08 2022-01-18 Lg Chem, Ltd. Photopolymer composition

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