WO2009063066A1 - Dispositif et procédé pour produire des hologrammes - Google Patents

Dispositif et procédé pour produire des hologrammes Download PDF

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Publication number
WO2009063066A1
WO2009063066A1 PCT/EP2008/065592 EP2008065592W WO2009063066A1 WO 2009063066 A1 WO2009063066 A1 WO 2009063066A1 EP 2008065592 W EP2008065592 W EP 2008065592W WO 2009063066 A1 WO2009063066 A1 WO 2009063066A1
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Prior art keywords
lens
storage layer
aspherical lens
aspherical
depth
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PCT/EP2008/065592
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German (de)
English (en)
Inventor
Susanna Orlic
Enrico Dietz
Marco Scheffler
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Technische Universitaet Berlin
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Technische Universitaet Berlin
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    • 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
    • G11B7/004—Recording, reproducing or erasing methods; Read, write or erase circuits therefor
    • G11B7/005—Reproducing
    • 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
    • G11B7/12—Heads, e.g. forming of the optical beam spot or modulation of the optical beam
    • G11B7/125—Optical beam sources therefor, e.g. laser control circuitry specially adapted for optical storage devices; Modulators, e.g. means for controlling the size or intensity of optical spots or optical traces
    • G11B7/127—Lasers; Multiple laser arrays
    • G11B7/1275—Two or more lasers having different wavelengths
    • 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
    • G11B7/12—Heads, e.g. forming of the optical beam spot or modulation of the optical beam
    • G11B7/135—Means for guiding the beam from the source to the record carrier or from the record carrier to the detector
    • G11B7/1365—Separate or integrated refractive elements, e.g. wave plates
    • 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
    • G11B7/12—Heads, e.g. forming of the optical beam spot or modulation of the optical beam
    • G11B7/135—Means for guiding the beam from the source to the record carrier or from the record carrier to the detector
    • G11B7/1372—Lenses
    • G11B7/1376—Collimator lenses
    • 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
    • G11B7/12—Heads, e.g. forming of the optical beam spot or modulation of the optical beam
    • G11B7/135—Means for guiding the beam from the source to the record carrier or from the record carrier to the detector
    • G11B7/1392—Means for controlling the beam wavefront, e.g. for correction of aberration
    • G11B7/13922—Means for controlling the beam wavefront, e.g. for correction of aberration passive
    • 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
    • G11B2007/0003—Recording, reproducing or erasing systems characterised by the structure or type of the carrier
    • G11B2007/0009—Recording, reproducing or erasing systems characterised by the structure or type of the carrier for carriers having data stored 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
    • G11B7/12—Heads, e.g. forming of the optical beam spot or modulation of the optical beam
    • G11B7/135—Means for guiding the beam from the source to the record carrier or from the record carrier to the detector
    • G11B7/1372—Lenses
    • G11B2007/13727—Compound lenses, i.e. two or more lenses co-operating to perform a function, e.g. compound objective lens including a solid immersion lens, positive and negative lenses either bonded together or with adjustable spacing
    • 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
    • G11B7/004—Recording, reproducing or erasing methods; Read, write or erase circuits therefor
    • G11B7/0065—Recording, reproducing or erasing by using optical interference patterns, e.g. holograms

Definitions

  • the present invention relates to an apparatus and a method for generating a plurality of holograms, in particular the present invention relates to a mikroholographischen data memory and a method for the production of mikroholographische interference gratings.
  • the method relates to the generation of micro-logical gratings with diffraction-limited laser beams within a storage medium.
  • the storage density it is crucial to localize the spatial extent of the lattice to the smallest possible volume elements. This is achieved by focusing the laser beam on both sides diffraction-limited into the photosensitive layer. The three-dimensional grid localization is then directly dependent on the focus size of the write beam. When reading the generated grids are to be detected without errors, i. the reading beam must have the same diffraction-limited focus size.
  • a diffraction-limited mapping is used when the performance of an optical system is limited only or at least significantly by the physical effect of the diffraction, but not by design or manufacturing defects.
  • There are different ways to determine if an optical system is diffraction limited for example, by calculating and measuring optical path length difference OPD, Strehl ratio, RMS radius, RMS OPD, standard deviation, and others. Due to the different criteria, it is possible that an optical system according to one of the aforementioned methods is classified as "diffraction-limited", but not as "diffraction-limited” according to another of the aforementioned methods.
  • NA the numerical aperture
  • the numerical aperture (NA) is a dimensionless quantity and characterizes the angular range within which an optical system can image or actually image light.
  • the minimum possible focus radius (airy disk radius) or focus diameter is determined by the wavelength of the light to be focused and the marginal beam inclination of the focused laser beam realized by the optics used.
  • the edge beam in the sense of the present invention is understood to be that beam which is not yet cut off or vignetted by the aperture stop of the system ,
  • the edge beam in the sense of the present invention is understood to be that beam whose intensity is 1% of the maximum intensity (Gaussian distribution of the Intensity).
  • the marginal beam of the laser radiation contacts exactly the aperture diaphragm.
  • the root-mean-square (root mean square) Radial size is called. That is, the distance between each ray and a reference point (optical axis or centroid of all rays) is squared, then averaged over all rays and then the square root drawn.
  • a reference point optical axis or centroid of all rays
  • an optical system is considered to be "diffraction-limited.”
  • the size of the RMS radius depends on the choice made by the Sys- from the rays to be calculated. Thus, it is possible that an optical system is not considered to be “diffraction-limited” after a certain beam selection and not “diffraction-limited” after another beam selection.
  • the RMS radius is determined by distributing over the aperture 5 rings a 10 beams (linearly radial and with respect to the running angle uniformly).
  • the rays are distributed as evenly as possible over the aperture.
  • the 5 rings are arranged equidistant from each other between marginal and optical axes (ie, the first ring is on the optical axis, the fifth ring is in the radial distance of the marginal rays from the optical axis and second to fourth ring are distributed equidistantly in between).
  • the 10 rays per ring are circumferential, so each distributed at an angle of 36 ° to each other.
  • the rays of the individual rings run on radial straight lines from the center point to the outside, ie in each case 5 rays of the individual 10 rings can be connected by radial (star-shaped) lines.
  • the depth multiplexing (multilayer) is used to maximize the total capacity of the storage medium as the multiple area capacity of a single data plane.
  • To write and read data in multiple data planes it is necessary to focus the laser beam into different depth regions of a storage layer (along the optical axis, i.e. along the beam direction).
  • an aspherical single lens adapted for focusing into a specific depth region of the storage layer is used for this purpose.
  • a single lens can not provide the necessary (diffraction-limited) imaging performance for a micro-lographic data store over a depth range (along the optical axis) greater than 100 ⁇ m.
  • the object of the present invention is to provide, on the basis of a commercially available, lightweight aspherical lens, a micro-holographic data memory and a method for generating micro-interference fringes which implement compensation for spherical aberration and thereby allow complete elimination of the aperture errors that occur.
  • Such compensation results in the technological system implementation in a higher storage capacity with little equipment expense.
  • the device according to the invention for generating a multiplicity of holograms has a monochromatic radiation source, a planar storage medium, a focusing unit (preferably a first lens) which focuses at least part of the light of the radiation source into the storage layer, a collimation focusing unit (preferably a second lens ) collimating at least part of the light passing through the storage layer, and a reflector for reflecting back the collimated light (laser radiation), the light reflected from the reflector being refocused into the storage layer by means of the collimation focusing unit (second lens), and wherein the focusing unit (first lens) and the collimating focusing unit (second lens) are designed to be displaceable relative to the storage layer to produce holograms at different depths along the optical axis of the storage layer, and further comprising means for comp Ensation of the spherical aber
  • a first, as plane-parallel plate formed, variable-thickness component between the first lens and the storage layer and a second formed as a plane-parallel plate, variable-thickness component between the storage layer and the second lens are provided, wherein the first lens and the storage layer for generating holograms at different depths at different distances from each other (along the optical axis), and the sum of optical thickness (product of geometric thickness and refractive index along the optical axis) of the first variable-thickness component and depth of focus through the first lens focused radiation (depth of focus in the storage layer along the optical axis from the radiation source facing, outer side of the storage layer) is constant in the storage layer and the sum of the optical thickness of the first variable thickness Component and the optical thickness of the second variable-thickness component is constant.
  • a monochromatic radiation source is understood to mean a radiation source whose half-width at the center wavelength is less than 10 nm.
  • holograms are generated at different depths along the optical axis, the outer holograms being spaced more than 50 ⁇ m (preferably more than 100 ⁇ m and more preferably more than 200 ⁇ m) from each other (along the optical axis).
  • a holographic data memory in which the memory layer (preferably a disk-shaped polymer layer surrounded by two substrates) is laterally displaceable in relation to the write optics (laser light source, first lens, first variable-thickness component, second lens, second variable-thickness component, and reflector) as well as along the optical axis (beam direction) is designed to be displaceable.
  • the lateral relative movement between the storage layer and writing optics is realized by rotating the disk-shaped storage layer and the longitudinal relative movement between storage layer and writing optics by moving the first lens and the second lens.
  • micro holograms that represent a bit generated. If there is no micro hologram at a position, no bit has been written there.
  • the minimum achievable size of the microholograms is defined by the wavelength of the light and the numerical aperture of the optics used, provided that there is a diffraction-limited image.
  • the spherical aberration is achieved according to the invention by using two aspherical single lenses (first lens and second lens) and by using two plane-parallel, thickness-variable components (with a refractive index not equal to 1).
  • the thickness of the first variable-thickness component and the second variable-thickness component changes according to the depth of focus in the memory layer such that the sum of the optical thickness of the depth of focus in the storage layer and the optical thickness of the first variable thickness component is always kept constant.
  • the thickness of the first variable-thickness component is always reduced, the deeper it is focused into the storage layer, and vice versa. Accordingly, the thickness of the second variable-thickness component is always increased, the deeper it is focused in the storage layer, and vice versa.
  • the first variable thickness component and the second variable thickness component comprise a material having a refractive index different from air and / or vacuum.
  • the optical thickness of the first variable thickness component is the product of geometric thickness of the first variable thickness component and refractive index of the first variable thickness component
  • the optical thickness of the second variable thickness component is the product of geometric thickness of the second variable thickness component and the refractive index the second variable-thickness component defined (refractive index based on the central wavelength of the light source).
  • the first lens and the second lens are positioned to the storage layer such that the depth of focus of the radiation focused by the first lens in the storage layer and the depth of focus of the radiation focused by the second lens in the storage layer are equal or substantially equal.
  • the first lens and the second lens are positioned to the storage layer such that the focus size of the radiation focused by the first lens in the storage layer and the focus size of the radiation focused by the second lens in the storage layer are diffraction limited.
  • the first and second lenses are adapted to perform a relative movement (to the storage layer) between 50 ⁇ m and 500 ⁇ m along the optical axis.
  • the variable thickness components are preferably adapted to change their thickness by an amount between 50 ⁇ m and 500 ⁇ m (along the optical axis).
  • the use of multiple data planes along the beam direction is also called deep-multiplexing.
  • wavelength division multiplexing can also be realized with the data memory according to the invention.
  • wavelength division multiplexing gratings are written in the same position within the storage layer but using different wavelengths (different laser light sources).
  • grids with different lattice constants are formed in the same position within the storage layer, which are superimposed and can be selectively read again using the respective different write wavelengths (fulfillment of the Bragg condition).
  • a second coherent radiation source having a (central) wavelength different from the first radiation source is provided in the range between 300 nm and 430 nm.
  • the first variable-thickness component is formed from a first plane-parallel plate having a first optical dispersion (first material) and a second plane-parallel plate having a second optical dispersion (second material), wherein the first optical dispersion differs from the second optical dispersion, and both the first plane-parallel plate and the second plane-parallel plate are formed variable in thickness.
  • the second variable-thickness component is formed from a third plane-parallel plate with a third optical dispersion and a fourth plane-parallel plate with a fourth optical dispersion, wherein the third optical dispersion differs from the fourth optical dispersion. sion differs and both the third plane-parallel plate and the fourth plane-parallel plate are formed variable in thickness.
  • the degree of optical dispersion may be specified, for example, by the Abbe number of the optical material (glass).
  • the total thickness (optical thickness) of the system (consisting of first variable-thickness component, the storage layer incl. Possibly present substrates and second variable-thickness component) can be kept constant for different wavelengths using the same lenses.
  • the first lens and / or the second lens is formed as a single aspherical lens.
  • the first lens and / or the second lens has a numerical aperture of greater than 0.5 (more preferably greater than 0.55 and more preferably greater than or equal to 0.6).
  • the focusing unit are formed by a first aspherical lens and a second aspherical lens and the means for collimation by a third aspherical lens and a fourth aspherical lens, wherein the second aspherical lens and the third aspherical lens are adapted Change in the depth of focus in the storage layer relative to the storage layer to be moved and the first aspherical lens adapted to be moved to change the depth of focus in the storage layer relative to the second aspheric lens and the third aspherical lens is a-adapted to change the depth of focus in the storage layer relative to the fourth aspherical lens to be moved.
  • the device is adapted such that the distance between the storage layer and the second aspheric lens for increasing the depth of focus in the storage layer is reduced and / or the distance between the storage layer and the third aspherical lens for increasing the depth of focus in the Storage layer is increased and / or the distance between the first aspheric lens and the second aspherical lens to increase the depth of focus in the storage layer is reduced and / or the distance between the third the aspherical lens and the fourth aspherical lens for increasing the depth of focus in the storage layer is increased.
  • means for displacing the first aspherical lens, the second aspherical lens, the third aspherical lens and / or the fourth aspheric lens along the optical axis are provided in accordance with a predeterminable position coordinate of the focus in the storage layer.
  • the means for displacing the first aspheric lens, the second aspherical lens, the third aspherical lens, and / or the fourth aspherical lens along the optical axis are each formed by an actuator or by a motor.
  • the refractive indices (materials) of all components are constant with respect to a wavelength, i. it is preferably always the same lenses used (no lens exchange).
  • the method according to the invention for producing a multiplicity of holograms comprises the following steps: irradiating light into a flat storage medium comprising a material which undergoes a refractive index change upon irradiation of electromagnetic radiation, focusing at least a portion of the irradiated light by means of a focusing unit (preferably first lens ), Collimation of at least part of the light passing through the storage layer by means of a collimating focusing unit (second lens), back reflection of the collimated light by means of a reflector, wherein the light reflected from the reflector by means of the collimation focusing unit (second lens) refocuses in the storage layer and in opposite directions with the irradiated light, wherein the focusing unit (first lens) and the collimating focusing unit (second lens) for generating holograms in different lateral positions and in different The depths of the storage layer are shifted relative to the storage layer, whereby the spherical aberration is kept constant along the different depths along the optical
  • the refractive indices (materials) of all components are constant with respect to a wavelength, i.
  • the same lenses are preferably always used (no lens exchange and no exchange of the variable-thickness elements).
  • a storage medium is provided with a storage layer whose refractive index undergoes a change upon irradiation of electromagnetic radiation, further focused electromagnetic radiation of a monochromatic light source and oppositely superimposed that in a predetermined spatial position of the storage layer due to the opposite superimposition forms an interference pattern and in focus in areas of constructive interference leads to a greater refractive index change than in areas of destructive interference, and due to the change in refractive index a hologram is generated with a plurality of layers with alternating refractive index, wherein in the storage layer offset in time a plurality of holograms in different lateral positions and at different depths of the storage layer are generated, wherein the radiation of the light source by means of a ers the aspherical lens and a second aspherical lens are focused into the storage layer and, after passing through the storage layer, collimated by means of a third aspherical lens and a fourth aspherical lens is refocused after reflection on a reflector in the
  • a holographic data memory in which the memory layer (preferably a disk-shaped polymer layer surrounded by two substrates) is both laterally displaceable relative to the optical system (first to fourth lens) and displaceable along the optical axis (beam direction) ,
  • the lateral relative movement between the storage layer and the optical system is realized by rotating the disk-shaped storage layer and the longitudinal relative movement between the storage layer and the optical system by movement of the first lens to the fourth lens.
  • focused in any position within memory layer reflected back and focused again and thus out-of-focus and back focus
  • micro holograms that represent a bit generated. If there is no micro hologram at a position, no bit has been written there.
  • the minimum achievable size of the microholograms is defined by the wavelength of the light and the numerical aperture of the optics used (first lens to fourth lens), provided there is a diffraction-limited image.
  • the spherical aberration is eliminated according to the invention by using two aspherical individual lenses each (first lens to fourth aspherical lens).
  • a lens in the context of the invention, a lens is understood, of the refractive surfaces of which at least one surface is non-spherical, that is not spherical.
  • all (both) refractive surfaces are non-spherical, ie aspherical.
  • the refractive surfaces formed rotationally symmetrical.
  • an aspherical surface is understood to mean a rotationally symmetrical surface shape, which is defined by a polynomial of the shape
  • f (h) A ⁇ ⁇ ⁇ ⁇ . , , where f (h) is the arrow height or z-coordinate along the optical axis, h is the distance perpendicular to the optical axis, R is the peak radius, k is the conical constant, and A 4 , A 6 , etc. are the aspherical parameters. At least one of the aspherical parameters A 4 , A 6 must be non-zero in order for an aspherical surface shape to result.
  • a single lens is understood to mean a lens having two outer rotationally symmetrical, refractive surfaces whose spacing is not variable relative to one another. In between, preferably only an optical material with a refractive index greater than 1 is present. However, it is also possible that further refracting surfaces (putty lens) are arranged between the outer refracting surfaces. However, the spacing of all refracting surfaces is fixed, i. not variable.
  • holograms are generated at different depths along the optical axis, the outer holograms being spaced more than 50 ⁇ m (preferably more than 100 ⁇ m and more preferably more than 200 ⁇ m) from each other (along the optical axis).
  • a particular advantage of the optical system proposed here is that only one additional (first and fourth) lens (in front of and behind the polymer) is required for the second and third aspheric lenses. Therefore, the system remains compact, and to compensate for the tracking error signal and focus error signal, the standard technologies of the CD and DVD development lines can be fully adopted since the weight of the lenses is not larger than the weight of a commercial DVD lens , The nominal imaging performance of the system can be referred to as diffraction-limited.
  • the focused light must subsequently be reflected back and focused again and counterposed in opposite directions.
  • the reflector is preferably designed as a plane mirror or a retroreflector.
  • the displacement of the first aspheric lens, the second aspherical lens, the third aspherical lens, and / or the fourth aspherical lens is along the optical axis respectively by means of actuators or motors realized.
  • the first aspherical lens, the second aspherical lens, the third aspherical lens and the fourth aspherical lens, ie no further optical components, are used for focusing and collimation.
  • the distance between the storage layer and the second aspheric lens for increasing the depth of focus in the storage layer is reduced.
  • the depth of the focus in the storage layer is the distance of the focus along the optical axis from the outer side of the storage layer facing the light source (laser). Any substrates surrounding the storage layer as part of the storage medium (disk) remain in the determination the depth of focus is disregarded).
  • the distance between the storage layer and the third aspherical lens is preferable to increase the distance between the storage layer and the third aspherical lens to increase the depth of focus in the storage layer. Furthermore, it is preferable to reduce the distance between the first aspherical lens and the second aspherical lens to increase the depth of focus in the storage layer. Furthermore, it is preferable to increase the distance between the third aspherical lens and the fourth aspherical lens to increase the depth of focus in the storage layer.
  • the position of the reflector (along the optical axis) need not be varied to set / vary the depth of focus, i. the reflector is preferably fixed or fixedly positioned.
  • a laser having a central wavelength in the range of 300 nm to 430 nm and a half-width of less than 10 nm is used as the light source.
  • a semiconductor laser having a central wavelength in the range of 400 nm - 430 nm and in terms of intensity with a half-width of less than 3 nm is used as the light source.
  • the beam diameter of the light source, the surface shape of the first aspherical lens, the second aspherical lens, the third aspherical lens and the fourth aspherical lens are selected such that the focusing of the electromagnetic radiation of the monochromatic light source into the memory layer having a numerical aperture greater than zero , 5 (more preferably greater than or equal to 0.6) takes place.
  • the beam diameter of the light source, the Surface shape of the first aspheric lens, de second aspherical lens, the third aspherical lens and the fourth aspherical lens selected such that the focusing of the electromagnetic radiation of the monochromatic light source into the storage layer diffraction-limited.
  • a calculation and optimization of the surface shapes of the lenses can be done (also taking into account definable tolerances) with appropriate optics software such as ZEMAX.
  • Fig. 1 shows an inventive device for generating holograms
  • the depth multiplexing with correction of the spherical aberration realized, in a schematic sectional representation
  • Fig. 2 shows an inventive device for generating holograms
  • FIG. 3 is a schematic representation of a thickness-variable component according to the invention in accordance with the first preferred embodiment
  • FIG. 4 shows a device according to the invention for generating holograms
  • the depth multiplexing with correction of the spherical aberration realized, in a schematic sectional representation
  • Fig. 5 is a schematic representation of the distances between the lenses in
  • Fig. 6 is a schematic representation of the distances between the lenses and the substrate (and thus the storage layer) as a function of the depth of focus in the storage layer.
  • FIG. 1 shows a device according to the invention for generating holograms (holographic data memory) according to a first, preferred embodiment, which realizes depth multiplexing with correction of the spherical aberration.
  • the holographic data memory comprises a laser diode 10, a first aspherical single lens 14, a first variable-thickness component 20, a means for receiving a planar storage medium 12 (for example, a storage medium for a disk-shaped storage medium 12), a second variable-thickness component 22, a second aspherical single lens 16 and a reflector 18.
  • the information is preferably stored bit by bit in the form of micro-heterologous interference gratings in a thin photosensitive layer 12.
  • the grating is generated in spatially limited volume elements by laser beams of the light source 10 reaching the optical diffraction limit, i. be focused diffraction limited.
  • the interference pattern generated by the superimposition of the incident and reflected beam is transmitted to a corresponding local modulation of the refractive index of the photosensitive material in the storage medium 12.
  • the storage medium 12 is realized, for example, in the form of a disk by applying the photosensitive layer on an optical disk substrate and encoding the data therein in a spiral track. The beam propagation during writing and reading takes place collinearly and on an axis which runs perpendicular to the storage medium 12.
  • the storage layer 12 is moved by the discrotation perpendicular to the laser beam axis, so that the gratings are dynamically induced as strips of any length.
  • the read-out signal is produced by diffraction of a laser beam at the inscribed gratings under Bragg condition.
  • the three-dimensional, strongly localized lattice structure allows the utilization of the entire volume of the storage medium 12 by storing the data in a plurality of discrete (preferably mutually equidistant) planes within the storage layer 12.
  • the memory layer 12 is regularly formed by a photopolymer layer having a thickness between 0.05 mm and 0.5 mm, which is surrounded by substrates having a thickness of between 0.1 mm and 1.2 mm on both sides.
  • the lateral position of the bits is varied by discrotation of the memory layer 12.
  • the variable-thickness component 20 undertakes the correction of the optical path length for different depth positions z within the storage layer 12.
  • the variable-thickness component 20 is always arranged between the lens 14 and the storage layer 12 and is preferably not moved when changing the depth position of the data plane.
  • a diffraction-limited focusing in different layer depths can be realized behind the storage layer 12 by means of only one aspherical lens 14 and one variable-thickness component 20 in front of the storage layer 12 and only one aspherical lens 16 and a variable-thickness component 22 (+ reflector 18) ,
  • variable thickness component is preferably realized as a compressible component.
  • a preferred realization consists in arranging a liquid 24 between two thin plane plates 26 and making the two plane plates 26 movable relative to each other, so that the thickness of the component 20, 22 can be varied.
  • the thickness-variable component 20, 22 may be fixedly arranged in the optical system.
  • the change in thickness of the compressible component is realized by suitable electromechanical actuators (electromagnetic, piezo, electrostatic).
  • electromechanical actuators electromechanical actuators (electromagnetic, piezo, electrostatic).
  • the task solution is that the two thin plane plates 26 are designed to be movable relative to each other. By the elastic regions 25 can escape or re-flow the liquid 24 located between the plane plates 26.
  • a solid, compressible material such as rubber or gelatin may be used, the thickness of which is then varied.
  • An important advantage of this solution is that in addition to the two single lens 14, 16 only one further optical element 20, 22 is present in the beam path. It is furthermore particularly advantageous that the thickness of such an element 20, 22 can be varied by applying a current or an electric field (electromagnetically, piezos, electrostatically). As a result, the number of mechanically moved components is reduced to a minimum, thus increasing the reliability of such a system. Furthermore, very fast switching times can be achieved because of the control over the electric field.
  • the path length of the compression is on the order of magnitude in the range of the focal depth range, ie in the range of 50-500 micrometers.
  • the variation of the thickness can be effected for example by magnetized area (which can be arranged in the edge region of the plane plates 26) and electrical contacts.
  • magnetized area which can be arranged in the edge region of the plane plates 26
  • electrical contacts each of which is disposed on one of the faceplates 26 - e.g., ITO contacts
  • the faceplates 26 are pressed against each other and the excess portion of the liquid 24 is forced into the resilient portions 25.
  • the thickness can be controlled by the strength of the electric field. If the field strength is reduced, the liquid 24 located in the elastic regions 25 again moves into the region between the plane plates 26 and the thickness increases.
  • a number of other means of varying the thickness are possible.
  • FIG. 2 shows a device according to the invention for generating holograms (holographic data memory) according to a first, preferred embodiment, which realizes depth multiplexing and wavelength division multiplexing with correction of the spherical aberration, in a schematic sectional representation.
  • holograms holographic data memory
  • the thickness-variable components Nenten 20, 22 each two thickness-variable plane-parallel plates 28, 30 and 32, 34 each with different dispersion.
  • a correction can also take place for different wavelengths.
  • it can be irradiated with different wavelengths (at the same time or preferably with a time offset) and thus in one position gratings with different lattice constants are generated.
  • the spherical aberration can be reduced by means of the thickness-variable plane-parallel components of different dispersion in such a way that diffraction-limited imaging is possible.
  • the lenses 14, 16 are preferably formed the same, i. same thickness, same material, same focal length, same aspheric coefficients (surface shape), etc. However, the first lens 14 and the second lens 16 are then preferably inserted mirror-inverted in the beam path. The same applies analogously to the thickness-variable components 20, 22.
  • the first lens 14 is pre-corrected for a given total optical thickness of thickness-variable component 20 and initial depth of focus with respect to the spherical aberration, accordingly, the second lens 16 is also for a given total optical thickness of variable thickness component 22 and initial focus depth pre-corrected.
  • Such pre-corrected lenses for certain focus depths are commercially available via glass catalogs such as Thorlabs.
  • the thickness-variable components 20, 22 are readjusted immediately (within a time of less than 100 milliseconds, preferably less than 20 milliseconds) by means of a corresponding device (actuators, motors, etc.).
  • the micro-holographic data storage is one of the promising technologies for the next generation of data storage and has considerable potential to replace the DVD.
  • the above solutions allow a significant increase in storage density, which can be achieved with other solutions (such as microscope lenses, sliding wedges), however, all alternative options are not commercially useful (too expensive, too vulnerable or too slow).
  • 4 shows a device according to the invention for generating holograms (holographic data memory) according to a second, preferred embodiment, which realizes depth multiplexing with correction of the spherical aberration, in a schematic sectional view.
  • the holographic data memory comprises a laser diode 10, a first aspherical single lens 1, a second aspherical single lens 2, a means for accommodating a planar storage medium 12 (for example a support means for a disk-shaped storage medium 12 - not shown in the figure), a third aspherical single lens 3, a fourth aspherical single lens 4 and a reflector 18.
  • the information is preferably stored bit by bit in the form of micro-heterologous interference gratings in a thin photosensitive layer 12.
  • the grating is generated in spatially limited volume elements by laser beams of the light source 10 reaching the optical diffraction limit, i. limited to diffraction.
  • the interference pattern generated by the superimposition of the incident and reflected beam is transmitted to a corresponding local modulation of the refractive index of the photosensitive material in the storage medium 12.
  • the storage medium 12 is realized, for example, in the form of a disk by applying the photosensitive layer on an optical disk substrate and encoding the data therein in a spiral track. The beam propagation during writing and reading takes place collinearly and on an axis which runs perpendicular to the storage medium 12.
  • the storage layer 12 is moved by the discrotation perpendicular to the laser beam axis, so that the gratings are dynamically induced as strips of any length.
  • the read-out signal is produced by diffraction of a laser beam at the inscribed gratings under Bragg condition.
  • the three-dimensional, highly localized lattice structure makes it possible to utilize the entire volume of the storage medium 12 by depositing the data in a plurality of discrete (preferably mutually equidistant) planes within the storage layer 12.
  • the memory layer 12 is regularly covered by a photopolymer layer with a dielectric layer. Between 0.05 mm and 0.5 mm, which is surrounded by substrates on both sides with a thickness between 0.1 mm and 1, 2 mm formed.
  • the lateral position of the bits is varied by discrotation of the memory layer 12.
  • the nearly linear displacement of the lenses 1 -4 can be taken for an embodiment of FIGS. 5 and 6.
  • the corresponding travel paths of the lenses 1 -4 can be calculated in advance and stored in the system.
  • a diffraction-limited focusing in different layer depths can be realized by means of only two aspheric lenses 1, 2 in front of the storage layer 12 and only two aspherical lenses 3, 4 (+ reflector 18) behind the storage layer 12.
  • the lenses 1 and 4 and the lenses 2 and 3 are preferably formed the same, ie the same thickness, the same material, the same focal length, the same Aspheric coefficients (surface shape), etc.
  • the first lens 1 and the fourth lens However, 4 are then preferably used mirror-inverted in the beam path.
  • the first lens 1 and second lens 2 are pre-corrected for an initial depth of focus with respect to the spherical aberration, respectively, and accordingly, the third lens 3 and the fourth lens 4 are also pre-corrected for the initial depth of focus.
  • the lenses 1 -4 immediately (within a time of less than 100 milliseconds, preferably less than 20 milliseconds) by means of a corresponding device (actuators, motors, etc.) readjusted.
  • micro-holographic data storage is one of the promising technologies for the next generation of data storage and has considerable potential to replace the DVD.
  • the above solution allows a significant increase in storage density, which can be achieved with other solutions (such as microscope lenses, sliding wedges), however, all alternative options are not commercially useful (too expensive, too vulnerable or too slow).

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  • Physics & Mathematics (AREA)
  • Optics & Photonics (AREA)
  • Holo Graphy (AREA)
  • Optical Head (AREA)

Abstract

L'invention concerne un dispositif et un procédé pour produire une multiplicité d'hologrammes. Elle concerne en particulier une mémoire de données microholographique et un procédé de production de réseaux d'interférence microholographiques. L'invention vise à fournir, sur la base d'une lentille légèrement asphérique disponible dans le commerce, une mémoire de données microholographique et un procédé de production de réseaux d'interférence microholographiques qui permettent de mettre en œuvre une compensation de l'aberration sphérique et d'éliminer ainsi totalement les aberrations sphériques rencontrées. A cet effet, un premier composant d'épaisseur variable (20), réalisé sous forme de plaque à faces planes et parallèles, est prévu entre la première lentille (14) et la couche d'écriture (12), et un deuxième composant d'épaisseur variable (22), réalisé sous forme de plaque à faces planes et parallèles, est prévu entre la couche d'écriture (12) et la deuxième lentille (16), sachant que, pour des distances relatives différentes entre la première lentille (14) et la couche d'écriture (12) : la somme de l'épaisseur optique du premier composant d'épaisseur variable (20) et de la profondeur de focale du rayonnement focalisé par la première lentille (14) dans la couche d'écriture (12) est constante; et la somme de l'épaisseur optique du premier composant d'épaisseur variable (20) et de l'épaisseur optique du deuxième composant d'épaisseur variable (22) est constante.
PCT/EP2008/065592 2007-11-14 2008-11-14 Dispositif et procédé pour produire des hologrammes Ceased WO2009063066A1 (fr)

Applications Claiming Priority (6)

Application Number Priority Date Filing Date Title
DE102007055011 2007-11-14
DE102007055011.3 2007-11-14
DE102007063494A DE102007063494A1 (de) 2007-11-14 2007-12-31 Verfahren und Vorrichtung zur Erzeugung von Hologrammen
DE102007063493A DE102007063493A1 (de) 2007-11-14 2007-12-31 Verfahren und Vorrichtung zur Erzeugung von Hologrammen
DE102007063493.7 2007-12-31
DE102007063494.5 2007-12-31

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Citations (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0414380A2 (fr) * 1989-07-24 1991-02-27 Matsushita Electric Industrial Co., Ltd. Appareil d'enregistrement et de reproduction optique

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* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US6272095B1 (en) * 1994-07-22 2001-08-07 California Institute Of Technology Apparatus and method for storing and/or reading data on an optical disk
DE10134769B4 (de) * 2000-07-13 2011-07-28 Hans Joachim Prof. Dr. 12105 Eichler Mikroholographische Datenspeicher mit dreidimensionalen Streifengittern
JP4723164B2 (ja) * 2002-11-29 2011-07-13 Ｈｏｙａ株式会社 光情報記録再生装置用対物レンズ
KR101039074B1 (ko) * 2003-05-15 2011-06-08 톰슨 라이센싱 높은 데이터 밀도의 체적 측정의 홀로그래픽 데이터 저장방법 및 시스템
US7388695B2 (en) * 2005-03-16 2008-06-17 General Electric Company Data storage devices and methods
DE102007004025A1 (de) * 2007-01-22 2008-07-31 Technische Universität Berlin Verfahren und Vorrichtung zum Herstellen eines Hologramms in einem optischen Medium

Patent Citations (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0414380A2 (fr) * 1989-07-24 1991-02-27 Matsushita Electric Industrial Co., Ltd. Appareil d'enregistrement et de reproduction optique

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