Method and device for the layered production of thin volume grid stacks, and beam combiner for a holographic display

Patent metadata

Field	Value
Publication number	US-9785114-B2
Application number	US-201214124377-A
Country	US
Kind code	B2
Filing date	Jun 6, 2012
Priority date	Jun 6, 2011
Publication date	Oct 10, 2017
Grant date	Oct 10, 2017

Abstract

The layered generation of at least one volume grating in a recording medium by way of exposure, the recording medium having at least one photosensitive layer which is sensitized for a presettable wavelength of the exposure light. Each volume grating is generated in the recording medium by at least two wave fronts of coherent light capable of generating interference, the wave fronts being superposed in the recording medium at a presettable depth, at a presettable angle and with a presettable interference contrast. The depth and the thickness of the refractive index modulation and/or transparency modulation of a volume grating in the recording medium is controlled by depth-specific control of the spatial and/or temporal degree of coherence of the interfering wave fronts in the direction of light propagation.

First claim

The invention claimed is:

1. A method for the layered generation of at least one volume grating in a recording medium by way of exposure with exposure light being emitted by a light source, said recording medium comprising at least one photosensitive layer which is sensitised for a presettable wavelength of the exposure light, the method comprising the steps of:
generating each volume grating in the recording medium by at least two wave fronts of coherent light which are capable of generating interference, superposing said wave fronts in the recording medium at a presettable depth, at a presettable angle and with a presettable interference contrast,
generating the at least two wave fronts of coherent light by diffracting a collimated wave field by a master grating, the master grating being disposed in front of the recording medium and being illuminated with the collimated wave field which is generated by the light source; and
controlling the depth and the thickness of at least one of a refractive index modulation and a transparency modulation of a volume grating in the recording medium by depth-specific control of at least one of a spatial and a temporal degree of coherence of the interfering wave fronts in the direction of light propagation,
wherein at least one of an amplitude grating and a phase grating is arranged in a plane of the light source which illuminates the master grating, the at least one of the amplitude grating and the phase grating generates the presettable depth-dependent profile of the interference contrast in a presettable depth range of the recording medium.

2. The method according to claim 1 , wherein downstream of the master grating there is a relative lateral offset in the direction of light propagation between the wave fields resulting from diffraction of the collimated wave field at the master grating and propagating further downstream, said relative lateral offset causing the presettable depth-dependent profile of the interference contrast of the interfering wave fields due to a preset complex-valued spatial and/or temporal coherence function of the illuminating wave field.

3. The method according to claim 2 , wherein the interfering wave fields result from different diffraction orders of diffraction at the master grating of the same collimated wave field.

4. The method according to claim 1 , wherein the interference contrast that is present at the presettable depth of the recording medium generates volume gratings in the recording medium in the form of at least one of a presettable refractive index modulation and a transparency modulation which corresponds with an apodisation function which allows the angular selectivity or wavelength selectivity of the volume gratings to be controlled in a presettable way and any side peaks of the angular selectivity or wavelength selectivity of the volume gratings to be suppressed in a presettable way.

5. The method according to claim 2 , wherein the plane of the light source, which illuminates the master grating, has a complex-valued optical transparency function which comprises at least one of an amplitude grating and a phase grating, at least one of an amplitude distribution and a phase distribution, at least one of an amplitude grating and a phase grating which is superposed by an apodisation function, or at least one of an amplitude distribution and a phase distribution which is superposed by an apodisation function.

6. The method according to claim 1 , wherein the shape of the angular selectivity or wavelength selectivity of the volume gratings which can be generated at a presettable depth is adjustable through the presettable profile of a refractive index modulation in the direction of light propagation, said profile being an apodisation function with the shape of a squared sinc, squared cosine, squared Gaussian or a squared approximated rectangular function.

7. The method according to claim 1 , wherein the angular selectivity of the volume gratings which are generatible at the presettable depth is controllable through the thickness of the volume gratings or where the recording medium has a presettable thickness which allows at least two volume gratings to be recorded in the recording medium, where the volume gratings are arranged one after another or in an interleaved manner in the direction of light propagation.

8. The method according to claim 1 , wherein multiple volume gratings which are generatible at presettable depths are each designed for a specific presettable light wavelength and only influence light of this wavelength by way of diffraction.

9. The method according to claim 1 , wherein a depth apodisation or a depth separation of the intensity modulation of the exposure light in the recording medium is controlled dynamically.

10. The method according to claim 1 , wherein the profile of the refractive index modulation of the volume grating in the recording medium is determined by a presettable adjustment of the complex amplitude in the plane of the light source which illuminates the master grating.

11. The method according to claim 1 , wherein the master grating is provided in the form of a surface profile grating whose illuminated surface is either a part of the surface of the recording medium of the volume grating or which corresponds to this surface.

12. The method according to claim 1 , wherein the at least one of the phase distribution and amplitude distribution being located in the plane of the light source comprises an asymmetry in order to generate an asymmetrical profile of the refractive index modulation in the recording medium.

13. The method according to claim 1 , wherein the recording medium has an initiator and where a constant light portion of the exposure light is used to activate the initiator of the recording medium.

14. The method according to claim 1 , wherein an optically or electrically addressable material serves as the recording medium for the generation of switchable volume gratings.

15. The method according to claim 1 , wherein reconstruction geometries such as plane wave to plane wave or plane wave to spherical wave, are realisable in a presettable fix or switchable form through diffraction at the generatible volume gratings.

16. The method according to claim 1 , wherein reflections during the recording of the volume gratings in the recording medium can be suppressed through a presettable choice of at least one of the spatial and temporal coherence properties of the exposure light.

17. The method according to claim 1 , wherein a phase grating whose period varies continuously or periodically is disposed in the plane of the light source which illuminates the master grating.

18. The method according to claim 1 , wherein at least two phase-shifted volume gratings are generated in the recording medium in order to deflect preset angular or wavelength ranges in preset directions or where volume gratings are generated such that they are staggered in depth in the recording medium, each serving different wavelengths in order to compensate transit time differences in light pulses.

19. The method according to claim 1 , wherein the recording of a volume grating with preset shape and thickness at a preset depth of the recording medium is achieved through chemical or optical depletion of an initiator in the recording medium from the surfaces inwards, where the recording of a volume grating with preset shape and thickness at a preset depth of the recording medium could especially be achieved through local optical depletion of an initiator in the recording medium.

Assignees

• Fuetterer Gerald
• Seereal Tech S A

Inventors

• Fuetterer Gerald

Classifications

• G03H2001/2615

  in physical contact, i.e. layered holograms · CPC title

• G03H2222/23

  Temporal coherence · CPC title

• G02F1/13342

  Holographic polymer dispersed liquid crystals · CPC title

• G03H1/20

  Copying holograms by holographic {, i.e. optical} means · CPC title

• G03H2001/266

  Wavelength multiplexing · CPC title