Phase masks for use in holographic data storage

• US 20050207313A1
• Filed: 01/27/2005
• Published: 09/22/2005
• Est. Priority Date: 01/27/2004
• Status: Active Grant

• Current Assignee: Citizen Finetech Miyota Company Limited (Citizen Electronics Company Limited)
• Original Assignee: Micron Technology, Inc.
• Inventors: Handschy, Mark A., Walker, Christopher M., O'Callaghan, Michael J.
• Granted Patent: US 7,656,768 B2
• Time in Patent Office: Days
• US Class Current: 369/103
• CPC Class Codes: G02F 1/133565 inside the LC elements, i.e. between the cell substrates
• CPC Class Codes: G02F 1/13363 Birefringent elements, e.g. for optical compensation
• CPC Class Codes: G02F 1/292 by controlled diffraction or phased-array beam steering controlled diffraction for optical switching G02F1/31
• CPC Class Codes: G03H 1/02 Details of features involved during the holographic process; Replication of holograms without interference recording
• CPC Class Codes: G03H 1/16 using Fourier transform G03H1/10, G03H1/12, G03H1/14 take precedence; analogue computers G06G, e.g. G06G7/19
• CPC Class Codes: G03H 2001/0224 Active addressable light modulator, i.e. Spatial Light Modulator [SLM] corresponding details, see subgroups of G03H2225/00
• CPC Class Codes: G03H 2223/13 Phase mask
• CPC Class Codes: G11B 7/0065 Recording, reproducing or erasing by using optical interference patterns, e.g. holograms
• CPC Class Codes: G11B 7/128 Modulators G11B7/1245 takes precedence
• CPC Class Codes: G11B 7/1369 Active plates, e.g. liquid crystal panels or electrostrictive elements

Abstract

A spatial light modulator (SLM) having a phase mask that is provided as an internal component thereof. The phase mask can be provided as a multilevel surface of relatively higher index of refraction material on an inner surface of a transmissive cover window or as a separate transmissive window between the cover window and the pixels of the SLM. If the phase mask is to be used with a liquid crystal SLM, then it may be desirable to planarize the surface of the cover window contacting the liquid crystal by providing a layer of relatively lower index of refraction material adjacent the multilevel surface. The phase mask can also be provided on the transmissive cover window by patterned ion deposition, exposing patterned light to a photopolymeric material, or in some other suitable fashion. Arranging for the pixel electrodes to be at one of multiple levels rather than lying in an exactly planar relationship can also effectively create the phase mask.

Claims

1. A write head for a holographic data storage system, the write head comprising:

a spatial light modulator that is arranged into an array of pixels that can each separately modulate light that is directed toward the spatial light modulator; and

a phase mask that is capable of varying the phase of light passing therethrough, the magnitude of the phase variation being dependent on the particular portion of the phase mask that the light passes through;

wherein the phase mask is provided on an interior surface of the spatial light modulator.

2. A write head as defined in claim 1, wherein the spatial light modulator is a liquid crystal spatial light modulator.

3. A write head as defined in claim 2, wherein the spatial light modulator is a ferroelectric liquid crystal spatial light modulator.

4. A write head as defined in claim 2, wherein the spatial light modulator includes a layer of liquid crystal material sandwiched between two substantially planar surfaces.

5. A write head as defined in claim 4, wherein one of the planar surfaces is on a layered substrate that includes a layer of relatively higher index of refraction material having a multilevel surface and a layer of relatively lower index of refraction material having a multilevel surface, wherein the two multilevel surfaces face each other.

6. A write head as defined in claim 5, wherein the layered substrate also includes a conductive electrode layer.

7. A write head as defined in claim 5, wherein the conductive electrode layer is located on the opposite side of the layer of relatively higher index of refraction material from the multilevel surface.

8. A write head as defined in claim 5, wherein the conductive electrode layer is located on the opposite side of the layer of relatively lower index of refraction material from the multilevel surface.

9. A write head as defined in claim 4, wherein one of the planar surfaces is on a substrate that includes a region of varying index of refraction that has been achieved by ion diffusion.

10. A write head as defined in claim 4, wherein one of the planar surfaces is on a layered substrate that includes a layer of photopolymer material that has been exposed to a pattern of light to make an index of refraction pattern.

11. A write head as defined in claim 4, wherein one of the planar surfaces is on the inner surface of a layered, transmissive window, with one of the layers adjacent the inner surface includes the phase mask.

12. A write head as defined in claim 1, wherein the phase mask is located within 200 μ

m of the pixels of the spatial light modulator.

13. A write head as defined in claim 1, wherein the phase mask is within a distance d of the pixels of the spatial light modulator, where d is equal to p²/λ

, p is the pitch of the pixels of the spatial light modulator, and λ

is the wavelength of the light directed toward the spatial light modulator.

14. A write head as defined in claim 1, wherein the holographic data storage system has an imaging system, and wherein the phase mask is sufficiently close to the pixels of the spatial light modulator to allow the imaging system of the holographic data storage system to resolve both the phase mask and the pixels.

15. A write head as defined in claim 1, wherein the phase mask is pixellated.

16. A write head as defined in claim 1, wherein the phase mask is not pixellated.

17. A write head for a holographic data storage system, the write head comprising:

a spatial light modulator that is arranged into an array of pixels that can each separately modulate light that is directed toward the spatial light modulator;

a glass window located on one side of the spatial light modulator in close proximity to the array of pixels of the spatial light modulator; and

a phase mask that is capable of varying the phase of light passing therethrough, the magnitude of the phase variation being dependent on the particular portion of the phase mask that the light passes through;

wherein the phase mask is located between the glass window and the array of pixels of the spatial light modulator.

18. A write head as defined in claim 17, wherein the phase mask is adjacent a surface of the glass window facing toward the pixels of the spatial light modulator.

19. A write head for a holographic data storage system, the write head comprising:

a spatial light modulator that is arranged into an array of pixels that can each separately modulate light that is directed toward the spatial light modulator; and

a phase mask that is capable of varying the phase of light passing therethrough, the magnitude of the phase variation being dependent on the particular portion of the phase mask that the light passes through;

wherein the phase mask is located within 200 μ

m of the pixels of the spatial light modulator.

20. A write head for a holographic data storage system, the write head comprising:

a spatial light modulator that is arranged into an array of pixels that can each separately modulate light that is directed toward the spatial light modulator, the pixels having a pitch of p; and

a phase mask that is capable of varying the phase of light passing therethrough, the magnitude of the phase variation being dependent on the particular portion of the phase mask that the light passes through;

wherein the phase mask is within a distance d of the pixels of the spatial light modulator, where d is equal to p²/λ

, where λ

is the wavelength of the light directed toward the spatial light modulator.

21. A write head for a holographic data storage system, the holographic data storage system having an imaging system, the write head comprising:

a spatial light modulator that is arranged into an array of pixels that can each separately modulate light that is directed toward the spatial light modulator; and

a phase mask that is capable of varying the phase of light passing therethrough, the magnitude of the phase variation being dependent on the particular portion of the phase mask that the light passes through;

wherein the phase mask is sufficiently close to the pixels of the spatial light modulator to allow the imaging system of the holographic data storage system to resolve both the phase mask and the pixels.

22. A write head as defined in claim 21, wherein the phase mask is located within the imaging system'"'"'s depth of focus of the pixels.