Surface Relief Volume Reflective Diffractive Structure

• US 20080309996A1
• Filed: 02/14/2008
• Published: 12/18/2008
• Est. Priority Date: 02/14/2007
• Status: Active Grant

• Current Assignee: Aztech Systems Limited
• Original Assignee: Aztech Systems Limited
• Inventors: Cowan, James J.
• Granted Patent: US 8,254,029 B2
• Time in Patent Office: Days
• US Class Current: 359/3
• CPC Class Codes: G02B 5/1814 structurally combined with one or more further optical elements, e.g. lenses, mirrors, prisms or other diffraction gratings G02B5/189 takes precedence
• CPC Class Codes: G02B 5/1861 Reflection gratings characterised by their structure, e.g. step profile, contours of substrate or grooves, pitch variations, materials G02B5/1809, G02B5/1828, G02B5/1833, G02B5/1838 and G02B5/1847 take precedence
• CPC Class Codes: G02B 5/32 Holograms used as optical elements
• CPC Class Codes: G03H 1/0244 Surface relief holograms replicating hologram without interference recording G03H1/0276
• CPC Class Codes: G03H 1/0248 Volume holograms
• CPC Class Codes: G03H 1/04 Processes or apparatus for producing holograms G03H1/26 takes precedence
• CPC Class Codes: G03H 1/0402 Recording geometries or arrangements G03H1/0443, G03H1/0476, G03H1/16 take precedence
• CPC Class Codes: G03H 1/041 Optical element in the object space affecting the object beam, not otherwise provided for
• CPC Class Codes: G03H 1/2205 using downstream optical component
• CPC Class Codes: G03H 1/2249 Holobject properties
• CPC Class Codes: G03H 1/26 Processes or apparatus specially adapted to produce multiple sub- holograms or to obtain images from them, e.g. multicolour technique
• CPC Class Codes: G03H 2001/0417 for recording single beam Lippmann hologram wherein the object is illuminated by reference beam passing through the recording material
• CPC Class Codes: G03H 2001/0419 for recording combined transmission and reflection holograms
• CPC Class Codes: G03H 2001/0473 Particular illumination angle between object or reference beams and hologram
• CPC Class Codes: G03H 2001/2635 Mixed volume and surface relief holograms
• CPC Class Codes: G03H 2210/63 Environment affecting the recording, e.g. underwater G03H2001/0432 takes precedence
• CPC Class Codes: G03H 2222/31 Polarised light
• CPC Class Codes: G03H 2223/18 Prism
• CPC Class Codes: G03H 2223/25 Index matching material
• CPC Class Codes: G03H 5/00 Holographic processes or apparatus using particles or using waves other than those covered by groups G03H1/00 or G03H3/00 for obtaining holograms; Processes or apparatus for obtaining an optical image from them G03H1/22 takes precedence; construction of electron microscopes H01J37/26; investigating or analysing materials by the use of microwaves G01N22/00, by the use of particles wave or X-rays G01N23/00, G21K7/00

Abstract

Disclosed is a surface relief structure. The structure includes a recording medium configured to be structurally modified when exposed to interfering and non-interfering portions of radiation beams, the structurally modified recording medium including, when viewed in a two-dimensional cross-section along one of the axes of the recording medium a plurality of equally spaced steps of fine-sized periodicity superimposed upon a plurality of deep depressions of substantially coarse-sized periodicity. The structurally modified recording medium is configured to produce in reflection single and multiple colors in a broad spectral range when illuminated by a source of light.

Claims

1. A surface relief structure comprising:

a recording medium configured to be structurally modified when exposed to interfering and non-interfering portions of radiation beams, the structurally modified recording medium including, when viewed in a two-dimensional cross-section along one of the axes of the recording medium;

a plurality of equally spaced steps of fine-sized periodicity superimposed upon a plurality of deep depressions of substantially coarse-sized periodicity, wherein the structurally modified recording medium is configured to produce in reflection single and multiple colors in a broad spectral range when illuminated by a source of light.

2. The structure of claim 1 wherein the radiation beams include at least one of:

light beams and electron beams.

3. The structure of claim 1 wherein the plurality of deep depressions of coarse-sized periodicity includes a grating structure varying along one direction in the two-dimensional cross-section view.

4. The structure of claim 3 wherein the period of the coarse-sized grating structure is substantially symmetric when viewed in the two-dimensional cross-section view.

5. The structure of claim 3 wherein a period of the coarse-sized grating structure is substantially asymmetric when viewed in the two-dimensional cross-section view.

6. The structure of claim 3 wherein a period of the coarse-sized grating structure is skewed when viewed in a two-dimensional cross-section view relative to a principal surface of the recording medium prior to exposing the recording medium to portions of the radiation beams.

7. The structure of claim 6 wherein the skewed grating structure includes at least one of:

an inclined grating structure and a non-symmetric grating structure.

8. The structure of claim 1 wherein the plurality of equally spaced steps of fine-sized periodicity are approximately half of a wavelength of illuminated light observed in reflection when the microstructure is coupled to an overcoating dielectric having an index of refraction approximately equal to 1.

9. The structure of claim 1 wherein the recording medium is overcoated with a clear dielectric having an index of refraction, n, such that the illuminated light observed in reflection corresponds to a wavelength equaling to approximately twice the product of n and a height value of any of the equally spaced steps.

10. The structure of claim 3 wherein light diffracted, upon illumination of the structure with a light source, includes light having wavelengths corresponding to predominantly a single color resonance whose bandwidth varies in inverse proportion to a number equaling the plurality of steps.

11. The structure of claim 1 wherein the plurality of deep depressions of coarse-sized periodicity includes a grating structure varying along in two directions of the two-dimensional cross-section view.

12. The structure of claim 11 wherein light diffracted, upon illumination of the structure with a light source, includes multiple single-color resonances of near-equal intensities.

13. The structure of claim 11 wherein light diffracted, upon illumination of the structure with a light source, includes a single color resonance that becomes narrower and bunched closer together such that it can fit under a broad spectral envelope as the number of steps increases.

14. The structure of claim 11 wherein light diffracted, upon illumination of the structure with a light source, includes a single color resonance that is accompanied by several adjacent resonances of lower intensity such that a perceived single color is modified by the spectral composition of the adjacent colors.

15. The structure of claim 3 wherein light diffracted, upon illumination of the structure with a light source, includes green and blue resonances that combine to produce light corresponding to the color cyan.

16. The structure of claim 3 wherein light diffracted, upon illumination of the structure with a light source, includes green and red resonances that combine to produce light corresponding to the color yellow.

17. The structure of claim 3 wherein light diffracted, upon illumination of the structure with a light source, includes blue and red resonances that combine to produce light corresponding to the color magenta.

18. The structure of claim 1 wherein each of the plurality of deep depressions of coarse-sized periodicity has depth sufficient to diffract light that, in the absence of steps, would have a minimal diffraction efficiency.

19. The structure of claims 1 further comprising a diffuse component such that parallax viewability is increased over a large horizontal and vertical range of angles.

20. A method for recording a holographic image of an object, the method comprising:

providing a recording medium configured to record a holographic image, the recording medium having two principal surfaces;

placing the object proximate one of the two principal surfaces of the recording medium; and

directing radiation beams at the other surface of the two principal surfaces of the recording medium at an angle with respect to a normal to the other of the two principal surfaces of the recording medium such that a resultant radiation beam reflected from the object interferes with a resultant first reference beam progressing in a direction that is at least partly similar to the progression direction of the radiation beam reflected from the object, both beams being separated by a small angle such that a first interference fringe structure is formed in the recording medium that is skewed with respect to any of the two principal surfaces of the recording medium, and such that a resultant second reference beam progresses in a general direction that is at least partly opposite to the direction of the radiation beams reflected from the object such that a fine-sized set of interference fringes is formed in the recording medium, the second set of interference fringe being skewed with respect to the any of the two principal surfaces of the recording medium.

21. The method of claim 20 wherein the skewed first interference fringe structure includes at least one of:

an inclined first interference fringe structure and a non-symmetric interference fringe structure.

22. The method of claim 20 wherein providing the recording medium comprises:

providing a photoresist medium.

23. The method of claim 20 wherein placing the object comprises:

encapsulating the object in an optically clear material; and

placing the encapsulated object proximate the one of the two principal surfaces of the recording medium.

24. The method of claim 23 wherein encapsulating the object in the optically clear material comprises encapsulating the object in an optically clear cement index matched to a cover glass.

25. The method of claim 20 wherein placing the object comprises:

placing a conventional volume hologram of a tangible object proximate the one of the two principal surfaces of the recording medium.

26. The method of claim 25 wherein the conventional volume hologram is encapsulated between flat glass plates, and wherein the conventional volume hologram is recorded in one of dichromated gelatin (DCG), photopolymer and silver halide.

27. The method of claim 25 wherein placing the conventional volume hologram comprises:

placing the conventional volume hologram at an angle with respect to any of the two principal surfaces of the recording medium.

28. The method of claim 20 further comprising:

reproducing holographic images of the object based, at least in part, on the first and second interference structures formed in the recording medium.

29. The method of claim 20 wherein providing the recording medium comprises:

providing a recording medium configured to be structurally modified when exposed to interfering and non-interfering portions of radiation beams, the structurally modified recording medium including, when viewed in a two-dimensional cross-section along one of the axes of the recording medium;

a plurality of equally spaced steps of fine-sized periodicity superimposed upon a plurality of deep depressions of substantially coarse-sized periodicity, wherein the structurally modified recording medium is configured to produce in reflection single and multiple colors in a broad spectral range when illuminated by a source of light.

30. A method for recording a holographic image of an object, the method comprising:

providing a recording medium configured to record holographic image, the recording medium having two principal surfaces;

placing the object proximate one of the two principal surfaces of the recording medium;

coupling a prism at a contact surface of the prism to the other of the two principal surfaces of the recording medium;

directing light beams at another surface of the prism such that such that a resultant radiation beam reflected from the object interferes with a resultant first reference beam progressing in a direction that is at least partly similar to the progression direction of the radiation beam reflected from the object, both beams being separated by a small angle such that a first interference fringe structure is formed in the recording medium that is skewed at an angle with respect to any of the two principal surfaces of the recording medium, and such that a resultant second reference beam progresses in a general direction that is at least partly opposite to the direction of the radiation beams reflected from the object such that a fine-sized set of interference fringes is formed in the recording medium, the second set of interference fringe being skewed with respect to the any of the two principal surfaces of the recording medium.

31. The method of claim 30 wherein the skewed first interference fringe structure includes at least one of:

an inclined first interference fringe structure and a non-symmetric interference fringe structure.

32. The method of claim 30 wherein providing the recording medium comprises:

providing a photoresist medium.

33. The method of claim 30 wherein placing the object comprises:

encapsulating the object in a clear material; and

placing the encapsulated object proximate the one of the two principal surfaces of the recording medium.

34. The method of claim 30 wherein coupling the prism comprises:

coupling an equilateral prism having an index of refraction, n, of approximately 1.5, at a contact surface of the equilateral prism.

37. The method of claim 30 wherein placing the object comprises:

placing a conventional volume hologram of a tangible object proximate the one of the two principal surfaces of the recording medium.

38. The method of claim 37 further comprising:

coupling one surface of a glass plate to the one of the two principal surfaces of the recording medium; and

coupling the conventional volume hologram to another surface of the glass plate using a material that includes gelatin.

39. The method of claim 38 further comprising:

coupling a second prism to a back side of the volume hologram; and

directing another radiation beam at the second prism such that the other radiation beam passes first through the second prism, the volume hologram, and the first prism to form an interference pattern with portions of the radiation beam that reflected from the object, wherein the radiation beam that reflected from the object and the other radiation beam progress, at least partly, in a similar direction.

40. A system to record a holographic image, the system comprising:

a recording medium having two principal surfaces and configured to record holographic image of an object placed proximate one of the two principal surfaces of the recording medium; and

a radiation source to direct radiation beams at the other surface of the two principal surface of the recording medium at an angle with respect to a normal to the other of the two principal surfaces of the recording medium such that a resultant radiation beam reflected from the object interfere with a resultant first reference beam progressing in a direction that at least partly is similar to the progression direction of the radiation beam reflected from the object, both beams being separated by a small angle such that a first interference fringe structure is formed in the recording medium that is inclined at an angle with respect to any of the two principal surfaces of the recording medium, and such that a resultant second reference beam progresses in a general direction that at least partly is opposite to the direction of the radiation beams reflected from the object such that a fine-sized set of interference fringes is formed in the recording medium, the second set of interference fringe being inclined with respect to the any of the two principal surfaces of the recording medium.

35. The method of claim 40 wherein coupling the prism comprises:

placing an interfacing material between the coupling surface of the prism and the other of two principal surfaces of the recording medium.

36. The method of claim 35 wherein the interfacing material comprises an index-matching liquid material that includes at least one of:

xylene, decalin and water.

41. The system of claim 40 wherein the radiation source is a laser light source.

42. A system to record a holographic image, the system comprising:

a recording medium having two principal surfaces and configured to record a holographic image of a volume hologram of an object placed proximate one of the two principal surfaces of the recording medium;

a prism coupled at a contact surface of the prism to the other of the two principal surfaces of the recording medium;

a light source to direct light beams at another surface of the prism such that such that a resultant radiation beam reflected from the object interferes with a resultant first reference beam progressing in a direction that is at least partly similar to the progression direction of the radiation beam reflected from the object, both beams being separated by a small angle such that a first interference fringe structure is formed in the recording medium that is inclined at an angle with respect to any of the two principal surfaces of the recording medium, and such that a resultant second reference beam progresses in a general direction that is at least partly opposite to the direction of the radiation beams reflected from the object such that a fine-sized set of interference fringes is formed in the recording medium, the second set of interference fringe being inclined with respect to the any of the two principal surfaces of the recording medium.

43. The system of claim 42 wherein the light source is a laser light source.