Light Modulating Device

• US 20100277779A1
• Filed: 10/20/2008
• Published: 11/04/2010
• Est. Priority Date: 10/19/2007
• Status: Active Grant

• Current Assignee: SeeReal Technologies S.A.
• Original Assignee: SeeReal Technologies S.A.
• Inventors: Futterer, Gerald, Kroll, Bo, Buschbeck, Steffen
• Granted Patent: US 8,427,725 B2
• Time in Patent Office: Days
• US Class Current: 359/9
• CPC Class Codes: G02F 1/1335 Structural association of cells with optical devices, e.g. polarisers or reflectors
• CPC Class Codes: G02F 1/133509 Filters, e.g. light shielding masks
• CPC Class Codes: G02F 1/133524 Light-guides, e.g. fibre-optic bundles, louvered or jalousie light-guides
• CPC Class Codes: G03H 1/02 Details of features involved during the holographic process; Replication of holograms without interference recording
• CPC Class Codes: G03H 1/22 Processes or apparatus for obtaining an optical image from holograms G03H1/26 - G03H1/34 take precedence
• CPC Class Codes: G03H 1/2205 using downstream optical component
• CPC Class Codes: G03H 1/2294 Addressing the hologram to an active spatial light modulator
• CPC Class Codes: G03H 2001/0216 Optical components G03H2001/0224, G03H1/0256 take precedence; corresponding details, see subgroups of G03H2223/00
• 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 2001/0858 Cell encoding wherein each computed values is represented by at least two pixels of the modulator, e.g. detour phase coding
• CPC Class Codes: G03H 2001/221 Element having optical power, e.g. field lens
• CPC Class Codes: G03H 2222/35 Transverse intensity distribution of the light beam
• CPC Class Codes: G03H 2223/13 Phase mask
• CPC Class Codes: G03H 2223/14 Diffuser, e.g. lens array, random phase mask
• CPC Class Codes: G03H 2223/16 Optical waveguide, e.g. optical fibre, rod
• CPC Class Codes: G03H 2223/19 Microoptic array, e.g. lens array
• CPC Class Codes: G03H 2225/24 Having movable pixels, e.g. microelectromechanical systems [MEMS]
• CPC Class Codes: G03H 2225/31 Amplitude only
• CPC Class Codes: G03H 2225/32 Phase only
• CPC Class Codes: G03H 2225/55 Having optical element registered to each pixel
• CPC Class Codes: G03H 2240/41 : Binary
• CPC Class Codes: G03H 2240/42 : Discrete level

Abstract

The present invention relates to a light modulating device, comprising a SLM and a pixelated optical element, in which a group of at least two adjacent pixels of the SLM in combination with a corresponding group of pixels in the pixelated optical element form a macropixel, the pixelated optical element being of a type such that its pixels comprise a fixed content, each macropixel being used to represent a numerical value which is manifested physically by the states of the pixels of the SLM and the content of the pixels of the pixelated optical element which form the macropixel.

Claims

1. A light modulating device, comprising a spatial light modulator and a pixelated optical element, in which a group of at least two adjacent pixels of the spatial light modulator in combination with a corresponding group of pixels in the pixelated optical element form a macropixel, the pixelated optical element being of a type such that its pixels comprise a fixed content, the spatial light modulator being of a type such that its pixels comprise a variable content, each macropixel being used to represent a numerical value which is manifested physically by the states of the pixels of the spatial light modulator and the content of the pixels of the pixelated optical element which form the macropixel.

2. The light modulating device of claim 1, wherein the spatial light modulator is of a type such that its pixels are adjustable to different values of a limited number of possible discrete values, the number of values being ≧

2 or wherein the spatial light modulator has k different values of a limited number of possible discrete values and a macropixel has N pixels, k and N being natural numbers, k and N preferably not having the same value.

4. The light modulating device of claim 1, wherein the spatial light modulator is of a type such that its pixels are adjustable to different values within a continuous range of possible values or wherein the spatial light modulator comprises a ferroelectric liquid crystal.

5. The light modulating device of claim 1, wherein the spatial light modulator is of a type such that its pixels are adjustable to modulate the amplitude of the light interacting with the spatial light modulator or wherein the pixels of the spatial light modulator are adjustable only between two different amplitude values, especially to adjust the amplitude of the light interacting with the spatial light modulator to a minimum or to a maximum value, especially to 0% or to 100%.

7. The light modulating device of claim 1, wherein the spatial light modulator is of a type such that its pixels are adjustable to modulate the phase of the light interacting with the spatial light modulator or wherein the spatial light modulator is of a type such that its pixels are adjustable to modulate the phase of the light interacting with the spatial light modulator and wherein the pixels of the spatial light modulator are adjustable only between two different phase values, especially between the values 0 and π

or between the values 0 and π

/2 or between the values 0 and π

/4.

9. The light modulating device of claim 1, wherein the spatial light modulator comprises a micromirror unit, the individual mirrors of the micromirror unit comprise layers with a characteristic suitable to modulate the phase or the amplitude of the light interacting with the micromirror unit or wherein the spatial light modulator comprises a micromirror unit, the pixelated optical element being implemented into the micromirror unit by lowering the maximum reflectivity of individual mirrors of each macropixel down to different predetermined values or to generate a fixed offset of the individual minors of each macropixel in their height on the substrate which corresponds to a predetermined phase offset between individual pixels.

12. The light modulating device of claim 1, wherein the number of accessible states for each macropixel is greater than the number of states accessible by the group of pixels of each spatial light modulator of the macropixel, or wherein the number of accessible states for each macropixel is greater that the number of the fixed states of the group of pixels of the pixelated optical element.

13. The light modulating device of claim 1, wherein the pixelated optical element comprises a diffractive element or wherein the pixelated optical element is located in front of or behind the spatial light modulator with respect to the propagation of light interacting with the light modulating device.

14. The light modulating device of claim 1, wherein several individual pixels of the spatial light modulator or of the pixelated optical element being used as parts of a macropixel comprise different sizes or shapes or sizes and shapes or comprise differences in some other characteristic or wherein a macropixel consists of individual pixels of different sizes, the macropixel being encoded such that the individual terms in the electric field sum are weighted with additional amplitude factors corresponding to their size or factor of contribution to the value which is generated at the output plane of the macropixel.

15. The light modulating device of claim 1, wherein the pixelated optical element is of a type such that some of its pixels comprise different modulation values of a limited possible modulation number of discrete values, the number of modulation values being ≧

2.

16. The light modulating device of claim 1, wherein the pixelated optical element is of a type such that some of its pixels are adjustable to modulate the amplitude or the phase of the light interacting with the pixelated optical element or wherein the pixelated optical element is of a type such that some of its pixels are adjustable to modulate the amplitude or the phase of the light interacting with the pixelated optical element and wherein some of the pixels of the pixelated optical element comprise at least two different grey scale values for modulating the amplitude of the light interacting with the pixelated optical element.

18. The light modulating device of claim 1, wherein a pixel of the pixelated optical element comprises an optical medium having a predetermined optical pathlength for modulating the phase of the light interacting with this pixel depending on the predetermined optical pathlength or an optical medium having a predetermined absorption or reflection for modulating the amplitude of the light interacting with this pixel depending on the predetermined absorption or reflection.

19. The light modulating device of claim 1, wherein a pixel of the pixelated optical element is provided as an element inside the substrate glass of the spatial light modulator for modulating the phase of the light interacting with the pixel of the pixelated optical element or wherein a pixel of the pixelated optical element is provided as an element inside the LC substrate glass of the SLM for modulating the amplitude of the light interacting with the pixel of the pixelated optical element.

22. The light modulating device of claim 1, wherein each pixel of the spatial light modulator is allocated to exactly one pixel of the pixelated optical element or wherein groups of at least two adjacent pixels of the spatial light modulator in combination with the corresponding groups of—

preferably adjacent—

allocated pixels of the pixelated optical element are used to form each macropixel.

24. The light modulating device of claim 1, wherein different macropixels of the pixelated optical element have different structures or content or wherein different macropixels comprise a different number of single pixels of the spatial light modulator or of the pixelated optical element.

26. The light modulating device of claim 1, wherein a pixelated optical element adapted to modulate the amplitude of the light interacting with the pixelated optical element is combined with a spatial light modulator being adapted to modulate the—

preferably discrete—

amplitude or phase of the light interacting with the spatial light modulator or wherein a pixelated optical element adapted to modulate the amplitude of the light interacting with the pixelated optical element is combined with a spatial light modulator being adapted to modulate the—

preferably discrete—

amplitude or phase of the light interacting with the spatial light modulator and wherein the individual pixels comprise one of the following;

greyscale values and nonlinear greyscale values and greyscale values without a common factor.

28. The light modulating device of claim 1, wherein a pixelated optical element adapted to modulate the phase of the light interacting with the pixelated optical element is combined with a spatial light modulator being adapted to modulate the amplitude of the light interacting with the spatial light modulator, and wherein at least one pixel of the pixelated optical element of a macropixel comprises a phase value different to the phase values of the other pixels of the pixelated optical element of the macropixel.

29. The light modulating device of claim 28, wherein the pixels of the spatial light modulator or of the pixelated optical element are adapted such that the possible complex output values result in essentially the same spacing either in the real or in the imaginary direction in the complex plane or wherein the pixels of the spatial light modulator or of the pixelated optical element are adapted such that the possible complex output values result in essentially the same spacing either in the real or in the imaginary direction in the complex plane and wherein the macropixel is adapted such that it generates the point (0+0i) in the complex plane.

31. The light modulating device of claim 1, wherein a pixelated optical element adapted to modulate the phase of the light interacting with the pixelated optical element is combined with a spatial light modulator being adapted to modulate the—

preferably discrete—

phase of the light interacting with the spatial light modulator.

36. The light modulating device of claim 1, wherein a predetermined value to be represented by a macropixel is transferred by a transferring means from an external source where the predetermined value has been calculated, and wherein the switching state of the individual pixels inside a macropixel is determined locally in the local region encompassing the macropixel.

37. The light modulating device of claim 1, wherein for each macropixel a homogenizing element is present in the optical path after the macropixel, the homogenizing element comprising an optical input and an optical output, the homogenizing element being adapted such that output light of the macropixel is entering the optical input of the homogenizing element and is mixed within the homogenizing element and is output at the optical output of the homogenizing element.

38. The light modulating device of claim 37, wherein the optical input of a homogenizing element comprises at least one input aperture or wherein the optical output of a homogenizing element comprises an output aperture or wherein the homogenizing element is adapted to generate output light comprising a characteristic being essentially equivalent to the light output of one homogeneous pixel.

40. The light modulating device of claim 38, wherein the homogenizing element is adapted to generate output light with a predetermined amplitude or phase variation over the output aperture of the homogenizing element or wherein the output apertures of the homogenizing elements comprise essentially the same size or form or size and form or wherein the size of the output aperture of the homogenizing element is approximately equal to the size of a macropixel.

42. The light modulating device of claim 38, wherein the homogenizing element comprises a common input aperture for all pixels of a macropixel or wherein the homogenizing element comprises at least two separated input apertures for the pixels of a macropixel.

45. The light modulating device of claim 37, wherein a homogenizing element comprises a rod for achieving a macropixel homogenisation, where the integrator rod comprises dimensions being adapted to the dimensions being typical for macropixel structures or wherein an array of rods is provided, a rod of the array being assigned to a macropixel.

48. The light modulating device of claim 45, wherein for rods in the rod array, the core of the rod comprises a higher refractive index than the refractive index of the cladding of the rod or wherein a very thin LC spatial light modulator substrate glass being compounded with a rod array substrate.

51. The light modulating device of claim 45, wherein a rod array is integrated into a spatial light modulator substrate plate, the refractive index of the substrate plate is modulated periodically consistent with the dimensions of the rod array in order to implement cores and claddings of the rod array.

52. The light modulating device of claim 37, wherein a homogenizing element comprises a capillary plate for achieving a macropixel homogenisation.

53. The light modulating device of claim 45, wherein a matrix arrangement of light pipes is generated by writing into an optical medium in a targeted manner by way of optical exposure causing a difference in the refractive index of the optical medium, especially into an optically polymerizable medium or into a photopolymer or wherein a matrix arrangement of light pipes is generated by illuminating a silver halide film with an interference pattern and developing the silver halide film and preferably applying a chemical solution to the silver halide film.

55. The light modulating device of claim 53, wherein a first line pattern is generated into the optical medium by exposing the optical medium by way of two-beam interference of two light beams comprising a predetermined wavelength or defined by the angle between the propagation directions of the two light beams or wherein a second line pattern is generated into the optical medium by exposing the optical medium by way of two-beam interference of two light beams again after either the optical medium or the light sources have been turned by a predefined angle about an axis perpendicular to the plane of the exposed medium.

59. The light modulating device of claim 37, wherein a glass plate with periodic holes in one-to-one correspondence with a macropixel grid is used to homogenize light or wherein “

Lithography galvano forming”

is applied to generate metallic structures with high aspect ratios for light homogenization or for a replication master which is used to generate said light guiding structures.

61. The light modulating device of claim 37, wherein the optical input of the homogenizing element comprises an array of optical fibre fan-in elements, the optical fibre fan-in elements being adapted to combine light coming from several pixels of a macropixel into the optical output of the homogenizing element or wherein the homogenizing element comprises a fiber optic face plate including an array of fan-in elements, the array of fan-in elements being combined with a LC-spatial light modulator such that there is one fiber for each pixel of the light modulating element and at the output there is one fiber for each macropixel.

63. The light modulating device of claim 37, wherein the homogenizing elements are used for mixing the signals of phase pixels or complex pixels including phase information, such that the mean optical path length through the element is the same for each individual pixel of the macropixel or wherein the homogenizing element is adapted to generate predetermined optical path lengths for light of each individual pixel in a macropixel, the predetermined optical path lengths preferably being different.

64. The light modulating device of claim 37, wherein the values of the individual pixels of a macropixel are calculated in such a way as to compensate for non-ideal effects of the homogenizing element or wherein the relation of input states of individual spatial light modulator pixels in the macropixel to the output states of the homogenizing element are listed in a look-up table and for a desired output state the combination of input pixel values that fit best to this output state are chosen and are written to the pixels of the spatial light modulator.

68. The light modulating device of claim 37, wherein a scatter means is implemented at or near the optical input of the homogenizing elements, especially at or near an entrance plane of the homogenizing elements being realized by light pipes.

69. The light modulating device of claim 68 in a holographic display according to claim 81, wherein the scatter means is designed such that a suppression of higher diffraction orders in the plane of a virtual observer window of a holographic display is achieved.

70. The light modulating device of claim 68, wherein the scatter means is designed such that a predicted or desired intensity distribution or angular emission of the light emitting or passing the macropixel can be achieved or wherein a scatter means is implemented at or near the exit plane of the homogenizing elements, especially of the light pipe.

72. The light modulating device of claim 68, wherein a phase profile element is implemented near to or at the exit plane of the spatial light modulator or wherein a phase altering means is arranged downstream of the spatial light modulator with respect of the propagation of the light, the phase altering means being arranged between the spatial light modulator and the scatter means.

74. The light modulating device of claim 72, wherein the phase altering means comprises a micro lens array or a structure being comparable to a micro lens array or wherein the phase altering means is operating on a diffractive basis or wherein the phase altering means being a diffractive binary surface profile or a graded index profile.

77. The light modulating device of claim 72, wherein the scatter means is arranged in a predetermined distance to the phase profile element or the phase altering means, the predetermined distance having a value between the range of 0.1 to 2 mm, the predetermined distance preferably being 0.5 mm.

78. Method of modulating light being emitted by a coherent light source using a light modulating device of claim 1.

79. A display device or a holographic display device comprising a light modulating device of claim 1.

81. The holographic display of claim 79, wherein at least one virtual observer window is created at the eyes of one or more observers or wherein at least one virtual observer window is created at the eyes of one or more observers and wherein the extension of the virtual observer windows is determined to be equal to or smaller than ow=Dλ

/mp, with D being the distance of an observer to the display, λ

, being the wavelength of a light source as part of the holographic display and mp being the pitch of the macropixel grid.

83. The holographic display of claim 79, wherein the light modulating device with a homogenizing element is adapted to be operated such that undesirable eye crosstalk between the observer windows for both eyes of an observer compared to the use of the same light modulating device without homogenizing elements is reduced or wherein binary optical elements are transformable into continuous level working elements, or elements which have a greater number of levels than a binary state device.

85. A device for use in fast optical information transfer, the device comprising a light modulating device of claim 1, the device further comprising at least one fast switching optical data array for an optical interconnect.

86. Method of obtaining a predetermined value C for a macropixel of a light modulating device of claim 1 or for a holographic display of claim 79, the method comprising the step of generating a value C to be encoded into a macropixel of the light modulating device by applying the equation

C=a₁ exp(ip₁)+a₂ exp(ip₂)+a₃ exp(ip₃)+ . . . +a_N exp(ip_N),

where a_j is one of the possible values of the amplitude of the spatial light modulator pixel j, j=1 to N, N being the number of the pixels of a macropixel of the spatial light modulator, and p_j is the fixed phase value of pixel j of the pixelated optical element of the macropixel, and the method comprising the step of finding a set of possible values a_j and/or p_j to solve or approximate the equation.

87. Method of obtaining a predetermined value C for a macropixel of a light modulating device of claim 1 or for a holographic display of claim 79, wherein the method comprising the step of generating a value C to be encoded into a macropixel of the light modulating device by applying the equation

C=exp i(p₁+sl₁)+exp i(p₂+sl₂)+exp i(p₃+sl₃)+ . . . +exp i(p_N+sl_N)

where the p_j is the fixed phase value of pixel j of the pixelated optical element of the macropixel, j=1 to N, N being the number of the pixels of a macropixel of the spatial light modulator, and the sl_j is one of the possible values representing a switchable phase value of the spatial light modulator pixel j, and the method comprising the step of finding a set of possible values sl_j and/or p_j to solve or approximate the equation.

88. The method of claim 86, wherein the values C are to be generated such that a predetermined dense and uniform distribution set of possible states in the complex plane is generated or wherein values C are to be generated such that the number of degenerate states is relatively low, or zero.

90. The method of claim 86, wherein the number of the possible different complex values C_m which can be generated are 2^N or wherein the step size of the binary SLM is a further variable to be found.

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