Light modulator for representing complex-valued data

• US 8,169,682 B2
• Filed: 04/29/2008
• Issued: 05/01/2012
• Est. Priority Date: 04/30/2007
• Status: Active Grant

• Current Assignee: SeeReal Technologies S.A.
• Original Assignee: SeeReal Technologies S.A.
• Inventors: Kroll, Bo, Schwerdtner, Armin, Leister, Norbert
• Primary Examiner(s): Mack, Ricky
• Assistant Examiner(s): TRA, TUYEN Q
• Application Number:
  US12/598,232
• Publication Number:
  US 20100149617A1
• Time in Patent Office: 1,463 Days
• Field of Search: 359/249, 359/290, 359/291, 359/293, 359/295, 359/220, 359/223, 359/224, 359/256
• US Class Current: 359/249
• CPC Class Codes: G02F 1/133631 with a spatial distribution of the retardation value
• CPC Class Codes: G02F 1/133632 with refractive index ellipsoid inclined relative to the LC-layer surface
• CPC Class Codes: G03H 1/02 Details of features involved during the holographic process; Replication of holograms without interference recording
• CPC Class Codes: G03H 1/2294 Addressing the hologram to an active spatial light modulator
• 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 2223/13 Phase mask
• CPC Class Codes: G03H 2225/32 Phase only
• CPC Class Codes: G03H 2225/33 Complex modulation
• CPC Class Codes: G03H 2225/55 Having optical element registered to each pixel
• CPC Class Codes: G03H 2240/13 Amplitude and phase complex modulation

Abstract

A light modulator is disclosed for representing complex-valued data, comprising an encoding area that has an arrangement of pixels, the phase of which can be controlled. This largely avoids an interfering optical path difference between adjacent pixels or pixel groups when a complex value is encoded in several adjacent phase pixels of the encoding area, the optical path difference varying according to the angle. One respective specific structured delaying layer, which causes the optical path of an incident linearly polarized beam to change according to the angle, is associated with at least one predefined pixel of a group of adjacent pixels of the encoding area. The thickness of the delaying layer is designed such that the modification of the optical path caused by the delaying layer runs in the opposite direction from the angle-related modification of the optical path difference between individual pixels of the pixel group.

Claims

1. Light modulator for representing complex-valued information, comprising an encoding surface and a certain structured retardation layer, where the encoding surface comprises an arrangement of pixels, whose transmissive or reflective phase shift can be controlled, where for encoding individual components of a complex number at least one given pixel of a pixel group of adjacent pixels of the encoding surface is assigned with the certain structured retardation layer, which causes an angle-specific change in an optical path length of an incident bundle of rays having linear polarisation, the angle-specific change relating to an angle between an exiting bundle of rays and the encoding surface, wherein the layer thickness of the retardation layer is dimensioned such that when encoding the individual components of a complex number the change in the optical path length through the retardation layer counteracts the angle-specific change in the retardation among individual pixels of the pixel group, and compensates the angle-specific change in the retardation at least partly or even entirely.

2. Light modulator according to claim 1, wherein the certain structured retardation layer is disposed near the encoding surface, where the retardation layer can be disposed either in front of and/or behind the encoding surface, preferably in close contact with the pixels.

3. Light modulator according to claim 1, wherein pixels are arranged one-dimensionally or are arranged one-dimensionally in a stripe-shaped manner, or two-dimensionally, related to the encoding surface.

4. Light modulator according to claim 1, wherein the encoding surface or a carrier layer being in contact with the encoding surface is designed either as a flexible or as an inelastic layer.

5. Light modulator according to claim 1, wherein the encoding surface which comprises the arrangement of the pixels is in contact with at least one carrier layer or with at least one orientation layer which is disposed on at least one side of the encoding surface.

6. Light modulator according to claim 5, wherein the encoding surface is a plane liquid crystal layer or wherein the encoding surface of the light modulators comprises an arrangement of micro-fluidic droplet pixels which can be manipulated by an electric field, where the light modulator is designed in the form of an electro-wetting phase-modulating light modulator.

7. Light modulator according to claim 1, wherein the encoding surface which comprises the arrangement of the pixels is assigned to at least one switching element layer or to at least one switching element layer being an electrode layer which is disposed on both sides of the encoding surface for controlling the pixels.

8. Light modulator according to claim 1, wherein the retardation layer is disposed between an electrode and a carrier layer, on the inside face of the carrier layer or on the outside face of the carrier layer.

9. Light modulator according to claim 1, comprising

The encoding surface which comprises the arrangement of pixels,

Optionally one orientation layer, which is disposed on at least one of the two sides of the encoding surface,

At least one electrode layer for controlling the pixels which is disposed on the two free sides, and

At least one carrier layer which is disposed on at least one of the two free sides,

thus providing a one- or two-dimensional arrangement of pixels, which can be controlled with the help of the potentials which are supplied to the electrode layers, and where a structured retardation layer is disposed between at least one of the electrode layers and the carrier layer which is adjacent to the electrode layer.

10. Light modulator according to claim 1, wherein the certain structured retardation layers are disposed between electrode layers and carrier layers on both sides of the plane encoding surface.

11. Light modulator according to claim 1, wherein, for controlling the encoding surface, electrodes and orientation layers for controlling and orienting the pixels are disposed on the side of the retardation layers which faces the encoding surface.

12. Light modulator according to claim 1, wherein a mask is situated between one electrode and the retardation layers on the side through which the light beams are emitted after having passed the pixels, said mask having a structure which prevents the light beams having linear polarisation from passing through two retardation layers which are of different nature and which are disposed opposing each other on either side of the encoding surface, if the light is incident at an oblique angle, and where corresponding mask apertures are provided at positions where incident light beams having linear polarisation pass retardation layers and of same design in front of and/or behind the encoding surface.

13. Light modulator according to claim 1, wherein the structure width of the structured retardation layers largely corresponds to an extent of a pixel group, which comprises multiple pixels.

14. Light modulator according to claim 1, wherein with a two-phase encoding method where two adjacent pixel columns are used in order to encode a complex number in each row, the structured retardation layers exhibit a column arrangement of a size which corresponds roughly to the dimensions of the pixels.

15. Light modulator according to claim 1, wherein the structured retardation layers are structured layers made of a single birefringent material or a combination of multiple birefringent materials, where only an extraordinary beam passes through the retardation layer because of an use of polarised light beams, and where birefringent materials exhibit angle-specific changes in the refractive index and thus cause changes in the optical path lengths of light transmitted at different angles.

16. Light modulator according to claim 1, wherein the retardation layer which respectively follows the pixels causes light beams with an oblique angle of incidence to cover different optical path lengths for an angle through the pixels which are separated by one pixel such that the retardation to the adjacent pixels is compensated partly or even entirely.

17. Light modulator according to claim 1, wherein the light beams which are transmitted through the retardation layer have linear polarisation, where the retardation is achieved when only an extraordinary beam passes through the retardation layer, where the linear polarisation is obtained by using a light source which only emits polarised light, or by disposing the linear polariser on the entry side of the light modulator.

18. Light modulator according to claim 1, wherein the change in the optical path length for an angle is relative to a given reference angle, where the differences in optical path length for this reference angle are compensated by writing modified phase values to one of the two pixels of a group.

19. Light modulator according to claim 1, wherein two different retardation layers are disposed in front of the two adjacent pixels of the groups, where light beams emitted by one pixel of the group cover a longer optical path length relative to a reference angle, than light beams emitted by the other pixel, which cover a shorter optical path length relative to the reference angle, because the retardation layers exhibit properties which differ from those of the retardation layers.

20. Light modulator according to claim 1, wherein an identical birefringent material, but with different orientation of an optical axis, can be used for an adjacent retardation layer to the retardation layer, such that in one case the optical path length in the one retardation layer increases with an angle and in the other case the optical path length in the adjacent retardation layer decreases with the angle, or vice versa.

21. Light modulator according to claim 1, wherein the retardation layer is made of different birefringent materials.

22. Light modulator according to claim 1, wherein the retardation layers which are disposed on only one side are split into two-piece retardation layers, which are disposed on both planer sides of the encoding surface in order to minimise the layer thickness.

23. Light modulator according to claim 1, wherein the retardation layers are disposed right next to the encoding surface, inside the glass plates or outside thereof.

24. Light modulator according to claim 1, wherein the structured retardation layers are provided when using a micro-mirror array, in particular a tip-mirror array for phase modulation, which represents the arrangement of pixels, where the structured retardation layers are alternately applied on adjacent columns of micro-mirrors of the micro-mirror array.