Volumetric display

1. An apparatus for a volumetric display, the apparatus comprising:

an imaging system having an object plane and an image plane;

a source image generation apparatus for forming a source image in the object plane in accordance with received image data, the source image generation apparatus comprising a light source; and

a control apparatus for supplying image data to the source image generation apparatus, the image data corresponding to a series of two-dimensional images,

wherein the imaging system comprises a diffractive optical element and the control apparatus is arranged to generate at least one control signal to vary at least one of a wavelength of light emitted by the light source and a focal length associated with the diffractive optical element to vary the location of the image plane within a volume of real space in synchronism with the formation of the series of two-dimensional images in the object plane so as to construct a volumetric three-dimensional image in accordance with the received image data.

2. The apparatus according to claim 1 , wherein the diffractive optical element has a focal length that varies with optical frequency, and wherein the control apparatus is arranged to generate a control signal to vary the optical frequency of the light source to provide the series of image planes.

3. The apparatus according to claim 1 , wherein the diffractive optical element is a composite diffractive optical element having an array of spatially separated sub-elements, each sub-element having a respective focal length,

wherein the composite diffractive optical element further comprises an array of shutter elements, each shutter element to control illumination of one or more sub-elements of the diffractive optical element, and

wherein the control apparatus is arranged to generate a first control signal to address selectively the array of shutter elements to select the focal length, and to generate a second control signal to vary the optical frequency of the light source to provide the series of image planes.

4. The apparatus according to claim 3 , wherein the composite diffractive element comprises a first sub-element having a first focal length, a second sub-element having a second focal length and a third sub-element having a third focal length, wherein the first focal length in a first spectral sub-band overlaps the second focal length in a second spectral sub-band and the third focal length in a third spectral sub-band.

5. The apparatus according to claim 4 , wherein the first spectral sub-band corresponds to a red region of the spectrum, the second spectral sub-band corresponds to a green region of the spectrum and third spectral sub-band correspond to a blue region of the spectrum.

6. The apparatus according to claim 1 , wherein the diffractive optical element is an active diffractive optical element having a variable focal length, and

wherein the control apparatus is arranged to generate a control signal to the diffractive optical element to control the focal length of the active diffractive optical element to provide the series of image planes.

7. The apparatus according to claim 1 , wherein the diffractive optical element is a holographic optical element.

8. The apparatus according to claim 1 , wherein the light source comprises a tunable narrowband light source.

9. The apparatus according to claim 1 , wherein the source image generation apparatus comprises a projection system having a spatial light modulator arranged to modulate light from the light source in accordance with the image data from the control apparatus.

10. The apparatus according to claim 1 , wherein the source image generation apparatus comprises an array of liquid crystal shutters, with the light source arranged as a backlight, operable to form a source image in response to received image data.

11. The apparatus according to claim 1 , wherein the light source comprises an array of light emitters that are selectively addressable in dependence on the image data from the control apparatus to form the source image.

12. The apparatus according to claim 1 , wherein the light source is operable to output red, green and blue light, and wherein the control apparatus is arranged to control the imaging apparatus and diffractive optical element to provide spatially overlapping red, green and blue image planes.

13. The apparatus according to claim 1 , wherein the control apparatus is arranged to provide the series of image planes in a repeating sequence.

14. The apparatus according to claim 1 , wherein the control apparatus comprises a processor operable to process an image file comprising three-dimensional data to generate image data for the imaging system in synchronism with the at least one control signal to display a volumetric three-dimensional image corresponding to the three-dimensional data.

15. The apparatus according to claim 14 , wherein the processor is arranged to process a sequence of image files to generate a corresponding sequence of volumetric three-dimensional images.

16. The apparatus according to claim 14 , wherein the processor performs image processing functions such as scaling, inversion and normalization, or corrections for aberrations or distortion.

17. The apparatus according to claim 1 , wherein the imaging system comprises at least two diffractive optical elements.

18. A method of constructing a volumetric image in accordance with three-dimensional image data, the method comprising:

sequentially forming a series of two-dimensional images in accordance with received image data; and

in synchronism with forming the series of images, varying the location of the image plane so that each of the series of images is formed in a respective image plane so as to construct a volumetric three-dimensional image,

wherein the forming of the sequence of images comprises transmitting of light through a diffractive optical element; and

wherein the varying of the location of the image plane comprises adjusting at least one of i) a wavelength of the light transmitted through the diffractive optical element, and ii) a focal length associated with the diffractive optical element.

19. The method according to claim 18 , wherein the diffractive optical element has an associated chromatic dispersion and the location of the image plane is varied by varying the wavelength of the light transmitted through the diffractive optical element.

20. The method according to claim 18 , wherein the diffractive optical element is a composite diffractive optical element having an array of spatially separated sub-elements, each sub-element having a respective focal length, and the location of the image plane is varied by selectively addressing the array of spatially-separated sub-elements.