This invention relates to methods and apparatus for displaying images holographically. A method of displaying an image holographically using a spatial lightmodulator (SLM), said SLM having a plurality of SLM pixels, the method comprising: displaying a diffraction pattern on said pixels of said SLM; and illuminating said pixels of said SLM such that light diffracted by said diffraction pattern on said SLM pixels comprises a content of said displayed image, a variation in brightness of said displayed image across said displayed image being modulated by an intensity envelope determined by the diffraction pattern of an individual said pixel, for example a sinc envelope; and wherein the method further comprises moving a peak or centre of gravity of said intensityenvelope away from a zero order spot and towards a centre of said displayed image by imposing a pattern of phase delay across said SLM pixels, said pattern of phase delay repeating at a spatial interval corresponding to a pixel interval of said SLM.

Holographic image display systems

Speckle noise reduction is best tested on a precise speckle contrast measurement bench, which should be able to measure 100% contrast in fully developed speckle as well as the smallest contrast (for example, less than 10%) after its reduction. On such a test bench, we have measured very efficient speckle contrast reduction by temporal averaging using a moving diffuser on a tuning fork, which vibrates at 100Hz over 60μm in amplitude, a distance that is three times the surface roughness correlation length of the diffuser.

Very efficient speckle contrast reduction realized by moving diffuser device

An eye tracker having a waveguide for propagating illumination light towards an eye and propagating image light reflected from at least one surface of an eye, a light source optically coupled to the waveguide, and a detector optically coupled to the waveguide. Disposed in the waveguide is at least one grating lamina for deflecting the illumination light towards the eye along a first waveguide path and deflecting the image light towards the detector along a second waveguide path.

Apparatus for eye tracking

An Electrically Switchable Bragg Grating (ESBG) despeckler device comprising at least one ESBG element recorded in a hPDLC sandwiched between transparent substrates to which transparent conductive coatings have been applied. At least one of said coatings is patterned to provide a two-dimensional array of independently switchable ESBG pixels. Each ESBG pixel has a first unique speckle state under said first applied voltage and a second unique speckle state under said second applied voltage.

Laser illumination device

There is provided a transparent wearable data display comprising: a source of collimated light; a means for deflecting said collimated light into a scanned beam; a first array comprising one column and integer N TOWS of switchable grating elements sandwiched between first and second parallel transparent substrates, the substrates together functioning as a first light guide; an second array comprising M columns and N rows of switchable grating elements sandwiched between third and fourth, parallel transparent substrates the substrates together functioning as a second light guide; transparent electrodes applied to opposing faces of the first and second and the third and fourth substrates. Hie apparatus further comprises a first coupling means tor directing the scanned beam into a first TIR light path between the outer surfaces of the first lightguide along the first array column; and a second coupling means for directing the first HR light into a second TIR path between the outer surfaces of the second lightguide along a row of elements of the second array.

Wearable data display

The condition for a diffuser to produce the maximum speckle contrast reduction with the minimum number of distinct phase patterns is derived. A binary realization of this optimum diffuser is obtained by mapping the rows or columns of a Hadamard matrix to the phase patterns. The method is experimentally verified in the Grating Light Valve laser projection display.

Jahja I. Trisnadi

Papers

Hadamard speckle contrast reduction