Holographic Projection System
A holographic projection system includes a detector arrangement arranged to detect light received by a first detection area. The system is arranged to perform an optical alignment process including selecting a first pixel of an array of pixels; forming a first holographic reconstruction of a first picture; moving the first holographic reconstructionin a first dimension of a replay plane such that the first holographic reconstruction is moved between a plurality of positions; and determining a value for a parameter of the light received by the first detection area in each of the plurality of positions and comparing each respective determined parameter value to a threshold condition. If the threshold condition is not met, the holographic projection system is arranged to repeat the optical alignment process by: selecting a second pixel of the array of pixels; and forming a second holographic reconstruction of a second picture.
1 . A holographic projection system for forming, at a replay plane, a holographic reconstruction of a picture comprising an array of pixels, the system comprising a detector arrangement arranged to detect light received by a first detection area; wherein the holographic projection system is arranged to perform an optical alignment process comprising:
selecting a first pixel of the array of pixels;
forming a first holographic reconstruction of a first picture, the first picture comprising a primary control region comprising the selected first pixel;
moving the first holographic reconstruction with respect to the first detection area in a first dimension of the replay plane such that the first holographic reconstruction is moved between a plurality of positions; and
determining a value for a parameter of the light received by the first detection area in each of the plurality of positions and comparing each respective determined parameter value to a threshold condition;
wherein, if the threshold condition is not met over the plurality of positions, the holographic projection system is arranged to repeat the optical alignment process by: selecting a second pixel of the array of pixels that neighbours the first pixel; and forming a second holographic reconstruction of a second picture, the second picture comprising a primary control region comprising the second pixel.
2 . The holographic projection system as claimed in claim 1 , wherein the detector arrangement is further arranged to detect light received by a second detection area.
3 . The holographic projection system as claimed in claim 2 , wherein the optical alignment process further comprises selecting a third pixel of the array of pixels, and wherein the first picture further comprises a secondary control region comprising the selected third pixel.
4 . The holographic projection system as claimed in claim 2 , wherein the optical alignment process further comprises detecting, at the plurality of positions of the first holographic reconstruction, a parameter of the light received by the second detection area and comparing the detected parameter to a threshold condition.
5 . The holographic projection system as claimed in claim 4 , wherein the holographic projection system is arranged to determine a first aligned position of a holographic reconstruction of the first primary control region based on the threshold condition being met by the detected parameter of the light received by the first detection area; and a second aligned position of a holographic reconstruction of the first secondary control region based on the threshold condition being met by the detected parameter of the light received by the second detection area.
6 . The holographic projection system as claimed in claim 5 , wherein the holographic projection system is arranged to determine an average of the first and second aligned positions.
7 . The holographic projection system as claimed in claim 3 , wherein the repeated optical alignment process comprises selecting a fourth pixel of the array of pixels that neighbours the second pixel; and wherein the second picture further comprises a secondary control region comprising the selected fourth pixel.
8 . The holographic projection system as claimed in claim 3 , wherein the first pixel neighbours the third pixel in a first direction of the first dimension, and the second pixel neighbours the fourth pixel in a second direction of the first dimension opposite to the first direction.
9 . The holographic projection system as claimed in claim 1 , wherein the parameter of light measured by the first detection area relates to optical power.
10 . The holographic projection system as claimed in claim 1 , wherein the holographic projection system is arranged to select the second pixel as a nearest neighbour of the first pixel in a direction of the first dimension.
11 . The holographic projection system as claimed in claim 1 , wherein the first and second primary control region of the respective first and second picture consist, respectively, of the selected first or second pixel.
12 . The holographic projection system as claimed in claim 1 , wherein the holographic projection system is arranged to move the first holographic reconstruction in the first dimension a total distance that is less than or equal to a pixel pitch of the first holographic reconstruction.
13 . The holographic projection system as claimed in claim 1 , wherein the holographic projection system comprises a display device arranged to display a diffractive pattern comprising a hologram of a picture and to spatially modulate light incident thereon in accordance with the diffractive pattern to form a holographic wavefront.
14 . The holographic projection system as claimed in claim 13 , wherein the holographic projection system is arranged such that a diffractive pattern comprising a first hologram of the first picture is displayed on the display device during the step of forming the first holographic reconstruction of the first picture.
15 . The holographic projection system as claimed in claim 14 , wherein the holographic projection system is arranged such the diffractive pattern further comprises a grating function, and wherein the holographic projection system is arranged to change the grating function of the diffractive pattern to move the first holographic reconstruction.
16 . The holographic projection system as claimed in claim 15 , wherein the holographic projection system is arranged to change the grating function of the diffraction pattern to move the first holographic reconstruction between the plurality of positions.
17 . The holographic projection system as claimed in claim 15 , wherein the holographic projection system is arranged to determine the grating function which gives rise to the greatest detected parameter.
18 . The holographic projection system as claimed in claim 1 , further comprising a mask comprising an aperture, wherein the first detection area is arranged to detect light received through the aperture of the mask.
19 . The holographic projection system as claimed in claim 18 , wherein the width of the aperture in the first dimension is less than a dimension of the first pixel in the first dimension.
20 . An optical alignment method for a holographic projection system arranged to form a holographic reconstruction of a picture comprising an array of pixels, the method comprising:
selecting a first pixel of the array of pixels;
forming a first holographic reconstruction of a first picture, the first picture comprising a first primary control region comprising the selected first pixel;
moving the first holographic reconstruction with respect to the first detection area in a first dimension of the replay plane such that the first holographic reconstruction is moved between a plurality of positions; and
determining a value for a parameter of the light received by a first detection area of a detector of the holographic projection system in each of the plurality of positions and comparing each respective determined parameter value to a threshold condition;
wherein, if the threshold condition is not met over the plurality of positions, the method comprises repeating the optical alignment process by: selecting a second pixel of the array of pixels that neighbours the first pixel; and forming a second holographic reconstruction of a second picture, the second picture comprising a second primary control region comprising the second pixel.