Methods and apparatus to calibrate spatial light modulators
Methods and apparatus to calibrate spatial light modulators are disclosed. Examples include processor circuitry to execute and/or instantiate instructions to provide a greyscale image to a spatial light modulator (SLM) to define voltages to be applied to individual pixels of the SLM. The voltages associated with pixel values in the greyscale image. The pixel values arranged in a double-slit grating pattern. The SLM to produce an interference pattern based on the double-slit grating pattern. The processor circuitry is to determine a phase difference between first and second gratings of the double-slit grating pattern based on the interference pattern. The processor circuitry is to generate a phase curvature based on the phase difference.
1. An apparatus comprising:
at least one memory;
instructions in the apparatus; and
at least one processor circuit to execute and/or instantiate the instructions to:
provide a greyscale image to a spatial light modulator (SLM), the greyscale image including pixel values that define voltages to be applied to individual pixels of the SLM, the pixel values arranged in a double-slit grating pattern, the SLM to produce an interference pattern based on the double-slit grating pattern;
determine a phase difference between first and second gratings of the double-slit grating pattern based on the interference pattern; and
generate a phase curvature based on the phase difference.
2. The apparatus of claim 1 , wherein variations in phase exhibited across the phase curvature are indicative of imperfections in at least one of a light source or an optical element used to produce an input beam of light incident on the SLM used to produce the interference pattern, one or more of the at least one processor circuit to calibrate operation of the SLM based on the phase curvature to compensate for the imperfections.
3. The apparatus of claim 1 , wherein the phase curvature is indicative of a nature of a wavefront of an input beam of light incident on the SLM used to produce the interference pattern.
4. The apparatus of claim 1 , wherein the greyscale image is a first greyscale image, one or more of the at least one processor circuit to generate a second greyscale image for the SLM using the phase curvature.
5. The apparatus of claim 1 , wherein one or more of the at least one processor circuit is to:
provide a series of greyscale images to the SLM, the series of greyscale images including the greyscale image, successive ones of the greyscale images including pixel values arranged in the double-slit grating pattern, the double-slit grating pattern to be at different locations in different ones of the greyscale images; and
determine different phase differences between the first and second gratings of the double-slit grating pattern at the different locations.
6. The apparatus of claim 5 , wherein the different locations shift along a line of the SLM for successive ones of the greyscale images in the series of greyscale images.
7. The apparatus of claim 6 , wherein an amount of shift between successive ones of the different locations corresponds to a spacing distance between the first and second gratings of the double-slit grating pattern.
8. The apparatus of claim 6 , wherein the line extends in a direction perpendicular to an elongate length of the first and second gratings of the double-slit grating pattern.
9. The apparatus of claim 6 , wherein the series of greyscale images is a first series of greyscale images, and the line is a first line, one or more of the at least one processor circuit to provide multiple additional series of greyscale images to the SLM, the multiple additional series of greyscale images including pixel values arranged in the double-slit grating pattern at additional locations along multiple additional lines parallel to and offset from the first line.
10. The apparatus of claim 9 , wherein one or more of the at least one processor circuit is to provide a final series of greyscale images to the SLM, the final series of greyscale images including pixel values arranged in the double-slit grating pattern at final locations along a final line perpendicular to the first line and the multiple additional lines.
11. The apparatus of claim 5 , wherein one or more of the at least one processor circuit is to:
define a reference phase associated with a first position of the first grating of the double-slit grating pattern at a first one of the different locations; and
determine a phase, relative to the reference phase, for positions of the first and second gratings of the double-slit grating pattern at the different locations based on the different phase differences.
12. The apparatus of claim 1 , wherein the greyscale image is a first greyscale image, the double-slit grating pattern is a first double-slit grating pattern associated with a first location of the SLM, and the phase difference is a first phase difference, one or more of the at least one processor circuit to:
provide a second greyscale image to the SLM, the second greyscale image including pixel values arranged in a second double-slit grating pattern, the second double-slit grating pattern associated with a second location of the SLM different than the first location; and
determine a second phase difference between first and second gratings of the second double-slit grating pattern.
13. The apparatus of claim 12 , wherein the first grating of the first double-slit grating pattern is at a first position and the second grating of the first double-slit grating pattern is at a second position, the second location to be offset relative to the first location such that the first grating of the second double-slit grating pattern is at the second position.
14. The apparatus of claim 13 , wherein one or more of the at least one processor circuit is to:
assign a first phase value for a first phase associated with the first position, the first phase designated as a reference phase;
determine a second phase value for a second phase associated with the second position, the second phase value corresponding to the first phase value plus the first phase difference; and
determine a third phase value for a third phase associated with a third position corresponding to the second grating of the second double-slit grating pattern, the third phase value corresponding to the second phase value plus the second phase difference.
15. The apparatus of claim 1 , wherein one or more of the at least one processor circuit is to:
obtain an image of the interference pattern from an image sensor; and
determine the phase difference based on an analysis of the image.
16. The apparatus of claim 1 , wherein one or more of the at least one processor circuit is to:
provide a series of greyscale images to the SLM, successive ones of the greyscale images including pixel values arranged in the double-slit grating pattern, the pixels values to alternate between low and high pixel values along a length of the first and second gratings, the low and high pixels values to be incremented by a fixed incremental amount in successive ones of the greyscale images;
determine different phase differences between the first and second gratings of the double-slit grating pattern associated with different ones of the low and high pixel values; and
generate a phase response transfer curve based on the different phase differences.
17. The apparatus of claim 16 , wherein the low pixels values for the second grating are higher than the low pixel values for the first grating by the fixed incremental amount.
18. The apparatus of claim 16 , wherein the series of greyscale images is a first series of greyscale images, one or more of the at least one processor circuit to:
provide additional series of greyscale images to the SLM, different ones of the additional series of greyscale images corresponding to the double-slit grating pattern at different locations; and
generate different phase response transfer curves for the different locations.
19. The apparatus of claim 18 , wherein one or more of the at least one processor circuit is to generate a different greyscale image for the SLM to cause the SLM to output a holographic image, the different greyscale image including pixel values defined based on the different phase response transfer curves.
20. The apparatus of claim 1 , wherein the interference pattern is a non-zero order interference pattern spaced apart from a zero order interference pattern.
21. At least one non-transitory computer readable medium comprising instructions that, cause at least one processor to at least:
provide a greyscale image to a spatial light modulator (SLM), the greyscale image including pixel values that cause application of corresponding voltages to individual pixels of the SLM, the pixel values arranged in a double-slit grating pattern, the SLM to produce an interference pattern based on the double-slit grating pattern;
determine a phase difference between first and second gratings of the double-slit grating pattern based on the interference pattern; and
generate a phase curvature based on the phase difference.
22. The at least one non-transitory computer readable medium of claim 21 , wherein the instructions cause one or more of the at least one processor to:
provide a series of greyscale images to the SLM, the series of greyscale images including the greyscale image, successive ones of the greyscale images including pixel values arranged in the double-slit grating pattern, the double-slit grating pattern to be at different locations in different ones of the greyscale images; and
determine different phase differences between the first and second gratings of the double-slit grating pattern at the different locations.
23. The at least one non-transitory computer readable medium of claim 21 , wherein the greyscale image is a first greyscale image, the double-slit grating pattern is a first double-slit grating pattern associated with a first location of the SLM, and the phase difference is a first phase difference, the instructions to cause one or more of the at least one processor to:
provide a second greyscale image to the SLM, the second greyscale image including pixel values arranged in a second double-slit grating pattern, the second double-slit grating pattern associated with a second location of the SLM different than the first location; and
determine a second phase difference between first and second gratings of the second double-slit grating pattern.
24. An apparatus comprising:
a spatial light modulator (SLM);
an image sensor; and
processor circuitry including one or more of:
at least one of a central processing unit, a graphic processing unit, or a digital signal processor, the at least one of the central processing unit, the graphic processing unit, or the digital signal processor having control circuitry to control data movement within the processor circuitry, arithmetic and logic circuitry to perform one or more first operations corresponding to instructions, and one or more registers to store a result of the one or more first operations, the instructions in the apparatus;
a Field Programmable Gate Array (FPGA), the FPGA including logic gate circuitry, a plurality of configurable interconnections, and storage circuitry, the logic gate circuitry and the interconnections to perform one or more second operations corresponding to the instructions, the storage circuitry to store a result of the one or more second operations; or
Application Specific Integrate Circuitry (ASIC) including logic gate circuitry to perform one or more third operations corresponding to the instructions;
the processor circuitry to perform at least one of the first operations, the second operations or the third operations to instantiate:
greyscale image generation circuitry to generate a greyscale image, the greyscale image to define voltages to be applied to individual pixels of the SLM, the voltages defined by pixel values in the greyscale image, the pixel values arranged in a double-slit grating pattern, the SLM to produce an interference pattern based on the double-slit grating pattern;
interference pattern analysis circuitry to determine a phase difference between first and second gratings of the double-slit grating pattern based on the interference pattern obtained by the image sensor; and
phase curvature generation circuitry to generate a phase curvature based on the phase difference.
25. The apparatus of claim 24 , wherein the greyscale image is a first greyscale image, the greyscale image generation circuitry to generate a second greyscale image for the SLM using the phase curvature.