Retinal projection display device and phase profile optimization method thereof
A retinal projection display device is provided. The retinal projection display device includes a light source configured to emit light, a spatial light modulator configured to generate diffracted light by diffracting the emitted light, a holographic optical element configured to reflect the diffracted light by duplicating the diffracted light into a plurality of complex wavefronts, and a field lens configured to focus the plurality of complex wavefronts to a plurality of respective focal points in an eye-box, wherein the plurality of complex wavefronts overlap each other.
1. A retinal projection display device comprising:
a light source configured to emit light;
a spatial light modulator configured to generate diffracted light by diffracting the light emitted by the light source;
a holographic optical element configured to reflect the diffracted light by duplicating the diffracted light into a plurality of complex wavefronts;
a field lens configured to focus the plurality of complex wavefronts to a plurality of focal points in an eye-box; and
a processor configured to:
determine a loss value between a reconstructed virtual image and a target image, and
based on the loss value, update a phase profile,
wherein the plurality of complex wavefronts are continually arranged to overlap each other.
2. The retinal projection display device of claim 1 , wherein a distance between each of the plurality of focal points is less than a diameter of a pupil of an eye of a user.
3. The retinal projection display device of claim 1 , wherein the spatial light modulator comprises one of:
a phase modulator configured to perform phase modulation; or
a complex modulator configured to perform amplitude modulation and phase modulation.
4. The retinal projection display device of claim 1 , wherein the holographic optical element comprises a multiplexed holographic optical element comprising a plurality of interference patterns configured to duplicate the diffracted light into each of the plurality of complex wavefronts.
5. The retinal projection display device of claim 4 , wherein the holographic optical element comprises a photopolymer, and
wherein the plurality of interference patterns are provided in a form of a bulk grid.
6. The retinal projection display device of claim 4 , wherein the plurality of interference patterns of the holographic optical element comprise at least three interference patterns.
7. The retinal projection display device of claim 1 , further comprising a relay optical system configured to transmit the diffracted light generated by the spatial light modulator to the holographic optical element.
8. The retinal projection display device of claim 7 , further comprising a noise removal filter configured to remove noise from the diffracted light transmitted through the relay optical system.
9. The retinal projection display device of claim 7 , further comprising a first light brancher provided between the light source and the spatial light modulator,
wherein the first light brancher is configured to:
reflect the light emitted from the light source toward the spatial light modulator; and
transmit the diffracted light emitted from the spatial light modulator to the relay optical system.
10. The retinal projection display device of claim 9 , further comprising a second light brancher provided between the relay optical system and the holographic optical element,
wherein the second light brancher is configured to:
reflect the diffracted light emitted from the relay optical system toward the holographic optical element; and
transmit, to the field lens, the plurality of complex wavefronts emitted from the holographic optical element.
11. The retinal projection display device of claim 10 , wherein the first light brancher and the second light brancher comprise beam splitters or half mirrors.
12. The retinal projection display device of claim 1 , wherein the processor is further configured to provide the phase profile to the spatial light modulator.
13. The retinal projection display device of claim 12 , wherein
the loss value is greater than a predetermined threshold value.
14. The retinal projection display device of claim 1 , wherein the processor is further configured to determine the loss value based on a loss function represented as:
F loss =L 2Norm[ s×|v ( x t ,y t )|− A target ( x t ,y t )]
where s is a scale factor, v (x t , y t ) is a signal value of an (x t , y t ) coordinate of the reconstructed virtual image, and A target (x t , y t ) is a signal value of an (x t , y t ) coordinate of the target image.
15. The retinal projection display device of claim 1 , wherein the processor is further configured to update the phase profile such that the loss value is decreased.
16. A phase profile optimization method of a retinal projection display device, wherein the retinal projection display device comprises:
a light source configured to emit light;
a spatial light modulator configured to generate diffracted light by diffracting the light emitted by the light source;
a holographic optical element configured to reflect the diffracted light by duplicating the diffracted light into a plurality of complex wavefronts; and
a field lens configured to focus the plurality of complex wavefronts to a plurality of respective focal points in an eye-box,
the phase profile optimization method comprising:
inputting an arbitrary phase profile to the spatial light modulator;
performing a first propagation simulation on the plurality of complex wavefronts duplicated by the holographic optical element;
performing a second propagation simulation until a virtual image is reconstructed, based on the plurality of complex wavefronts on which the first propagation simulation is performed;
determining a loss value between the reconstructed virtual image and a target image;
based on the loss value being greater than a predetermined threshold value, updating a current phase profile; and
based on the loss value being less than or equal to the predetermined threshold value, ending the update.
17. The phase profile optimization method of claim 16 , wherein the performing the first propagation simulation comprises determining a coherent sum of the plurality of complex wavefronts.
18. The phase profile optimization method of claim 16 , wherein the determining the loss value comprises determining the loss value based on a loss function represented as:
F loss =L 2Norm[ s×|v ( x t ,y t )|− A target ( x t ,y t )]
where s is a scale factor, v (x t , y t ) is a signal value of an (x t , y t ) coordinate of the virtual image, and A target (x t , y t ) is a signal value of an (x t , y t ) coordinate of the target image.
19. The phase profile optimization method of claim 18 , wherein the signal value of the (x t , y t ) coordinate of the virtual image is determined based on phase profile information and a propagation function modeled based on a propagation distance between the eye-box and the virtual image.
20. The phase profile optimization method of claim 16 , wherein the updating the current phase profile comprises updating the current phase profile such that the loss value is decreased by the updated phase profile.
21. A non-transitory computer-readable storage medium storing instructions that, when executed by at least one processor, cause the at least one processor to:
input an arbitrary phase profile to a spatial light modulator;
perform a first propagation simulation on a plurality of complex wavefronts duplicated by a holographic optical element;
perform a second propagation simulation until a virtual image is reconstructed, based on the plurality of complex wavefronts on which the first propagation simulation is performed;
determine a loss value between the reconstructed virtual image and a target image;
based on the loss value being greater than a predetermined threshold value, update a current phase profile; and
based on the loss value being less than or equal to the predetermined threshold value, end the update.