Switchable Diffractive Optical Element for Near-Eye Display Waveguides
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Solution Overview
Problem
Existing near-eye display (NED) technologies face challenges in achieving a large field of view (FOV), high transmittance, and a large eye-box while maintaining a compact form factor suitable for augmented reality (AR) and mixed reality (MR) applications.
Innovation Solution
The optical device employs a waveguide display system with switchable diffractive optical elements, specifically surface relief gratings (SRGs) filled with active liquid crystals, which can be switched between a diffraction state and a non-diffraction state via an external electric field. This allows for time-multiplexing of multiple light fields across different portions of the FOV.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of stationary object
If multiple diffractive gratings are integrated into a single waveguide to expand FOV, then the field of view increases, but the device complexity and manufacturing difficulty increase significantly
Solution Approach 1:
The patent employs switchable diffractive optical elements that can dynamically change their diffraction state in response to electrical signals. This allows a single waveguide to sequentially present multiple diffractive gratings corresponding to different FOV portions, eliminating the need for multiple permanently integrated gratings and reducing overall device complexity while maintaining expanded FOV capability
Solution Approach 2:
The diffractive optical elements utilize changes in the refractive index of liquid crystal materials through electrical field application to switch between different diffraction states. This parameter change approach allows a single physical structure to function as multiple diffractive gratings with different parameters, reducing manufacturing complexity compared to fabricating multiple distinct gratings
2Area of stationary object
If multiple diffractive gratings are integrated into a single waveguide to expand FOV, then the field of view increases, but the manufacturing precision requirements increase
Solution Approach 1:
By using dynamically switchable diffractive optical elements rather than multiple fixed gratings, the patent reduces manufacturing precision requirements. A single waveguide with switchable elements requires precise manufacturing of one structure, whereas multiple integrated gratings would require precise alignment and fabrication of multiple separate optical elements with different parameters
3Volume of moving object
If a single waveguide is used with switchable diffractive elements, then the device compactness is maintained, but the transmittance may be affected by the switching mechanism
Solution Approach 1:
The patent uses liquid crystal materials whose refractive index can be changed through electrical field application. When properly designed, these materials can achieve high contrast switching between diffraction states with minimal absorption losses, maintaining high transmittance while enabling the compact single-waveguide configuration
Solution Approach 2:
The patent replaces mechanical grating structures with electrically controlled liquid crystal-based diffractive optical elements. This substitution eliminates mechanical moving parts and reduces physical space requirements, maintaining device compactness while achieving efficient optical modulation with minimal energy loss
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The solution enables the delivery of multiple light fields corresponding to different portions of the FOV in a time-multiplexing manner, effectively expanding the FOV and maintaining high transmittance and a large eye-box, thereby enhancing the performance of NEDs for AR and MR applications.
Implementation Method 1
switchable between a diffraction state and a non-diffraction state via an external electric field applied to the at least one switchable diffractive optical element
Implementation Method 2
The switchable DOE includes a surface relief diffraction grating (SRG) on a surface of the substrate, a layer of liquid crystal material in contact with the SRG
Implementation Method 3
a light-transmissive substrate configured to propagate light rays through total internal reflection
Implementation Method 4
a surface relief diffraction grating (SRG) on a surface of the substrate...configured to input and/or output light rays to and/or from the substrate
Data Source
Figure 1A~1B
Figure 2A
Figure 2B
AI summary
An optical device includes a light source assembly configured to generate an image light; and at least one waveguide including an in-coupling element and an out-coupling element configured to transmit, via the at least one waveguide, a plurality of light fields of the image light to an eye-box of the optical device, in a time-multiplexing manner. At least one of the in-coupling element or the out-coupling element includes at least one switchable diffractive optical grating, which includes a surface relief grating (SRG) filled with an optically anisotropic material having a first principal refractive index along a groove direction of the SRG and a second principal refractive index along an in-plane direction perpendicular to the groove direction. One of the first and second principal refractive indices substantially matches a refractive index of the SRG, and the other mismatches.