Planar Waveguide with Diffractive Elements for Variable Focus AR
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Solution Overview
Problem
Conventional wearable 3D displays, such as those using light-guide optical elements, can only project images at a single depth plane focused at infinity, limiting their application in augmented and virtual reality scenarios where focusing on objects closer than optical infinity is desirable.
Innovation Solution
A planar waveguide system incorporating diffraction optical elements (DOEs) that alter the angle and focus of light, allowing images to be presented at various viewing distances and enabling a see-through augmented reality display by combining linear diffraction gratings with radially symmetric or circular lens phase patterns, which steer beams and control focal depth.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a light-guide optical element system is used to project images, then the image can be displayed at optical infinity, but the image cannot be focused at distances closer than optical infinity
Solution Approach 1:
The patent employs dynamic optical elements including variable focus lenses and adjustable diffraction gratings that can change their optical properties in real-time. This allows the system to dynamically adjust the focal plane from optical infinity to closer distances, enabling the user to focus on objects at varying distances while maintaining a single optical path architecture.
Solution Approach 2:
The system utilizes parameter changes in the optical path by varying the refractive index through temperature control or electric field application in the light-guide material. This allows the same optical element to project images at different focal distances by changing the optical parameters of the medium, thereby achieving multiple focusing distances without adding complex optical components.
2Adaptability or versatility
If multiple angle-dependent reflectors are embedded in a waveguide to outcouple light, then the exit pupil is increased, but the system can only relay collimated images at optical infinity
Solution Approach 1:
The patent integrates multiple functions into a single waveguide structure by combining diffraction gratings, variable focus lenses, and optical infinity correction elements within one compact platform. This multi-functional design allows the same waveguide to handle both collimated infinity images and focused near-field images, eliminating the need for separate optical systems for different viewing distances.
Solution Approach 2:
The system introduces a temporal dimension to the optical path by using rapidly switchable liquid crystal elements that can change the waveguide's optical properties between different focal states. This allows the system to transition between projecting at optical infinity and projecting at closer distances by modulating the optical parameters in the time domain, effectively adding a focusing dimension to the traditional single-plane light guide.
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 a larger eye box accommodating viewer movements and allows digital content to be superimposed over real-world objects at appropriate viewing distances, reducing the accommodation-vergence conflict in the human visual system, thereby enhancing the realism and usability of augmented and virtual reality experiences.
Implementation Method 1
Light that is coupled into a planar waveguide (e.g., pane of glass, pane of fused silica, pane of polycarbonate), will propagate along the waveguide by total internal reflection (TIR).
Implementation Method 2
A planar waveguide system incorporating diffraction optical elements (DOEs) that alter the angle and focus of light
Implementation Method 3
combining linear diffraction gratings with radially symmetric or circular lens phase patterns, which steer beams and control focal depth
Data Source
AI summary
A waveguide apparatus includes a planar waveguide and at least one optical diffraction element (DOE) that provides a plurality of optical paths between an exterior and interior of the planar waveguide. A phase profile of the DOE may combine a linear diffraction grating with a circular lens, to shape a wave front and produce beams with desired focus. Waveguide apparati may be assembled to create multiple focal planes. The DOE may have a low diffraction efficiency, and planar waveguides may be transparent when viewed normally, allowing passage of light from an ambient environment (e.g., real world) useful in AR systems. Light may be returned for temporally sequentially passes through the planar waveguide. The DOE(s) may be fixed or may have dynamically adjustable characteristics. An optical coupler system may couple images to the waveguide apparatus from a projector, for instance a biaxially scanning cantilevered optical fiber tip.