Planar Waveguide Diffractive Elements Focus Control
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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 diffractive optical elements (DOEs) that alter the characteristics of light, allowing it to escape and steer beams, enabling focus control and presentation of images at various viewing distances, and allowing for see-through augmented reality displays.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If conventional light-guide optical elements are used, then the device structure is simple and easy to manufacture, but the display can only project images at a single depth plane focused at infinity, limiting focus control
Solution Approach 1:
The optical system is segmented into multiple functional layers: input coupling region, waveguide core, and output coupling region with diffractive elements. Each layer performs a specific function, allowing independent optimization and manufacturing while achieving overall focus control capability
Solution Approach 2:
Diffractive optical elements serve as intermediaries between the waveguide and the external environment, enabling light to escape the waveguide at controlled angles and positions. These elements act as mediators that transform guided light into viewable images at multiple depth planes
2Illumination intensity
If multiple angle-dependent reflectors are embedded in the waveguide, then light can be outcoupled from the waveguide face, but the exit pupil remains limited and light energy is lost at each encounter
Solution Approach 1:
The diffractive optical element is segmented into multiple zones or regions, each responsible for outcoupling light at different angles or positions. This segmentation allows distributed light extraction, reducing the energy loss at any single location while maintaining overall efficiency
Solution Approach 2:
The diffractive element parameters (grating period, depth, shape) are varied across different regions to optimize light outcoupling efficiency at each location. By changing these parameters spatially, the system maximizes light extraction while minimizing total energy loss
3Adaptability or versatility
If the linear diffraction grating changes the angle of incident light beyond the threshold of TIR, then light escapes from lateral faces, but only a fraction of light energy is directed out each time
Solution Approach 1:
The waveguide is designed with multiple encounters between light and diffractive elements along its length. Instead of extracting all light at one location, the system continuously extracts portions of light at multiple points, maintaining useful action throughout the light propagation path and reducing cumulative energy loss
Solution Approach 2:
The light extraction process is segmented into multiple stages along the waveguide length. Each diffractive element encounters light at a different position and extracts a portion for outcoupling, while the remaining light continues propagation. This segmented extraction improves overall efficiency compared to single-point extraction
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 system provides a large eye box accommodating viewer movements and enables stereoscopic volumetric displays that match ocular vergence and accommodation, allowing users to focus on real-world objects and virtual content simultaneously.
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
If the light encounters one or more diffraction optical elements (DOE) in or adjacent to the planar waveguide, the characteristics of that light (e.g., angle of incidence, wavefront shape, wavelength, etc.) can be altered
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.