Birefringent Waveguide Combiner for Multi-Focal MR Headsets
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Conventional mixed-reality head-mounted display (HMD) devices suffer from vergence-accommodation conflict, where the natural link between vergence and accommodation is broken, leading to visual discomfort and fatigue due to fixed accommodation and varying vergence with image contents.
Innovation Solution
An optical combiner in an HMD device using a birefringent lens and a ferroelectric liquid crystal (FLC) modulator with a reflective waveguide to provide multiple focal planes, allowing dynamic adjustment of focus cues to match the user's accommodation, enabling comfortable mixed-reality experiences.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional separate optical engines are used for each focal plane, then each plane can be independently optimized, but the overall device complexity and size increase significantly
Solution Approach 1:
The patent combines multiple optical engines into a single integrated optical engine that serves multiple focal planes (near, intermediate, and far fields). This consolidation reduces the number of separate optical systems while maintaining the ability to independently control each focal plane through a shared waveguide and modulator array, thereby reducing overall device complexity while preserving optical performance.
Solution Approach 2:
The shared waveguide and modulator array serve multiple functions by routing light to different focal planes simultaneously. The single optical engine performs the work of multiple separate engines by using spatial light modulators to direct light to specific regions of the waveguide that correspond to different focal planes, enabling one system to perform what previously required multiple specialized systems.
2Adaptability or versatility
If multiple separate optical engines are used for different focal planes, then each focal plane can be independently controlled, but the device size and weight increase
Solution Approach 1:
Multiple optical engines are merged into a single integrated system where a shared waveguide and modulator array serve all focal planes. This consolidation dramatically reduces the weight of moving components in the headset while maintaining the capability to independently control near, intermediate, and far field focal planes through electronic modulation rather than physical separation of optical paths.
Solution Approach 2:
The patent uses the temporal dimension and spatial modulation within a single optical path to achieve what previously required physical separation in space. By using spatial light modulators to dynamically route light to different regions of the waveguide corresponding to different focal planes, the system achieves multi-focal plane capability without multiplying the physical mass of optical components.
3Device complexity
If a single optical engine is used for all focal planes, then device complexity is reduced, but independent optimization of each focal plane becomes difficult
Solution Approach 1:
While the optical engine is unified, the system segments the optical path into distinct regions within the waveguide that correspond to different focal planes. Each region can be independently addressed and optimized using spatial light modulators, allowing precise control over light routing to near, intermediate, and far field planes while maintaining a single integrated optical engine that reduces overall complexity.
4Reliability
If separate optical engines are used for each focal plane, then optical performance can be optimized, but the overall device cost increases
Solution Approach 1:
The patent merges multiple expensive optical engines into a single cost-effective system by sharing common components including the waveguide, light source, and control electronics. This consolidation reduces manufacturing costs while maintaining optical performance through precise electronic control of light routing to different focal planes, avoiding the need to manufacture and integrate multiple separate optical systems.
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 provides a comfortable visual experience by dynamically adjusting focus cues, eliminating the need for mechanical components and reducing weight, with faster switching speeds and higher display refresh rates, thus minimizing visual discomfort and fatigue.
Implementation Method 1
A birefringent material may be used to redirect light to different locations on the waveguide, depending on the state of polarization of the incident light
Implementation Method 2
A polarizer can be used to ensure that only light in a desired state of polarization is incident on the birefringent material
Implementation Method 3
The waveguide can then reflect light from the birefringent material to the user's eye
Data Source
Figure 1
Figure 2
Figure 3A~3C
AI summary
An optical combiner in a display system of a mixed-reality head-mounted display (HMD) device comprises a lens of birefringent material and a ferroelectric liquid crystal (FLC) modulator that are adapted for use with a reflective waveguide to provide multiple different focal planes on which holograms of virtual-world objects (i.e., virtual images) are displayed. The birefringent lens has two orthogonal refractive indices, ordinary and extraordinary, depending on the polarization state of the incident light. Depending on the rotation of the polarization axis by the FLC modulator, the incoming light to the birefringent lens is focused either at a distance corresponding to the ordinary refractive index or the extraordinary refractive index. Virtual image light leaving the birefringent lens is in-coupled to a see-through reflective waveguide which is configured to form an exit pupil for the optical combiner to enable an HMD device user to view the virtual images from the source.