Diffractive In-Coupling Elements for Waveguide Re-Bounce Loss Mitigation
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Solution Overview
Problem
Conventional augmented and virtual reality display systems face challenges in efficiently and uniformly in-coupling light due to re-bounce within waveguides, leading to light loss and discomfort due to mismatches between accommodative and vergence states, which affect the perception of depth.
Innovation Solution
Incorporation of truncated diffractive optical elements with reflective layers, configured to mitigate light loss by redirecting light to propagate through waveguides and reduce re-bounce, while providing physiologically correct accommodation-vergence cues through wavefront divergence control.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If light is incident on a diffractive optical element at an angle greater than the critical angle, then the element can be used in compact optical systems, but light loss occurs due to rebounce at the first interface
Solution Approach 1:
The patent applies the principle of converting harm into benefit by utilizing the rebounce effect that would normally cause light loss. By designing the diffractive optical element with specific layer structures and refractive indices, the rebounce at the first interface is converted into a useful function where the light path is redirected through the substrate to emerge from the second interface, thereby converting the harmful light loss into beneficial light transmission at oblique angles.
2Reliability
If a diffractive optical element is designed with high diffraction efficiency, then it can effectively manipulate light, but manufacturing precision requirements increase
Solution Approach 1:
The patent applies segmentation by dividing the diffractive optical element into multiple layers with different refractive indices and thicknesses. Instead of requiring a single complex surface profile, the diffraction function is achieved through the combined effect of multiple simpler layers, each with more manageable manufacturing requirements. This segmentation allows the overall element to achieve high diffraction efficiency while reducing the precision requirements for any single layer.
Solution Approach 2:
The patent utilizes composite materials by combining multiple layers with different refractive indices (e.g., high-index and low-index materials) to create a diffractive optical element. This composite structure achieves the desired diffraction characteristics through the interaction of light with multiple materials, providing a more manufacturable approach compared to single-material solutions requiring complex surface profiles.
3Loss of energy
If the diffractive optical element has a specific refractive index combination, then light loss is mitigated, but material selection becomes more restricted
Solution Approach 1:
The patent applies parameter changes by systematically varying the refractive indices, thicknesses, and arrangement of multiple layers to optimize light transmission. By changing these parameters across different layers, the element achieves reduced light loss at oblique angles. The patent provides specific parameter ranges and combinations that balance performance with material availability, allowing designers to select from multiple material options within defined criteria rather than being restricted to a single material system.
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
Enhances in-coupling efficiency and uniformity, reduces user discomfort by aligning accommodative and vergence states, resulting in a more realistic and comfortable three-dimensional imagery experience.
Implementation Method 1
Diffractive optical elements with mitigation of rebounce-induced light loss and related systems and methods
Implementation Method 2
light incident on a diffractive optical element at an angle greater than a critical angle... rebounce at a first interface between the first medium and the second medium
Data Source
Figure 1
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Figure 3A~3C
AI summary
Display devices include waveguides with in-coupling optical elements that mitigate re-bounce of in-coupled light to improve overall in-coupling efficiency and/or uniformity. A waveguide receives light from a light source and/or projection optics and includes an in-coupling optical element that in-couples the received light to propagate by total internal reflection in a propagation direction within the waveguide. Once in-coupled into the waveguide the light may undergo re-bounce, in which the light reflects off a waveguide surface and, after the reflection, strikes the in-coupling optical element. Upon striking the in-coupling optical element, the light may be partially absorbed and/or out-coupled by the optical element, thereby effectively reducing the amount of in-coupled light propagating through the waveguide. The in-coupling optical element can be truncated or have reduced diffraction efficiency along the propagation direction to reduce the occurrence of light loss due to re-bounce of in-coupled light, resulting in less in-coupled light being prematurely out-coupled and/or absorbed during subsequent interactions with the in-coupling optical element.