Wedged Cavity Combiner Optic for Near-Eye Displays
Solution Overview
Problem
Conventional combiner optics for Head-Up Displays (HUDs) are bulky and aesthetically unpleasing due to their large axial dimension, which hinders the integration of high-quality, simultaneous viewing of remote objects and projected images, especially in near-eye displays.
Innovation Solution
The development of combiner optics with two partial reflectors forming a wedged reflective cavity, allowing imaging light to follow a path with three reflections, enabling a thinner design that reduces the axial dimension and enhances aesthetics by allowing more nearly perpendicular orientation of the partial reflectors relative to the optical axis.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Length of moving object
If conventional combiner optics are used, then optical functionality is achieved, but axial dimension becomes large making the device bulky and aesthetically unpleasing
Solution Approach 1:
The patent reconfigures the optical path by introducing multiple reflections (three reflections) within a compact wedged cavity structure. This transforms the light propagation from a single-pass linear path to a multi-bounce compact path, effectively reducing the axial dimension while maintaining optical functionality. The wedged cavity geometry allows the light to traverse a longer effective optical path within a shorter physical distance by utilizing the third dimension (depth) of the wedge structure.
Solution Approach 2:
The patent embeds the reflective cavity within the combiner optic structure, nesting the multiple reflection paths inside a compact geometric configuration. The wedged cavity acts as a nested structure where light bounces between reflective surfaces in a confined space, achieving complex optical functionality within a reduced volume envelope.
2Ease of operation
If partial reflectors are tilted at large angles to achieve image projection, then projection functionality is achieved, but the combiner optic becomes thicker
Solution Approach 1:
The patent uses a wedged cavity geometry where the tilt angle is compensated by the wedge shape. The light path achieves the necessary angular deviation for projection functionality not through a single large tilt, but through multiple smaller reflections off the wedged surfaces, distributing the angular change across multiple interaction points and reducing the required tilt angle for each individual reflector.
Solution Approach 2:
The patent divides the single large-angle reflection function into multiple smaller-angle reflections. Instead of one reflector tilted at a large angle, the system uses multiple reflectors arranged in a wedged cavity, each tilted at a smaller angle, collectively achieving the same projection functionality while reducing overall thickness.
3Shape
If the combiner optic is made thinner for aesthetic purposes, then aesthetics and weight are improved, but optical performance for wide-angle viewing may deteriorate
Solution Approach 1:
The patent compensates for the reduced physical thickness by utilizing the wedged cavity's three-dimensional geometry. The wedge angle and cavity depth create an extended effective optical path length within the thin profile, allowing wide-angle viewing performance to be maintained despite the reduced external dimensions. The light traverses a longer effective path through multiple reflections, achieving wide-angle coverage without requiring a thicker component.
Solution Approach 2:
The patent optimizes the wedged cavity parameters (wedge angle, cavity depth, reflector positioning) to maximize wide-angle viewing performance within the constrained thin profile. By carefully tuning these geometric parameters, the system achieves broad viewing angles and high optical quality despite the reduced thickness, transforming the thickness constraint into an opportunity for optimized optical design.
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
This design results in a lightweight, aesthetically pleasing HUD with improved optical performance for wide-angle viewing of both remote objects and projected images, achieved through the reduced thickness and optimized reflectivity of the partial reflectors.
Implementation Method 1
The combiner optic includes first and second partial reflectors that form a wedged reflective cavity, and the imaging light follows a light path to the user's eye that includes three reflections in the wedged reflective cavity
Data Source
AI summary
An image combiner, also referred to as a combiner optic, of a near-eye display system or the like transmits enough light so a user can see remote objects in a “world view”, while also reflecting enough light so the user can simultaneously see a projected image in a “projected” (augmented) view. The disclosed image combiners use two partial reflectors configured to form a wedged reflective cavity. In the display system, light from an imaging device follows a path to the user's eye that includes three reflections in the wedged cavity. By using this capability of the wedged cavity, the combiner optic can have a substantially reduced thickness, and lower profile, than a combiner optic that uses only one partial reflector and only one reflection in the optical path.