Waveguide In-Coupling Layout With Folded Multi-Pass Light Recycling
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Solution Overview
Problem
Existing near-eye display systems face inefficiencies in light coupling due to limited transmission paths through waveguide stacks, which affect the overall brightness and clarity of mixed-reality or virtual-reality images.
Innovation Solution
The implementation of a waveguide display system with stacked waveguide plates and a polarization-based optical arrangement that folds the light transmission path through the stack multiple times, utilizing birefringent reflective polarizers and quarter-wave plates to enhance light coupling efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If light passes through the waveguide stack only once, then the transmission path is simple, but the light coupling efficiency is limited
Solution Approach 1:
The patent implements periodic action by routing light through the waveguide stack multiple times in a repeating cycle. The optical path is designed so that light passes through the stack four times before exiting, with each pass utilizing the same input coupler and waveguide plates. This periodic transmission path increases the cumulative light coupling efficiency while maintaining a relatively simple overall structure.
2Productivity
If a mirror is provided behind the input couplers to increase light coupling, then the amount of light coupled into waveguide plates increases, but the device structure becomes more complex
Solution Approach 1:
The patent applies multi-functionality by designing the input coupler to serve multiple purposes: it couples light into the waveguide plates during each of the four passes and also acts as a reflective element to redirect light back through the stack. The waveguide plates themselves perform both light transmission and internal reflection functions, eliminating the need for separate mirrors and reducing overall component complexity while maintaining high light coupling efficiency.
3Productivity
If the transmission path is folded to allow light to traverse the waveguide stack multiple times, then the in-coupling efficiency is increased, but the optical path length increases
Solution Approach 1:
The patent implements nesting by placing the optical path folds within the compact thickness of the waveguide stack. The light path is routed through the stack multiple times in a nested configuration where each pass occupies minimal space. This allows the optical path length to be extended to four passes while the physical footprint remains compact, effectively nesting the extended path within the thin waveguide structure.
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 approach significantly increases the amount of light coupled into the waveguide plates, enhancing image brightness and clarity in mixed-reality or virtual-reality applications by allowing light to traverse the waveguide stack up to four times, thereby improving the overall display quality.
Implementation Method 1
a birefringent reflective polarizer is used to direct the image light to the waveguide stack. The birefringent reflective polarizer transmits the light in the first linear polarization state and reflects light in a second linear polarization state orthogonal to the first linear polarization state
Implementation Method 2
The circularly polarized light is then reflected by a mirror back to the quarter-wave plate with its phase reversed. The quarter-wave plate converts the light to the second linear polarization state and directs it back through the waveguide stack
Implementation Method 3
Light corresponding to an image generated by a reflective microdisplay of the display engine is diffracted into the waveguide by the input diffraction grating, so it can travel by way of total internal reflection to an output coupler and viewed by a human eye
Implementation Method 4
The waveguide plates each include a transparent substrate and input and output couplers such as diffractive optical elements (DOEs) for coupling light into and out of the waveguide substrates, respectively
Data Source
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AI summary
A waveguide display for use in a near-eye display system includes a waveguide stack having at least one waveguide substrate, an input coupler coupling light into the waveguide substrate and an optical arrangement that includes a birefringent reflective polarizer, a mirror and a polarization state converting element configured to convert light in a linear polarization state to a circular polarization state and to convert light in a circular polarization state to a linear polarization state. The mirror is arranged to receive light from the polarization state converting element and reflect the light back to the polarization state converting element. The optical arrangement causes a transmission path of light that traverses the waveguide stack a first time to be folded back through the waveguide stack such that at least a portion of light not coupled into the waveguide substrate is caused to traverse the waveguide stack a plurality of additional times.