Optical Waveguide Grating Structure for Edge-Free Light Expansion
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Solution Overview
Problem
Existing optical waveguide display devices require highly reflective surfaces along the slab waveguide edges for light reflection, which is difficult to manufacture and expensive, and involve three separate gratings for in-coupling, pupil expansion, and out-coupling.
Innovation Solution
The use of two functioning diffraction gratings from a common grating structure, with an intermediate diffraction grating optically coupling them, eliminating the need for reflective edges and simplifying manufacturing, and enhancing optical performance by spatially expanding light without the need for precise alignment.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If highly reflective surfaces are provided along edges of the slab waveguide for light reflection, then light can be reflected back towards the second and third areas, but manufacturing becomes difficult and expensive due to the need for very flat polished surfaces
Solution Approach 1:
The patent introduces a third diffraction grating area as an intermediary element between the first and second grating areas. This intermediate grating performs the light expansion function that previously required reflective surfaces, thereby eliminating the need for highly polished reflective edges while achieving the same optical coupling effect.
Solution Approach 2:
The patent replaces the mechanical/optical system of reflective surfaces with a diffraction-based system. Instead of using physically polished reflective edges, the invention uses diffraction gratings with specific groove patterns to achieve light redirection and expansion, substituting a manufacturing-intensive mechanical process with a more easily manufacturable diffraction structure.
2Reliability
If three separate gratings are used for in-coupling, pupil expansion, and out-coupling, then each function can be optimized independently, but the device complexity and alignment requirements increase
Solution Approach 1:
The patent merges three separate grating structures into a single common grating structure with three different areas. The first area has grooves for in-coupling, the second area has grooves for pupil expansion, and the third area has grooves for out-coupling. All three areas are formed as one integrated structure, reducing device complexity while maintaining independent optimization of each optical function through area-specific groove design.
3Ease of manufacture
If reflective edges are eliminated and diffraction gratings are used instead, then manufacturing is simplified and optical performance is enhanced, but the grating structure becomes more complex
Solution Approach 1:
The patent applies local quality by giving different groove characteristics to different areas of the common grating structure. The first area has grooves optimized for in-coupling, the second area has grooves optimized for pupil expansion, and the third area has grooves optimized for out-coupling. This allows each area to have the specific properties needed for its function while being part of a single manufactured 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 solution simplifies the manufacturing process and enhances optical performance by allowing the optical waveguide to transmit light without the need for reflective edges, achieving efficient light expansion and output without geometric or chromatic distortions.
Implementation Method 1
an optical waveguide (1) arranged to transmit light by total internal reflection
Implementation Method 2
a first diffractive grating region (8) associated with the optical waveguide (1) and arranged to receive light and diffract the received light along the optical waveguide
Implementation Method 3
an intermediate diffraction grating (10) associated with the optical waveguide (1) and optically coupled to the first diffractive grating region (8) by the optical waveguide, arranged to receive light diffracted from the first diffraction grating and to expand the received light in a first dimension by diffraction
Implementation Method 4
a second diffractive grating region (9) associated with the optical waveguide (1) and optically coupled to the intermediate diffraction grating (10) by the optical waveguide, arranged to receive light expanded in the first dimension by the intermediate diffraction grating, to expand the received light in a second dimension orthogonal to the first dimension by diffraction
Data Source
Figure 1A~1B
Figure 2
Figure 3
AI summary
An optical waveguide (2) arranged to transmit light under total internal reflection has a first diffractive grating region (8) arranged to receive light and diffract the received light along the optical waveguide (2), an intermediate diffraction grating (10) optically coupled to the first diffractive grating region (8) arranged to expand received light in a first dimension and a second diffractive grating region (9) optically coupled to the intermediate diffraction grating (10) arranged to expand light in a second dimension, orthogonal to the first dimension and to output the light expanded in the first and second dimensions from the optical waveguide (2) by diffraction. The first and second diffractive grating regions (8,9) are fabricated as a common grating whereas the second grating is fabricated above the common grating in an area where the common grating is erased by a coating.