Monolithic Diffractive Optical Element for Near-Eye Displays
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Solution Overview
Problem
Near eye display systems using polymeric materials in diffractive optical elements (DOEs) suffer from optical interference, known as 'banding,' which reduces display uniformity and optical resolution due to lower optical properties compared to glass, and require tight manufacturing tolerances, making volume production costly and complex.
Innovation Solution
A monolithic three-dimensional optical microstructure with a waveguide substrate incorporating a DOE that integrates in-coupling, exit pupil expansion, and out-coupling functions within a single optical element, utilizing a two-dimensional grating that minimizes optical path length differences beyond the coherence length, thereby reducing interference and enhancing resolution.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Weight of moving object
If polymeric materials are used in volume production of the DOE to minimize system weight, then weight is reduced, but optical interference (banding) increases due to less optimal optical properties compared to glass
Solution Approach 1:
The patent combines multiple optical functions (in-coupling, exit pupil expansion, and out-coupling) into a single integrated DOE structure. This integration eliminates discontinuities at boundaries between separate gratings, reducing optical interference and banding effects while maintaining the lightweight polymeric material advantage.
Solution Approach 2:
The patent addresses the inherent optical interference problem of polymeric materials by designing a 2D grating structure where multiple optical paths are intentionally created with path length differences exceeding the coherence length. This converts the potential harm of interference into a beneficial effect by ensuring that interference patterns fall outside the visible range, thereby eliminating banding while maintaining weight advantages.
2Manufacturing precision
If multiple separate optical elements are used for in-coupling, exit pupil expansion, and out-coupling, then each function can be optimized independently, but device complexity and component count increase
Solution Approach 1:
The patent integrates three separate optical functions (in-coupling, exit pupil expansion, and out-coupling) into a single monolithic DOE structure with continuous 2D grating patterns. This eliminates the need for multiple discrete components and their associated alignment tolerances, reducing overall system complexity while maintaining functional optimization through unified design.
Solution Approach 2:
The DOE structure is designed to perform multiple optical functions simultaneously within a single element. The 2D grating pattern enables the same structure to provide in-coupling, exit pupil expansion, and out-coupling functions, making the component universal and eliminating the need for separate specialized elements for each function.
3Manufacturing precision
If separate gratings are used for in-coupling and out-coupling functions, then each grating can be optimized for its specific function, but discontinuities at boundaries reduce optical resolution
Solution Approach 1:
The patent employs continuous 2D grating patterns that extend across the entire DOE structure without discontinuities or boundaries between separate gratings. This continuous structure eliminates scattering and diffraction artifacts at grating boundaries, significantly improving optical resolution while maintaining the ability to perform multiple optical functions through the unified grating 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
The integrated DOE design reduces optical interference, increases display uniformity and resolution, and minimizes component count and weight, addressing the limitations of polymeric materials while maintaining lightweight and compact design requirements.
Implementation Method 1
Diffractive optical elements (DOEs) are optical elements with a periodic structure that are commonly utilized in applications ranging from bio-technology, material processing, sensing, and testing to technical optics and optical metrology. By incorporating DOEs in an optical field of a laser or emissive display, for example, the light's 'shape' can be controlled and changed flexibly according to application needs.
Implementation Method 2
In an optical near eye display system, a monolithic three-dimensional optical microstructure is formed by a waveguide substrate with at least one DOE having grating regions that integrate the functions of in-coupling of incident light into the waveguide, exit pupil expansion in one or two directions, and out-coupling of light from the waveguide
Data Source
AI summary
In an optical near eye display system, a monolithic three-dimensional optical microstructure is formed by a waveguide substrate with at least one DOE having grating regions that integrate the functions of in-coupling of incident light into the waveguide, exit pupil expansion in one or two directions, and out-coupling of light from the waveguide within a single optical element. An in-coupling region of the DOE couples the incident light into the waveguide and to a beam steering and out-coupling region. The beam steering and out-coupling region provides exit pupil expansion and couples light out of the waveguide. The beam steering and out-coupling region of the DOE can be configured with a two-dimensional (2D) grating that is periodic in two directions.