Multiphase Diffraction Grating for Near-Eye Display
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Solution Overview
Problem
Conventional near-to-eye optical systems in head-mounted displays (HMDs) face limitations due to inefficiencies in diffraction gratings, requiring precise tuning, leading to color separation and a limited field of view, which results in bulky and costly devices.
Innovation Solution
A near-to-eye optical system utilizing a diffraction grating that reflects and focuses light, eliminating the need for external focusing optics, with a reflective diffraction grating embedded in a transparent substrate, allowing for see-through displays and improved field of view without increasing device size.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If single phase diffraction gratings are used for in-coupling and out-coupling light, then the device structure is simplified, but optical efficiency deteriorates due to poor light reflection and color separation
Solution Approach 1:
The patent combines the in-coupling and out-coupling diffraction gratings into a single integrated multiphase diffraction grating structure. This merged grating performs both functions simultaneously, eliminating the need for two separate single-phase gratings. The integration improves optical efficiency by properly directing light while maintaining a simplified overall device structure.
Solution Approach 2:
The patent transitions from single-phase diffraction gratings to multiphase diffraction gratings by changing the phase parameters of the grating structure. This parameter change enables the grating to reflect higher order diffractions effectively while maintaining proper color alignment, thereby improving optical efficiency without significantly increasing device complexity.
2Adaptability or versatility
If waveguide structure width is increased to improve field of view, then field of view is improved, but device size and weight increase making it bulky and uncomfortable
Solution Approach 1:
The patent uses high index optical materials to change the refractive index parameter of the waveguide structure. This parameter change allows for a narrower waveguide width while maintaining or improving the field of view, thereby reducing device weight and bulk without sacrificing optical performance.
Solution Approach 2:
The patent employs composite material structures combining high index materials with the diffraction grating elements. This composite approach enables enhanced light guidance efficiency, allowing for a more compact waveguide design that improves field of view while minimizing weight and size.
3Reliability
If lens is used to create virtually displaced image, then image focusing is achieved, but device size increases due to bulky lens element
Solution Approach 1:
The patent replaces the traditional mechanical lens-based focusing system with a diffractive optical system using multiphase diffraction gratings. This substitution eliminates the need for bulky lens elements while maintaining effective image focusing capability through diffraction-based light manipulation.
Solution Approach 2:
The patent extracts the focusing function from the separate lens element and integrates it directly into the diffraction grating structure. By taking out the dedicated lens and embedding focusing capability within the grating itself, the system achieves compact design without sacrificing image quality.
4Reliability
If input and output diffraction gratings are precisely tuned, then color separation is eliminated, but manufacturing difficulty and cost increase due to extreme tolerance control requirements
Solution Approach 1:
The patent merges the input and output diffraction gratings into a single multiphase grating structure. This integration ensures inherent matching between the gratings, eliminating the need for precise separate tuning and extreme tolerance control. The unified structure naturally maintains proper color alignment while simplifying manufacturing.
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 solution enhances the efficiency and field of view of HMDs by using a diffraction grating that bends and focuses light, reducing the need for bulky external optics and enabling more comfortable, lightweight designs while maintaining see-through capabilities.
Implementation Method 1
Optical system 200 uses a diffraction grating 205 to bend and focus light
Implementation Method 2
a reflective diffraction grating 205 that reflects and focuses light
Data Source
AI summary
A near-to-eye optical system includes an optically transmissive substrate having a see-through display region and a repeating pattern of diffraction elements. The repeating pattern of diffraction elements is disposed across the see-through display region of the optically transmissive substrate and organized into a reflective diffraction grating that bends and focuses computer generated image (“CGI”) light impingent upon the reflective diffraction grating. The see-through display region is at least partially transmissive to external ambient light impingent upon an exterior side of the optically transmissive substrate and at least partially reflective to the CGI light impingent upon an interior side of the optically transmissive substrate opposite the exterior side.