Multiple-Wavelength Light Guides With Diffractive Optics for HMD Imaging
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Solution Overview
Problem
Conventional image light guide arrangements in Head-Mounted Displays (HMDs) face challenges in achieving desired virtual image brightness and resolution while managing bulk and cost, with issues in diffraction and propagation of certain wavelengths.
Innovation Solution
An image light guide system utilizing multiple waveguides and diffractive optics for angular encoding and decoding of image-bearing light beams, including in-coupling and out-coupling diffractive optics to propagate and replicate light beams across multiple waveguides, enhancing brightness and resolution while maintaining compactness.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Weight of stationary object
If conventional image light guide arrangements are used to reduce bulk and cost, then weight and manufacturing cost are reduced, but image resolution and virtual image brightness deteriorate
Solution Approach 1:
The system divides the light guide into multiple waveguides (first waveguide, second waveguide) that propagate different wavelength ranges separately. Each waveguide has dedicated in-coupling and out-coupling diffractive optics optimized for specific wavelengths, allowing each segment to achieve high resolution and brightness without compromising overall system compactness
Solution Approach 2:
Different waveguides and diffractive optics are designed with specialized properties for specific wavelength ranges. The first waveguide optimizes for blue light (450-480 nm) while the second waveguide optimizes for green light (500-560 nm), with each having tailored refractive indices, grating periods, and optical path lengths to maximize local image quality for its designated wavelength
2Volume of stationary object
If conventional image light guide arrangements are used to reduce bulk and cost, then volume and manufacturing cost are reduced, but virtual image brightness and resolution deteriorate
Solution Approach 1:
The system segments the wavelength spectrum into multiple bands handled by separate waveguides, allowing each waveguide to be optimized for maximum brightness in its specific range. The first waveguide handles blue wavelengths (450-480 nm) and the second handles green wavelengths (500-560 nm), with each having optimized in-coupling and out-coupling optics to maximize light extraction efficiency and virtual image brightness without increasing overall bulk
Solution Approach 2:
The system varies key optical parameters across different waveguides including refractive index (1.46 for first waveguide, 1.50 for second waveguide), grating periods (1.8 micrometers for first, 2.0 micrometers for second), and optical path lengths to optimize brightness for each wavelength range. These parameter changes enable high virtual image brightness across multiple wavelengths while maintaining compact form factor
3Ease of manufacture
If conventional image light guide arrangements are used, then cost is reduced, but diffraction performance and light propagation for certain wavelengths deteriorate
Solution Approach 1:
The system segments the optical system into multiple specialized waveguides, each with diffractive optics optimized for specific wavelength ranges. The first waveguide with 1.8 micrometer grating period optimizes for blue light diffraction (450-480 nm) while the second waveguide with 2.0 micrometer grating period optimizes for green light diffraction (500-560 nm), ensuring reliable diffraction performance for each wavelength without requiring a single complex multi-wavelength optic
Solution Approach 2:
Each waveguide and its associated diffractive optics are designed with local quality optimized for its specific wavelength range. The in-coupling and out-coupling optics in each waveguide have specialized refractive indices, grating orientations, and surface profiles tailored to maximize diffraction efficiency and light propagation reliability for their designated wavelengths, rather than using generic optics that compromise performance across all wavelengths
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 system achieves improved virtual image brightness and resolution with reduced bulk and cost, providing expanded eyebox dimensions and minimizing positional sensitivity for the viewer.
Implementation Method 1
a first in-coupling diffractive optic formed along the first waveguide, wherein the first in-coupling diffractive optic is operable to diffract a first portion of image-bearing light beams from a first image source into the first waveguide in an angularly encoded form
Implementation Method 2
a first waveguide operable to propagate image-bearing light beams
Implementation Method 3
a first out-coupling diffractive optic formed along the first waveguide, wherein the first out-coupling diffractive optic is operable to replicate the first portions of image-bearing light beams and direct the replicated image-bearing light beams from the first waveguide in an angularly decoded form
Data Source
AI summary
An image light guide system for conveying a virtual image that includes a first waveguide and a second waveguide operable to propagate image-bearing light beams. The first waveguide includes a first in-coupling diffractive optic formed along the first waveguide, wherein the first in-coupling diffractive optic is operable to diffract a first portion of image-bearing light beams from a first image source into the first waveguide in an angularly encoded form and a first out-coupling diffractive optic formed along the first waveguide, and wherein the first out-coupling diffractive optic is operable to replicate the first portions of image-bearing light beams and direct the replicated image-bearing light beams from the first waveguide in an angularly decoded form.