Diffractive Optical Assembly for Head-Mounted Displays
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Solution Overview
Problem
Current head-mounted displays using diffractive optical elements suffer from limited field of view and poor optical efficiency due to the wavelength and angle dependence of volume holographic optical elements, leading to energy loss and inefficiency, especially with broadband light sources.
Innovation Solution
A diffractive optical assembly is designed with an input coupler and an output coupler, where one has a more sensitive Bragg condition holographic optical element and the other a diffraction optical element, and an image source generating light with a two-dimensional spatial distribution of wavelengths that comply with Bragg selectivity, enhancing diffractive efficiency and field of view.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If a volume holographic optical element (HOE) is used as the coupler to diffract planar waves, then the diffractive efficiency is improved for a specific wavelength, but the field of view is limited due to the narrow angle tolerance (lower than 10 degrees)
Solution Approach 1:
The invention divides the HOE into multiple discrete elements (first HOE, second HOE, third HOE, fourth HOE) with different Bragg conditions. Each HOE is responsible for diffracting light within a specific angular range, collectively covering a wider field of view while maintaining high diffractive efficiency for each segment.
Solution Approach 2:
The invention extends the solution from a single HOE to multiple HOEs arranged in a dimensional array, where each HOE handles a different angular sector. This dimensional expansion allows the system to maintain the narrow angular selectivity of individual HOEs while achieving a broad overall field of view.
2Adaptability or versatility
If a volume HOE is used as the coupler for broadband light source, then only a portion of the planar wave can be diffracted at each angle of incidence, but the energy loss exceeds 90 percent resulting in poor optical efficiency
Solution Approach 1:
The invention segments the broadband spectrum handling across multiple HOEs, each optimized for specific wavelength ranges and angular ranges. This segmentation allows efficient utilization of the broadband light source by directing different spectral components through appropriate HOEs, significantly reducing energy loss.
Solution Approach 2:
Each HOE is designed with specific local properties (different Bragg conditions, different angular ranges, different wavelength sensitivities) to optimize performance for its designated portion of the broadband spectrum. This local optimization ensures that each region of the optical element operates at peak efficiency for its assigned function.
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 configuration preserves energy and improves diffractive efficiency, expanding the field of view while maintaining optical efficiency in head-mounted displays, leading to better energy utilization.
Implementation Method 1
Bragg condition of the most critical HOE is more sensitive than Bragg condition of the DOE. The image light has a plurality of incident angles to the input coupler and a plurality of wavelengths corresponding to the incident angles.
Implementation Method 2
The dispersive element is configured to disperse the source light passing through the dispersive element to irradiate the SLM, and wavelengths of the source light on the SLM have a two-dimensional spatial distribution.
Implementation Method 3
Sizes of the quantum dots vary on the plane of the image source, such that the wavelengths of the image light on the image source has the two-dimensional spatial distribution.
Data Source
AI summary
A diffractive optical assembly includes an input coupler, an output coupler, and an image source. The output coupler is next to the input coupler. One of the input coupler and the output coupler has a most critical holographic optical element (HOE), and another one has a diffractive optical element (DOE). Bragg condition of the most critical HOE is more sensitive than Bragg condition of the DOE. The image source is configured to generate image light that is incident to the input coupler then propagates to the output coupler. The image light has incident angles to the input coupler and wavelengths corresponding to the incident angles. The wavelengths of the image light on the image source have a two-dimensional spatial distribution, such that relationships between the incident angles and the wavelengths of the image light comply with Bragg selectivity of the most critical HOE.