Composite Diffraction Stack for Wavelength and Angle Selectivity
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Solution Overview
Problem
Existing transmissive holograms used in image projection systems face challenges in achieving wavelength selectivity and angle selectivity, and are prone to zeroth-order light issues, making them difficult to produce stably and effectively.
Innovation Solution
A composite diffraction element comprising a stack structure of three diffraction elements, where the second element diffractively reflects light to the first, the first diffractively reflects light to the third, and the third transmits and reflects zeroth-order light, mimicking a transmissive hologram's functionality.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If a thin transmissive hologram is used to be provided at the lens portion, then the form factor is reduced and it can be integrated into eyeglasses, but wavelength selectivity and angle selectivity cannot be achieved
Solution Approach 1:
The patent divides the single transmissive hologram into multiple reflective holograms arranged in a stack. Each reflective hologram processes a specific portion of the light, and through cumulative diffraction across multiple layers, the system achieves wavelength selectivity and angle selectivity that would be impossible in a single thin layer.
Solution Approach 2:
The patent transitions from a two-dimensional thin film structure to a three-dimensional stacked structure. By arranging multiple reflective holograms in layers along the optical path, the system gains volumetric diffraction capability while maintaining a relatively compact overall form factor suitable for eyeglass integration.
2Device complexity
If a transmissive hologram is used, then the structure is simple and can be formed as a thin film, but diffraction efficiency is highly sensitive to film thickness variation making stable production difficult
Solution Approach 1:
The patent segments the diffraction function across multiple reflective holograms rather than relying on a single transmissive hologram. This segmentation reduces the sensitivity to individual layer thickness variations, as the cumulative diffraction effect across multiple layers provides more stable overall performance even when individual layers have manufacturing tolerances.
Solution Approach 2:
The patent changes the operational parameters from transmissive to reflective mode for each hologram layer. Reflective holograms have different diffraction characteristics that are less sensitive to thickness variations compared to transmissive holograms, thereby improving manufacturing stability and diffraction efficiency consistency.
3Speed
If a transmissive hologram is used to guide image display light, then the optical path is direct, but zeroth-order light interference occurs reducing diffraction performance
Solution Approach 1:
The patent converts the harmful zeroth-order light that passes through reflective holograms into a useful component by introducing a fourth reflective hologram specifically designed to diffract this zeroth-order light. This fourth element redirects the previously wasted zeroth-order light into the desired first-order diffraction path, eliminating interference and improving overall diffraction efficiency.
Solution Approach 2:
The patent introduces a fourth reflective hologram as an intermediary element that mediates the interaction between the zeroth-order light and the final image output. This intermediary component specifically targets and redirects the zeroth-order light, preventing it from causing interference while maintaining the direct optical path efficiency.
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 composite diffraction element effectively reduces zeroth-order light interference, allowing for stable production and improved diffraction performance, including wavelength selectivity and angle selectivity, while maintaining a thin film design.
Implementation Method 1
the first diffraction element diffractively reflects the light diffractively reflected by the second diffraction element
Implementation Method 2
the first diffraction element diffractively reflects the light diffractively reflected by the second diffraction element, toward the third diffraction element
Implementation Method 3
the second diffraction element diffractively reflects light that has passed through the first diffraction element and reached the second diffraction element, toward the first diffraction element
Implementation Method 4
the second diffraction element diffractively reflects light
Implementation Method 5
the third diffraction element transmits the light diffractively reflected by the first diffraction element, and diffractively reflects zeroth-order light
Implementation Method 6
the third diffraction element diffractively reflects zeroth-order light that has passed through the first diffraction element and the second diffraction element
Data Source
AI summary
The present technology aims to provide a diffraction element that functions like a transmissive hologram, and more particularly, aims to provide a diffraction element suitable for forming an image projection system. The present technology provides a composite diffraction element that includes a stack structure including a first diffraction element, a second diffraction element, and a third diffraction element in this order. The second diffraction element diffractively reflects light that has passed through the first diffraction element and reached the second diffraction element, toward the first diffraction element. The first diffraction element diffractively reflects the light diffractively reflected by the second diffraction element, toward the third diffraction element. The third diffraction element transmits the light diffractively reflected by the first diffraction element, and diffractively reflects zeroth-order light that has passed through the first diffraction element and the second diffraction element.