Diffractive Optical Element Remnant Layer Thin-Film Interference
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Solution Overview
Problem
Conventional augmented reality optical display devices suffer from uneven diffraction efficiency across the field of view due to the interaction of light with diffractive optical elements, leading to brightness differentials, which can be costly to address with additional dielectric coatings and complex grating profiles.
Innovation Solution
The implementation of a diffractive optical element with a surface relief grating and a remnant layer, where the remnant layer's thickness is controlled to enable thin-film interference at a partially reflective interface, achieving phase matching and improved diffraction efficiency across a range of angles and wavelengths without the need for dielectric coatings.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If conventional diffractive optical elements with blazed gratings are used, then light coupling efficiency is improved, but illumination uniformity across the field of view deteriorates due to uneven diffraction efficiency
Solution Approach 1:
The patent changes the physical parameters of the diffractive optical element by introducing a remnant layer with specific thickness (50-200nm) and refractive index mismatch. This parameter modification enables thin-film interference effects that compensate for the uneven diffraction efficiency of conventional blazed gratings, achieving uniform illumination across the field of view while maintaining high light coupling efficiency
Solution Approach 2:
The remnant layer acts as an intermediary between the substrate and the diffractive grating structure. This intermediate layer with controlled optical properties mediates the light interaction, creating constructive interference for uniform diffraction efficiency across different angles of incidence, thereby resolving the contradiction between coupling efficiency and illumination uniformity
2Illumination intensity
If dielectric coatings are applied to improve illumination uniformity, then brightness differential is reduced, but manufacturing complexity and cost increase
Solution Approach 1:
The patent employs a self-service approach where the remnant layer, which is inherently present as a byproduct of the grating fabrication process, is utilized to achieve the desired optical effect. By controlling its thickness to enable thin-film interference, the system uses its own manufacturing residue to improve illumination uniformity without requiring additional dielectric coating steps, thereby reducing manufacturing complexity while maintaining brightness uniformity
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 solution provides a more uniform illumination over a broad field of view, enhancing the user experience by ensuring even brightness and reducing manufacturing costs, while maintaining the efficiency of light coupling into and out of the substrate.
Implementation Method 1
the thickness of the remnant layer is controlled to enable thin-film interference for light having a predetermined wavelength that is received at the partially reflective interface from the substrate at a predetermined angle of incidence
Implementation Method 2
a diffractive optical element comprising a surface relief grating
Implementation Method 3
a partially reflective interface is provided between the substrate and the remnant layer
Implementation Method 4
Light is received at the input diffractive optical element 111 from a range of angles, as illustrated by input beams 114, 115. The input beams are diffracted by the input diffractive optical element 111
Implementation Method 5
The projected light is totally internally reflected within the waveguide. The trapped beams 116, 117 continue to travel through the substrate or waveguide 113
Data Source
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AI summary
An optical display device (600, 700) is disclosed. A diffractive optical element (618, 718) is mounted on a substrate (611, 711). The diffractive optical element comprises a blazed grating (619, 719) and a remnant layer (617, 717) which is formed of the same polymer-based material as the blazed grating. The remnant layer (617, 717) is positioned adjacent the substrate (611, 711) and a refractive index mismatch is provided between the two. The depth of the remnant layer is selected so that light diffracted by the grating and light reflected by the interface re-combine and interfere constructively for selected angles of incidence in order to undergo thin-film interference.