Inverted Master Holographic Waveguide Recording
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Solution Overview
Problem
Holographic waveguide mastering tools face issues with reflected orders causing spurious gratings and haze in large-scale applications like automotive heads-up displays and near-to-eye waveguides, where thick glass traps are impractical due to size and scatter concerns.
Innovation Solution
The inverted master approach, which positions the master grating substrate with a reflective film directly over an air gap, uses anti-reflection coatings on the bottom substrate, and incorporates a light trap to absorb or direct unwanted reflected beams away from the exposure cell, reducing interference and haze.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If thick glass traps are used to suppress reflected orders, then reflection suppression is improved, but device size and light scatter increase
Solution Approach 1:
The patent extracts the harmful reflected first-order beam from the system by using an air gap to prevent its formation at the master substrate interface. The air gap eliminates the reflective boundary that would otherwise generate the spurious reflected order, thereby removing the harmful factor without requiring thick glass traps.
Solution Approach 2:
The patent introduces an air gap as an intermediary layer between the master substrate and the exposure cell. This air gap acts as a mediator that prevents the formation of reflected first-order beams by eliminating the reflective interface, while still allowing the useful diffracted beams to pass through and interfere in the exposure cell.
2Object-affected harmful factors
If thick glass traps are used to suppress reflected orders, then reflection suppression is improved, but light scatter and haze increase
Solution Approach 1:
The patent extracts the source of light scatter by eliminating the thick glass trap entirely. By using an air gap instead, the system removes the material that would otherwise cause scattering and haze, while still achieving the goal of suppressing reflected orders through the absence of a reflective interface.
3Ease of manufacture
If conventional master substrate configuration is used, then manufacturing is simplified, but reflected first-order beams cause spurious gratings
Solution Approach 1:
The patent inverts the conventional master substrate configuration by placing the grating modulated surface facing away from the exposure cell, with the non-grating modulated surface facing the exposure cell. This inversion, combined with the air gap, prevents the formation of reflected first-order beams that would otherwise create spurious gratings, while maintaining ease of manufacture through straightforward substrate fabrication.
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 method effectively suppresses reflected orders, achieving low haze and high diffraction efficiency, suitable for large-scale and near-to-eye waveguide applications, while maintaining a compact and cost-effective process.
Implementation Method 1
the grating modulated surface supports a master grating which is configured to diffract the recording beam into a diffracted first-order beam and a refracted zero-order beam
Implementation Method 2
the diffracted first order beam interferes with a neighboring refracted zero-order beam in the exposure cell
Implementation Method 3
a bottom substrate with opposing light transmitting surfaces coated with anti-reflection coatings
Implementation Method 4
incorporates a light trap to absorb or direct unwanted reflected beams away from the exposure cell
Data Source
AI summary
Disclosed herein is methods and apparatus for recording a holographic waveguide utilizing an inverted holographic master technique. In some embodiments, an apparatus for recording a holographic waveguide is provided. The apparatus may include a source of light configured to provide a recording beam; a master substrate with a non-grating modulated surface and a grating modulated surface, wherein the grating modulated surface is opposite to the non-grating modulated surface and is configured to diffract the recording beam; a bottom substrate with opposing light transmitting surfaces coated with anti-reflection coatings overlaying the grating modulated surface of the substrate and separated from the master substrate by a gap; and an exposure cell containing holographic recording material directly facing the non-grating modulated surface of the master substrate. Advantageously, the inverted holographic master technique mitigates the effects of unwanted reflected exposure light.