Waveguide Master Grating Tool Fabrication
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Solution Overview
Problem
The fabrication of waveguides with large diffraction gratings is challenging due to the difficulty in achieving high image quality, as protrusions from the master grating tool edges cause light to emerge at oblique angles, leading to secondary images, especially when using UV-curable polymers with slight refractive index differences.
Innovation Solution
A method involving the creation of single master grating tools with reduced edge protrusions by using photoresist layers and laser-derived interference patterns to etch grating profiles directly onto substrates, followed by replication and lamination with UV-curable polymers to ensure matching refractive indices and eliminate gaps, thereby minimizing light deviation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If master grating tools with thick gratings are used to enable mounting of multiple gratings, then the ability to incorporate multiple diffraction gratings is improved, but protrusions are created at the edges causing light to emerge at oblique angles and creating secondary images
Solution Approach 1:
The master grating tool is divided into multiple separate grating elements mounted on a substrate, allowing each grating to be optimized independently while maintaining the ability to incorporate multiple gratings. This segmentation enables the inclusion of multiple diffraction gratings with different profiles without requiring a single thick monolithic structure that would create protrusions.
Solution Approach 2:
The harmful protrusion edges are extracted and removed from the master grating tool design. By using thin gratings mounted on a substrate rather than a single thick grating, the protrusions that cause oblique light emergence are eliminated, while the functional capability to incorporate multiple gratings is preserved through the modular mounting approach.
2Ease of manufacture
If UV-curable polymers are used for replication with slight refractive index differences, then the ease of replication process is improved, but light deviation occurs causing secondary images
Solution Approach 1:
The refractive index parameter of the UV-curable polymer is carefully selected and controlled to match the waveguide substrate material. By adjusting this parameter to minimize refractive index differences, the patent maintains the ease of UV-curable polymer replication while preventing light deviation and secondary images.
3Area of stationary object
If large waveguides with large diffraction gratings are fabricated, then the pupil expansion capability is improved, but the manufacturing precision required for high image quality becomes more challenging
Solution Approach 1:
Large diffraction gratings are segmented into multiple smaller grating elements mounted on a substrate. This approach enables the fabrication of large effective aperture for pupil expansion while maintaining manufacturing precision, as each individual grating element can be fabricated with controlled tolerances rather than requiring a single large precision component.
Solution Approach 2:
The master grating tool with precisely fabricated gratings is used to create replicas in UV-curable polymer that are then transferred to the waveguide substrate. This copying process allows the high precision of the master grating to be replicated across large areas, enabling large waveguide apertures while maintaining manufacturing precision through the replication process.
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 approach prevents secondary images by eliminating significant protrusions and ensuring consistent refractive indices, improving the diffraction efficiency and image quality of waveguides by ensuring light propagates at the intended angles without deviation.
Implementation Method 1
applying a layer of photoresist over substantially the whole of a surface of each of the first and the second tool substrates; exposing the photoresist applied to the first tool substrate to record a first grating pattern
Implementation Method 2
replication with UV-curable polymers to ensure matching refractive indices
Implementation Method 3
Two or three different diffraction gratings may be embedded within a waveguide or provided on or close to the surface of a waveguide to couple collimated light into and out of the waveguide and to cause expansion of the pupil of light
Data Source
AI summary
There is provided a method for fabricating a waveguide master grating imprint tool. The method comprises: coating a substrate with at least one photoresist layer; selectively exposing a first diffraction grating master profile onto a first area of the at least one photoresist layer; selectively exposing a second diffraction grating master profile onto a second area of the at least one photoresist layer; and processing the substrate to form the first diffraction grating master profile and the second diffraction grating master profile. Each of the first diffraction grating profile and the second diffraction grating profile comprises an edge between the substrate and the respective grating profile that is substantially perpendicular to the substrate surface and each of the edges is substantially the same height as a maximum depth of the first diffraction grating master profile and the second diffraction grating master profile