Waveguide Combiner Staircase Gratings for Diffraction Efficiency
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Solution Overview
Problem
Existing waveguide combiners face challenges in achieving improved diffraction efficiency for overlaying virtual images on ambient environments in augmented reality systems.
Innovation Solution
A method of forming waveguide combiners with staircase and binary structures using a litho-etch process cycle, where staircase structures are formed in the incoupler and binary structures are formed in the outcoupler and exit-pupil-expander, enhancing diffraction efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If surface gratings are used to couple light into and out of waveguide combiners, then light coupling function is achieved, but diffraction efficiency is insufficient
Solution Approach 1:
The waveguide combiner is divided into multiple functional zones with different grating structures: staircase gratings in the incoupler region for high diffraction efficiency, and binary gratings in the outcoupler and exit-pupil-expander regions. This segmentation allows each region to be optimized for its specific function while maintaining overall manufacturability through a unified fabrication process.
Solution Approach 2:
Different grating structures are implemented in different locations of the waveguide combiner substrate. The incoupler region features staircase gratings with specific geometric profiles optimized for light coupling efficiency, while the outcoupler and exit-pupil-expander regions use binary gratings. This local differentiation optimizes performance for each functional region without requiring complete redesign of the entire device.
2Loss of energy
If varied structures are formed on the same substrate to improve diffraction efficiency, then optical performance is enhanced, but process complexity increases
Solution Approach 1:
Multiple grating structures (staircase and binary) are combined into a single waveguide combiner device on one substrate. The fabrication process integrates the formation of both grating types through a unified litho-etch sequence, where photoresist patterns define both staircase and binary grating regions simultaneously. This merging approach achieves varied optical structures while maintaining process efficiency.
Solution Approach 2:
The patent utilizes the lateral dimension of the substrate to differentiate between various grating structures. By positioning staircase gratings in specific lateral zones (incoupler regions) and binary gratings in other zones (outcoupler and exit-pupil-expander regions), the design achieves structural variety without adding vertical complexity or requiring multiple fabrication steps.
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 method increases diffraction efficiency by allowing for varied structures on the same substrate, improving the performance of augmented reality devices.
Implementation Method 1
depositing a photoresist layer stack including a plurality of photoresist sublayers over the hardmask layer stack, etching the hardmask layer stack to produce a plurality of hardmask segments
Implementation Method 2
etching the hardmask layer stack to produce a plurality of hardmask segments, etching the device layer to produce a staircase structure
Implementation Method 3
trimming a sublayer of the photoresist layer stack, the sublayer being an optical planarizing layer (OPL) horizontally, etching the device layer to produce at least one step the at least one step forming a staircase structure
Implementation Method 4
Light is coupled into and out of augmented waveguide combiners using surface gratings. Accordingly, what is needed in the art are waveguide combiners with improved diffraction efficiency.
Data Source
AI summary
Embodiments of the present disclosure generally relate to methods of forming waveguide combiners for augmented, virtual, and mixed reality. More specifically, embodiments described herein provide methods for forming waveguide combiners with staircase structures and binary structures. The method includes depositing a device layer comprising a plurality of device sublayers over a substrate, depositing a hardmask layer stack comprising a plurality of hardmask stack sublayers over the device layer, depositing a photoresist layer stack including a plurality of photoresist sublayers over the hardmask layer stack, etching the hardmask layer stack to produce a plurality of hardmask segments, depositing the photoresist layer stack comprising a second plurality of photoresist segments over the hardmask layer stack, the photoresist layer stack comprising the plurality of photoresist sublayers, and etching the device layer to produce a staircase structure.