Diffractive Grating Phase Perturbation for Waveguide Color Alignment
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Solution Overview
Problem
Surface deformations in waveguides used in augmented reality eyewear lead to lateral color misalignment, degrading image quality due to varying thickness and non-parallel major surfaces.
Innovation Solution
Introducing a phase perturbation to the diffractive gratings of the waveguide, specifically modifying the pitch and/or angle of the gratings to offset the lateral color misalignment caused by surface deformations, and using an eye tracker for image distortion compensation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a waveguide is used to transfer light in AR eyewear, then light can be guided from the projector to the eye, but surface deformations cause lateral color misalignment that degrades image quality
Solution Approach 1:
The patent applies preliminary anti-action by introducing a phase perturbation to the diffractive grating that pre-compensates for the lateral color misalignment caused by surface deformations. The phase perturbation is designed to counteract the dispersive effect of the waveguide's thickness variations, thereby maintaining color alignment without requiring post-manufacturing adjustments or complex corrective optics.
Solution Approach 2:
The patent modifies the parameter of the diffractive grating by introducing a phase perturbation that varies along the grating structure. This parameter change allows the grating to compensate for the lateral color misalignment caused by surface deformations, effectively correcting the optical path differences for different wavelengths without changing the physical shape of the waveguide.
2Ease of manufacture
If the waveguide has varying thickness due to manufacturing, then production becomes simpler, but lateral color misalignment occurs that degrades image quality
Solution Approach 1:
The patent converts the harmful effect of surface deformations into a beneficial correction by designing the phase perturbation to match the expected deformation profile. The phase perturbation uses the same spatial frequency and orientation as the manufacturing-induced deformations, effectively turning the manufacturing imperfection into a correctable optical parameter rather than an irreversible defect.
3Device complexity
If no correction is applied for lateral color misalignment, then the device complexity remains low, but image quality degrades
Solution Approach 1:
The patent merges the correction function with the existing diffractive grating structure by superimposing the phase perturbation onto the grating's existing geometry. This integration allows the grating to serve dual purposes: its primary function of diffracting light and its secondary function of compensating for color misalignment, thereby avoiding the need for separate corrective optical elements.
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 phase perturbation effectively realigns colors, improving image quality by reducing lateral color misalignment, and the eye tracker ensures consistent image quality across different pupil positions within the eyebox.
Implementation Method 1
a phase perturbation is added to a diffractive grating such that a lateral color misalignment is offset
Implementation Method 2
Introducing a phase perturbation to the diffractive gratings of the waveguide, specifically modifying the pitch and/or angle of the gratings
Implementation Method 3
light from a projector of the wearable display device enters the waveguide of the optical combiner through an incoupler, propagates along the waveguide
Data Source
AI summary
One or more diffractive gratings of a waveguide introduce a phase perturbation to offset a lateral color misalignment due to surface deformations such as non-parallelism of the major surfaces of the waveguide. In some embodiments, a pitch and/or angle of the diffractive grating is tuned to change the k-vector of the grating in the direction of a change in total thickness variation (TTV) across the waveguide.