Lightguide Intensity Modulation for Near-Eye Display Uniformity
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Solution Overview
Problem
Near-eye displays face challenges in achieving uniform illumination across the field of view due to intrinsic non-uniformities in lightguide-based systems, leading to intensity fringes and color variations, which existing techniques have not fully addressed.
Innovation Solution
The implementation of electronic intensity modulation applied to the image data via a control unit, utilizing a characterizing intensity transfer function map to correct for non-uniformity, by generating a correction intensity map that compensates for intensity variations across the optical system's field of view, ensuring improved light uniformity at the viewer's eye pupil.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If lightguide-based optical systems are used for near-eye displays, then compact virtual image projection is achieved, but intrinsic non-uniformities cause intensity fringes and color variations across the field of view
Solution Approach 1:
The patent applies preliminary action by pre-calculating and storing a correction map that compensates for the lightguide's intrinsic non-uniformities. Before displaying the actual image, the system determines the characterizing intensity transfer function of the lightguide and applies the corresponding correction map to the image data, thereby pre-compensating for the uniformity issues that would otherwise appear in the final display.
Solution Approach 2:
The patent employs parameter changes by dynamically adjusting the intensity distribution of the input light based on the measured or simulated characterizing intensity transfer function of the lightguide. The system modifies the intensity parameters of different regions in the field of view to counteract the non-uniformities introduced by the lightguide's optical path, thereby achieving uniform output illumination.
2Illumination intensity
If existing coating techniques are applied to average brightness, then some uniformity improvement is achieved, but the complexity of the optical system increases and the solution is not fully effective
Solution Approach 1:
The patent replaces the mechanical/optical approach of using physical coatings on optical elements with an electronic/digital approach. Instead of modifying the physical lightguide with brightness-averaging coatings, the system uses computational methods to calculate correction maps and applies them to the image data, thereby substituting a complex optical modification with a simpler electronic processing step.
3Illumination intensity
If masking optical elements with spatially varying transmission profiles are used, then intensity uniformity is improved, but the device complexity and manufacturing difficulty increase
Solution Approach 1:
The patent uses copying by creating a digital correction map that replicates the compensatory function of physical masking elements. Instead of manufacturing complex masking optical elements with spatially varying transmission profiles, the system creates a digital representation (correction map) that can be easily stored, transmitted, and applied to image data, thereby avoiding the manufacturing complexities of physical masking components.
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 effectively enhances the intensity uniformity of images displayed in near-eye displays by dynamically adjusting the image data to compensate for optical system-specific intensity transfer functions, resulting in a more consistent and uniform light output across the field of view.
Implementation Method 1
light waves, indicative of a virtual image, are trapped inside a substrate by total internal reflections from the major surfaces of the substrate
Data Source
AI summary
A display device (10) for producing images to be viewed by an observer includes an optical system (14) and a control unit (20). The optical system receives input light indicative of an image into a light propagation channel (14A) and produces, at an exit pupil (14B), output light having a field of view (FOV) corresponding to the image to be presented to the observer (18). The light propagation channel has an intensity transfer function map I1(x,φ) of the optical system across a lateral dimension x of the exit pupil and an angular 20 span φ of the FOV. The control unit (20) modifies the image data which is to be input in the optical system by applying thereto intensity modulation based on a correction intensity map that at least partially compensates intensity non-uniformity in the intensity transfer function map I1(x,φ) of the optical system, such that the light output at the exit pupil of the optical system and indicative of the image, has a modulated intensity map which is observed by the viewer with improved intensity uniformity.