Optical Waveguide Pulse-Width Modulation for Visible Interference
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Current optical waveguide-based exit pupil expanders using coherent light sources, such as lasers, suffer from visible interference due to the coherent nature of the light, which can result in undesirable interference patterns on displays, particularly in head-mounted display systems.
Innovation Solution
The system dynamically changes the pulse width of the coherent light source for each image frame, altering the interference patterns to make them less detectable, using an interference engine that can select and apply different pulse widths for each frame, either fixed or dynamically based on detected interference.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If coherent light sources are used in optical waveguide-based exit pupil expanders, then high sequential contrast ratios and lower weight and size are achieved, but visible interference patterns appear on the display
Solution Approach 1:
The patent applies periodic action by modulating the coherent light source with pulses at a frequency corresponding to the frame rate of the display (e.g., 120 Hz). This periodic pulsing causes the interference patterns to fluctuate rapidly over time, averaging them out to reduce visibility. The light source is turned on and off in sync with the display refresh rate, creating temporal variation that diminishes the persistence of interference patterns in the viewer's eye.
Solution Approach 2:
The patent employs dynamics by making the pulse width of the coherent light source variable rather than fixed. The pulse width is adjusted dynamically based on detected interference patterns, allowing the system to adapt to different viewing conditions and interference characteristics. This dynamic adjustment optimizes the reduction of visible interference while maintaining image quality.
2Object-affected harmful factors
If pulse width is changed to reduce visible interference, then interference patterns become less detectable, but system complexity increases due to dynamic pulse width modulation
Solution Approach 1:
The patent implements feedback by using a camera or sensor to detect interference patterns on the display, then using this detection information to adjust the pulse width of the coherent light source. The system continuously monitors the interference patterns and dynamically modifies the pulse width parameters to minimize visibility, creating a closed-loop control system that adapts to real-time conditions.
Solution Approach 2:
The patent applies parameter changes by modifying the pulse width parameter of the coherent light source to reduce visible interference. By changing this temporal parameter, the system affects the coherence properties of the light and the resulting interference patterns, making them less detectable without fundamentally changing the hardware architecture.
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 reduces the visibility of interference patterns by averaging them out over high frame rates, providing a clearer image in head-mounted display systems that utilize coherent light sources.
Implementation Method 1
The remaining light that does not exit the grating structure may reflect off of the internal surfaces of the waveguide before finally exiting through the grating structure
Implementation Method 2
travels through the waveguide in a direction, while some of the light exits a grating structure of the waveguide to a display
Implementation Method 3
Coherent light sources when split into multiple paths by the waveguide will generally interfere with themselves when received by the display if the difference in optical path length traversed by each optical path of the light is less than a coherence length associated with the coherent light source
Data Source
Figure 1
Figure 2
Figure 3
AI summary
In an optical system that includes a coherent light source and an optical waveguide, a pulse width used by the optical waveguide to project image frames on a display is changed on a frame-by-frame basis. By changing the pulse width for each image frame, the locations and characteristics of visible interference patterns on the display are changed for each successive image frame. Changing the interference patterns for each image frame may result in the interference patterns being less detectable to a viewer. The change in pulse width for each image frame may be fixed or dynamic, and may be made in response to interference patterns being detected on the display.