Optical Waveguide Coherent Light Interference Reduction
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Solution Overview
Problem
Current optical waveguides designed for coherent light sources face interference issues due to the close optical path lengths of light rays, leading to a diminished user experience, as they are optimized for incoherent light sources and result in wasted light with low-efficiency single pass grating structures.
Innovation Solution
The optical waveguide incorporates multiple optical elements to increase the relative optical path length of light, allowing a portion to exit through a first set of pupils and another portion through a second set with a greater optical path length, ensuring non-overlapping exit pupils and preventing interference, thereby enabling closer placement and improved uniformity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If multiple exit pupils are placed close together to achieve uniform display intensity, then field of view uniformity is improved, but light interference occurs due to similar optical path lengths
Solution Approach 1:
The optical waveguide divides the exit pupils into multiple sets (first set and second set) with different optical path lengths. This segmentation allows pupils to be placed closer together while maintaining uniformity, as the path length differentiation prevents interference between pupils from different sets.
Solution Approach 2:
The patent introduces optical path length as an additional dimension for differentiating exit pupils. By varying the optical path length in addition to spatial positioning, the system can place pupils closer together in space while preventing interference through path length diversity, effectively adding a dimensional degree of freedom to the pupil arrangement.
2Ease of manufacture
If single pass grating structures are used to achieve pupil uniformity, then manufacturing complexity is reduced, but light efficiency decreases due to wasted light
Solution Approach 1:
The optical waveguide implements multi-pass light propagation where light that does not exit through gratings in one pass continues to propagate and may exit in subsequent passes. This continuous useful action ensures that light is not wasted but rather utilized multiple times, significantly improving light efficiency while maintaining manufacturing simplicity.
3Illumination intensity
If coherent light sources are used to increase brightness, then illumination intensity is improved, but interference patterns diminish user experience due to overlapping optical paths
Solution Approach 1:
The patent applies local quality by assigning different optical path lengths to different sets of exit pupils. This creates local differentiation in the optical characteristics of pupils, where pupils from the first set have one path length and pupils from the second set have a different path length, preventing interference while maintaining overall system brightness.
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 solution allows for the effective use of coherent light sources in optical waveguides by preventing light interference, enhancing display intensity and uniformity, and increasing the optical path density without causing interference, thus improving the user experience.
Implementation Method 1
light from the exit pupil of the imaging system is received in the waveguide through an entrance or in-coupling, and travels through the waveguide
Implementation Method 2
some of the light exits a grating structure of the waveguide creating an expanded pupil
Data Source
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AI summary
A waveguide increases the optical path of a portion of light received from a coherent light source. The waveguide includes a first element that allows light from an exit pupil of a coherent light source to enter the waveguide, and a second element that directs some of the entered light to exit the waveguide through a first set of pupils. The waveguide includes additional elements that cause the remaining light to make an additional path through the waveguide and the second element before exiting through a second set of pupils to increase the path of the exiting light. The pupils of the first set and the second set are staggered so that light exiting a pupil does not interfere with the light exiting via the neighboring pupils.