Off-Axis Optical Assembly for Holographic Zero-Order Light Removal
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Solution Overview
Problem
Spatial light modulators in holographic displays generate unwanted zero-order light beams due to light falling on non-addressable areas or phase errors, which are difficult to remove and can cause harsh edges and safety hazards.
Innovation Solution
An optical assembly with a light-modulation element, focusing system, light remover, and terminal optical element that focuses zero-order light in a different plane from the replay image, using off-axis illumination to separate and remove the zero-order light before it reaches the viewer.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a spatial light modulator is used to generate a holographic replay image, then a three-dimensional image can be created, but an unwanted zero-order light beam is generated that is difficult to remove
Solution Approach 1:
The patent segments the light paths by separating the zero-order light beam from the holographic replay image through spatial and temporal differentiation. The zero-order light is directed to a first detector while the replay image is directed to a second detector, allowing independent processing and removal of the harmful zero-order component while preserving the useful holographic image.
Solution Approach 2:
The patent extracts and removes the zero-order light beam from the optical path using a light modulator that selectively blocks or redirects the zero-order light while allowing the holographic replay image to pass through. This extraction process eliminates the harmful factor without compromising the holographic display functionality.
2Object-generated harmful factors
If zero-order light is removed using a light modulator, then the harmful zero-order light can be blocked, but the light modulator may introduce additional phase errors and dead space
Solution Approach 1:
The patent introduces an intermediary optical element (light modulator or beam splitter) that mediates between the zero-order light and the holographic replay image. This intermediary component selectively interacts with the zero-order light to remove or redirect it, while having minimal impact on the phase accuracy of the holographic image through proper optical design and alignment.
3Productivity
If parallel light is used to illuminate the light-modulation element, then the replay image is formed, but the zero-order light focuses in the same plane causing harsh edges
Solution Approach 1:
The patent applies local quality by creating different focal planes for different light components. The zero-order light is focused in a first plane while the holographic replay image is focused in a second plane, allowing selective removal of the zero-order light at its focal plane without affecting the replay image quality, thereby eliminating harsh edges.
Solution Approach 2:
The patent resolves the harsh edges problem by moving the zero-order light removal to a different dimensional plane (focal plane) than the replay image formation plane. By focusing the zero-order light in a first plane and the replay image in a second plane, the system can remove the harmful zero-order light without compromising the image quality in the replay plane.
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
Prevents harsh edges and reduces the impact of conjugate images, ensuring viewer safety by converging zero-order light before it reaches the retina, improving image quality and safety.
Implementation Method 1
The use of spatial light modulators in such displays to control the phase of light to reproduce a 3-dimensional image has also been considered
Implementation Method 2
a focusing system arranged after the light-modulation element and configured to focus modulated light from the light-modulation element and the zero-order light beam
Implementation Method 3
a light remover positioned after the focusing system configured to remove the zero-order light beam from the light focused by the focusing system
Data Source
AI summary
An optical assembly is provided for use in holographic display of a replay image. The optical assembly may be of particular use is an augmented reality headset. The optical assembly includes a light-modulation element arranged to be illuminated off-axis by a light beam. The light-modulation element modulates the incident light to generate a replay image and generates a zero-order light beam. A focusing system is arranged after the light-modulation element. A light remover is positioned after the focussing system and is configured to remove the zero-order light beam from the light focussed by the focussing system. The focussing system is configured to focus zero-order light from the light-modulation element in a first plane different from a second plane which is the plane of focus of parallel light of the replay image. The light remover removes the zero-order light in the first plane.