Diffractive Optical Element Waveguide for Holographic Projectors
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Solution Overview
Problem
Holographic projectors face limitations in redirecting wavefronts to specific angles for applications like head-up displays, particularly in vehicles, where the waveguide's orientation restricts the range of emitted angles, leading to the need for tilting the projector or additional optics, which increases volume or complexity, and existing solutions like prism arrays introduce dark bands and limited turning angles.
Innovation Solution
Incorporating a diffractive optical element that redirects wavefront replicas with fine control in two orthogonal directions without creating dark bands, allowing for precise control of diffraction orders and maximizing the intensity of the principal non-zero diffraction order to direct light to the eye-box without tilting the projector, using a waveguide with complementary surfaces and a diffractive optical element that redirects replicas into a common non-zero diffraction order.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a waveguide with reflective surfaces is used to emit wavefront replicas, then the holographic projector can generate multiple replicas of the wavefront, but the waveguide's orientation restricts the range of emitted angles
Solution Approach 1:
A diffractive optical element is introduced as an intermediary component between the waveguide and the target display area. This element mediates the angular redirection of wavefront replicas, enabling the system to achieve a broader range of emitted angles without requiring the entire projector to be tilted or reoriented.
Solution Approach 2:
The angular redirection function is segmented from the waveguide structure itself and assigned to a separate diffractive optical element. This segmentation allows the waveguide to maintain its replica-generating function while the diffractive element handles the angular distribution, resolving the contradiction between versatility and complexity.
2Ease of operation
If prism arrays are used to redirect wavefronts, then turning angles can be achieved, but dark bands are introduced and turning angles are limited
Solution Approach 1:
The invention changes the operational parameters of the diffractive optical element, specifically optimizing the diffraction order selection and feature dimensions to maximize light redirection efficiency. By carefully controlling the diffraction parameters, the system achieves effective wavefront redirection while minimizing light loss and avoiding the dark band artifacts associated with prism arrays.
Solution Approach 2:
The mechanical prism array system is replaced with a diffractive optical element that uses optical diffraction principles instead of geometric refraction. This substitution eliminates the inherent limitations of prism arrays, including dark bands and restricted turning angles, while maintaining the wavefront redirection capability.
3Adaptability or versatility
If additional optics are added to redirect wavefronts to specific angles, then the desired emission angles can be achieved, but the device volume and complexity increase
Solution Approach 1:
The diffractive optical element is designed to integrate closely with the waveguide structure, merging the angular redirection function with the existing replica-generating component. This integration minimizes the additional volume required while achieving precise emission angle control without requiring separate tilt mechanisms or additional optical assemblies.
4Ease of operation
If the projector is tilted to achieve desired emission angles, then the correct angles can be obtained, but the packaging and system alignment become more difficult
Solution Approach 1:
The diffractive optical element serves as an intermediary that provides angular adjustment capability without requiring mechanical tilting of the entire projector assembly. This mediator enables precise emission angle control while maintaining a fixed, easily packageable projector orientation, simplifying both manufacturing and system integration.
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
Enables effective redirection of wavefronts to the desired angle without scattering or dark bands, minimizing wasted light and eliminating the need for global tilting, thus improving the packaging and image quality in holographic projections, especially in head-up displays.
Implementation Method 1
The diffractive optical element is arranged to diffract the wavefront of each replica. For example, the diffractive optical element may comprise features having a feature size less than the wavelength of the wavefront. Each diffracted wavefront may comprise a zeroth order of diffraction (also referred to as a zero order) and one or more non-zero or 'higher' orders of diffraction.
Implementation Method 2
The waveguide comprises a pair of surfaces. The pair of surfaces are arranged to waveguide a wavefront therebetween. A first surface of the pair of surfaces is reflective-transmissive or 'transflective'. In other words, the first surface is partially reflective-partially transmissive. In this way, a plurality of replicas of the wavefront are emitted from the first surface.
Implementation Method 3
A first surface of the pair of surfaces is reflective-transmissive or 'transflective'. In other words, the first surface is partially reflective-partially transmissive. In this way, a plurality of replicas of the wavefront are emitted from the first surface.
Data Source
AI summary
A holographic projector includes a waveguide that includes a pair of opposing reflective surfaces arranged to receive and waveguide a hologram/holographic wavefront therebetween. A first surface of the pair of complementary surfaces is partially reflective-partially transmissive such that a plurality of replicas of the hologram/holographic wavefront are emitted therefrom. The holographic projector further includes a diffractive optical element arranged to receive the plurality of replicas of the hologram/holographic wavefront from the first surface of the waveguide and principally redirect each replica into a respective non-zero diffractive order defined by a diffraction angle. The holographic projector also includes an array of louvres arranged to receive the hologram/holographic wavefront from the diffractive optical element, where the array of louvres is substantially transmissive at the non-zero diffraction angle and substantially non-transmissive at a zeroth diffraction angle of the diffractive optical element.