Compact Waveguide Coupling via Polarizing Beam Splitter
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing optical systems for virtual and augmented reality displays face challenges in efficiently coupling an image from a projector into a waveguide, leading to incomplete filling of the waveguide and non-uniform illumination.
Innovation Solution
The optical system employs a light-guide optical element (LOE) with a coupling prism and a reflective polarizing beam splitter, where the projector is oriented to inject illumination at angles greater than the critical angle for internal reflection, and a waveplate is used to convert polarization, ensuring efficient coupling and uniform illumination.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If a conventional coupling prism is used to couple image illumination from a projector into a light-guide optical element, then the waveguide can be filled with the image, but the system becomes bulky and the projector aperture must be large
Solution Approach 1:
The patent introduces a beam splitter dimension that separates the coupling path for incoming light from the propagation path for guided light. By adding this dimensional separation with the beam splitter at a 45-degree angle, the system achieves efficient coupling in a compact configuration without requiring a large projector aperture or bulky coupling prism
2Productivity
If the projector is oriented to inject illumination at angles greater than the critical angle for internal reflection, then coupling efficiency is improved, but the chief ray does not propagate parallel to the waveguide surface
Solution Approach 1:
The beam splitter acts as an intermediary element that receives light at a 45-degree angle from the projector and redirects it horizontally into the waveguide. This intermediary component enables the chief ray to enter the waveguide parallel to the surface while maintaining efficient coupling angles, resolving the contradiction between coupling efficiency and propagation direction
3Shape
If a beam splitter is introduced to redirect the chief ray parallel to the waveguide surface, then the light path is corrected, but the system complexity increases
Solution Approach 1:
The beam splitter is designed to perform multiple functions simultaneously: it redirects the chief ray parallel to the waveguide surface, maintains efficient coupling angles for internal reflection, and works with the polarization optics to manage light polarization states. This multi-functionality reduces overall system complexity despite adding a component
4Illumination intensity
If polarization optics are added to manage light polarization states, then illumination uniformity is improved, but the device complexity increases
Solution Approach 1:
The patent uses waveplates to change the polarization parameter of the light to achieve uniform illumination. By carefully selecting the waveplate orientation and type (quarter-wave or half-wave), the system converts polarized light from the projector into states that ensure uniform coupling into the waveguide, improving illumination uniformity through parameter control rather than adding complex mechanical systems
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 configuration allows for compact and efficient coupling of the projector image into the waveguide, achieving uniform illumination and reducing energy loss, while also enabling the use of a generic projector design with a smaller aperture.
Implementation Method 1
a light-guide optical element (LOE) formed from transparent material and having mutually-parallel first and second major external surfaces for guiding light by internal reflection
Implementation Method 2
a reflective polarizing beam splitter deployed at an interface between the major external surface and the coupling prism parallel to the major external surfaces, at least part of the illumination being incident on the beam splitter with a first polarization and being transmitted by the beam splitter
Implementation Method 3
a waveplate deployed in a path of at least part of the illumination to convert the illumination between the first polarization and the second polarization
Data Source
AI summary
An optical system includes a light-guide optical element (LOE) (10) having mutually-parallel first and second major external surfaces (11, 12) for guiding light by internal reflection, and a projector (100) that projects illumination corresponding to a collimated image from an aperture (101). The projector injects light in to the LOE via a coupling prism (30) attached to the first major external surface (11) that projects an image injection surface. A reflective polarizing beam splitter (51) is deployed at an interface between the major external surface (11) and the coupling prism (30) parallel to the major external surfaces, to selectively transmit illumination from the coupling prism into the LOE while trapping light already within the LOE so as to propagate within the LOE by internal reflection.