Folded Optical Arrangement for HMDs with Collimating Element
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Solution Overview
Problem
Existing folded optical arrangements for head-mounted displays (HMDs) face issues such as light loss, increased size, and residual aberrations, which affect image quality and user experience.
Innovation Solution
A folded optical arrangement comprising a collimating element with a first optically powered surface and a second optically powered surface, arranged to define a plurality of interfaces along the folded optical path, with a refractive index change at each interface to control light direction, and a pupil expanding element using a waveguide to expand the exit pupil.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If traditional lens trains or folded optical designs are used, then image relay function is achieved, but the device size and weight increase
Solution Approach 1:
The patent combines multiple optical functions (collimation, folding, field of view control) into a single integrated optical element with multiple surfaces, each providing specific optical power. This merging eliminates the need for separate lens trains and reduces overall device weight while maintaining image relay functionality.
Solution Approach 2:
The optical element is designed to perform multiple functions simultaneously: collimating light from the display, folding the optical path to reduce device size, and controlling the field of view. This multi-functionality allows a single element to replace what would traditionally require multiple separate components.
2Volume of moving object
If beamsplitter and spherical combiner are used in folded optical design, then compact size is achieved, but light loss increases and image brightness decreases
Solution Approach 1:
The patent extracts the beamsplitter and spherical combiner from the optical design, replacing them with a single optical element that achieves compact folding without the light loss associated with partial reflection. This extraction eliminates the fundamental cause of brightness reduction while maintaining the compact form factor.
Solution Approach 2:
The patent introduces an optical waveguide as an intermediary element that enables compact optical folding through total internal reflection, avoiding the need for beamsplitters. The waveguide mediates between the display and the user's eye, providing a compact path while maintaining high light transmission efficiency.
3Adaptability or versatility
If beamsplitter and spherical combiner are made semi-transparent to allow external view, then environmental visibility is improved, but light loss from image source increases
Solution Approach 1:
The optical waveguide acts as an intermediary that separates the image light path from the external view path. Image light is coupled into the waveguide and transmitted to the user's eye with high efficiency, while external light passes through the waveguide surface to the user's eye. This mediation allows both functions to coexist without significant light loss from the image source.
4Device complexity
If light passes twice through the beamsplitter, then optical path folding is achieved, but light loss increases and ghost images are introduced
Solution Approach 1:
The patent removes the beamsplitter from the optical path, eliminating the multiple passes through the same element. The optical waveguide provides the necessary path folding through total internal reflection at its boundaries, ensuring light passes through each optical interface only once and maintaining high transmission efficiency without ghost image formation.
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
The solution achieves a compact, lightweight optical design with improved image quality by minimizing light loss and residual aberrations, while allowing the user to view the external environment without distortion.
Implementation Method 1
a refractive index change at each interface is predetermined to control the direction of light passing through the or each interface
Implementation Method 2
a collimating element configured to receive light forming the image from an image source, and to collimate and output the light
Implementation Method 3
a pupil expanding element using a waveguide to expand the exit pupil
Data Source
AI summary
An optical arrangement to transmit an image from an image plane to a user's eye. The arrangement providing a folded optical transmission path comprising a collimating element, having a first optical element with a first plurality of optically powered surfaces; and a second optical element comprising at least one optically powered surface. The collimating element to receive light forming the image from an image source and collimate and output the light. The optically powered surfaces having a plurality of interfaces along the folded optical path. A refractive index change at each interface is predetermined to control the direction of light passing through each interface. One surface of each of the first and the second optical elements being adjacent to one another. The adjacent surfaces having dissimilar shapes and each defining an angle with a respective other surface of the relevant optical element at opposing ends of the adjacent surfaces.