Diffractive Beam Expander for Virtual Display Image Size
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Solution Overview
Problem
Conventional small display devices in portable devices can only show a small portion of a large image at a glance while maintaining resolution, limiting the size of the display and the ability to present large images effectively.
Innovation Solution
A diffractive beam expander is used, comprising a substantially planar waveguiding substrate with input and output gratings, and additional grating portions to deflect and restore light beams, allowing for expansion of the light beam in two dimensions, enabling a larger virtual image to be displayed without increasing the size of the device.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of stationary object
If a conventional small display is used in portable devices, then the device size remains small, but the display area and image size are limited
Solution Approach 1:
The patent applies dimensionality change by transitioning from a conventional 2D display plane to a 3D virtual image space. The waveguiding substrate with diffractive gratings redirects light to create a virtual image that extends in depth and lateral dimensions, allowing a small physical display area to present a much larger virtual image area without increasing device volume.
Solution Approach 2:
The waveguiding substrate acts as an intermediary between the microdisplay and the observer's eye. It receives light from the small microdisplay, processes it through total internal reflection and diffractive gratings, and outputs an expanded virtual image, effectively mediating the transformation from small physical display to large virtual display.
2Area of stationary object
If the display size is increased to show large images, then more image content is visible, but the device becomes larger and less portable
Solution Approach 1:
The invention creates a virtual image that exists in 3D space rather than on a 2D plane. The waveguiding substrate uses total internal reflection and diffractive gratings to project an enlarged virtual image that can be viewed at a distance, allowing large image dimensions without increasing the physical length of the device.
3Area of stationary object
If a diffractive beam expander is used to expand the light beam, then the virtual image size increases, but the waveguiding substrate requires precise manufacturing
Solution Approach 1:
The waveguiding substrate utilizes total internal reflection, a self-service phenomenon where the substrate's own refractive index difference with air creates the reflection mechanism. This eliminates the need for additional reflective coatings or complex optical components, reducing manufacturing complexity despite the need for precise grating patterns.
4Ease of manufacture
If the waveguiding substrate is made flexible to allow slight deviations, then manufacturing ease improves, but optical quality may deteriorate
Solution Approach 1:
The patent acknowledges that the waveguiding substrate can have slight deviations in flatness and uses parameter changes to compensate. By optimizing the grating patterns and their orientations, the system maintains optical quality despite variations in substrate geometry, allowing for more tolerant manufacturing processes.
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 improved parallelism and quality of the output light beam, enabling a larger virtual image to be perceived as if it is at an infinite distance, while allowing for slight deviations in the waveguiding substrate, such as being bent, to focus light at a few meters away, enhancing the display experience.
Implementation Method 1
an input grating to provide an in-coupled beam propagating within said substrate by diffracting light of an input beam into said substrate
Implementation Method 2
a substantially planar transparent waveguiding substrate... to provide an in-coupled beam propagating within said substrate
Implementation Method 3
an output grating to provide an out-coupled beam by diffracting in-coupled light out of said substrate
Implementation Method 4
four or more further grating portions to expand the height of the in-coupled beam. A part of the in-coupled light is diffracted by a first beam-deflecting grating portion to provide a first deflected beam
Implementation Method 5
The first deflected beam impinges on a first direction-restoring grating portion and the second deflected beam impinges on a second direction-restoring grating portion. The first restoring grating portion provides a first restored beam which has the same direction as the original in-coupled beam
Data Source
Figure 1
Figure 2a~2b
Figure 3a~3b
AI summary
A diffractive beam expander (50) comprises a substantially planar waveguiding substrate, an input grating (10) to provide an in-coupled beam (B1 ) propagating within said substrate, and an output grating (30) to provide an out-coupled beam. The expander (50) comprises also four or more further grating portions to expand the height of the in-coupled beam (B1 ). A part of the in-coupled light is diffracted by a first deflecting grating portion (21 a) to provide a first deflected beam. A part of the in-coupled light is diffracted by a second deflecting grating portion (22a) to provide a second deflected beam. The first deflected beam propagates downwards and the second deflected beam propagates upwards with respect to the in-coupled beam (B1 ). The first deflected beam impinges on a first direction-restoring grating portion (21 b) and the second deflected beam impinges on a second direction-restoring grating portion (22b). The first restoring grating portion (21 b) provides a first restored beam (V1 ) and the second restoring grating portion (22b) provides a second restored beam (V2), which both have the same direction as the in-coupled beam (B1 ). Out-coupling provides an output beam which is parallel to the input beam, and has a greater vertical dimension than said input beam.