FOV Expansion Device for Near-Eye Displays
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Solution Overview
Problem
Compact Near-Eye Display systems face limitations in field of view (FOV) expansion due to the size constraints of the Projector of Display (POD) and tolerable distortion and chromatic aberration in the projected image.
Innovation Solution
An optical FOV expansion device that couples light from the POD into a Non-Sequential (NS) optical element, using a refractive index greater than the NS element, with a prismatic shape and vertex angles between 35-50 degrees, to significantly expand the angular FOV, and compensates for optical aberrations using spatial light modulators and narrow-band illumination sources.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If the size of the POD is reduced to meet form factor requirements, then the compactness of the NED system is improved, but the FOV size is limited
Solution Approach 1:
A non-sequential optical element is introduced as an intermediary component between the POD and the user's eye. This optical element refracts and directs light rays to expand the FOV without requiring an increase in POD size, effectively mediating between the compact projector and the desired wide field of view
Solution Approach 2:
The optical element utilizes changes in refractive index parameters to bend and redirect light paths. By strategically positioning high-index material regions within the optical element, the system expands the angular FOV while maintaining a compact POD form factor
2Area of moving object
If the FOV is expanded using a larger POD, then the projected image angular size is improved, but the distortion and chromatic aberration increase beyond tolerable limits
Solution Approach 1:
The optical element incorporates regions with different refractive indices positioned at specific locations to address local optical quality issues. High-index material is strategically placed to correct distortion and chromatic aberration in critical areas of the light path while maintaining FOV expansion
Solution Approach 2:
The optical element is constructed as a composite structure combining materials with different refractive indices. This composite approach enables simultaneous achievement of FOV expansion and optical quality maintenance by using material properties to counteract distortion and chromatic aberration effects
3Area of moving object
If a non-sequential optical element is used to expand FOV, then the angular FOV is improved, but the optical distortion and chromatic aberration are introduced
Solution Approach 1:
The optical element converts the potentially harmful effects of refraction-induced distortion and chromatic aberration into beneficial FOV expansion. By carefully designing the refractive index distribution, the system transforms what would normally be optical defects into the mechanism for achieving wide-angle viewing
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 FOV expansion ratio of up to 1.6, allowing for a compact form-factor while improving user experience by expanding the projected image format without significant distortion or chromatic aberration.
Implementation Method 1
A refractive index of the device is greater than that of the NS optical element. Furthermore, a FOV expansion ratio of the device, defined as a ratio between the projected angular aperture and the incident angular aperture, is greater than or equal to a pre-determined threshold value.
Data Source
AI summary
A field of view (FOV) expansion device for use in a near-eye display includes a first surface which receives incident illumination from a projector of departure of the near-eye display. The incident illumination, which may consist of a multiplicity of incident illumination fields is characterized by an incident angular aperture. The expansion device is adjacent to a non-sequential (NS) optical element which projects output light to an observer. The refractive index of the device is greater than that of the NS optical element. A FOV expansion ratio, which is equal to the ratio between a projected angular aperture of the output light and an incident angular aperture of the incident illumination, is greater than or equal to a pre-determined threshold value. The first surface of the FOV expansion device is transparent in one embodiment and reflective in another.