Compact HMD Projector With NAE for Aberration Correction
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Solution Overview
Problem
Existing laser projectors for head-mounted displays suffer from optical aberrations such as spherical, chromatic, and field curvature, limiting image resolution and requiring bulky mechanical components that are difficult to implement.
Innovation Solution
A compact projector design incorporating an illumination section, a numerical aperture expander (NAE), and a relay section, with optical elements that correct for aberrations and include a scanner and focusing lenses to enhance image resolution, using illumination sources like laser diodes and micro-LEDs, and a curved NAE surface to correct field curvature.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a laser projector uses scanning mirrors and pupil imaging to maintain beam coupling into the waveguide, then the entrance pupil can be fully illuminated and coupled, but the optical system becomes bulky and difficult to implement in head-mounted displays
Solution Approach 1:
The patent segments the optical system into distinct functional modules: illumination section with laser sources, scanning section with mirrors, NAE section with micro-lens arrays, and relay section with lenses. This modular segmentation allows each component to be optimized independently and facilitates compact integration in head-mounted displays while maintaining proper beam coupling through the waveguide entrance pupil
Solution Approach 2:
The patent employs nested optical arrangements where the NAE micro-lens arrays are positioned within the optical path between the scanner and relay section, and the relay section is integrated close to the waveguide entrance pupil. This nesting approach allows multiple optical functions to be stacked in a compact configuration, reducing the overall form factor while preserving beam coupling efficiency
2Adaptability or versatility
If a laser focusing lens focuses rays over a large numerical aperture to form a large projected field of view, then the field of view is increased, but spherical aberration occurs which limits image resolution
Solution Approach 1:
The patent introduces the NAE (Numerical Aperture Expander) as an intermediary optical element between the scanning section and relay section. The NAE uses micro-lens arrays to expand the numerical aperture of the laser beam while maintaining focus quality, thereby enabling a larger field of view without introducing spherical aberration that would degrade image resolution
Solution Approach 2:
The patent changes the numerical aperture parameter through the NAE section, which expands the beam diameter and adjusts the convergence angle. By dynamically controlling the numerical aperture expansion ratio and beam parameters through the micro-lens array configuration, the system achieves a larger projected field of view while maintaining acceptable image resolution across the field
3Adaptability or versatility
If red, green, and blue laser illumination is combined into a single collimated beam, then color display is achieved, but chromatic aberrations are introduced by differing ray paths
Solution Approach 1:
The illumination section is segmented into separate laser sources for red, green, and blue wavelengths, each with its own optical path through the scanner. The NAE section uses wavelength-specific micro-lens arrays that compensate for chromatic aberrations by adjusting the focal length and beam expansion for each color channel, thereby maintaining image resolution while enabling full-color display capability
4Quantity of substance
If refractive optical elements are used to expand numerical aperture, then positive field curvature aberration occurs, but if reflecting elements are used, then negative field curvature aberration occurs, both limiting image resolution
Solution Approach 1:
The NAE employs micro-lens arrays with locally optimized lens parameters, where each micro-lens is designed with specific curvature and focal length to compensate for field curvature aberrations in its local region. This local quality approach allows the system to expand numerical aperture while correcting field curvature effects that would otherwise degrade image resolution across the projected field
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 design achieves high image resolution by correcting optical aberrations, ensuring full illumination and coupling into the waveguide, while reducing bulkiness and maintaining mechanical integrity.
Implementation Method 1
the NAE configured to receive light from the illumination section, the received light having a first average numerical aperture, and to transmit light to the relay section, the transmitted light having a second average numerical aperture which is greater than the first by an NAE average expansion ratio which is greater than unity
Implementation Method 2
the relay section including optical elements which collimate light from the image plane onto an exit pupil
Implementation Method 3
a focusing lens which converges light onto an image plane
Implementation Method 4
a scanner having one or more scanning mirrors is used to steer the laser beam over a projected field
Data Source
AI summary
A compact projector for use in a head-mounted display device consists of an illumination section, a relay section, and a numerical aperture expander (NAE). The illumination section includes one or more illumination sources, a scanner, and a focusing lens which converges light onto an image plane. The NAE receives light from the illumination section, expands the average numerical aperture of the light, and transmits the light to the relay section. The relay section includes optical elements which collimate light from the image plane onto an exit pupil. The projector may also be fitted with lateral-axis and/or vertical-axis stops which prevent stray light from passing through the exit pupil.