DMD Micromirrors for Pupil Expansion via Intermediate Tilt Angles
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Solution Overview
Problem
Designing optical systems for displays, such as virtual and augmented reality headsets, is challenging due to the need for components that are not only aesthetically pleasing and compact but also efficient in terms of power consumption and optical performance.
Innovation Solution
The use of a head-mounted device with near-eye displays that incorporate a display module and a waveguide, featuring a digital-micromirror device (DMD) panel with micromirrors that rotate between tilt angles, allowing for pupil expansion by emitting pulses of illumination light at intermediate tilt angles, which omits the need for a cross-coupler, thereby maximizing throughput and brightness.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of moving object
If traditional pupil expansion components such as cross-couplers are used in the waveguide, then the pupil size can be expanded, but the number of diffractions increases which reduces throughput and brightness
Solution Approach 1:
The patent removes the cross-coupler component from the waveguide system entirely. Instead of using traditional pupil expansion components, the invention extracts only the necessary pupil expansion function and implements it through the micromirror device's intermediate tilt angles, thereby eliminating unnecessary diffractions and maximizing light throughput and brightness
Solution Approach 2:
The patent introduces intermediate tilt angles as an intermediary mechanism between the ON and OFF states of the micromirrors. These intermediate angles serve as a mediator that enables pupil expansion through temporal multiplexing without requiring additional optical components like cross-couplers, thus avoiding extra diffractions and energy loss
2Device complexity
If the micromirror device uses only ON and OFF states, then the control is simple, but the pupil expansion capability is limited
Solution Approach 1:
The patent applies dynamics by introducing temporal variation to the micromirror states. Instead of static ON/OFF control, the system dynamically transitions through intermediate tilt angles during the frame period. This temporal dynamics enables pupil expansion while maintaining relatively simple control architecture, as the intermediate states are achieved through controlled transition rather than additional control mechanisms
Solution Approach 2:
The patent utilizes periodic action by cycling the micromirrors through ON and OFF states at the frame rate, with intermediate tilt angles occurring during the transition periods. This periodic switching, synchronized with the light source pulsing, creates the temporal multiplexing effect that expands the effective pupil size while maintaining simple binary control logic
3Area of moving object
If the device includes more components for pupil expansion, then the pupil size increases, but the device becomes bulkier and less compact
Solution Approach 1:
The patent makes the micromirror device multi-functional by having it perform both the primary display function (ON/OFF states) and the pupil expansion function (intermediate tilt angles) simultaneously. This universality eliminates the need for separate pupil expansion components, thereby maintaining device compactness while achieving effective pupil expansion through the same micromirror array
Solution Approach 2:
The patent merges the pupil expansion function with the existing micromirror device structure. By combining the temporal multiplexing capability with the spatial modulation function, the system achieves pupil expansion without adding separate optical components, thus maintaining a compact device form factor while expanding the effective pupil area
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 approach enables expanded pupils of image light and virtual objects in different focal planes at the eye box, enhancing display performance while minimizing diffractions and maintaining compactness.
Implementation Method 1
The micromirror may reflect the pulses of illumination light as offset pupils of image light
Implementation Method 2
An input coupler may couple the image light into the waveguide. An output coupler may couple the image light out of the waveguide
Data Source
AI summary
A display having a reflective display panel may provide image light to an eye box. The panel may include mirrors rotatable between first and second angles. The mirrors may take a non-zero time period to transition between the first and second angles. During the non-zero time period, the light source may emit pulses of illumination. The mirrors may reflect the pulses of illumination as offset pupils of image light. The mirrors may be at respective intermediate angles while reflecting each of the pulses of illumination. The mirrors may toggle between the first and second angles at a sufficiently fast rate such that the offset pupils form an effective pupil that is expanded in at least one dimension. If desired, the offset pupils may be used to display virtual objects in different focal planes at the eye box.