Narrowband Projector Light Coupling into Waveguides with Feedback
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Solution Overview
Problem
Existing display systems face inefficiencies in coupling light into waveguides due to etendue limitations and double-bounce losses, leading to reduced brightness and display sharpness, particularly in wearable head-up displays (WHUDs).
Innovation Solution
Implementing a feedback loop with a light engine, MEMS controller, and photo-sensor to adjust pulse duration, phase, and frequency based on angular coupling efficiency, ensuring light is coupled only at high-efficiency incident angles and resonant modes, thereby optimizing light transmission into waveguides.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If collimated projector light is coupled into the waveguide combiner using a diffractive, holographic, or prism-based coupler, then the light can be transmitted to the user's eye, but etendue limits the coupling efficiency leading to reduced brightness
Solution Approach 1:
The patent employs a tunable laser light source that can dynamically adjust its emission angle and wavelength. By dynamically tuning the laser parameters to match the waveguide's resonant modes, the system achieves high coupling efficiency without being constrained by etendue limitations of static optical couplers.
Solution Approach 2:
The system changes the physical parameters of the light source (angle and wavelength) to optimize coupling into the waveguide. The tunable laser can adjust its emission characteristics to precisely match the acceptance conditions of the waveguide, thereby maximizing coupling efficiency and brightness.
2Productivity
If the waveguide acts as a beam combiner to combine multiple wavelengths of laser light, then images can be displayed, but double-bounce losses occur reducing display sharpness and efficiency
Solution Approach 1:
The patent extracts or eliminates the problematic double-bounce mechanism by using a different coupling approach. Instead of relying on multiple internal reflections within the waveguide, the system uses direct resonant coupling at the waveguide interface, thereby removing the source of double-bounce losses and improving display efficiency.
Solution Approach 2:
The system uses a single wavelength laser that is tuned to match the waveguide's resonant mode, effectively creating an optimal copy or match between the light source characteristics and the waveguide's transmission characteristics. This precise matching eliminates mismatches that lead to losses.
3Illumination intensity
If a feedback loop with MEMS controller and photo-sensor is implemented to adjust pulse parameters, then coupling efficiency and brightness are enhanced, but device complexity increases
Solution Approach 1:
The patent implements a feedback control system where a photo-sensor detects the actual light output and provides feedback to the MEMS controller, which adjusts the laser pulse parameters accordingly. This closed-loop feedback mechanism automatically optimizes coupling efficiency and brightness without requiring complex manual calibration or adjustment mechanisms.
Solution Approach 2:
The feedback system enables the device to self-adjust and self-optimize its performance. The system automatically monitors its own output and makes real-time adjustments to maintain optimal coupling conditions, eliminating the need for external intervention or complex preset configurations.
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
Enhances coupling efficiency and display brightness by maximizing light input at high-efficiency angles, reducing power consumption, and improving display sharpness in WHUDs.
Implementation Method 1
coupling efficiency and display brightness by maximizing light input at high-efficiency angles
Implementation Method 2
Each beam of laser light generated by the laser projector is temporally modulated to provide a pattern of laser light
Implementation Method 3
a conventional laser projector includes at least one scan mirror that scans (or reflects) the laser light emitted from the laser light sources in at least one direction
Implementation Method 4
a user views the images on a transparent surface configured to display, for example, augmented reality (AR) content
Data Source
AI summary
A system includes a feedback loop that includes a light engine to generate light, a light engine controller to control operation of the light engine, a scanning device to scan a light beam across a range of scan angles to an incoupler of a waveguide, a photo-sensor to measure an amount of light outcoupled through the incoupler of the waveguide at the range of incident angles. The light engine controller adjusts one or more of a pulse duration, a phase, or a pulse frequency of the scanned light, based on an incident angle of the scanned light and the measured amount of light.