Laser Diode Thermal Feedback Control for Mobile Displays
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Solution Overview
Problem
Existing laser display systems face challenges with optical feedback methods, which increase circuit complexity, power consumption, and reduce viewable area due to the need for photodiodes and analog-to-digital converters, making them unsuitable for mobile and space-constrained applications like augmented reality glasses.
Innovation Solution
The use of thermal feedback to control laser diodes by measuring temperature and determining drive currents based on threshold and efficiency models, simplifying circuitry and increasing optical efficiency, allowing for reduced power consumption and enhanced brightness and dynamic range.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If optical feedback methods are used to control laser diodes, then color and brightness accuracy can be maintained, but circuit complexity increases due to photodiodes and analog-to-digital converters
Solution Approach 1:
The patent replaces the optical feedback mechanism (photodiodes and analog-to-digital converters) with a thermal feedback mechanism. By measuring temperature changes in the laser diode and using pre-characterized efficiency and threshold models, the system determines drive currents without requiring complex optical sensing circuitry. This substitution eliminates photodiodes and ADCs while maintaining color and brightness accuracy through mathematical compensation for temperature-induced variations.
2Measurement precision
If optical feedback methods are used to control laser diodes, then color and brightness accuracy can be maintained, but power consumption increases
Solution Approach 1:
The patent substitutes the power-intensive optical feedback system with a low-power thermal feedback approach. Temperature sensing consumes significantly less power than photodiode-based optical detection and analog-to-digital conversion. The system achieves color and brightness accuracy by using temperature measurements combined with pre-computed efficiency and threshold models, eliminating the need for continuous optical power measurement and ADC operation.
3Measurement precision
If optical feedback methods are used to control laser diodes, then color and brightness accuracy can be maintained, but viewable area is reduced
Solution Approach 1:
The patent extracts and removes the photodiodes and analog-to-digital converters from the display optical path. By eliminating these components that physically occupy space within the projection system, the viewable area is increased. The thermal feedback mechanism operates outside the optical path, using temperature sensors that do not interfere with the light projection area, thereby maximizing the display's viewable surface.
4Device complexity
If thermal feedback is used to control laser diodes, then circuit complexity is reduced, but temperature measurement precision is required
Solution Approach 1:
The patent implements a thermal feedback control loop where temperature measurements from the laser diode are continuously monitored and fed back to the controller. The controller uses these temperature readings to query pre-characterized efficiency and threshold models, which provide compensation factors for adjusting drive currents. This feedback mechanism ensures that even with temperature measurement variations, the system maintains color and brightness accuracy through dynamic compensation.
Solution Approach 2:
The patent performs preliminary characterization of the laser diode's efficiency and threshold parameters across a range of temperatures before operation. These pre-computed models are stored in memory and used during operation to quickly determine compensation factors. This preliminary action eliminates the need for real-time complex calculations and reduces the precision requirements for temperature sensing, as the system uses lookup-based compensation rather than real-time physical modeling.
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
Thermal feedback simplifies circuitry, reduces power consumption, and increases optical efficiency, resulting in improved brightness and dynamic range for laser displays, particularly in mobile devices like augmented reality glasses.
Implementation Method 1
a temperature sensor configured to measure a temperature of the laser diode
Implementation Method 2
a light engine including a laser diode
Implementation Method 3
generating a plurality of pulses of light from the laser diode
Implementation Method 4
measuring a plurality of optical powers for the plurality of pulses of light from the laser diode using a photodiode
Data Source
AI summary
A laser display may include a light engine, which includes a laser diode and a temperature sensor configured to measure a temperature of the laser diode. The light engine may be coupled to a controller configured to determine a drive current for the laser diode to generate an optical power based on a threshold of the laser diode and an efficiency of the laser diode. The controller is configured to calculate the threshold and the efficiency of the laser diode at the measured temperature using a threshold model and an efficiency model of the laser diode, which are generated using a calibration process.