Laser Diode Luminance Compensation via Feedback Control
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Solution Overview
Problem
Laser projection systems using laser diodes face variations in luminance due to aging and temperature changes, leading to non-uniform greyscale displays and color balance issues, as the output luminance of laser diodes changes over time and with ambient temperature variations.
Innovation Solution
A laser projection apparatus with a feedback loop and mapping component that adjusts the drive current to maintain a linear system characteristic by using a calibration pulse to measure and compensate for changes in laser diode characteristics, ensuring consistent luminance across different operating conditions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If laser diode drive current is increased to maintain luminance output, then luminance consistency is improved, but temperature variations and self-heating effects worsen
Solution Approach 1:
The patent implements a feedback control system using a photodetector to monitor the actual luminance output of the laser diode. The system compares the measured luminance with the target luminance and dynamically adjusts the drive current to compensate for temperature variations and aging effects, thereby maintaining consistent luminance output without causing excessive temperature increases
Solution Approach 2:
The system dynamically adjusts the drive current based on real-time temperature measurements and luminance feedback. By making the drive current adaptive rather than fixed, the system can maintain optimal luminance consistency across varying temperature conditions while preventing thermal runaway through continuous monitoring and adjustment
2Productivity
If laser diode operates continuously to maintain display output, then productivity is improved, but luminance uniformity deteriorates due to aging and temperature changes
Solution Approach 1:
The system continuously monitors luminance output through a photodetector and adjusts the drive current in real-time to compensate for aging and temperature drift, enabling continuous operation while maintaining luminance uniformity across the display
Solution Approach 2:
The system performs preliminary characterization of the laser diode's luminance-current relationship at different temperatures and stores this data in lookup tables. During operation, the system pre-adjusts drive current based on measured temperature and stored calibration data, preventing luminance non-uniformity before it occurs during continuous display output
3Reliability
If temperature compensation is implemented to maintain luminance, then luminance consistency is improved, but device complexity increases
Solution Approach 1:
The system uses a simple photodetector-based feedback loop that directly measures luminance output and adjusts drive current through a controlled current source. This feedback mechanism provides temperature compensation and aging compensation without requiring complex multi-parameter sensing or control algorithms
Solution Approach 2:
The system compensates for temperature and aging effects by dynamically changing the drive current parameter based on measured luminance feedback and temperature readings. By focusing compensation efforts on the primary control parameter (drive current) rather than attempting to control multiple parameters simultaneously, the system achieves luminance consistency with minimal added complexity
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 effectively maintains consistent luminance and color balance by continuously adjusting the drive current, thereby stabilizing the output luminance and reducing variations caused by aging and temperature changes, resulting in improved image quality and color accuracy.
Implementation Method 1
Laser diodes emit light when current is passed through the diode. The output luminance of the laser diode varies as the drive current through the diode is varied.
Implementation Method 2
A photodetector measures an output luminance of the laser diode and generates a feedback signal
Data Source
Figure 1
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Figure 4
AI summary
The luminance of a laser diode (110) is a function of laser diode drive current. The luminance is also a function of other factors, such as age and temperature. A laser projection device (100) includes laser diodes to generate light in response to a commanded luminance, and also includes photodiodes (120) to provide a measured luminance. The commanded luminance and measured luminance are compared, and drive currents for the laser diodes are adjusted to compensate for changes in laser diode characteristics.