Laser Modulation Efficiency via Variable Duty Ratio Control
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Solution Overview
Problem
Scanned beam projection systems face inefficiencies in light source modulation due to factors like wavelength, modulation frequency, threshold current, and laser diode voltage, which affect the generation of pixels and overall image quality.
Innovation Solution
The system employs a pixel drive generator that maps commanded light power values to digital drive values, controlling both the amplitude and duration of light pulses using a digital-to-analog converter (DAC) to optimize laser diode operation, ensuring high efficiency by maintaining current amplitude at peak efficiency levels and incrementally adjusting pulse duration based on commanded light power.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If the laser is modulated with fixed duty ratio as in prior art, then the modulation is simple, but the efficiency is low especially at lower optical power levels
Solution Approach 1:
The patent applies dynamics by making the duty ratio variable rather than fixed. The system dynamically adjusts the duty ratio based on the commanded light power value, allowing the laser to operate at peak efficiency across a wide range of optical power levels. This is achieved through a lookup table that maps commanded light power values to optimal duty ratios, enabling adaptive modulation that responds to changing operational requirements.
Solution Approach 2:
The patent changes the parameter of duty ratio from a fixed value to a variable parameter that depends on the commanded light power. By varying the duty ratio according to the required optical power level, the system optimizes laser efficiency for each operating condition. The lookup table stores pre-calculated optimal duty ratio values that are selected based on the current operational requirements.
2Use of energy by moving object
If the laser operates at peak efficiency current amplitude, then energy efficiency is improved, but the ability to vary light power output is limited
Solution Approach 1:
The patent uses periodic pulsed action to achieve variable light power output while maintaining peak efficiency. Instead of continuously varying the current amplitude, the system uses pulses with different duty ratios (pulse width modulation). The laser is driven at peak efficiency current amplitude in pulsed mode, and the average optical power is controlled by adjusting the pulse width, thereby maintaining high efficiency across different power levels.
Solution Approach 2:
The system dynamically adjusts the duty ratio of the pulsed current to vary the average light power output while keeping the peak current amplitude at the efficiency-optimizing value. This dynamic control of pulse width allows the laser to operate at peak efficiency for each pulse while providing continuous variation in average optical power output through changes in pulse duration.
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 significantly enhances the efficiency of light power output, particularly at lower optical power levels, by maintaining current amplitude near peak efficiency while adjusting pulse duration, resulting in improved image quality and reduced energy consumption.
Implementation Method 1
controlling both the amplitude and duration of light pulses using a digital-to-analog converter (DAC)
Data Source
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AI summary
A scanning laser projector (100) drives laser light sources with waveforms for higher efficiency. Optical light power values for pixels are mapped to amplitude/duration pairs. Laser diodes are driven with electrical currents having the amplitude for time period specified by the duration. For increasing optical light power values, amplitude values are increased, and then durations are increased.