Scanned Beam Intensity Modulation for Laser Projectors
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Solution Overview
Problem
Scanned beam projection systems face challenges in maintaining consistent pixel width and light intensity due to varying beam velocity across the scan region, leading to dimensional errors and image artifacts.
Innovation Solution
The system adjusts the duty cycle and amplitude of laser drive signals based on beam position, using a digital-to-analog converter (DAC) with a fixed frequency clock, and employs a pixel drive generator to select the closest DAC clock period and modify drive amplitude, ensuring monotonic input code to light intensity output relationships, and compensates for laser variations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a fixed frequency DAC clock is used to generate output pixel drive signals, then the system operates with simple timing control, but the pixel width varies across the scan region due to changing beam velocity
Solution Approach 1:
The system dynamically adjusts the number of DAC clock periods allocated to each output spatial pixel based on the instantaneous beam velocity at that position. When beam velocity is high (center of scan), fewer DAC periods are assigned; when velocity is low (edges of scan), more DAC periods are assigned. This dynamic allocation compensates for velocity variations and maintains consistent pixel width across the scan region.
Solution Approach 2:
The system changes the temporal parameter (number of DAC clock periods) allocated to each spatial pixel based on position-dependent beam velocity. By varying the duration of light output for each spatial pixel according to the beam's instantaneous velocity, the system maintains uniform pixel dimensions despite the sinusoidal scanning motion.
2Speed
If the beam velocity varies across the scan region, then the scanning mirror covers the full scan area, but the number of DAC clock periods per pixel changes causing dimensional errors
Solution Approach 1:
The system implements dynamic pixel timing allocation where the number of DAC clock periods assigned to each spatial pixel is adjusted in real-time based on the beam velocity at that position. This dynamic compensation ensures that pixels at high-velocity regions (scan center) and low-velocity regions (scan edges) all achieve the same dimensional accuracy.
3Device complexity
If fixed amplitude light output is used for each spatial pixel, then the modulation is simple, but the light intensity is inconsistent due to varying dwell time at different scan positions
Solution Approach 1:
The system changes the temporal parameter (duration of light output in DAC clock periods) for each spatial pixel based on position-dependent beam velocity. By allocating more DAC periods to pixels at low-velocity regions and fewer periods to pixels at high-velocity regions, the system ensures that each spatial pixel receives consistent light intensity despite varying dwell times.
Data Source
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AI summary
A scanning laser projector (100) includes a scanning mirror (162) that moves in a sinusoidal motion on at least one axis. Pixels are displayed by modulating a laser beam that is reflected by the scanning mirror. Pixels are generated using light pulses of different duty cycles based on the position and/or angular velocity of the laser beam.