Laser Light Source Temperature Compensation Using Polynomial Approximation
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Solution Overview
Problem
Existing head-up display systems using laser light sources face challenges in maintaining consistent optical output due to temperature variations, leading to reduced laser light utilization efficiency and deteriorated image luminance, as they require scanning outside the image display region to detect output characteristics.
Innovation Solution
A light source device comprising a laser light source, temperature sensor, and laser control unit that approximates threshold current and slope efficiency using quartic and quadratic expressions to control the laser light source, eliminating the need for scanning outside the image display region, and an image display device with additional laser light sources using linear expressions for different wavelengths to maintain optical output stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If laser light scans the screen in a region outside the image display region to detect output characteristics, then the laser light source output variation due to temperature change can be restrained, but the laser light utilization efficiency deteriorates and image luminance decreases
Solution Approach 1:
The patent applies preliminary action by pre-storing the relationship between temperature and laser light source characteristics (threshold current, slope efficiency, wavelength) in a lookup table or memory. Before actual image display, the system detects temperature and retrieves the corresponding characteristics, allowing immediate compensation without needing to scan outside the display region during operation. This eliminates the time loss and efficiency deterioration while maintaining output stability.
Solution Approach 2:
The patent replaces the mechanical scanning method (physically moving laser light outside the display region to detect characteristics) with an electronic/information-based approach. By storing characteristic data in memory and using temperature sensing combined with data retrieval and calculation, the system substitutes physical scanning with information processing, thereby eliminating the trade-off between detection accuracy and display efficiency.
2Measurement precision
If the screen has a detection light emitting region and a display region sufficiently apart from each other, then laser light does not affect the display region during detection, but image display time is shortened and image luminance deteriorates
Solution Approach 1:
The system performs detection and characterization of laser light source properties in advance (preliminarily) by storing the relationships in memory. During actual image display, no additional scanning or detection time is needed - the system simply retrieves pre-stored data based on current temperature. This eliminates the time loss while maintaining detection precision through the use of pre-acquired accurate characteristic data.
Solution Approach 2:
The patent creates a copy of the laser light source characteristics data (threshold current, slope efficiency, wavelength vs. temperature relationships) and stores it in memory. Instead of performing real-time detection during display, the system uses this copied data combined with current temperature measurement to determine characteristics. This copying approach allows instantaneous retrieval without occupying display time.
3Measurement precision
If the laser light source is driven with two or more values of current larger than threshold current, then the photodetector can detect emission intensity at each current value, but the device complexity and control complexity increase
Solution Approach 1:
The patent applies preliminary action by pre-measuring and storing the relationships between current values, temperature, and laser characteristics in a lookup table or memory during the manufacturing or calibration phase. During operation, the system only needs to detect temperature and retrieve the corresponding pre-stored characteristics, eliminating the need for complex real-time multi-current scanning and photodetector measurements. This significantly reduces control system complexity while maintaining measurement precision.
Solution Approach 2:
Instead of using multiple current values and photodetector measurements to determine characteristics in real-time, the patent inverts the approach: it pre-determines the characteristics at various temperatures and current values, stores them in memory, and then simply retrieves the appropriate data during operation. This inversion from real-time measurement to pre-measurement-and-retrieval simplifies the control system dramatically.
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 configuration effectively restrains optical output variation due to temperature changes without deteriorating laser light utilization efficiency, enabling smooth adjustment of display image parameters like luminance and white balance.
Implementation Method 1
a temperature sensor that detects temperature around the laser light source
Implementation Method 2
a laser light source that emits laser light having a wavelength in a range from 635 nm to 645 nm inclusive
Data Source
AI summary
The disclosure provides a light source device and an image display device. The light source device includes a laser light source configured to emit laser light having a wavelength in a range from 635 nm to 645 nm inclusive, a temperature sensor configured to detect temperature around the light source device, and a laser control circuit configured to control the laser light source. The laser control circuit approximates, with use of a quartic expression, change in threshold current of the laser light source relative to temperature, and approximates, with use of a quadratic expression, change in slope efficiency of the laser light source relative to temperature, to obtain threshold current and slope efficiency of the laser light source corresponding to detection temperature of the temperature sensor, and controls the laser light source in accordance with the threshold current and the slope efficiency thus obtained.