Laser Display Luminance Control via Temperature Wavelength Tuning
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Solution Overview
Problem
Display devices, particularly scanning projection types, face challenges in adjusting luminance effectively due to non-linear relationships between driving current and light output near threshold currents, limiting luminance adjustment ranges and requiring separate means to manage light amounts based on environmental brightness.
Innovation Solution
Incorporating an optical scanning device with a light source, an optical filter, and a temperature control unit that adjusts the light amount by controlling the temperature of the optical scanning device and optical filter, allowing for precise luminance adjustments based on environmental light conditions, even in devices lacking inherent luminance adjustment capabilities.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If the driving current of the light source is adjusted to control luminance, then the luminance can be controlled, but the adjustment range is narrowed due to non-linear relationship near threshold current
Solution Approach 1:
The patent changes the control parameter from driving current to temperature. By controlling the temperature of the light source, the wavelength of the output light is shifted, which in turn changes the transmittance of the optical filter, thereby achieving luminance adjustment with a wider and more linear control range compared to current adjustment near threshold current.
2Illumination intensity
If a separate means for adjusting light amount is added to scanning projection type display devices, then luminance adjustment capability is achieved, but device complexity increases
Solution Approach 1:
The temperature control unit, originally designed for stabilizing the light source operation, is made to serve dual purposes: maintaining stable operation and adjusting luminance by controlling the temperature. This eliminates the need for separate luminance adjustment mechanisms, thereby avoiding increased device complexity.
Solution Approach 2:
The patent utilizes the temperature parameter to achieve both wavelength stabilization and luminance adjustment. By changing the temperature, the system can control both the operational stability and the output luminance, combining multiple functions into a single control mechanism.
3Illumination intensity
If temperature control is used to adjust light amount, then accurate luminance adjustment is achieved, but temperature shifts may alter light source wavelength or color
Solution Approach 1:
The patent introduces an optical filter as an intermediary between the light source and the display. The filter transmits only specific wavelength bands, so even when the light source wavelength shifts due to temperature changes, the filter blocks the shifted wavelengths and only allows the desired wavelength range to pass through, thereby maintaining color accuracy while enabling luminance control.
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 solution enables accurate adjustment of light amounts directed to the display, ensuring optimal visibility of projection images across varying environmental light conditions, while minimizing power consumption and preventing excessive temperature shifts that could alter the light source's wavelength or color.
Implementation Method 1
the optical filter may be a filter of which a band characteristic has temperature dependence
Implementation Method 2
the light source may be a light source of which a wavelength of the output light has temperature dependence
Data Source
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AI summary
In a display device (1), a light amount of laser light (L) directed from an optical filter (21) to a combiner (5) is controlled through control of a temperature of a light source (13) using temperature dependence of a wavelength of the light source (13). Accordingly, even when the display device (1) is a scanning projection type in which the combiner (5) itself is incapable of luminance adjustment, it is possible to adjust the amount of light directed to the combiner (5) according to the brightness of environmental light, and to satisfactorily ensure the visibility of a projection image displayed on the combiner (5). Further, in the display device (1), since the adjustment of the light amount is performed using the temperature dependence of the wavelength of the light source (13) instead of adjusting a power supply voltage of the light source (13), it is possible to accurately adjust the light amount of the laser light (L) directed to the combiner (5).