Angle-Selective Phosphor Filter for Lower-Étendue Light Engines
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Solution Overview
Problem
Existing light engines using laser-phosphor light sources face challenges in increasing luminance due to high étendue and bulkiness of reflectors, making it difficult to achieve compact and efficient designs.
Innovation Solution
Employing a specially designed optical filter, such as a diffractive Bragg reflector, to recycle and re-emit light emitted by the phosphor at larger angles under a smaller emission angle, reducing étendue and enabling a more compact design.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If a parabolic reflector is used to recycle light and increase luminance, then the luminance of the light source is improved, but the size of the light engine increases making it less compact
Solution Approach 1:
The patent extracts the light recycling function from a bulky parabolic reflector and implements it through a thin-film optical filter deposited on the phosphor layer. This filter selectively reflects specific wavelengths back into the phosphor while allowing other wavelengths to pass through, achieving light recycling without the volume penalty of traditional reflectors.
Solution Approach 2:
The patent employs thin-film optical filters deposited directly on the phosphor layer to achieve wavelength-selective light recycling. These thin films replace the need for bulky mechanical reflectors while maintaining the light recycling function, enabling compact projector designs.
2Illumination intensity
If multiple light sources are combined to increase luminance, then the brightness is improved, but the device complexity increases
Solution Approach 1:
The patent changes the spectral parameters of the light source by using a laser-phosphor combination where a blue laser excites a yellow phosphor to generate green light. By controlling the excitation wavelength and phosphor material properties, the system achieves high luminance through spectral transformation rather than combining multiple complex light sources.
Solution Approach 2:
The patent introduces a wavelength conversion layer (phosphor) as an intermediary that converts blue laser light into green light. This intermediary approach simplifies the system compared to directly combining multiple laser sources, as the phosphor layer performs wavelength conversion through a single material component rather than requiring multiple light sources and combination optics.
3Illumination intensity
If the emission angle of phosphor light is reduced to decrease étendue, then the luminance is improved, but the light collection efficiency decreases
Solution Approach 1:
The patent applies local quality by using a wavelength-selective optical filter deposited on the phosphor layer that differentiates between wavelengths. The filter reflects green light (wavelengths around 530-560 nm) back into the phosphor to increase luminance while allowing blue excitation light (wavelengths around 440-480 nm) to pass through to the light collection optics, maintaining collection efficiency.
Solution Approach 2:
The patent segments the light spectrum into different wavelength bands and applies different optical treatments to each band. The wavelength-selective filter separates green light for recycling from blue light for collection, allowing independent optimization of luminance and collection efficiency for each spectral component.
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 enhances luminance by reducing étendue and light losses, allowing for a more efficient and compact light engine system.
Implementation Method 1
Employing a specially designed optical filter, such as a diffractive Bragg reflector, to recycle and re-emit light emitted by the phosphor at larger angles under a smaller emission angle
Implementation Method 2
Light recycling can be used when the source doesn't absorb its own radiation. Part of the light from the source is redirected towards the source itself and then reflected within the same etendue.
Implementation Method 3
a blue laser is used to excite a phosphor convertor and generate yellow light
Implementation Method 4
The light emitted by a phosphor is unpolarised therefore polarisation combination cannot be used. The laser-phosphor light source is a rather broadband source
Data Source
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AI summary
An angle selective filter for a light projection system comprising a wavelength conversion material illuminated by an excitation light source in a first wavelength range, the wavelength conversion material re-emitting light in a second wavelength range after excitation by the light in the first wavelength range, wherein the filter is configured to have a first average transmission which is high for light in the first wavelength range and for angles of incidence in the range [y 1,y 2], in a third wavelength range, the filter is configured to have a second average transmission which is high for light having an incidence angle in the range [β 1,β 2], and a third average reflectivity which is high for light having an incidence angle in the range [β 2 ,β 3 ], after reflection on the wavelength conversion material.