Angle-Selective Filter for Compact High-Luminance Light Engines
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Solution Overview
Problem
Existing light engines using laser-phosphor sources face challenges in increasing luminance due to high etendue and bulkiness of reflectors, making it difficult to combine multiple sources for improved brightness without increasing size, especially in compact projection systems.
Innovation Solution
Employing an angle selective 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 etendue and enabling more efficient light collection.
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
Solution Approach 1:
The patent applies parameter changes by transitioning from a conventional parabolic reflector to a selectively reflective diffuser (SRD) with specific optical parameters. The SRD has wavelength-selective and angle-selective reflection properties, where it reflects excitation light (405-480nm) at certain angles while transmitting converted light (480-650nm) at other angles. This parameter-based differentiation allows the system to achieve light recycling without the bulky structure of traditional reflectors, reducing light engine size while maintaining luminance enhancement.
Solution Approach 2:
The selectively reflective diffuser represents a composite optical material that combines properties of both reflectors and diffusers. It integrates wavelength-selective reflection (acting like a dichroic filter) with angle-selective diffusion (acting like a scattering medium). This composite material approach enables the system to achieve multiple optical functions in a single compact component, eliminating the need for separate reflectors and reducing overall light engine volume while maintaining effective light recycling.
2Illumination intensity
If multiple light sources are combined to increase luminance, then the brightness of the projector is improved, but the device complexity increases
Solution Approach 1:
The patent applies self-service by designing a system where the selectively reflective diffuser automatically separates and directs different wavelength ranges without requiring external control mechanisms. The SRD inherently reflects excitation light back toward the conversion material while transmitting converted light to the output, creating a self-regulating optical path. This eliminates the need for complex control systems, switches, or additional optical components that would be required to manage multiple light sources, thereby reducing device complexity while achieving enhanced brightness through effective light recycling.
3Illumination intensity
If light is recycled by redirecting it toward the source, then the apparent luminance is increased, but light losses occur due to absorption
Solution Approach 1:
The patent minimizes light losses by implementing parameter changes in the selectively reflective diffuser's reflection characteristics. The SRD is designed to reflect excitation light (405-480nm) with high efficiency at specific angles while maintaining high transmission for converted light (480-650nm). By optimizing the reflection angle and wavelength selectivity parameters, the system redirects light that would otherwise be lost back toward the conversion material, maximizing apparent luminance while minimizing absorption losses through precise parameter 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
The solution reduces light losses, allows for a more compact design, and enhances luminance by improving the efficiency of the light source, making it suitable for compact projection systems.
Implementation Method 1
Employing an angle selective 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
The filter is configured to have, in a third wavelength range, a second average transmission which is high for light having an incidence angle in the range [β1,β2]
Implementation Method 3
a wavelength conversion material (e.g. a phosphor) in combination with an excitation light source (e.g. LED or laser)
Implementation Method 4
the wavelength conversion material re-emitting light in a second wavelength range after excitation by the light in the first wavelength range
Data Source
AI summary
An angle selective filter for a light projection system including 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. 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 [γ1,γ2], 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 [β1,β2], and a third average reflectivity which is high for light having an incidence angle in the range [β2,β3], after reflection on the wavelength conversion material.