Compact LED Illuminator Using Electrically Switchable Bragg Gratings
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Solution Overview
Problem
Current LED illuminators for microdisplays face challenges such as bulkiness, high heat dissipation, short lamp lifetime, noise, and poor color saturation due to incoherent light sources and mechanical complexity, while LED-based systems struggle with large emittance angles and thermal issues, making it difficult to achieve compact and efficient illumination.
Innovation Solution
The development of a compact and efficient LED illuminator using Electrically Switchable Bragg Gratings (ESBGs) and diffractive optical elements, which are configured as a stack of separately switchable layers to diffract red, green, and blue light, allowing for a single grating to combine light from multiple sources and adjust diffraction efficiency electrically, thereby optimizing light distribution and reducing bulkiness.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If incoherent light sources (UHP lamps) are used for illumination, then high lumen output is achieved, but the system suffers from bulk, warm up time lag, high heat dissipation, power consumption, short lamp lifetime, noise, and poor color saturation
Solution Approach 1:
The patent replaces mechanical color wheel systems with electrically switchable holographic Bragg gratings (ESBGs) that use electrical fields to control light diffraction. This substitution eliminates moving parts, reduces mechanical complexity, and removes noise associated with rotating color wheels while maintaining color sequential illumination capability
Solution Approach 2:
The patent uses electrically controllable diffraction efficiency of ESBGs to dynamically adjust light distribution. By changing the electrical field strength, the diffraction efficiency can be modulated to control which wavelengths are diffracted and which pass through, enabling color sequencing without mechanical movement
2Volume of moving object
If LED sources are used to reduce bulk and heat, then compact form factor is achieved, but large emittance angles make it difficult to collect and relay light through narrow acceptance cones of microdisplay
Solution Approach 1:
The patent employs electrically switchable ESBGs that can dynamically adjust their diffraction characteristics. By controlling the electrical field, the system can optimize light routing for different LED sources and adjust the acceptance angle matching, thereby improving light collection efficiency from LEDs with large emittance angles
Solution Approach 2:
The patent uses separate ESBG layers for different wavelength ranges (red, green, blue) that can be independently controlled. This segmentation allows each layer to be optimized for specific wavelength collection and routing, improving overall light collection efficiency from multi-color LED sources
3Adaptability or versatility
If multiple LED sources are combined using traditional optical elements, then color illumination is achieved, but thermal problems occur if die are configured too closely
Solution Approach 1:
The patent arranges LED sources and ESBG layers in a three-dimensional configuration where red, green, and blue LEDs can be positioned at different spatial locations and angles. This dimensional arrangement allows thermal separation of LED die while maintaining optical integration through the volumetric ESBG structure
4Adaptability or versatility
If X-cube architectures are used for LED illumination, then color separation is achieved, but the X-cube itself loses around one third of the light from the LEDs
Solution Approach 1:
The patent uses ESBGs with electrically controllable diffraction efficiency to minimize light loss. By optimizing the electrical field strength and grating parameters, the system can achieve high diffraction efficiency for the desired wavelengths while allowing minimal loss, unlike fixed X-cube architectures that inherently lose approximately one-third of the light
Solution Approach 2:
The patent applies different ESBG layers with specific optical properties tailored to different wavelength ranges. Each layer is optimized for its specific wavelength band, achieving high local diffraction efficiency for red, green, and blue light separately, thereby minimizing overall light loss compared to universal X-cube designs
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 a compact, efficient, and flexible LED illuminator that can combine light from multiple sources with similar peak wavelengths using a single grating, providing improved light throughput and color accuracy while minimizing bulk and thermal issues, thus addressing the limitations of prior art.
Implementation Method 1
Each ESBG is operative to diffract at least one wavelength of red, green or blue light
Implementation Method 2
Electrically Switchable Bragg Gratings (ESBGs)... adjust diffraction efficiency electrically
Implementation Method 3
Diffractive optical elements (DOEs) offer a route to solving the problems of conventional optical designs
Implementation Method 4
diffractive optical elements... configured as a stack of separately switchable layers to diffract red, green, and blue light
Data Source
AI summary
There is provided a color sequential illumination device comprising in series: first and second light sources; a condenser lens; and a grating device. The grating device comprises at least one Bragg grating. The condenser lens directs light from the first and second sources into the grating device at first and second incidence angles respectively. The grating device diffracts light from the first and second sources into a common direction. Desirably, the Bragg gratings are Electrically Switchable Bragg Gratings. In one embodiment of the invention the light sources are Light Emitting Diodes. Alternatively lasers may be used.