Narrow-band reflector for diffractive waveguide display brightness
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Conventional diffractive waveguide displays suffer from reduced see-through transmittance due to mirrors used in out-coupling gratings, which affects brightness and user privacy, especially when binary gratings are employed.
Innovation Solution
Employing a narrow-band reflector, such as a dielectric multilayer reflector, to enhance see-through transmittance and brightness by matching its reflectance bands with the in-coupled wavelength peaks, while using a narrow spectral bandwidth light source like lasers or filtered LEDs, and optimizing the reflector's design for high transmittance and wavelength selectivity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If a mirror is used in the out-coupling grating to reflect light back to the user, then the brightness of the virtual image is improved and user privacy is enhanced, but the see-through transmittance of the lightguide is reduced too much
Solution Approach 1:
The reflector is designed with wavelength-selective properties, reflecting only specific wavelength bands (corresponding to projector output) while transmitting other wavelengths (ambient light). This local quality differentiation resolves the contradiction by making the reflector selectively reflective only where needed for image brightness, while maintaining transmittance for ambient light wavelengths.
Solution Approach 2:
The invention changes the optical parameters of the reflector from broad-spectrum reflection (conventional mirrors) to narrow-band reflection (wavelength-selective reflector). By changing the reflectance spectrum parameters to match the projector's output wavelengths, the system achieves high image brightness while maintaining high ambient light transmittance.
2Illumination intensity
If a conventional mirror is used to double the brightness of the virtual image, then the brightness is improved, but the coupling of projector light to the surroundings increases
Solution Approach 1:
The wavelength-selective reflector applies the local quality principle by being selectively reflective only at the projector's output wavelengths while being transparent at other wavelengths. This prevents projector light from coupling to the surroundings (since only the intended wavelength band is reflected) while still achieving brightness enhancement for the virtual image.
3Illumination intensity
If binary gratings are used as out-couplers to direct light to the user's eye, then the image brightness is improved, but the light is also out-coupled in the opposite direction towards the world side
Solution Approach 1:
The combination of binary grating and wavelength-selective reflector creates a system where the grating directs light in multiple directions but the reflector selectively reflects only the intended wavelength band back to the user. This local quality differentiation in wavelength space prevents harmful light coupling to the surroundings while maintaining image brightness.
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 achieves improved brightness and user privacy by directing image-forming wavelengths only to the user while maintaining high ambient light transmittance, reducing light coupling to the surroundings, and minimizing interference artifacts.
Implementation Method 1
the reflectance band or bands of the narrow-band reflector are set to correspond to the in-coupled wavelength peaks
Implementation Method 2
the reflector element comprises a dielectric multilayer structure, in particular one comprising a stack of alternating layers having different indices of refraction
Implementation Method 3
The out-coupling grating diffracts light out of the waveguide, reproducing the image originally displayed to the in-coupling grating
Implementation Method 4
light is directed from a projector to an in-coupling grating, which diffracts the wavelengths of the incoming light into the waveguide
Implementation Method 5
where they propagate via total internal reflections towards an out-coupling grating
Data Source
Figure 1~2
Figure 3~4
AI summary
The invention relates to a diffractive waveguide display element comprising a waveguide body (13) having a first surface and a second surface opposite to the first surface, an outcoupling-diffractive optical element on said first surface for coupling light propagating inside the waveguide body out of the waveguide body, and a narrow-band reflector element (21) on said second surface. The invention also relates to a display device comprising such element.