Interference Filter Recovers Leaked Light in Image Light Guide
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Solution Overview
Problem
Head-mounted near-eye displays using image light guides suffer from forward-leaking light, which compromises security and efficiency by allowing others to see the virtual images and reducing brightness, as the leaked light is not utilized to form images within the wearer's eyes.
Innovation Solution
Incorporating a narrow spectrum interference filter that reflects forward-leaking light back into the image light guide, increasing the brightness and efficiency of virtual images while mitigating its effects on real-world images by using an absorber layer to counteract color distortion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a transparent waveguide is used to convey virtual images, then the wearer can simultaneously view the real world through the aperture, but light leaks out of the front of the waveguide compromising security and efficiency
Solution Approach 1:
The patent converts the harmful forward-leaking light into a beneficial resource by using an interference filter to reflect the leaked light back into the waveguide. This recovered light is then redirected to the wearer's eye, transforming the security and efficiency problem into a performance enhancement opportunity.
Solution Approach 2:
The interference filter acts as an intermediary element between the waveguide and the external environment. It selectively reflects image-bearing light back into the system while allowing real-world light to pass through, mediating between the conflicting requirements of image delivery and real-world viewing.
2Device complexity
If forward-leaking light is allowed to exit the waveguide, then the system structure remains simple, but the virtual image brightness decreases due to light loss
Solution Approach 1:
The interference filter converts the previously wasted leaked light into useful image-bearing light by reflecting it back into the waveguide. This increases the amount of light reaching the wearer's eye without requiring a more complex light generation system.
Solution Approach 2:
The patent changes the optical parameters of the waveguide system by introducing an interference filter with specific spectral characteristics. The filter's reflectance and transmittance properties are optimized to recover image light while maintaining real-world viewing capability, thereby improving brightness without proportionally increasing complexity.
3Loss of energy
If an interference filter is added to reflect leaked light, then light efficiency increases, but the filter may distort real-world image colors
Solution Approach 1:
The interference filter is designed with local quality characteristics, having different optical properties for different wavelengths and directions. It selectively reflects image-bearing wavelengths while transmitting real-world viewing wavelengths, and is positioned at a specific location within the optical system to achieve directional selectivity.
Solution Approach 2:
The patent carefully selects and optimizes the spectral parameters of the interference filter, including its center wavelength, bandwidth, and angular dependence. By adjusting these parameters, the system recovers maximum image light while minimizing color distortion in the real-world view, balancing efficiency and visual fidelity.
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 the brightness and security of virtual images by redirecting leaked light back into the system, improving the overall efficiency of image formation and maintaining the perception of real-world colors by adjusting the spectral transmittance curves of the interference filter and absorber layer.
Implementation Method 1
an interference filter configured to reflect at least a sub-portion of the second portion of the image-bearing light beams and direct the sub-portion of the second portion of the image-bearing light beams towards the eyebox
Implementation Method 2
an out-coupling diffractive optic operable to direct at least a first portion of the image-bearing light beams from the image light guide toward an eyebox and direct a second portion of the image-bearing light beams from the image light guide away from the eyebox
Implementation Method 3
an in-coupling diffractive optic operable to couple image-bearing light beams into the image light guide
Data Source
AI summary
An image light guide system including an image light guide having a first surface and a second surface opposite the first surface, an in-coupling diffractive optic operable to couple image-bearing light beams into the image light guide, an out-coupling diffractive optic operable to direct at least a first portion of the image-bearing light beams from the image light guide toward an eyebox and direct a second portion of the image-bearing light beams from the image light guide away from the eyebox, and an interference filter configured to reflect at least a sub-portion of the second portion of the image-bearing light beams and direct the sub-portion of the second portion of the image-bearing light beams towards the eyebox.