Angle-Dependent Reflective Film for Ghost Light Suppression in Virtual Image Displays
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Solution Overview
Problem
Existing virtual image display devices face challenges in providing high-quality see-through observation due to ghost light issues, limited display size, and complex optical systems that require time-difference image display and misaligned optical modes.
Innovation Solution
A virtual image display device incorporating a light guiding member with a reflective film that has angle-dependent reflectance, preventing ghost light by increasing reflectance at larger angles of incidence, and a light transmitting member for see-through, allowing external light observation while maintaining image quality.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a light guiding optical system with emission opening smaller than pupil size is used to realize see-through, then the device structure is simplified, but the display size of virtual image cannot be made large and the effective pupil diameter is limited
Solution Approach 1:
The patent transitions from a two-dimensional light guiding plate to a three-dimensional light guiding optical system with multiple optical surfaces. The light guiding portion has a first optical surface for light incidence, a second optical surface for light emission, and a third optical surface as a half mirror, creating a volumetric structure that increases display size while maintaining see-through capability.
Solution Approach 2:
The optical system is divided into distinct functional segments: a light guiding portion with specific reflective surfaces, a light transmitting member with see-through portion, and a reflective film with angle dependency. This segmentation allows each component to be optimized independently for its specific function while working together to achieve both large display size and see-through observation.
2Volume of moving object
If a light guiding optical system smaller than pupil size is used, then the device is compact, but the effective pupil diameter cannot be made large to correspond to individual pupil width
Solution Approach 1:
The patent creates a three-dimensional light guiding structure that extends beyond the two-dimensional plane of the pupil. The light guiding portion with its multiple optical surfaces and the light transmitting member with see-through portion create a volumetric optical path that accommodates larger effective pupil diameter while keeping the overall device compact.
3Volume of moving object
If emission opening or casing is physically disposed in the vicinity of the pupil, then the light guiding structure is compact, but a blind spot is generated and perfect see-through is not achieved
Solution Approach 1:
The patent introduces a light transmitting member with see-through portion as an intermediary component between the light guiding portion and the observer's eye. This intermediary allows light to pass through to the pupil while the reflective film prevents ghost light, achieving perfect see-through without blocking the optical path with the emission opening or casing.
4Adaptability or versatility
If a see-through prism is connected to the light guiding member, then the optical system is complete, but ghost light is generated due to this member and easily reaches the eye
Solution Approach 1:
The patent converts the potential harm of ghost light into a beneficial solution by using a reflective film with angle dependency. The film is positioned to specifically reflect ghost light at certain angles while allowing useful light to pass through, thus converting the harmful ghost light effect into a controlled optical function that improves image quality.
Solution Approach 2:
The reflective film is applied selectively to specific regions where ghost light is generated, rather than covering the entire optical system. This local application targets the specific problem areas while maintaining transparency in regions where useful light transmission is needed, achieving ghost light suppression without compromising overall see-through quality.
5Adaptability or versatility
If liquid crystal panel displays center and left-right images with time difference for multi-optical modes, then multiple optical modes are supported, but the device becomes complex and observed image becomes dark
Solution Approach 1:
The patent merges multiple optical modes into a single simultaneous display architecture. Instead of sequentially displaying different optical modes with time differences, the light guiding optical system with its multiple optical surfaces and the light transmitting member with see-through portion enable multiple optical modes to coexist and be observed simultaneously, simplifying the display system and improving 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 enables high-quality virtual image display with reduced ghost light and increased display size, allowing for clear see-through observation without the need for complex time-difference image display and misaligned optical modes.
Implementation Method 1
a reflective film having a light transmitting property and an angle dependency in which when an angle of incidence becomes larger than the angle of incidence range of the image light, reflectance increases is provided between the light emission portion and the light transmitting member
Data Source
AI summary
A half mirror layer has an angle dependency in which when an angle of incidence becomes larger than the angle of incidence range of image light, reflectance increases, such that it is possible to prevent unintended light, which is emitted to a light transmitting member from a light guiding member and is reflected inside a light transmitting member, from being returned to a Eight emission portion of the light guiding member after passing through the half mirror layer as a reflective film at a relatively large angle of incidence. Therefore, it is possible to prevent the image light passed through the light transmitting member from becoming ghost light while mitigating the demand for increasing processing accuracy of the light transmitting member, and bonding accuracy between the light guiding member and the light transmitting member, to provide a high quality virtual image displayed by a virtual image display device.