Quarter-wave retarder ghost image reduction in waveguide displays
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Solution Overview
Problem
Near-eye and heads-up display systems using optical waveguides often suffer from ghost images due to diffractively out-coupled light reflecting off the reflective microdisplay, which can limit field of view and affect industrial design when attempting to mitigate these images by tilting the waveguide.
Innovation Solution
Incorporating a quarter-wave retarder (QWR) between the polarizing beam splitter (PBS) and the input diffraction grating of the optical waveguide to convert linearly polarized light to circularly polarized light, and optionally using a linear polarizer to absorb orthogonal polarized light, preventing ghost images by directing diffracted light away from the reflective microdisplay.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If the waveguide is tilted to mitigate ghost images, then ghost image reduction is achieved, but field of view is compromised
Solution Approach 1:
The patent changes the polarization state parameter of light from linear to circular using a quarter-wave retarder. This parameter change allows the system to eliminate ghost images through polarization control rather than geometric tilting, thus preserving the waveguide's orientation and field of view while still achieving ghost image reduction
Solution Approach 2:
The quarter-wave retarder acts as an intermediary optical element between the diffraction grating and the reflective microdisplay. It mediates the light's polarization state, converting linearly polarized light to circularly polarized light, which then interacts with the reflective microdisplay and converts back to linear polarization at a different orientation, directing ghost light away from the user's eye without requiring waveguide tilting
2Object-affected harmful factors
If the waveguide is tilted to reduce ghost images, then ghost image visibility is reduced, but industrial design is affected
Solution Approach 1:
By changing the polarization parameter of light using the quarter-wave retarder, the system achieves ghost image elimination through optical property modification rather than structural reconfiguration. This maintains the waveguide's original shape and form factor while still addressing the ghost image problem
Solution Approach 2:
The patent converts the potentially harmful reflection off the reflective microdisplay into a beneficial effect. By using circularly polarized light, the reflected light becomes linearly polarized at a different orientation and is directed away from the user's eye. The harmful reflection is transformed into a controlled optical path that eliminates ghost images without requiring design compromises
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
Effectively reduces or eliminates ghost images without compromising the field of view or form factor, maintaining the optical waveguide's design constraints and enhancing image clarity.
Implementation Method 1
Incorporating a quarter-wave retarder (QWR) between the polarizing beam splitter (PBS) and the input diffraction grating of the optical waveguide to convert linearly polarized light to circularly polarized light
Implementation Method 2
The optical waveguide, which can include an input diffraction grating and an output coupler, can be configured to cause at least a portion of light corresponding to an image, that is diffracted into the waveguide by the input diffraction grating, to travel by way of total internal reflection (TIR) to the output coupler
Implementation Method 3
The input diffraction grating of the optical waveguide can be configured to diffract light corresponding to the image, that is incident on the input diffraction grating, into the optical waveguide
Implementation Method 4
The PBS of the display engine can be positioned relative to the optical waveguide to cause linearly polarized light corresponding to the image and having the first linear polarization state to be directed toward the input diffraction grating of the optical waveguide, wherein the first linear polarization state is one of the P and S linear polarization states
Data Source
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AI summary
In a near-eye or heads-up display system including a display engine and an optical waveguide, a quarter-wave retarder (QWR) is positioned between a polarizing beam splitter (PBS) of the display engine and an input diffraction grating of the waveguide. Additionally, a linear polarizer can be positioned between the PBS and the QWR. Light corresponding to an image generated by a reflective microdisplay of the display engine is diffracted into the waveguide by the input diffraction grating, so it can travel by way of total internal reflection to an output coupler and viewed by a human eye. The QWR alone, or in combination with the linear polarizer, prevents a ghost image that may otherwise occur if a portion of the light corresponding to the image, that is diffracted into the waveguide by the input diffraction grating, is diffractively out-coupled by the input diffraction grating and thereafter reflects off the reflective microdisplay.