Polarization Volume Hologram Optics for Compact HMD Eye Tracking
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Solution Overview
Problem
Conventional Head-Mounted Displays (HMDs), particularly smart glasses, face challenges in integrating eye tracking components due to their small size, making it difficult to achieve effective eye tracking and gaze direction determination for improved display quality and user experience.
Innovation Solution
An optical system utilizing polarization volume hologram (PVH) layers with liquid crystal molecules spatially oriented to reflect infrared light for eye tracking, enabling compact design and accurate gaze direction determination through manipulation of LC molecule alignments for optical functions such as deflection and lensing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If conventional eye tracking components are integrated into HMD, then eye tracking function is achieved, but device size increases making it difficult for smart glasses form factor
Solution Approach 1:
The patent combines the eye tracking optical path with the existing display optical path by integrating a polarization beam splitter and wave plates into the existing PVH structure. This merging of functions allows eye tracking capability to be added without requiring separate dedicated eye tracking optical components, thereby minimizing volume increase
Solution Approach 2:
The PVH layer serves dual purposes: it functions as both the display waveguide grating for projecting images and as the optical element for reflecting infrared light to enable eye tracking. This multi-functionality eliminates the need for separate eye tracking optical components, resolving the volume contradiction
2Measurement precision
If PVH layers with liquid crystal molecules are used for infrared reflection, then accurate gaze direction determination is achieved, but manufacturing precision requirements increase
Solution Approach 1:
The liquid crystal molecules self-align through their inherent anisotropic properties and respond to applied voltages to control infrared reflection. This self-aligning capability reduces the need for extremely precise manual alignment during manufacturing, as the LC molecules can be oriented through field control rather than requiring sub-micron mechanical precision
Solution Approach 2:
The patent controls the optical properties of the PVH layer by changing parameters such as voltage applied to the liquid crystal, temperature, and molecular orientation angles. By dynamically adjusting these parameters, the system achieves precise gaze direction determination while allowing for manufacturing tolerances in the static structure
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 PVH layers allow for precise eye tracking and enhanced user experience by accurately determining gaze direction and psychological state, facilitating improved display quality and content delivery based on user activity, while maintaining a compact HMD form factor.
Implementation Method 1
a first PVH layer... a first image... reflected by the first PVH layer... a wavelength corresponding to a first Bragg period of a first Bragg grating formed by liquid crystal (LC) molecules in the first PVH layer
Implementation Method 2
polarization volume hologram (PVH) layer... polarized light reflected by the first PVH layer... liquid crystal (LC) molecules spatially orientated to enable at least one optical function
Implementation Method 3
liquid crystal molecules spatially orientated to enable at least one optical function of the PVH layer, such as, e.g., deflection and lensing
Data Source
Figure 1A~1B
Figure 1C~1D
Figure 2A
AI summary
An optical system includes a substrate and a polarization volume hologram (PVH) composite film formed over the substrate. The PVH composite film includes a first PVH layer formed over the substrate and having a helix twist of a first handedness, and a second PVH layer coupled to the first PVH layer and having a helix twist of a second handedness orthogonal to the first handedness. The first PVH layer is configured to reflect and converge circularly polarized light having the first handedness. The second PVH layer is configured to reflect and converge circularly polarized light having the second handedness.