Spatial Light Modulator Waveguide Coupling for Compact HMDs
Solution Overview
Problem
Incorporating spatial light modulators into head-mounted display devices is challenging due to the need for high-resolution, compact, and lightweight configurations that provide uniform illumination and efficient coupling of light for high-quality image projection.
Innovation Solution
The optical device includes a spatial light modulator, one or more lenses, and a polarization-selective reflector, with a waveguide that undergoes total internal reflection, and output couplers to redirect image light, enabling compact and lightweight configurations suitable for head-mounted displays.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If spatial light modulators are incorporated into head-mounted display devices, then high brightness and high efficiency are achieved, but the device size and weight increase
Solution Approach 1:
The patent embeds the spatial light modulator within the waveguide structure, nesting multiple optical components in a compact arrangement. The SLM is positioned at a specific location within the head-mounted device where it can be integrated with the waveguide and optical elements, allowing high brightness performance while minimizing overall device volume and weight.
Solution Approach 2:
The patent utilizes waveguide optics to redirect light paths in three-dimensional space, allowing the optical engine to be compact in the dimensions constrained by the head-mounted form factor. The waveguide enables light to travel through the device volume efficiently, reducing the need for large linear optical paths and allowing high brightness performance in a compact, lightweight package.
2Illumination intensity
If spatial light modulators are incorporated into head-mounted display devices, then high brightness and high efficiency are achieved, but the device complexity increases
Solution Approach 1:
The patent combines multiple optical functions into an integrated waveguide structure. The waveguide serves as both a light transmission medium and a structural element that guides and redirects light. The in-coupler and out-coupler are integrated into the waveguide surfaces, merging coupling functions with the waveguide structure itself, thereby reducing the number of separate components and simplifying the overall optical system while maintaining high brightness performance.
Solution Approach 2:
The waveguide structure performs multiple functions: it transmits light from the SLM, provides a platform for the in-coupler and out-coupler, and redirects light to the user's eye. This multi-functionality reduces the need for additional separate components, simplifying the optical system design while achieving high brightness and efficiency.
3Productivity
If lenses are added between the spatial light modulator and waveguide, then light coupling efficiency is improved, but the device size increases
Solution Approach 1:
The lenses are positioned within the compact optical engine volume, nested among other optical components. The optical design integrates the lenses into the existing space between the SLM and waveguide, optimizing light coupling efficiency without requiring additional device volume. The lenses are strategically placed to achieve efficient coupling while maintaining a compact form factor suitable for head-mounted displays.
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
This configuration enhances the brightness and efficiency of spatial light modulators in head-mounted displays, reducing the screen door effect and providing high-quality images while maintaining a compact and lightweight design.
Implementation Method 1
redirect at least a first portion of the image light so that the first portion of the image light enters the first waveguide and undergoes total internal reflection inside the first waveguide
Implementation Method 2
a diffractive lens, and a polarization-selective reflector. The spatial light modulator defines an optical axis. The diffractive lens is positioned to receive the image light from the spatial light modulator
Implementation Method 3
The polarization-selective reflector having a polarization-selective reflective surface is positioned in an orientation that is non-perpendicular to the optical axis of the spatial light modulator
Implementation Method 4
The polarization-selective reflector is positioned to receive the image light from the diffractive lens
Data Source
AI summary
An optical device includes a first waveguide having a first side and an opposing second side, a spatial light modulator configured to project image light, one or more lenses disposed between the spatial light modulator and the first waveguide, and a first in-coupler coupler coupled with the first waveguide. The spatial light modulator is positioned on the first side of the first waveguide. The first in-coupler is positioned to receive the image light projected by the spatial light modulator and transmitted through the one or more lenses and to redirect at least a first portion of the image light so that the first portion of the image light enters the first waveguide and undergoes total internal reflection inside the first waveguide.