Single-Reflector SLM Illumination for Compact Head-Mounted Displays
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Solution Overview
Problem
Conventional head-mounted display devices face challenges in achieving high-resolution displays that are both compact and lightweight, leading to visible pixel spacing and limited application in wearable devices.
Innovation Solution
The use of an optical assembly configured to direct illumination light from a light source towards a spatial light modulator, such as an LCoS spatial light modulator, utilizing a compact illuminator with reflective surfaces and polarization selective elements to provide uniform illumination.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If high-resolution displays are used in head-mounted display devices, then pixel spacing becomes invisible to users, but the display size and weight increase
Solution Approach 1:
The display system is segmented into multiple functional components: a spatial light modulator (SLM) for high-resolution image generation, optical waveguides for light transport, and reflective polarizers for light control. This segmentation allows the heavy display panel to be replaced with lighter optical components while maintaining high resolution
Solution Approach 2:
An optical assembly acting as an intermediary is introduced between the light source and the SLM, including reflective polarizers and waveguide structures. This intermediary system enables compact light transport and uniform illumination without requiring a large, heavy display structure
2Manufacturing precision
If high-resolution displays are used in head-mounted display devices, then pixel spacing becomes invisible to users, but the display volume increases
Solution Approach 1:
The optical system utilizes three-dimensional light transport through waveguide structures and reflective surfaces at different angles and positions. Light is redirected through multiple dimensions (reflection angles, waveguide thickness, polarizer orientations) to achieve compact illumination geometry without increasing overall device volume
Solution Approach 2:
The optical components are nested within a compact structure where the reflective polarizer is positioned between the light source and SLM, and waveguide structures are integrated into the housing. This nesting arrangement minimizes the overall volume occupied by the illumination system
3Illumination intensity
If a compact illuminator with reflective surfaces is used, then uniform illumination is achieved, but device complexity increases
Solution Approach 1:
The reflective polarizer serves multiple functions simultaneously: it reflects light toward the SLM, controls polarization state, and contributes to uniform illumination distribution. This multi-functionality reduces the need for separate components, thereby managing device complexity while achieving uniform illumination
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 enables lightweight and compact head-mounted displays with uniform illumination, enhancing user experience in virtual and augmented reality applications.
Implementation Method 1
The first reflective surface is configured to receive illumination light from the light source and to reflect the illumination light toward the spatial light modulator
Implementation Method 2
The polarizing beam splitting system may include first and second prisms where the volume of the first prism is no greater than half the volume of the second prism
Data Source
Figure 1
Figure 2
Figure 3A
AI summary
A display device includes a light source, a spatial light modulator, and an optical element. The optical element includes a reflective surface. The optical assembly is positioned relative to the light source so that at least a portion of the illumination light received by the optical element is reflected at the reflective surface back toward the light source. The spatial light modulator is positioned to receive at least a portion of the illumination light reflected by the reflective surface. A method performed by the display device is also disclosed.