Folded Optics With Reflective Polarizers for HMD Light Loss
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Solution Overview
Problem
Existing head-mounted displays (HMDs) face challenges in reducing the form factor of their lens systems while maintaining efficient light transmission, particularly in configurations using folded optics, which often result in significant light loss due to reflections from partial mirrors.
Innovation Solution
The use of reflective polarizers in a lens system with folded optics, where a partial reflector and waveplates are integrated with plano-convex lenses to recapture light reflected by the partial mirror, and symmetrically arranged lenses with bonded waveplates and reflective polarizers to enhance light transmission efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If folded optics are used in HMD lens systems, then the form factor is reduced, but light transmission efficiency deteriorates due to significant light loss from partial mirror reflections
Solution Approach 1:
The patent converts the harmful reflected light from the partial mirror into beneficial transmitted light by using a reflective polarizer and waveplate combination. The reflected light is captured by the reflective polarizer, redirected through the waveplate, and transmitted through the partial mirror to reach the user's eye, thereby transforming light loss into light transmission.
Solution Approach 2:
The patent changes the polarization state of light using waveplates (quarter-wave or half-wave plates) to control how light interacts with the partial mirror and reflective polarizer. By manipulating polarization parameters, the system optimizes light transmission efficiency while maintaining the compact folded optics configuration.
2Loss of energy
If reflective polarizers and waveplates are integrated into the lens system, then light transmission efficiency is improved, but device complexity increases
Solution Approach 1:
The patent merges multiple optical components (reflective polarizer, waveplates, and existing lens elements) into an integrated optical system. The reflective polarizer and waveplates are positioned within the existing folded optics architecture, combining their functions with the partial mirror to create a unified light transmission path that improves efficiency without requiring separate subsystems.
3Manufacturing precision
If symmetrically arranged lenses with bonded waveplates are used, then manufacturing precision is improved, but device complexity increases
Solution Approach 1:
While the overall lens arrangement maintains symmetry for manufacturing benefits, the patent introduces asymmetric elements (waveplates with specific fast axis orientations, reflective polarizer positioning) that break the symmetry at the component level. This controlled asymmetry enables precise control of polarization states and light paths while the symmetric macro-structure simplifies manufacturing and alignment.
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 reduces light loss to 50% theoretical loss, improving the efficiency of light transmission and minimizing the form factor of the lens system in HMDs.
Implementation Method 1
a first reflective polarizer arranged so that the first lens is between the first waveplate and the first reflective polarizer; and a second reflective polarizer arranged so that the second lens is between the second waveplate and the second reflective polarizer
Implementation Method 2
a first waveplate between the partial reflector and the first lens; a second waveplate between the partial reflector and the second lens
Data Source
AI summary
An optics system includes a first lens, a second lens, a first waveplate, a partial reflector, and a second waveplate. The partial reflector is between the first lens and the second lens. The first waveplate is between the first lens and the partial reflector. The second waveplate is between the second lens and the partial reflector. Reflective polarizers are on curved surfaces of the first lens and the second lens.