Optical Attenuator for Laser Beam Safety in Head-Mounted Displays
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Solution Overview
Problem
Head-mounted displays using laser beams for retinal imaging face challenges in safely reducing light energy to protect eyes, as neutral density filters can fail, allowing high-intensity laser beams to reach the retina, and maintaining stable laser oscillation and gradation levels is difficult with current laser sources.
Innovation Solution
Incorporating an optical attenuator with a refractive effect that shifts the laser beam's path to a mirror surface, ensuring safety by diverting the beam away from the eyes even if the attenuator is damaged, and using a configuration of first and second optical attenuators to counteract wavelength-dependent refractive changes and dispersion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If a neutral density filter is used to attenuate laser beam energy to protect eyes, then eye safety is improved, but the system becomes vulnerable to filter damage which could allow high-intensity laser beams to reach the retina
Solution Approach 1:
The patent introduces a beam shifting optical system as an intermediary mechanism between the laser source and the neutral density filter. This system uses a beam shifting optical member (such as a prism or wedge) to laterally displace the laser beam path, causing the beam to strike the neutral density filter at a shifted position. This intermediary beam shifting mechanism ensures that even if the filter is damaged at its original position, the displaced beam will still be properly attenuated by the undamaged portions of the filter, thereby maintaining both eye safety and system reliability
Solution Approach 2:
The patent implements preliminary action by pre-shifting the laser beam path before it reaches the neutral density filter. The beam shifting optical member is positioned upstream in the optical path to preemptively redirect the beam. This preliminary beam displacement ensures that the beam always interacts with intact portions of the filter, preventing any scenario where damaged filter areas could expose the retina to high-intensity laser beams
2Manufacturing precision
If a high-power laser source is used to ensure stable laser oscillation and sufficient gradation range, then image formation quality is improved, but the risk to eye safety increases due to higher light energy
Solution Approach 1:
The patent applies segmentation by dividing the optical path into distinct functional segments: a high-power laser source segment for generating sufficient gradation range, a beam shifting segment for path displacement, and a neutral density filter segment for energy attenuation. This segmentation allows the system to maintain high image formation quality through the high-power source while ensuring eye safety through the separate attenuation mechanism, resolving the contradiction between performance and safety
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
Prevents high-intensity laser beams from reaching the eyes by diverting the optical path when the attenuator is damaged, enhancing safety and maintaining image formation quality by equalizing optical path lengths across different wavelengths.
Implementation Method 1
an optical attenuator disposed in an optical path between the laser source unit and the light scanner, the optical attenuator being configured to attenuate a passing laser beam and shift an optical path of the passing laser beam by utilizing a refractive effect
Implementation Method 2
the optical attenuator being configured to attenuate a passing laser beam
Data Source
AI summary
An optical attenuator, when damaged, loses not only a light attenuation function but also part of an optical path shift function utilizing a refractive effect, and thus an optical path shift function in a normal state is lost. Thus, it is possible to diverts an optical path of modulate light, which is a laser beam, from a direction toward a mirror surface, that is, a direction toward the eye of an observer.