Diffractive Optical Element with Undiffracted Light Expansion
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Solution Overview
Problem
High-intensity infrared (IR) illumination required for advanced 3D sensors poses an eye-safety hazard due to the intensity of non-diffracted light, which is not effectively reduced by existing methods.
Innovation Solution
An eye-safe diffraction system is implemented by using a diffractive optical element set that aberrates diffracted light while a refractive optical element aberrates non-diffracted light, effectively canceling aberrations on diffracted light and defocusing non-diffracted light to safe levels.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If higher IR illumination power is used to achieve higher resolution and larger field of view, then the sensing performance is improved, but the intensity of non-diffracted light increases creating an eye-safety hazard
Solution Approach 1:
The patent segments the optical path into two distinct channels: a diffracted light path that maintains high intensity for 3D sensing, and a non-diffracted light path that is defocused to reduce intensity. The DOE separates these two light components spatially, allowing independent treatment of each to resolve the contradiction between sensing performance and eye safety.
Solution Approach 2:
The patent applies different optical qualities to different spatial regions: the diffracted light regions maintain sharp focus and high intensity for sensing, while the non-diffracted light region is defocused to create a larger, lower-intensity spot. This local differentiation allows the system to achieve high resolution where needed while ensuring eye safety where hazards exist.
2Object-affected harmful factors
If a second DOE is used to reduce non-diffracted light intensity by replicating the dot pattern, then the intensity power is decreased by factor N2, but the total IR illumination power is reduced counter to the need for increased power
Solution Approach 1:
The patent extracts the non-diffracted light component from the total optical path and treats it separately. By using a defocusing element specifically targeted at the non-diffracted light path, the system removes the harmful intensity without requiring multiple DOEs that would reduce total power. This extraction approach allows independent control of intensity reduction while preserving total illumination power.
Solution Approach 2:
The patent introduces a defocusing element as an intermediary component between the DOE and the target. This intermediary selectively affects only the non-diffracted light by defocusing it, while leaving the diffracted light pattern intact. This mediator approach reduces non-diffracted light intensity without the power loss associated with using multiple DOEs in series.
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 system achieves eye safety by reducing the intensity of non-diffracted light while maintaining the intensity of diffracted light, thus enabling higher IR illumination power without posing a hazard to the eye.
Implementation Method 1
a diffractive optical element set that aberrates diffracted light
Implementation Method 2
a refractive optical element aberrates non-diffracted light, effectively canceling aberrations on diffracted light and defocusing non-diffracted light to safe levels
Data Source
AI summary
Aspects of the subject disclosure are directed towards safely projecting a diffracted light pattern, such as in an infrared laser-based projection/illumination system. Non-diffracted (zero-order) light is refracted once to diffuse (defocus) the non-diffracted light to an eye safe level. Diffracted (non-zero-order) light is aberrated twice, e.g., once as part of diffraction by a diffracting optical element encoded with a Fresnel lens (which does not aberrate the non-diffracted light), and another time to cancel out the other aberration; the two aberrations may occur in either order. Various alternatives include upstream and downstream positioning of the diffracting optical element relative to a refractive optical element, and/or refraction via positive and negative lenses.