Micron Diffractive Layers for Low Zero-Order TOF Projection
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Solution Overview
Problem
Current surface light source projection devices for time-of-flight ranging sensing face limitations due to heat accumulation issues with polymer diffuser or diffractive sheets, especially under short-wavelength laser irradiation, leading to degradation and safety hazards, and struggle with maintaining light intensity and directivity for long-range sensing.
Innovation Solution
A surface light source projection device with a diffractive optical element module featuring two micron diffraction layers with microstructures having specific dimensions and recesses, formed by dry etching on a transparent crystal or glass substrate, which reduces zero-order diffraction intensity and maintains light intensity and directivity for long-range sensing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If polymer material embossing is used for diffusing or diffracting light, then light diffusion capability is improved, but heat accumulation occurs and material structure deteriorates under short-wavelength laser irradiation
Solution Approach 1:
The patent changes the material parameter from polymer to glass, and changes the structural parameter by introducing recesses with specific depth-to-diameter ratios (0.3-0.7) in the microstructures. These parameter changes enable the diffractive element to withstand short-wavelength laser irradiation while maintaining light diffusion capability, resolving the contradiction between light diffusion performance and material stability under laser heating.
2Use of energy by moving object
If diffractive element is used to project light spots, then light utilization efficiency is improved, but zero-order light spot brightness becomes too high affecting depth calculation accuracy
Solution Approach 1:
The patent applies local quality by introducing recesses specifically in the regions corresponding to the zero-order diffraction maxima. This localized structural modification selectively reduces the intensity of the problematic zero-order spots while preserving the diffraction efficiency for other light spots, thereby maintaining light utilization efficiency while improving depth calculation accuracy.
Solution Approach 2:
The patent converts the harmful effect of high zero-order spot brightness into a beneficial feature by using the recess structures to deliberately reduce zero-order diffraction intensity. This transforms the originally problematic high brightness into a controlled, reduced intensity that no longer interferes with depth measurement, while the same structural features maintain overall high diffraction efficiency.
3Length of moving object
If collimated light system is used for time-of-flight sensing, then projection distance is improved, but device thickness increases making it unsuitable for mobile devices
Solution Approach 1:
The patent extracts and eliminates the collimating lens from the optical system by using a surface light source that inherently emits divergent light suitable for direct diffraction. This removal of the collimating lens component significantly reduces device thickness while maintaining effective projection distance through the diffractive element, making the system suitable for mobile devices.
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 solution provides a stable and effective beam diffuser that withstands high-energy laser irradiation, enabling long-term and long-range sensing with uniform light intensity and high density dot matrix patterns, suitable for special environments and resistant to photo-degradation.
Implementation Method 1
the diffractive optical element module outputting a diffracted light from the light exit surface after the light beam has passed through the diffractive optical element module
Data Source
AI summary
The present invention provides a surface light source projection device with improved zero-order diffraction, which includes a light exit module and a diffractive optical module. Wherein, the diffractive optical module has two micron diffractive layers, the micron diffractive layers include a plurality of microstructures, and the microstructures are provided with a first recess, and the first recess has a first depth and a first outer diameter. The outer diameter of the microstructures is between 5 times and 200 times the incident wavelength of the narrow half-wave width, and the first outer diameter of the first recess is between 0.3 and 0.7 times the outer diameter. As such, a surface light source projection device that can generate a diffraction pattern with uniform spot intensity and can illuminate for a long time is provided.