Dual Diffractive Optical Elements for Zero Order Reduction
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Solution Overview
Problem
Existing optical pattern projection methods using diffractive optical elements suffer from uncontrolled zero-order energy issues, leading to poor uniformity and potential safety concerns, particularly in applications requiring high contrast and efficient energy distribution.
Innovation Solution
The use of a dual diffractive optical element configuration, where the second diffractive optical element receives and redirects the zero-order beam to form a secondary diffraction pattern, significantly reducing uncontrolled energy and enhancing the uniformity of the overall intensity distribution by distributing diffraction effects between the two elements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If a diffractive optical element is used to project patterns, then projection efficiency is improved, but uniformity of intensity distribution deteriorates due to uncontrolled zero order energy
Solution Approach 1:
The patent divides the diffraction process into two separate stages using two distinct diffractive optical elements. The first DOE performs the primary diffraction to generate the pattern, while the second DOE specifically addresses the zero order beam. This segmentation allows each element to be optimized for its specific function, resolving the contradiction between maintaining high projection efficiency and achieving uniform intensity distribution.
Solution Approach 2:
The second diffractive optical element acts as an intermediary component that processes the zero order beam produced by the first DOE. This intermediary element redirects and redistributes the uncontrolled zero order energy, converting it into useful diffracted orders that contribute to the overall pattern. This mediator approach maintains high projection efficiency while improving uniformity by eliminating the harmful concentrated zero order energy.
2Illumination intensity
If a diffractive optical element is used to project patterns, then high contrast is achieved, but uncontrolled zero order energy creates safety concerns
Solution Approach 1:
The patent converts the harmful zero order energy into a beneficial component of the diffraction pattern. The second diffractive optical element takes the concentrated zero order beam (which would normally be a safety hazard) and diffracts it into multiple lower-intensity beams that contribute to the overall pattern. This transforms the harmful concentrated energy flux into useful, distributed energy that maintains contrast while eliminating safety concerns.
3Device complexity
If a single diffractive optical element is used, then device complexity is reduced, but uniformity of intensity distribution deteriorates
Solution Approach 1:
The patent segments the diffraction function across two separate optical elements, with each element having a specific optimized role. The first DOE generates the primary pattern with high contrast, while the second DOE specifically processes the zero order beam to improve uniformity. This segmentation, while increasing component count, provides the functional specialization needed to achieve uniform intensity distribution without compromising the other performance parameters.
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 approach effectively reduces the peak-to-average power ratio of diffracted beamlets, minimizing uncontrolled energy and achieving a more uniform intensity distribution across the projected area, thereby improving the efficiency and safety of optical pattern projection.
Implementation Method 1
Patterns may be projected using diffractive optical elements (DOEs). However, the DOEs may suffer from the so-called zero order problem. A zero order beam is the portion of the incident beam that is not diffracted by the projection setup and thus continues through the system onto the projection volume.
Data Source
Figure 1A~1B
Figure 2
Figure 3A~3B
AI summary
Apparatus (10) for projecting a pattern includes a first diffractive optical element (DOE) (12) configured to diffract an input beam (20) so as to generate a first diffraction pattern (23) on a first region (22) of a surface (24), the first diffraction pattern including a zero order beam (32). A second DOE (14) is configured to diffract the zero order beam so as to generate a second diffraction pattern (29) on a second region (27) of the surface such that the first and the second regions together at least partially cover the surface.