Diffractive Optical Element With 4π Phase Profile
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Solution Overview
Problem
Conventional diffractive optical elements face challenges in efficiently generating structured light distributions with pre-specified diffractive order positions while avoiding a hot spot at the zero diffraction order, particularly in applications like 3D sensing where eye safety is a concern.
Innovation Solution
A diffractive optical element with microstructures on a surface of an optical material, featuring a phase profile that is at least partially phase unwrapped, specifically a 2πP unwrapped phase profile, to diffract input illumination into structured light with uniform intensity across diffraction orders, avoiding a strong zero diffraction order.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If a conventional diffractive optical element with a 2π phase depth is used, then the device complexity is low and manufacturing is easier, but a strong zero diffraction order hot spot is generated which poses eye safety issues
Solution Approach 1:
The patent applies parameter changes by transitioning from a conventional 2π phase depth to a 4π phase depth in the diffractive optical element. This parameter change fundamentally alters the diffraction efficiency distribution, suppressing the zeroth order while enhancing higher diffraction orders, thereby eliminating the eye safety hazard without requiring additional optical components
Solution Approach 2:
The patent inverts the conventional approach by intentionally strengthening the zeroth order diffraction through a 4π phase profile rather than trying to suppress it with additional elements. This inversion transforms the problematic zeroth order into a controlled component of the structured light pattern, eliminating the need for extra suppression mechanisms
2Object-affected harmful factors
If a double-sided DOE is used to suppress the zero diffraction order, then eye safety is improved, but the manufacturing precision and efficiency are reduced due to multiple fabrication steps
Solution Approach 1:
The patent merges the zeroth order suppression function with the primary beam splitting function into a single diffractive optical element. By integrating both functions into one component with a 4π phase profile, the need for multiple separate DOEs or additional suppression elements is eliminated, simplifying both the optical system and manufacturing process
Solution Approach 2:
The patent segments the phase profile into multiple 2π periods within the 4π total phase depth, creating a multi-periodic structure that independently controls different diffraction orders. This segmentation allows precise control over the zeroth order suppression while maintaining manufacturing feasibility through standardized fabrication techniques
3Illumination intensity
If a 4π unwrapped phase profile is used, then uniform intensity distribution across diffraction orders is achieved, but the manufacturing complexity increases
Solution Approach 1:
The patent achieves uniform intensity distribution by changing the phase depth parameter from 2π to 4π and applying an unwrapped phase profile. This parameter change ensures that all diffraction orders receive equal energy distribution, eliminating intensity non-uniformity while the phase unwrapping technique maintains manufacturability by providing a continuous, fabrication-friendly profile
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 effectively distributes illumination efficiently without a zero diffraction order hot spot, maintaining uniform intensity across diffraction orders, and operates over a broader wavelength range than conventional elements.
Implementation Method 1
A diffractive optical element can allow the projection of an image pattern by patterning of a surface relief on a substrate material... The surface relief acts on an incident illumination source by altering its wavefront phase content in such a way that the diffraction pattern observed in the far field is tailored according to a desired format
Data Source
AI summary
A diffractive optical element including microstructures, along a surface of an optical material, having a phase profile to diffract input illumination into structured light of a plurality of different diffraction orders; wherein the phase profile is at least partially phase unwrapped is disclosed. Methods of generating the diffractive optical element is also disclosed.