Continuous Diffractive Optical Element via Laser-Formed Bulge Profiles
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Solution Overview
Problem
The production of diffractive optical elements (DOEs) with high diffraction efficiency is complex and limited by the stair-step height profile resulting from lithographic etching processes, which restricts diffraction efficiency to around 98% and limits the number of achievable levels.
Innovation Solution
A procedure for producing a continuous diffractive optical element by generating microstructures in a laser mirror using focused heating laser rays, which creates a majority of vaults in the dielectric layer with heights perpendicular to the dielectric layer, achieving very high diffraction efficiency comparable to quasicontinuous DOEs with over 2500 steps.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If lithographic etching process is used to produce DOEs, then manufacturing precision can be improved by increasing the number of steps, but device complexity and manufacturing effort increase significantly
Solution Approach 1:
The patent replaces the mechanical lithographic etching process with a direct laser writing process that uses photopolymerization to create the height profile. This substitution eliminates the need for repeated etching steps and associated masking processes, directly achieving continuous height profiles without the complexity of multilevel manufacturing.
Solution Approach 2:
The patent changes the manufacturing approach from subtractive etching to additive photopolymerization. By using two-photon polymerization with focused laser beams, the process directly writes the desired height profile into the polymer layer, transforming the manufacturing paradigm from mechanical removal to optical construction.
2Ease of manufacture
If multilevel DOEs with around 16 steps are produced, then manufacturing effort is reduced, but diffraction efficiency is limited to around 98%
Solution Approach 1:
The patent replaces the step-wise mechanical etching process with direct optical writing using two-photon polymerization. This allows the creation of truly continuous height profiles without discrete steps, achieving diffraction efficiencies exceeding 99% while maintaining manufacturing simplicity.
Solution Approach 2:
The patent achieves continuous height profiles through direct laser writing, eliminating the discrete step structure inherent in multilevel DOEs. The continuous modulation of the polymer layer height enables smooth phase transitions and maximizes diffraction efficiency without the limitations of stepped approximations.
3Reliability
If quasi-continuous DOEs are produced using two-photon polymerization, then diffraction efficiency exceeds 50 steps equivalence, but thermal damage threshold is too low for high-power lasers
Solution Approach 1:
The patent uses composite structures combining a substrate with a polymer layer that has been selectively modified. The substrate provides mechanical strength and thermal resistance, while the polymer layer provides the diffractive optical functionality. This composite approach allows high-power laser operation while maintaining high diffraction efficiency.
Solution Approach 2:
The patent introduces a substrate as an intermediary that mediates between the optical requirements and thermal requirements. The substrate serves as a thermally stable platform that supports the polymer layer, allowing the system to withstand high-power laser irradiation while the polymer layer maintains the precise height profile for high diffraction efficiency.
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 method enables the production of continuous DOEs with extremely high diffraction efficiency, surpassing the limitations of multilevel DOEs, and allows for finely graded height profiles, suitable for high-performance lasers.
Implementation Method 1
generating a plurality of bulges of the dielectric layer by treating the laser mirror with a series of focused heating laser beams
Implementation Method 2
the thermal material expansion of the molten modification causes the workpiece surface to curve outward into a convex surface structure
Implementation Method 3
Different optical path lengths at the DOE cause phase modulation of the laser beam, resulting in interference patterns. The intensity of the laser beam is spatially modulated through constructive and destructive superposition.
Data Source
Figure 1~2
AI summary
The invention relates to a method for producing a diffractive optical element (10) for beam shaping of a laser beam at a first wavelength (λ1) of at least 100 nm, comprising the steps of: - providing a laser mirror (12), the laser mirror (12) having a layer-like construction made of a substrate (14), a dielectric materials layer (18) and optionally an absorption layer (16), the dielectric materials layer (18) adjoining the substrate (14) or the absorption layer (16) being situated between the substrate (14) and the dielectric materials layer (18), and - generating a plurality of bulges (24) in the dielectric materials layer (18) by treating the laser mirror (12) with a series of focused heating laser beams (38) at a second wavelength (λ2), the plurality of bulges (24) having a height (32) perpendicular to the dielectric materials layer (18) and at least one bulge having a height (32) of at least half the first wavelength (λ1).