Diffractive Optical Element Phase Modulation via Variable Resist Depth
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Solution Overview
Problem
Existing diffractive optical elements face challenges in producing continuous curved surfaces with varying phase modulation, leading to difficulties in achieving high diffraction efficiency due to limitations in fill factor and structure depth, making stable and accurate production difficult.
Innovation Solution
A phase modulation type diffractive optical element is created with microstructures having concave and convex portions smaller than the wavelength of incident light, where the ratio of convex and concave portion widths and depth are varied to achieve different phase modulation regions, using dry etching with resist patterns as masks to form structures with specific etching conditions that adjust depth based on fill factor.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If the number of steps is increased to improve diffraction efficiency, then diffraction efficiency is improved, but the number of process times increases making production difficult
Solution Approach 1:
The patent combines multiple etching steps into a single etching process by using a resist pattern with varying thickness. The resist pattern itself encodes the depth information that would otherwise require multiple separate etching steps, allowing different region depths to be formed simultaneously in one process.
Solution Approach 2:
The patent performs preliminary action by forming the resist pattern with predetermined thickness variations before the etching process. This preliminary structuring of the resist pattern defines the final microstructure depths without requiring subsequent adjustment steps, enabling direct formation of the desired phase modulation profile.
2Manufacturing precision
If the fill factor is increased to modulate refractive index, then phase modulation capability is improved, but stable production becomes difficult
Solution Approach 1:
The patent changes the parameter of resist thickness instead of relying solely on fill factor variations. By controlling the thickness of the resist pattern in different regions, the patent achieves precise control over etching depth and resulting phase modulation, providing a more stable and controllable manufacturing approach.
3Manufacturing precision
If the depth of structure is increased to implement desired phase modulation amount, then phase modulation capability is improved, but it becomes difficult to form the structure
Solution Approach 1:
The patent performs preliminary action by pre-forming the resist pattern with the exact thickness required for the final microstructure depth. This preliminary definition of depth information in the resist pattern allows the etching process to directly create the desired deep structures in a single step without requiring multiple sequential deep-etching operations.
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 method allows for the easy production of diffractive optical elements with desired phase modulation amounts by determining effective refractive index and depth for each region, enabling efficient diffraction and simplifying the production process.
Implementation Method 1
a step of forming a microstructure formed with concave and convex portions by performing dry etching using the resist patterns as a mask
Implementation Method 2
a phase modulation type diffractive optical element is used for branching a laser beam or changing the shape of a laser profile
Data Source
AI summary
A diffractive optical element having, on a surface of a transparent substrate, a plurality of types of regions which provide different phase modulation to an incident light, wherein each of the regions has a microstructure formed with concave and convex portions of which sizes are smaller than the wavelength of the incident light, and wherein in the microstructure, a ratio of the width of the convex portion and the width of the concave portion in the concave and convex portions and the depth of the concave portion are different for each type of region.