Diffractive Optical Element With Continuous Relief Structure
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Solution Overview
Problem
Existing diffractive optical elements lack control over their Fourier spectrum, limiting their miniaturization and the quality of diffracted images, such as in computer-generated holograms, and requiring complex systems for multi-color in-coupling.
Innovation Solution
A method for producing diffractive optical elements with a continuous relief structure using a thermal scanning-probe lithography device, allowing for precise control over the Fourier spectrum by including only desired Fourier components.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If binary masks are used in serial etching to produce multilevel diffractive optical elements, then the structural complexity is reduced to manufacturable levels, but the control over the Fourier spectrum is lost
Solution Approach 1:
The patent replaces the mechanical serial etching process with multiple binary masks with a direct-write nanofabrication process using a scanning probe tip. This allows continuous modulation of the refractive index without discrete steps, achieving full Fourier spectrum control while maintaining manufacturability through direct physical writing of the continuous relief structure.
Solution Approach 2:
The invention changes the fabrication approach from discrete binary states (0 or 1) to continuous parameter modulation. By controlling the tip interaction parameters (force, speed, temperature) during scanning, the refractive index modulation can be continuously varied, enabling precise Fourier spectrum control that was impossible with binary mask methods.
2Manufacturing precision
If multiple diffractive optical elements are used for multi-color in-coupling, then the diffraction quality for each color is optimized, but the device complexity and size increase
Solution Approach 1:
The patent creates a single diffractive optical element that performs multiple functions simultaneously - it can diffract multiple wavelengths (colors) of light with optimized quality for each. The continuous relief structure acts as a universal optical component that replaces what would otherwise require multiple separate binary mask-fabricated elements, reducing system complexity while maintaining diffraction quality.
Solution Approach 2:
The invention merges the functionality of multiple wavelength-specific diffractive elements into a single continuous relief structure. By combining the diffraction control for different colors into one continuously variable refractive index profile, the system achieves multi-color functionality without requiring multiple separate components, thereby reducing overall device complexity.
3Manufacturing precision
If a continuous relief structure is fabricated with high precision, then the Fourier spectrum control is achieved, but the manufacturing difficulty increases
Solution Approach 1:
The patent replaces complex multi-step lithographic and etching processes with a direct-write scanning probe method. This mechanical writing approach simplifies manufacturing by eliminating the need for alignment of multiple masks and complex etching sequences, while directly achieving the continuous relief structure needed for Fourier spectrum control.
Solution Approach 2:
The scanning probe tip serves multiple functions in one pass: it writes the continuous relief structure, controls the refractive index modulation depth, and defines the spatial frequency profile. This self-service capability of the probe eliminates the need for separate fabrication steps for each aspect of the continuous structure, reducing manufacturing difficulty while achieving high precision.
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
Enables the production of high-quality diffractive optical elements with full control over their Fourier spectrum, facilitating miniaturization and improved hologram quality, while simplifying the production process.
Implementation Method 1
Diffractive optical elements are based on periodic or aperiodic structures, wherein the Fourier spectrum of the refractive index modulation along these structures controls how incident electromagnetic radiation is diffracted
Implementation Method 2
A method for producing diffractive optical elements with a continuous relief structure using a thermal scanning-probe lithography device
Data Source
AI summary
A method of producing a diffractive optical element (1) comprises the steps of providing at least one substrate (3) having a surface (4) and generating a relief structure (2) in the surface (4) of the substrate (3) using a processing device (5). The relief structure (2) is generated such that a distance (D) between a surface (8) of the relief structure (2) and the surface (4) of the substrate (3) along the third direction (z) varies essentially continuously. A diffractive optical element (1) comprises a relief structure (2), wherein at least in a portion of the relief structure (2) a distance (D) between the surface (8) of the relief structure (2) and the surface (4) of the substrate (3) varies essentially continuously. A virtual image display device comprises at least a first and a second of such diffractive optical elements (1).