Reflective Diffraction Grating UV-Absorbing Layer
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Solution Overview
Problem
Conventional reflective diffraction gratings face challenges such as instability at high temperatures and complex, costly manufacturing processes, along with issues like interference patterns due to light reflection during holographic patterning.
Innovation Solution
A reflective diffraction grating design featuring a UV-absorbing layer to minimize substrate reflection, a binary surface-relief grating layer with rectangular or trapezoidal ridges, and a conforming reflective layer, fabricated using holographic lithography, which includes a method of depositing a UV-absorbing layer, patterning a photoresist layer, and etching the grating layer to form a stable and efficient diffraction grating profile.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If metal-coated diffraction gratings are produced by replication using a resin grating layer, then manufacturing is simplified, but the grating becomes unstable at high temperatures and requires careful temperature control during manufacturing
Solution Approach 1:
The patent changes the material parameters by replacing the temperature-sensitive resin grating layer with a temperature-stable dielectric grating layer formed by direct etching. This allows the grating to withstand high temperatures (e.g., during wafer bonding processes) while maintaining the replicated manufacturing approach for the metallic diffraction grating structure.
Solution Approach 2:
The patent uses a composite structure combining a stable dielectric grating layer (e.g., silicon dioxide) with a metallic reflective layer. The dielectric layer provides thermal stability while the metallic layer provides the necessary optical diffraction properties, resolving the contradiction between ease of manufacture and thermal reliability.
2Reliability
If multilayer dielectric gratings are produced by direct etching, then thermal stability is improved, but manufacturing becomes difficult and expensive due to large number of process steps
Solution Approach 1:
The patent segments the manufacturing process into two distinct parts: (1) forming the stable dielectric grating layer structure through direct etching, and (2) replicating the metallic diffraction grating pattern onto this stable substrate. This segmentation allows each part to be optimized independently, reducing overall manufacturing complexity while maintaining thermal stability.
Solution Approach 2:
The patent performs preliminary action by first forming the thermally stable dielectric grating layer structure before applying the metallic reflective layer. This preliminary stabilization of the substrate eliminates the need for complex temperature control during subsequent manufacturing steps, simplifying the overall process.
3Ease of manufacture
If holographic patterning is used to pattern the etch mask, then manufacturing is simplified, but light reflection by the substrate creates undesired interference patterns detrimental to the surface-relief pattern
Solution Approach 1:
The patent introduces an intermediary absorbing layer between the substrate and the photoresist layer. This layer absorbs excess light and prevents unwanted reflections from the substrate that would create interference patterns, thereby improving pattern quality while maintaining the simplicity of holographic patterning.
Solution Approach 2:
The patent converts the harmful effect of light reflection by the substrate into a beneficial outcome. By deliberately adding an absorbing layer, the reflected light is converted into absorbed energy, preventing interference patterns and improving the quality of the holographically patterned surface relief structure.
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 results in a stable and efficient diffraction grating with reduced interference patterns and lower manufacturing costs, capable of high diffraction efficiency across various wavelength ranges, suitable for applications like wavelength-selective switches.
Implementation Method 1
an ultraviolet (UV)-absorbing layer disposed over the substrate for absorbing light at a UV recording wavelength to minimize reflection thereof by the substrate
Implementation Method 2
patterning the photoresist layer by holography at the UV recording wavelength
Implementation Method 3
etching the grating layer through the patterned photoresist layer to form a binary surface-relief pattern therein
Implementation Method 4
depositing a conforming reflective layer over the binary surface-relief pattern to form a grating profile
Data Source
AI summary
A reflective diffraction grating and a fabrication method are provided. The reflective diffraction grating includes a substrate, a UV-absorbing layer, a grating layer having a binary surface-relief pattern formed therein, and a conforming reflective layer. Advantageously, the UV-absorbing layer absorbs light at a UV recording wavelength to minimize reflection thereof by the substrate during holographic patterning at the UV recording wavelength.