Thin Film TIR Diffraction Grating for High Efficiency
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Solution Overview
Problem
Existing reflective diffraction gratings suffer from significant insertion loss due to the use of metallic materials like gold, which have less than 100% reflectance, and require a large number of dielectric thin film layers to achieve high diffraction efficiency, making them expensive and complex to manufacture, while also experiencing roll-off in efficiency as wavelength deviates from the design wavelength and allowing propagation of transmitted orders that cause additional insertion loss.
Innovation Solution
The implementation of thin film dielectric reflective diffraction gratings using a small number of reflective dielectric thin film layers, incorporating an etch stop layer to prevent substrate etching, a marker layer to indicate etch end-point, and an encapsulation layer for protection, which operate based on total internal reflection (TIR) to achieve high diffraction efficiency without propagation of transmitted orders.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If metallic materials like gold are used for reflective diffraction gratings, then the grating structure is simple to manufacture, but insertion loss increases due to less than 100% reflectance
Solution Approach 1:
The patent changes the material parameter from metallic (gold) to dielectric materials, and changes the operating principle from metallic reflection to total internal reflection (TIR). This parameter change enables near-100% reflectance while maintaining manufacturing simplicity through direct writing or lithography of the dielectric layer with refractive index greater than 1.45.
Solution Approach 2:
The patent uses composite material structure consisting of a dielectric layer with refractive index greater than 1.45 formed on a substrate. This composite structure (dielectric layer + substrate) enables TIR-based diffraction with high efficiency, replacing the single metallic material approach.
2Loss of energy
If a large number of dielectric thin film layers are used to achieve high diffraction efficiency, then diffraction efficiency improves, but manufacturing complexity and cost increase
Solution Approach 1:
The patent extracts the essential function of high diffraction efficiency from the complex multi-layer dielectric structure and achieves it through a single dielectric layer with refractive index greater than 1.45 operating on TIR principle. This eliminates the need for numerous thin film layers while maintaining high diffraction efficiency.
Solution Approach 2:
The patent changes the key parameter from the number of layers to the refractive index value (greater than 1.45). This parameter change allows achieving high diffraction efficiency with a single layer instead of multiple layers, significantly reducing manufacturing complexity.
3Loss of energy
If conventional reflective diffraction gratings are used, then the grating structure is established, but roll-off in efficiency occurs as wavelength deviates from the design wavelength
Solution Approach 1:
The patent changes the operating principle parameter from metallic reflection to total internal reflection (TIR). TIR maintains near-100% efficiency across a broader wavelength range without the roll-off effect seen in metallic gratings, as TIR efficiency is not dependent on material reflectance which varies with wavelength.
4Ease of manufacture
If conventional diffraction gratings allow propagation of transmitted orders, then the grating structure is complete, but additional insertion loss occurs
Solution Approach 1:
The patent inverts the approach by using TIR instead of transmission or metallic reflection. By forming the dielectric layer with refractive index greater than 1.45 on the substrate and operating at appropriate incident angles, the grating achieves high diffraction efficiency while preventing propagation of transmitted orders that would cause insertion loss.
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 thin film TIR diffraction gratings achieve high diffraction efficiency (>94%) for both TM and TE polarizations with reduced insertion loss and manufacturing complexity, maintaining efficiency across a range of wavelengths without the need for extensive dielectric layers or epoxy embedding, which minimizes bending and warping issues.
Implementation Method 1
The thin film TIR diffraction gratings achieve high diffraction efficiency (>94%) for both TM and TE polarizations... which operate based on total internal reflection (TIR) to achieve high diffraction efficiency
Data Source
AI summary
A diffraction grating may include a substrate. The diffraction grating may include an etch stop layer to prevent etching of the substrate. The etch stop layer may be deposited on the substrate. The diffraction grating may include a marker layer to indicate an etch end-point associated with etching of a dielectric layer. The marker layer may be deposited on a portion of the etch stop layer. The diffraction grating may include the dielectric layer to form a grating layer after being etched. The dielectric layer may be deposited on at least the marker layer.