Partially Metallized Immersion Grating for High Efficiency
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Solution Overview
Problem
Existing diffraction gratings face challenges in achieving high efficiency and broad spectral range with minimal optical loss, as they often allow undesirable energy pathways such as specular reflection and non-diffracted transmission, making it difficult to design gratings with high diffraction efficiency into a single desired order.
Innovation Solution
A partially metallized total internal reflection immersion grating is designed with specific parameters such as ridge spacing, width, height, and metal layer thickness, allowing for controlled polarization dependence or independence, and by arranging the grating morphology to direct nearly 100% of incident optical signal energy into the first diffraction order within the high-index medium, eliminating undesirable pathways.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If conventional diffraction gratings are used, then diffraction efficiency can be improved, but undesirable energy pathways such as specular reflection and non-diffracted transmission increase
Solution Approach 1:
The patent applies local quality by selectively metallizing only the ridge tops of the grating structure while leaving the trench bottoms unmetallized. This localized differentiation allows the ridge tops to reflect light into the desired diffraction order while the unmetallized trench bottoms eliminate specular reflection and non-diffracted transmission pathways, thereby concentrating energy into the first diffraction order and reducing harmful energy pathways.
2Loss of energy
If total internal reflection immersion grating is used, then diffraction efficiency into first order is improved, but polarization-dependent loss increases
Solution Approach 1:
The patent applies parameter changes by optimizing the metal layer thickness parameter to a specific range (10-100 nm) and adjusting the grating geometry parameters (ridge width, trench width, ridge height) to achieve polarization independence. By carefully selecting these parameters, the grating maintains high diffraction efficiency for both s-polarized and p-polarized light, thereby reducing polarization-dependent loss while preserving the total internal reflection mechanism.
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 solution achieves near-unity diffraction efficiency into the first order with reduced polarization-dependent loss, enabling efficient optical signal transmission and minimizing optical loss across a substantial spectral range.
Implementation Method 1
The substrate can be arranged so that an optical signal is incident on the diffractive elements from within the substrate (i.e., the diffraction grating is a so-called immersion grating) at an incidence angle that exceeds the critical angle
Implementation Method 2
A diffraction grating comprises a substrate with a set of diffractive elements formed on its surface
Data Source
AI summary
A diffraction grating comprises a substrate with a set of protruding ridges and intervening trenches characterized by a ridge spacing Λ, width d, and height h. The substrate comprises a dielectric or semiconductor material with a refractive index n1; the first substrate surface faces an optical medium with a refractive index n2 that is less than n1. Each ridge has a metal layer on its top surface of thickness t; at least a portion of the bottom surface of each trench is substantially free of metal. Over an operational wavelength range, λ/2n1<Λ<λ/(n1+n2) can be satisfied. An optical signal can be incident on the diffractive elements from within the substrate at an incidence angle that exceeds the critical angle. The parameters n1, n2, Λ, d, h, and t can be selected to yield desired polarization dependence or independence of the diffraction efficiency.