Asymmetric Coating Optical Grating Coupler Design
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Solution Overview
Problem
Existing optical grating couplers face limitations in achieving high diffraction efficiency, particularly for specific diffraction orders, and struggle with reducing zero-order transmitted light, which affects their performance in multi-color applications and signal contrast in sensors.
Innovation Solution
The implementation of asymmetric dielectric, metallic, or semiconductor coatings on symmetric diffraction grating elements allows for coupling efficiencies higher than 50% for the first or second diffraction order, enabling efficient light coupling into or out of waveguides or windows at any angle of incidence, using readily replicable and cost-effective binary diffraction grating structures.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If symmetric diffraction grating elements are used, then the structure is simple and easy to fabricate, but the diffraction efficiency for specific orders is limited to at most 50%
Solution Approach 1:
The patent applies asymmetry by depositing a dielectric coating at an oblique angle on symmetric diffraction grating elements. This creates asymmetric optical paths for light diffracted into positive and negative orders, breaking the symmetry that limits efficiency to 50%. The asymmetric coating structure enables preferential enhancement of specific diffraction orders while maintaining the simplicity of the underlying symmetric grating structure.
2Loss of energy
If blazed-type diffraction gratings are used to enhance diffraction efficiency for a specific wavelength, then the efficiency is improved, but the diffraction efficiency for other wavelengths is reduced
Solution Approach 1:
The patent applies local quality by using a dielectric coating with specific optical properties (refractive index and thickness) that are optimized for particular wavelength ranges. The coating's local optical characteristics are tailored to enhance diffraction efficiency for desired wavelengths while minimizing the negative impact on other wavelengths, thereby achieving a balance between specialized performance and broad spectral applicability.
3Loss of energy
If asymmetric grating profiles are used to improve diffraction efficiency, then the efficiency is enhanced, but the fabrication becomes challenging and costly
Solution Approach 1:
The patent merges two separate functions: the symmetric diffraction grating structure that is easy to fabricate, and the asymmetric dielectric coating that provides the efficiency enhancement. By combining these two elements, the invention achieves high diffraction efficiency without requiring complex asymmetric grating profiles, thus maintaining ease of fabrication while improving performance.
Solution Approach 2:
The dielectric coating acts as an intermediary layer that modifies the optical interaction between light and the symmetric grating structure. This intermediate coating introduces the necessary asymmetry in light diffraction without requiring changes to the underlying grating geometry, thereby avoiding the fabrication challenges associated with creating asymmetric grating profiles directly.
4Loss of energy
If the focus is on enhancing diffraction efficiency for a specific diffraction order, then that order's efficiency is improved, but the zero-order transmitted light remains a source of undesirable light reducing contrast
Solution Approach 1:
The patent converts the potentially harmful zero-order transmitted light into a beneficial effect by using the asymmetric dielectric coating to redirect and suppress it. The coating's asymmetric structure causes the zero-order light to be diffracted into higher orders or absorbed, transforming what was previously unwanted stray light into enhanced diffraction efficiency for the desired orders while improving image contrast.
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 achieves high coupling efficiencies for a wide wavelength range, overcoming the 50% limit of symmetric gratings and providing flexible design options for optical systems, while being inexpensive and easy to fabricate, thus enhancing the performance of optical devices and sensors.
Implementation Method 1
The implementation of asymmetric dielectric, metallic, or semiconductor coatings on symmetric diffraction grating elements allows for coupling efficiencies higher than 50% for the first or second diffraction order
Data Source
Figure 1a~1b
Figure 1c
Figure 1d~1e
AI summary
The invention relates to a grating coupler comprising : - an optical substrate arranged to transfer a light beam, and - a diffraction grating arranged on, or imbedded in, the surface of said optical substrate, said diffraction grating comprising diffraction grating elements comprising each a coating arranged asymmetrically on said diffraction grating elements. The grating coupler is further arranged to satisfy the condition : (n1 x sin (ΙαΙ)+η2)/ λ x P > 1, wherein n1 is the refractive index of the optical medium to the incident light side of the diffraction grating elements, n2 is the refractive index of the optical medium to the diffracted light side of the diffraction grating elements, lal the absolute value of the incident angle of the light beam incident on the grating coupler λ is the vacuum wavelength of the diffracted light, and P is the period of the diffraction grating elements.