Grating Design for Aberration Correction in Switched Focal Plane Arrays
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Solution Overview
Problem
Photonic integrated circuit (PIC) devices face challenges in efficiently coupling light beams due to optical aberrations, which result in blurry spots and reduced coupling efficiency, especially when using optical gratings and coupling lenses, requiring complex grating designs and fabrication techniques to achieve optimal divergence and aperture matching.
Innovation Solution
The optical grating elements are configured to correct for the optical aberrations of the coupling lens, using grating geometry, waveguide geometry, and grating-waveguide spacing to direct light efficiently into the PIC, and a planar lens array or holographic elements can be used to adjust the phase and intensity profiles to match the numerical aperture and emission angle, allowing for sharper spots and improved coupling efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the grating design is optimized to give the necessary divergence of light outputs, then the coupling efficiency is improved, but the grating design becomes complicated and requires large up-front investment in PIC design
Solution Approach 1:
The patent applies parameter changes by modifying the grating pitch (spacing between grating elements) to control the divergence angle of light outputs. By adjusting this geometric parameter, the system achieves the necessary light divergence for optimal lens coupling without requiring complex multi-element grating structures, thus improving coupling efficiency while maintaining design simplicity.
2Manufacturing precision
If different fabrication techniques are required for small feature sizes in complicated grating designs, then the manufacturing precision may be improved, but the fabrication process becomes more complicated and costly
Solution Approach 1:
The patent uses parameter changes to design gratings with larger pitch values that can be fabricated using standard CMOS fabrication processes. By optimizing the grating pitch to be within the range achievable by conventional fabrication techniques, the patent avoids the need for specialized fabrication processes while maintaining sufficient manufacturing precision for effective light coupling.
3Ease of operation
If the light output is positioned at the center of the interface coupling surface, then the alignment with the coupling lens is simplified, but the light divergence may not be optimal for filling the lens aperture
Solution Approach 1:
The patent applies local quality by varying the grating pitch across different regions of the interface coupling surface. Gratings near the center have different pitch values compared to those at the edges, allowing each region to contribute optimally to filling the lens aperture while maintaining overall alignment simplicity. This spatially varying grating design enables both central positioning and optimal divergence.
4Reliability
If the grating is designed to minimize back reflection into the PIC, then the coupling performance is improved, but the grating design becomes more complex requiring destructive interference engineering
Solution Approach 1:
The patent uses parameter changes by optimizing the grating pitch and depth to naturally minimize back reflection through constructive interference of transmitted light. By carefully selecting these geometric parameters, the system achieves high coupling performance without requiring additional complex structures or multi-layer designs for destructive interference of reflected light.
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 solution enhances the coupling efficiency by correcting optical aberrations, reducing fabrication costs, and improving the resolution and range of LiDAR and free-space optical communication systems, while maintaining a compact device volume.
Implementation Method 1
optical grating elements arranged to direct light into the PIC
Implementation Method 2
a coupling lens (which might be either a single element or a lens train)... the coupling lens is characterized by one or more optical aberrations such that a point source in the scene conjugate plane is focused into a blurry spot on the PIC
Data Source
AI summary
A coupling interface arrangement is described for a photonic integrated circuit (PIC) device. The PIC includes an interface coupling surface having optical grating elements arranged to form optical output locations that produce corresponding light output beams. A coupling lens couples the light output beams into a conjugate plane at a far-field scene characterized by one or more optical aberrations that degrade optical resolution of the light outputs. The optical grating elements are configured to correct for the one or more optical aberrations.