Grating Coupler for Wafer-Level Photonic Chip Testing
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Solution Overview
Problem
Testing optical components in photonic chips is challenging, especially before they are mounted and aligned to optical cables, as edge couplers become inaccessible during fabrication, making it difficult to verify the functionality of components like optical modulators and detectors within the chip wafer.
Innovation Solution
Incorporating a grating coupler on the photonic semiconductor chip, which allows for optical signal transfer along a top plane perpendicular to the side plane, enabling testing and alignment even when the chip is still in a wafer form by connecting a test probe to the grating coupler, and using a splitter to direct optical signals to both the edge coupler and the optical component, ensuring functionality can be assessed before and after wafer separation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If edge couplers are used for optical signal transfer, then coupling efficiency is improved, but accessibility for testing deteriorates after wafer separation
Solution Approach 1:
The patent divides the optical coupling interface into two segments: edge couplers for high-efficiency signal transfer and grating couplers for accessible testing. This segmentation allows each component to serve its specialized function without compromising the other.
Solution Approach 2:
The grating coupler acts as an intermediary element that provides an accessible optical interface for testing while the edge coupler maintains the primary high-efficiency coupling path. The intermediary enables testing functionality without interfering with the main signal transfer path.
2Productivity
If testing is performed before wafer separation, then manufacturing efficiency is improved, but component accessibility deteriorates
Solution Approach 1:
The grating coupler is designed to enable preliminary testing actions before wafer separation. This allows quality verification and alignment procedures to be performed while the chip is still in the wafer state, improving manufacturing efficiency by eliminating post-separation testing requirements.
3Difficulty of detecting and measuring
If grating coupler is added for testing, then testability is improved, but device complexity increases
Solution Approach 1:
The grating coupler serves multiple functions: it enables optical testing, facilitates alignment procedures, and can potentially serve as an alternative coupling interface. This multi-functionality justifies the added complexity by providing versatile testing capabilities.
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
Enables the testing and alignment of optical components within photonic chips before they are separated from the wafer, ensuring functional verification and efficient alignment of fiber optic cables to edge couplers, maintaining consistency in testing across both wafer and individual chip stages.
Implementation Method 1
a grating coupler directly coupled to a second end of the second waveguide, wherein the grating coupler is arranged to transfer second optical signals along a top plane of the photonic semiconductor chip
Implementation Method 2
the edge coupler is arranged to transfer first optical signals along a side plane of the photonic semiconductor chip and wherein the edge coupler is configured to change a mode size as the first optical signals propagate through the edge coupler
Data Source
Figure 1~2
Figure 3A~3C
Figure 4A~4B
AI summary
Embodiments herein describe techniques for testing or aligning optical components (205, 225) in a photonic chip (200) using a grating coupler (220). In one embodiment, the photonic chip (200) may include an edge coupler (205) and a grating coupler (220) for optically coupling the photonic chip to external fiber optic cables (920). The edge coupler (205) may be disposed on a side or edge of the photonic chip while the grating coupler (220) is located on a top or side of the photonic chip. During fabrication, the edge coupler (205) may be inaccessible. Instead of using the edge coupler (205) to test the photonic chip, a testing apparatus (805) can use the grating coupler (220) along with a splitter (215) to transfer optical test signals between an optical component in the photonic chip (e.g., a modulator or detector) and a test probe (505) optically coupled to the grating coupler (220).