Fiber-Waveguide Coupler Alignment Using Crystallographic V-Grooves
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Solution Overview
Problem
The challenge in manufacturing photonic integrated circuits (PICs) lies in achieving precise alignment between V-Grooves and optical waveguides due to misalignment between the crystalline plane and the processing direction, often indicated by a wafer notch, leading to uncertainties in the orientation of V-Grooves and misalignment between the optical fiber and waveguide.
Innovation Solution
A fiber-waveguide coupler is designed with a crystalline substrate of type (100) having a V-groove and optical waveguide aligned such that the fiber core is within a predetermined distance from the waveguide core, utilizing anisotropic etching to adjust the V-groove dimensions based on determined misalignment angles, ensuring accurate alignment.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If anisotropic etching is used to create V-Grooves, then the V-Grooves serve as entry points for optical fibers, but misalignment between the crystalline plane (110) and processing direction causes uncertainty in V-Groove orientation and misalignment with waveguide
Solution Approach 1:
The patent applies preliminary action by creating reference marks and performing alignment measurements before the actual V-groove etching process. The method includes: (1) creating reference marks on the substrate, (2) measuring the angular deviation between the (110) crystalline plane and the processing direction, (3) calculating compensation values, and (4) using these pre-determined parameters to guide the subsequent V-groove etching. This preliminary characterization and compensation approach resolves the alignment uncertainty by establishing reference data before the critical etching step.
Solution Approach 2:
The patent applies parameter changes by adjusting the V-groove etching parameters based on the measured misalignment angle. Specifically, the method modifies: (1) the etching direction angle relative to the wafer notch, (2) the etching depth, and (3) the V-groove orientation. These parameter adjustments are calculated based on the measured deviation from the ideal (110) plane alignment, allowing the V-grooves to be precisely oriented to match the waveguide direction despite substrate orientation variations.
2Ease of manufacture
If the wafer surface is tilted with respect to the (100) Si crystalline plane, then the V-Groove can be etched, but the center of the optical fiber becomes misaligned with the optical waveguide
Solution Approach 1:
The patent applies feedback by implementing a closed-loop alignment process where: (1) the actual angular deviation of the wafer surface from the ideal (100) plane is measured using optical or mechanical measurement tools, (2) this measured feedback value is used to calculate the necessary compensation parameters, and (3) these compensation parameters are then applied to adjust the V-groove etching process. This feedback mechanism ensures that the fiber-core to waveguide core alignment is corrected based on the actual substrate orientation, resolving the misalignment issue caused by tilted wafer surfaces.
3Ease of manufacture
If standard lithography and etching processes are used for SiN waveguides, then waveguides can be fabricated, but alignment uncertainties persist due to crystalline plane misalignment
Solution Approach 1:
The patent applies asymmetry by introducing asymmetric compensation measures tailored to the specific measured misalignment of each substrate. Rather than using a symmetric, one-size-fits-all alignment approach, the method: (1) measures the unique angular deviation of each wafer's (110) plane from the processing direction, (2) calculates asymmetric compensation parameters specific to that deviation, and (3) applies these asymmetric corrections to the V-groove etching process. This asymmetric approach allows precise alignment despite variations in substrate orientation that would prevent alignment using standard symmetric processes.
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 provides a reliable fiber-waveguide coupler with minimized displacement between the fiber and waveguide cores, enhancing light coupling efficiency and reducing manufacturing uncertainties.
Implementation Method 1
The manufacturing process of photonic integrated circuits (PIC) recently relies on the strategic use of anisotropic etching using wet etching with e.g. TMAH to create V-Grooves
Data Source
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AI summary
The present invention provides a fiber-waveguide coupler (1), comprising a crystalline substrate (2) of a 〈100〉 type having a top surface (2a) and a crystallographic 〈100〉 plane (2100),the crystalline substrate (2) comprising: a V-groove (3) extending in a Z-direction (Z) in a projection towards the top surface (2a), wherein the Z-direction (Z) is within a 〈110〉 crystallographic plane (2110) of the crystalline substrate (2), wherein the top surface (2a) and a 〈100〉 crystallographic plane (2110) of the crystalline substrate (2) open a first angle (α1) in a X/Y-plane (XY) normal to the Z-direction(Z), and an optical waveguide (4) disposed on the top surface (2a) of the crystalline substrate(2), the optical waveguide (4) extending along the Z-direction (Z) in a projection towards the top surface, wherein the V-groove (3) and the optical waveguide (4) are configured such that when an optical fiber (5) of predetermined size and having a fiber core (51) and a fiber tip (52), set into the V-groove (3) such that a distance between an outer end (42) of the waveguide core (4) and the fiber tip (52) is less than a predetermined distance (d), the fiber core (51) is aligned with the waveguide core (41) such that a displacement of the fiber core (51) and the waveguide core (41) is less than a predetermined displacement. Further the present invention provides a method for manufacturing a fiber-waveguide coupler (1) as well as.