Polymer Waveguide Self-Alignment via Stub and Groove Adiabatic Coupling
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Solution Overview
Problem
There is a lack of effective techniques for achieving high-precision alignment and adiabatic coupling between single-mode polymer waveguides and silicon waveguides, which is crucial for efficient light transmission due to their small core cross-sections and differing numerical apertures.
Innovation Solution
The solution involves self-alignment of single-mode polymer waveguide arrays with silicon waveguide arrays using a combination of precisely fabricated stubs and grooves, where the stubs on the polymer are aligned with the groove on the silicon chip, utilizing a two-mask photolithography process to ensure accurate positioning and adiabatic coupling.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If Butt Coupling is used for single-mode waveguide coupling, then alignment simplicity is improved, but coupling efficiency deteriorates due to small core cross-section mismatch
Solution Approach 1:
The patent introduces an intermediary structure (the groove and stub configuration) between the single-mode polymer waveguide and silicon waveguide to facilitate adiabatic coupling. This intermediary mechanism enables efficient light transmission by guiding the evanescent field from the polymer waveguide into the silicon waveguide over an extended interaction length, resolving the coupling efficiency problem while maintaining alignment simplicity.
2Loss of energy
If adiabatic coupling is used for single-mode waveguide coupling, then coupling efficiency is improved, but alignment precision requirements worsen
Solution Approach 1:
The patent applies preliminary action by pre-fabricating the groove structure on the silicon chip and the stub structure on the polymer waveguide before coupling. These pre-formed structures serve as alignment guides that automatically position the waveguides correctly during assembly, reducing the actual alignment precision requirements while maintaining high coupling efficiency through adiabatic coupling.
Solution Approach 2:
The groove and stub structures create a self-aligning mechanism where the physical geometry of the structures guides the waveguides into proper alignment during assembly. The stub fits into the groove, automatically positioning the single-mode polymer waveguide relative to the silicon waveguide, thereby reducing dependency on external alignment precision controls.
3Measurement precision
If single-mode waveguides with small core cross-sections are used, then light transmission precision is improved, but coupling difficulty worsens due to numerical aperture differences
Solution Approach 1:
The patent transitions from a simple end-face coupling (zero-dimensional point contact) to an extended interaction region (one-dimensional linear contact) by implementing adiabatic coupling through the groove and stub structures. This dimensional change allows the small core cross-section single-mode waveguides to couple efficiently by distributing the coupling interaction over an extended length, overcoming the numerical aperture mismatch while preserving light transmission precision.
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 method enables high-precision alignment and efficient adiabatic coupling, minimizing light loss and ensuring reliable optical transmission between the polymer and silicon waveguide arrays, even with their size and refractive index differences.
Implementation Method 1
A single-mode polymer waveguide (PWG) array fabricated on polymer and a silicon waveguide (SiWG) array fabricated on a silicon (Si) chip are self-aligned according to a combination of a stub and a groove highly precisely fabricated on both sides
Implementation Method 2
adiabatic coupling can be used as an alternative method by which evanescent light in an optical axis direction along the array is captured and transmitted over a predetermined distance in the optical axis direction
Implementation Method 3
high-precision alignment of arrays in a single-mode polymer waveguide (PWG) so that an adiabatic coupling is provided
Implementation Method 4
the stub fabricated on the polymer is fabricated using a second mask arranged along the same alignment base line for a first mask used in a photolithography process for fabricating the PWG array
Data Source
AI summary
Alignment of a single-mode polymer waveguide (PWG) array fabricated on a polymer with a silicon waveguide (SiWG) array fabricated on a silicon (Si) chip and thereby realizing an adiabatic coupling. A stub and a groove are fabricated with high precision and made to function as the absolute positioning reference to provide a self-alignment according to the groove and the stub. In a PWG patterning by photolithography, plural masks are used, but the fabrication is made along the alignment base line for mask and thus a high precision is achieved with respect to error δx. In a PWG patterning by nano imprint, a high precision in the fabrication is also achieved with respect to error δx and δy.