Chiplet Mode Expander for Waveguide Fiber Coupling
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Solution Overview
Problem
Current optical waveguide technologies face challenges in efficiently coupling smaller optical modes in semiconductor waveguides to larger modes in optical fibers, leading to alignment and assembly issues and increased optical losses.
Innovation Solution
A mode expander is fabricated using a multi-layer chiplet with tapered stages of high bandgap semiconductor materials, which expands the optical mode from a smaller initial size to a larger output size, enhancing coupling efficiency and reducing alignment and assembly costs by adiabatically expanding the beam.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If direct coupling between semiconductor waveguide and optical fiber is used, then alignment precision is improved, but coupling efficiency deteriorates due to mode size mismatch
Solution Approach 1:
A mode expander structure is introduced as an intermediary component between the semiconductor waveguide and optical fiber. This mode expander gradually transforms the small optical mode from the waveguide into a larger mode that matches the optical fiber, serving as a mediator that resolves the mode size mismatch while maintaining alignment precision.
Solution Approach 2:
The mode expander utilizes dimensional transformation by expanding the optical mode in the lateral dimension while maintaining propagation in the longitudinal dimension. This dimensional change allows the mode size to be increased to match the optical fiber without compromising alignment precision.
2Loss of energy
If mode expander with multiple tapered stages is used, then coupling efficiency is improved, but device complexity increases
Solution Approach 1:
The mode expander is divided into multiple tapered stages, each with a specific taper angle and length. This segmentation allows the gradual mode expansion to be achieved in discrete steps, improving coupling efficiency by better matching the mode transformation to the optical fiber acceptance profile.
Solution Approach 2:
Each tapered stage in the mode expander has different geometric parameters (taper angle, length, width) optimized for specific portions of the mode transformation. By varying these parameters across stages, the mode expansion is optimized for maximum coupling efficiency while managing the increased device complexity through systematic parameter design.
3Loss of energy
If larger mode size is used at waveguide output, then coupling efficiency is improved, but manufacturing precision requirements increase
Solution Approach 1:
The mode expander performs the mode size transformation in advance, before the light enters the optical fiber coupling region. By pre-expanding the mode to the appropriate size, the subsequent coupling process becomes more tolerant to manufacturing variations, reducing the precision requirements for the final alignment and assembly.
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
The mode expander effectively increases coupling efficiency and reduces optical losses and alignment costs by adiabatically expanding the optical beam, improving the integration of semiconductor waveguides with optical fibers.
Implementation Method 1
expands the optical mode from a smaller initial size to a larger output size, enhancing coupling efficiency and reducing alignment and assembly costs by adiabatically expanding the beam
Data Source
AI summary
A method of fabricating a waveguide mode expander includes providing a substrate including a waveguide, bonding a chiplet including multiple optical material layers in a mounting region adjacent an output end of the waveguide, and selectively removing portions of the chiplet to form tapered stages that successively increase in number and lateral size from a proximal end to a distal end of the chiplet. The first optical material layer supports an input mode substantially the same size as a mode exiting the waveguide. One or more of the overlying layers, when combined with the first layer, support a larger, output optical mode size. Each tapered stage of the mode expander is formed of a portion of a respective layer of the chiplet. The first layer and the tapered stages form a waveguide mode expander that expands an optical mode of light traversing the chiplet.