Metamaterial Rib Edge Couplers for Insertion Loss Reduction
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Solution Overview
Problem
Edge couplers in photonics chips face issues such as significant insertion loss, back reflection, low coupling efficiency, poor power handling, and low fabrication tolerance due to mismatches in mode shape and size with lasers or optical fibers, and occupy excessive space.
Innovation Solution
A structure for an edge coupler featuring a waveguide core with notched sidewalls and segments arranged in a spaced pattern, along with a thinner slab layer, which provides improved mode matching and power handling by forming a rib waveguide structure that reduces insertion loss and back reflection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If a conventional inverse taper edge coupler is used, then mode transformation is supported, but insertion loss and back reflection are significant
Solution Approach 1:
The waveguide core is divided into multiple segments with different widths arranged in a spaced array rather than a continuous inverse taper. This segmentation creates discrete coupling regions that reduce insertion loss by improving mode matching while avoiding the complexity of a long continuous taper structure.
Solution Approach 2:
Different segments of the waveguide core are given different widths to create localized variations in coupling strength. The segments closer to the fiber interface have different dimensions than those farther away, allowing optimization of mode matching at each location to minimize overall insertion loss.
2Reliability
If the waveguide core cross-section is reduced at the tip, then mode size matching is improved, but the electromagnetic field cannot be fully confined
Solution Approach 1:
The waveguide core is segmented into discrete sections with varying widths. This allows the electromagnetic field to be progressively confined across multiple discrete regions rather than requiring a single narrow tip, improving both confinement and reducing field distribution losses.
Solution Approach 2:
The structure combines the waveguide core segments with a cladding layer to form a composite structure that enhances field confinement. The combination of core and cladding materials creates effective confinement without requiring the core alone to be sufficiently narrow.
3Manufacturing precision
If a longer inverse taper is used, then mode transformation is more gradual, but the layout area occupied increases
Solution Approach 1:
The transformation region is divided into multiple discrete segments rather than a single long continuous taper. This allows the mode transformation to occur across a more compact area by distributing the transformation function across several shorter segments arranged in a spaced configuration.
Solution Approach 2:
The segmented structure utilizes the transverse dimension more effectively by arranging multiple waveguide core segments side-by-side or in a spaced array, allowing mode transformation to occur in a more compact footprint compared to a long linear taper.
4Reliability
If the waveguide core is made narrower, then coupling to optical fiber is improved, but power handling capability deteriorates
Solution Approach 1:
The waveguide core is divided into multiple segments with different widths. Segments closer to the fiber interface can be narrower to improve coupling efficiency, while segments farther away can be wider to maintain power handling capability, allowing both requirements to be satisfied simultaneously across different locations.
Solution Approach 2:
Different segments are given different widths optimized for their specific function: narrower segments near the fiber for coupling efficiency and wider segments in the bulk for power handling. This local optimization allows the structure to satisfy both coupling and power handling requirements.
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 proposed structure enhances coupling efficiency, increases fabrication tolerance, reduces length, and improves power handling, making it more compact and resilient to power-related damage compared to conventional edge couplers.
Implementation Method 1
The plurality of segments and the waveguide core section have a first thickness, and the slab layer has a second thickness that is less than the first thickness. The plurality of segments positioned with a spaced arrangement adjacent to the end surface form a metamaterial rib structure that enhances coupling efficiency by transforming the electromagnetic mode profile
Implementation Method 2
The gradually-varying cross-section area of an inverse taper supports mode transformation and mode size variation associated with mode conversion when light is transferred from the laser or optical fiber to the photonics chip
Implementation Method 3
As its width increases, the inverse taper can support the entire incident mode and eventually confine the electromagnetic field inside the inverse taper
Implementation Method 4
An edge coupler may include a waveguide core section that defines an inverse taper and that is located adjacent to the laser or optical fiber
Data Source
AI summary
Structures for an edge coupler and methods of fabricating a structure for an edge coupler. A waveguide core includes a waveguide core section that has a first notched sidewall, a second notched sidewall, and an end surface connecting the first notched sidewall to the second notched sidewall. Segments are positioned with a spaced arrangement adjacent to the end surface of the waveguide core section, and a slab layer is adjoined to the segments, the first notched sidewall of the waveguide core section, the second notched sidewall of the waveguide core section, and the end surface of the waveguide core section. The segments and the waveguide core section have a first thickness, and the slab layer has a second thickness that is less than the first thickness.