Angled Edge Coupler Facets for Lower Optical Return Loss
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Solution Overview
Problem
Conventional edge couplers in photonics chips experience significant back reflection and optical return loss due to mode mismatch, which has proven difficult to correct effectively.
Innovation Solution
The structure includes a waveguide core with an end surface tilted at multiple acute angles relative to its longitudinal axis, and a method of patterning materials to form an edge coupler with a multi-directional tilt, which directs reflected light outside the numerical aperture of the light source, reducing optical return loss.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional edge coupler with a flat end surface is used, then the structure is simple and easy to manufacture, but significant back reflection and optical return loss occur due to mode mismatch
Solution Approach 1:
The patent applies asymmetry by tilting the end surface of the waveguide core at a specific angle (e.g., 10-20 degrees) relative to the propagation direction. This asymmetric orientation prevents reflected light from returning to the light source by directing it away from the numerical aperture, thereby reducing optical return loss while maintaining manufacturing feasibility through standard lithography and etching processes
Solution Approach 2:
The patent introduces a new dimensional parameter by tilting the end surface in the longitudinal direction. This adds an angular dimension to the previously flat two-dimensional end surface, creating a three-dimensional structure that directs reflected light away from the light source while maintaining compatibility with standard semiconductor fabrication processes
2Reliability
If the inverse taper tip cross-sectional area is reduced to improve mode transformation, then mode size variation is improved, but the electromagnetic field confinement deteriorates and back reflection increases
Solution Approach 1:
The patent combines the inverse taper asymmetry (gradual width variation) with end surface tilting asymmetry. The tapered profile provides gradual mode transformation while the tilted end surface asymmetrically directs reflected light away from the light source, allowing the tip to maintain a small cross-sectional area for good mode matching without increasing back reflection
Solution Approach 2:
The patent changes the geometric parameters of the waveguide core by introducing a tilt angle to the end surface. This parameter modification transforms the reflected light direction without affecting the taper profile parameters, enabling independent optimization of mode transformation and back reflection reduction
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 multi-directional angling of the edge coupler's end surface effectively minimizes optical return to the light source, addressing the issue of back reflection and improving light coupling efficiency.
Implementation Method 1
Conventional edge couplers may exhibit significant back reflection and optical return loss arising from mode mismatch. The end surface defines a plane tilted in a first direction at a first acute angle relative to the longitudinal axis and tilted in a second direction at a second acute angle relative to the longitudinal axis
Data Source
AI summary
Structures including an edge coupler, and methods of fabricating a structure that includes an edge coupler. The structure includes an edge coupler having a waveguide core with an end surface and a longitudinal axis. The end surface defines a plane tilted in a first direction at a first acute angle relative to the longitudinal axis and tilted in a second direction at a second acute angle relative to the longitudinal axis. The second direction differs from the first direction.