Optical Mode-Size Converter with Evanescent Low-Loss Coupling
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Solution Overview
Problem
Existing waveguide circuits face challenges in efficiently converting one guided mode to another with low transmission loss, particularly when dealing with waveguides of different mode areas, which is crucial for photonic applications such as data centre communications and coherent telecommunications.
Innovation Solution
A mode-size converter is designed to gradually change the guided mode from a larger area to a smaller area with minimal loss by using a guiding portion and embedded strips within a waveguide chip, optimizing the refractive index distribution and structure to facilitate efficient mode conversion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If conventional waveguide structures are used for mode conversion, then structural simplicity is maintained, but transmission loss increases and conversion efficiency decreases
Solution Approach 1:
The waveguide structure is divided into multiple functional segments: an input waveguide, a mode converter comprising first and second waveguides with tapered sections, and an output waveguide. Each segment performs a specific function in the mode conversion process, allowing optimized design for low loss while maintaining overall manageability through modular organization.
Solution Approach 2:
The invention introduces vertical layering with the first waveguide positioned at a first height and the second waveguide at a second height, creating a three-dimensional configuration. This vertical dimension enables evanescent field coupling between waveguides while maintaining horizontal separation, achieving low-loss mode conversion without excessive planar complexity.
2Productivity
If simple waveguide coupling is used, then device complexity is low, but mode conversion efficiency is insufficient
Solution Approach 1:
The waveguide structure incorporates tapered sections where the width gradually changes along the propagation direction. This dynamic geometric transformation enables adiabatic mode conversion, where the mode profile continuously adapts to the changing waveguide dimensions, achieving high conversion efficiency through controlled structural variation rather than static simple coupling.
Solution Approach 2:
The tapered sections employ curved transition profiles rather than sharp angular changes, creating smooth geometric transitions that minimize scattering losses. The curved geometry of the tapered regions enables gradual mode transformation, improving conversion efficiency while the curvature is designed within manufacturing capabilities to avoid excessive complexity.
3Loss of energy
If waveguides are placed close together for coupling, then coupling efficiency improves, but mode area mismatch increases leading to higher loss
Solution Approach 1:
The tapered sections dynamically adjust the waveguide width along the propagation direction, enabling the mode area to gradually transition from the larger input waveguide mode to the smaller output waveguide mode. This dynamic adaptation allows efficient coupling between waveguides of different mode areas while minimizing power loss through adiabatic transformation.
Solution Approach 2:
Different sections of the waveguide structure have different geometric properties optimized for their specific functions: the input and output waveguides have uniform cross-sections for efficient coupling to external components, while the intermediate tapered sections have varying cross-sections optimized for mode transformation. This local optimization of geometric quality enables low-loss conversion despite mode area differences.
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-size converter achieves low-loss conversion of optical modes, supporting reciprocal operation and minimizing power loss, making it suitable for various photonic applications including data centre communications and coherent telecommunications.
Implementation Method 1
at least a portion of the first adiabatic tapering is adjacent to the second adiabatic tapering, and wherein the first adiabatic tapering and the second adiabatic tapering are separated from each other by a constant gap
Implementation Method 2
a thick waveguide comprising a first adiabatic tapering from a first location to a second location, wherein the first adiabatic tapering is wider at the first location than at the second location
Data Source
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AI summary
An optical mode-size converter is presented, which includes a guiding portion, wherein at least a portion of the guiding portion extends between a first end and a second end along a first path, a first strip with a first refractive index, and a second strip with a second refractive index. The first strip and the second strip are embedded within the guiding portion extending along the first path such that a first optical mode received at the first end reaches the first strip before the second strip and such that the second strip extends to the second end. The first refractive index and the second refractive index are higher than a refractive index of the guiding portion, a cross section area of the first strip is smaller than a cross section area of the second strip, and a section of the first strip and a section of the second strip overlap to form an evanescent coupling region, such that converter is responsive to a first optical mode received at the first end to convert the first optical mode into a second optical mode with a smaller mode size along the first path towards the second end.