Asymmetric Waveguide Polarization Conversion
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Solution Overview
Problem
Existing optical waveguide devices for polarization conversion between TE and TM modes suffer from low efficiency due to weak interaction between evanescent light, requiring long waveguides and resulting in large device sizes.
Innovation Solution
The optical waveguide device features a pair of waveguides with asymmetric cross-sectional areas and refractive index distributions, where the effective refractive indices of TE and TM modes are quantitatively related differently at the input and output ends, allowing for efficient conversion between modes through continuous changes in core structures.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If a pair of waveguides is designed with asymmetric cross-section to enable polarization conversion, then mode interaction is achieved, but the conversion efficiency remains low due to weak evanescent light interaction
Solution Approach 1:
The patent applies parameter changes by varying the cross-sectional dimensions of the waveguide cores along the propagation direction. Specifically, the first and second cores have different cross-sectional areas at the input end of the conversion region, and these dimensions change continuously along the light traveling direction. This gradual parameter variation enables strong interaction between TE and TM modes while maintaining low loss, resolving the contradiction between conversion efficiency and energy transfer.
2Productivity
If the waveguide length is increased to improve polarization conversion efficiency, then mode conversion is enhanced, but the device size becomes large
Solution Approach 1:
The patent introduces dimensional variation by changing the cross-sectional area of the cores along the propagation direction (z-axis). Instead of maintaining a uniform waveguide structure, the first core has a larger cross-sectional area at the input end that gradually decreases, while the second core has a smaller cross-sectional area that gradually increases. This dimensional change enables efficient polarization conversion within a compact length, resolving the contradiction between conversion efficiency and device size.
3Productivity
If the cross-sectional area of cores is made different at the input end to enable mode interaction, then polarization conversion is achieved, but manufacturing precision requirements increase
Solution Approach 1:
The patent applies dynamics by designing the core cross-sectional dimensions to change continuously along the propagation direction rather than being static. The first core transitions from a larger cross-section at the input end to a smaller cross-section at the output end, while the second core does the opposite. This dynamic dimensional variation enables mode interaction and polarization conversion while providing manufacturing flexibility, as the gradual changes are easier to fabricate than abrupt dimensional 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
This design achieves high-efficiency polarization conversion with a shorter device length, reducing size and minimizing loss and reflection, while maintaining stable laser operation.
Implementation Method 1
an optical waveguide device that converts the polarization of light
Implementation Method 2
the polarization plane of the TM0-mode light is inclined, resulting in evanescent light being transferred to the other waveguide
Data Source
AI summary
An optical waveguide device includes a pair of waveguides. One of the waveguides includes a first core formed in a conversion region and a third core formed in an exit region. The other of waveguides includes a second core formed in the conversion region and a fourth core formed in the exit region. Cross-sectional areas of the first and second cores are different from each other at an input end. Distributions of a refractive index of the first and second cores are respectively asymmetric in a perpendicular direction. A quantitative relation provided at the input end between an effective refractive index of an odd mode of TE0 and an effective refractive index of an even mode of TM0 is opposite to the quantitative relation provided at the output end. Cross-sectional areas of the third and fourth cores are different from each other at an output end.