Asymmetric Slab Waveguide for Stable TE0-TE1 Mode Conversion
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Solution Overview
Problem
Existing optical waveguide devices face challenges in achieving efficient mode conversion between TE0 and TE1 modes over a wide wavelength band due to wavelength-dependent changes in effective refractive indexes, leading to increased loss and size issues.
Innovation Solution
The optical waveguide device is designed with a semi-rib waveguide for low-order mode (TE0) and a rib waveguide for high-order mode (TE1), where the effective refractive indexes are equalized by adjusting the width of the waveguides, ensuring the interaction point remains near the midpoint, reducing wavelength-dependent shifts and leakage, thus minimizing loss and enabling downsizing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If the effective refractive index difference between core and cladding is large to achieve strong light confinement and downsizing, then the device size is reduced, but polarization dependency of loss and electric field confinement increases
Solution Approach 1:
The patent introduces asymmetric slab structures with different heights (first slab height different from second slab height) to create intentional asymmetry in the waveguide configuration. This asymmetric design compensates for the strong confinement effects by differentially adjusting the effective refractive indexes of TE and TM modes, thereby reducing polarization dependency while maintaining the compact device size enabled by strong light confinement
2Loss of energy
If the effective refractive index of TE0 in the first waveguide is equalized with the effective refractive index of TE1 in the second waveguide to achieve efficient mode conversion, then mode conversion efficiency is improved, but the interaction point position shifts with wavelength changes causing increased loss
Solution Approach 1:
The patent employs parameter changes by adjusting the heights of the first and second slabs to precisely control the effective refractive indexes of the waveguides. By optimizing these geometric parameters, the interaction point remains stabilized near the midpoint across a wide wavelength range, enabling efficient mode conversion that is insensitive to wavelength variations and supporting broad wavelength bandwidth operation
3Loss of energy
If the interaction region is positioned at the midpoint between input and output ends for optimal mode conversion, then conversion efficiency is maximized, but wavelength changes cause the interaction point to shift away from the midpoint increasing loss
Solution Approach 1:
The patent applies local quality by creating distinct slab regions with different heights at specific locations within the waveguide structure. The first slab with a first height and the second slab with a second height are positioned to locally adjust the effective refractive index distribution, ensuring that the interaction point remains anchored near the midpoint despite wavelength variations, thereby stabilizing the interaction region position
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 configuration stabilizes mode conversion with reduced loss over a wide wavelength range and allows for a compact device by minimizing the shift of the interaction point with wavelength changes, achieving efficient TE0 to TE1 conversion while maintaining a small device size.
Implementation Method 1
An effective refractive index that indicates an effective refractive index of a TE0 mode in the first waveguide is equal to an effective refractive index that indicates an effective refractive index of a TE1 mode in the second waveguide
Data Source
AI summary
An optical waveguide device includes first and second waveguides formed parallel to each other. The first waveguide includes a first rib and a first slab. The first slab is formed in a region between the first rib and the second waveguide. The second waveguide includes a second rib, a second slab and a third slab. The second rib is provided between the second slab and the third slab. The first and second slabs are integrally formed. At one end of the optical waveguide device, a first effective refractive index that indicates an effective refractive index of a TEi mode in the first waveguide is higher than a second effective refractive index that indicates an effective refractive index of a TEj mode in the second waveguide. At another end, the first effective refractive index is lower than the second effective refractive index.