Asymmetric Rib Waveguide MMI Coupler for Reflected Light Suppression
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Solution Overview
Problem
Conventional MMI couplers face issues with reflected light being input back into the input waveguides, leading to optical resonance or interference, which can cause the device to malfunction. Additionally, the use of multi-mode or single-mode waveguides for unnecessary light waveguides either fails to fully reduce reflected light or introduces higher-order mode interference.
Innovation Solution
The proposed optical device incorporates an interference region with unnecessary light waveguides arranged parallel to the output waveguide, specifically designed as single-mode rib waveguides with a slab portion. These waveguides are configured to guide only the fundamental mode of light, reducing reflected light input to the input waveguides while meeting the single mode condition.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If multi-mode waveguides are used for unnecessary light waveguides, then the device size is reduced, but higher-order mode interference occurs
Solution Approach 1:
The patent changes the waveguide structure parameters by introducing an asymmetric rib configuration where the rib portion has a different height than the slab portion. This parameter change allows the waveguide to support only the fundamental mode while maintaining a larger cross-sectional area, thus preventing higher-order mode interference without increasing overall device volume.
Solution Approach 2:
The patent applies asymmetry by creating an asymmetric rib waveguide structure where the rib portion extends to a first height and the slab portion extends to a second height that is different from the first height. This asymmetric configuration creates different effective refractive indices for different modes, allowing only the fundamental mode to propagate while suppressing higher-order modes.
2Object-generated harmful factors
If single-mode waveguides are used for unnecessary light waveguides, then higher-order mode interference is prevented, but the waveguide width must be reduced which increases reflected light
Solution Approach 1:
The patent transitions from considering only the lateral dimension (waveguide width) to incorporating the vertical dimension (rib and slab portion heights). By adjusting heights in the vertical dimension, the patent achieves single-mode operation without necessarily reducing the lateral width, thus maintaining better optical coupling and reducing reflected light while still preventing higher-order mode interference.
Solution Approach 2:
The patent applies local quality by creating different structural characteristics in different regions of the waveguide cross-section. The rib portion has a specific height and width configuration, while the slab portion has different dimensions. This local differentiation creates the necessary conditions for single-mode operation while optimizing the overall waveguide dimensions to minimize reflections.
3Object-generated harmful factors
If the waveguide width is reduced to meet single mode condition, then higher-order mode interference is prevented, but reflected light increases
Solution Approach 1:
The patent compensates for reduced waveguide width by utilizing the vertical dimension through the asymmetric rib and slab structure. This allows the lateral dimensions to be smaller (preventing higher-order modes) while the vertical structure maintains adequate optical confinement and coupling, thereby reducing reflected light losses.
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 solution effectively reduces the amount of reflected light input to the input waveguides, preventing optical resonance and interference, and ensuring stable operation of the MMI coupler. This is achieved while maintaining the single mode condition, thus preventing higher-order mode interference.
Implementation Method 1
a slab portion 5B that has a smaller thickness than a core thickness of the rib portion 5A... guides only a fundamental mode of light
Implementation Method 2
light that is input from the input waveguide 102 to the interference region 104 is expanded to a plurality of waveguide modes of the interference region 104 that serves as a multi-mode waveguide, and optical power is distributed to the four output waveguides 103 by an optical self-imaging effect
Implementation Method 3
an optical waveguide that includes a substrate, a core that is formed on the substrate, and a clad that covers the core
Data Source
AI summary
An optical device includes an input waveguide and an output waveguide. The optical device includes an interference region that includes an input unit optically coupled with the input waveguide, that includes an output unit optically coupled with the output waveguide, and that has a larger waveguide width than a waveguide width of the input waveguide and a waveguide width of the output waveguide. Further, the optical device includes an unnecessary light waveguide that is included in the output unit in the interference region and that is arranged parallel to the output waveguide. The unnecessary light waveguide is a single-mode waveguide that includes a rib portion and a slab portion with a smaller thickness than a thickness of the rib portion, and that guides only a fundamental mode of light.