Multimode Interference Coupler Refractive Index Profile Optimization
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Solution Overview
Problem
Multimode interference couplers (MMIs) face challenges in achieving uniform intensity distribution and low losses across multiple output waveguides, particularly when a large number of outputs are involved, due to non-ideal refractive index profiles that affect the propagation of higher order modes.
Innovation Solution
A refractive index profile is designed with a locally oscillating course that increases amplitude from the center to the edge of the MMI, modeled by an equation that adjusts the effective refractive index for higher order modes without disturbing lower order modes, using a combination of basis functions and optimization to achieve a desired target profile.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a constant refractive index profile is used in the MMI, then the structure is simple to manufacture, but the intensity distribution across output waveguides becomes non-uniform and losses increase
Solution Approach 1:
The patent applies local quality by varying the refractive index profile across different regions of the MMI. Specifically, the refractive index is designed to be higher in the central region and lower at the edges, creating a non-uniform profile that compensates for mode-dependent losses and achieves uniform intensity distribution across all output waveguides.
2Device complexity
If a constant refractive index profile is used in the MMI, then the structure is simple, but the intensity distribution across output waveguides becomes non-uniform
Solution Approach 1:
The patent implements local quality by designing a refractive index profile that varies spatially within the MMI. The profile is engineered to have higher refractive index values in the central region and lower values at the edges, which compensates for the different propagation characteristics of various modes and achieves uniform intensity distribution across all output waveguides.
3Device complexity
If higher order modes are not properly accounted for, then the design is simpler, but the interference pattern and beam splitter performance deteriorate
Solution Approach 1:
The patent applies parameter changes by modifying the refractive index profile to specifically address higher order modes. The designed profile creates a gradient that compensates for the lower effective refractive index of higher order modes, ensuring they contribute appropriately to the interference pattern and maintaining reliable beam splitter performance across all output waveguides.
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 approach reduces losses and ensures a more uniform intensity distribution across output waveguides, improving the interference pattern and beam splitter performance by better approximating ideal quadratic behavior for propagating modes.
Implementation Method 1
the refractive index in a direction which is substantially perpendicular to the direction of the feed waveguide, has a locally oscillating course
Implementation Method 2
If several of the modes capable of propagation are excited, they will interfere within the MMI
Data Source
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AI summary
The invention relates to a multimode interference coupler (MMI) comprising at least one supply waveguide and at least one output waveguide, wherein the MMI has along its longitudinal extent in the direction of the supply waveguide at least one longitudinal section in which the refractive index has a locally oscillating profile in a direction running substantially at right angles to the direction of the supply waveguide. The invention furthermore relates to a method for the structural configuration of a multimode interference coupler.