Directional Coupler Polarization Independence via Mode Matching
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Solution Overview
Problem
Directional couplers using Si wire waveguides suffer from polarization dependence, limiting design flexibility due to fixed SOI substrate constraints, which restricts the optimization of optical waveguide core thickness and affects the performance of optical devices like wavelength filters.
Innovation Solution
A directional coupler design that allows for the propagation of multiple order modes of polarized waves, enabling the matching of mode coupling coefficients between parallel optical waveguide cores, thereby enhancing polarization independence and design freedom regarding waveguide core thickness.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If Si wire waveguide is used with fixed SOI substrate thickness, then manufacturing is simplified, but polarization dependence occurs and design flexibility is limited
Solution Approach 1:
The invention segments the waveguide core into multiple distinct layers (first waveguide core layer, second waveguide core layer) with different thicknesses. This segmentation allows each layer to be optimized for different polarization modes (TE and TM), resolving the contradiction by enabling polarization-independent operation while maintaining compatibility with standard SOI substrate manufacturing processes.
Solution Approach 2:
The invention applies local quality by creating waveguide core layers with non-uniform thickness distribution. The first waveguide core layer has a different thickness than the second waveguide core layer, allowing each region to have optimized properties for specific polarization modes. This local variation in thickness enables polarization independence while using standard manufacturing processes.
2Ease of manufacture
If optical waveguide core thickness is fixed by SOI substrate constraints, then manufacturing is easier, but mode coupling coefficient optimization is restricted
Solution Approach 1:
The invention introduces dynamics by making the waveguide core structure adjustable through the combination of two layers with different thicknesses. By varying the thicknesses of the first and second waveguide core layers independently, the overall effective thickness can be optimized for mode coupling coefficient matching, while still using fixed-thickness SOI substrates for manufacturing.
Solution Approach 2:
The invention uses composite material structure by combining two waveguide core layers of different materials or compositions with different thicknesses. This composite structure allows the effective optical properties to be tuned for optimal mode coupling, while each individual layer can be manufactured using standard SOI substrate processes.
3Device complexity
If single-layer waveguide core is used, then structure is simpler, but polarization independence cannot be achieved
Solution Approach 1:
The invention segments the waveguide core into multiple layers, where each layer is optimized for different polarization modes. This segmentation enables polarization independence by ensuring that both TE and TM modes experience similar effective refractive indices, while the overall structure remains relatively simple and manufacturable.
Solution Approach 2:
The multi-layer waveguide core structure serves multiple functions simultaneously: it guides both TE and TM polarizations with equal effectiveness, enables mode coupling coefficient optimization, and remains compatible with standard manufacturing processes. This multi-functionality achieves polarization independence without proportionally increasing device complexity.
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 allows for greater selectivity in mode coupling, enabling polarization-independent operation and increased design flexibility for optical waveguide elements and wavelength filters, improving their performance and adaptability.
Implementation Method 1
light is confined and propagated inside an optical waveguide
Implementation Method 2
there is an extremely large difference in the refractive index between the optical waveguide core and the cladding, it is possible to strongly confine the light inside the optical waveguide core
Data Source
AI summary
There is provided a directional coupler including a first optical waveguide core and a second optical waveguide core that are arranged in separate and parallel to each other and that propagate one of TE polarized waves and TM polarized waves of an m-th order and propagate the other of the TE polarized waves and the TM polarized waves of an n-th order. A separation distance between the first optical waveguide core and the second optical waveguide core and a width of the first optical waveguide core and the second optical waveguide core are set such that a mode coupling coefficient of a p-th mode of one of the polarized waves and a mode coupling coefficient of a q-th mode of the other polarized waves match between the first optical waveguide core and the second optical waveguide core.