Horizontal Coupling to Silicon Waveguides via Dielectric Trench
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Solution Overview
Problem
Coupling an optical fiber to a submicron silicon waveguide is challenging due to mode field size mismatch and potential optical leakage through the silicon substrate, which affects coupling efficiency and device performance.
Innovation Solution
A facet optical coupler is designed with a trench in the silicon substrate filled with dielectric material, positioning the waveguide at a distance from the substrate to reduce overlap and enhance coupling efficiency, and varying the waveguide's dimensions to accommodate different mode field sizes, allowing for improved horizontal coupling and reduced optical loss.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If the waveguide is positioned close to the silicon substrate, then the device complexity is reduced, but optical leakage through the substrate increases
Solution Approach 1:
A dielectric layer is introduced as an intermediary between the silicon substrate and the waveguide. This dielectric layer acts as a mediator that prevents direct optical coupling between the substrate and waveguide, thereby reducing optical leakage while maintaining a simple device structure.
Solution Approach 2:
The solution moves from a two-dimensional planar configuration to a three-dimensional vertical stacking configuration. By positioning the waveguide at a distance L above the substrate in the vertical dimension, the patent reduces optical leakage without increasing lateral device complexity.
2Reliability
If the waveguide mode field size is reduced, then the coupling efficiency to optical fiber improves, but the overlap with substrate modes increases
Solution Approach 1:
The dielectric layer serves as an intermediary that decouples the waveguide from the substrate modes. This allows the waveguide to have a small mode field size for efficient fiber coupling while the dielectric prevents unwanted overlap and coupling with substrate modes.
Solution Approach 2:
The harmful interaction between the waveguide and substrate modes is extracted or removed by introducing the dielectric layer. This separates the useful function (coupling to fiber) from the harmful effect (substrate mode overlap).
3Loss of energy
If the distance L between the waveguide and substrate is increased, then optical leakage is reduced, but the device complexity increases
Solution Approach 1:
The patent optimizes the distance parameter L to achieve the desired reduction in optical leakage. By carefully selecting L to be greater than half the mode field size, the system achieves effective leakage reduction without excessive vertical dimension increases.
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 simplifies fabrication, enhances coupling efficiency by minimizing substrate interference, and maintains mechanical strength, while allowing for efficient propagation of larger mode field sizes with reduced leakage, thus improving the overall performance of photonic integrated circuits.
Implementation Method 1
positioning the waveguide at a distance L from the first surface... minimize overlap and enhance coupling efficiency... reduced leakage
Data Source
AI summary
Techniques for forming a facet optical coupler that includes a waveguide formed over a trench of a silicon substrate are described. The trench is formed in a silicon substrate and then filled with a dielectric material. The waveguide is patterned on the dielectric material over the trench such that the waveguide is disposed a distance from the first surface. A first end of the waveguide has a first size and a second end of the waveguide distal the first end has a second size different than the first size. A material of the waveguide and the first size define a mode size of the waveguide.