Lithium Niobate Ridge Waveguide Modulator Design
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Solution Overview
Problem
High-speed optical modulators using lithium niobate substrates face challenges in achieving low drive voltage while maintaining satisfactory modulation characteristics, as reducing film thickness improves light confinement but increases drive voltage, and increasing thickness leads to multimode operation deteriorating modulation characteristics.
Innovation Solution
An electro-optic device with a lithium niobate film ridge waveguide structure, featuring a first waveguide section with a thickness of 1 μm or larger for electric field application and a second waveguide section with a thickness of 0.3 μm to 1 μm for mode removal, allowing the multimode waveguide to operate in single mode, thereby reducing drive voltage and enhancing modulation characteristics.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the thickness of the lithium niobate film is reduced to improve light confinement, then the drive voltage increases, but if the thickness is increased to reduce drive voltage, then the optical waveguide operates in multimode deteriorating modulation characteristics
Solution Approach 1:
The optical waveguide is divided into two distinct sections: a first waveguide section with thickness of 1 μm or more for low drive voltage operation, and a second waveguide section with thickness of 0.3 μm or more and less than 1 μm for single-mode operation. This segmentation allows each section to optimize for its specific function, resolving the contradiction between drive voltage and modulation characteristics.
Solution Approach 2:
Different portions of the optical waveguide are assigned different thickness characteristics tailored to their specific functional requirements. The first waveguide section (in the electric field application region) has larger thickness for voltage efficiency, while the second waveguide section (outside the electric field application region) has smaller thickness for mode control. This local differentiation resolves the global contradiction.
2Reliability
If the thickness of the lithium niobate film is increased to improve light confinement and reduce drive voltage, then the optical waveguide operates in multimode which deteriorates modulation characteristics
Solution Approach 1:
The optical waveguide is divided into two distinct sections: a first waveguide section with thickness of 1 μm or more for low drive voltage operation, and a second waveguide section with thickness of 0.3 μm or more and less than 1 μm for single-mode operation. This segmentation allows each section to optimize for its specific function, resolving the contradiction between drive voltage and modulation characteristics.
Solution Approach 2:
Different portions of the optical waveguide are assigned different thickness characteristics tailored to their specific functional requirements. The first waveguide section (in the electric field application region) has larger thickness for voltage efficiency, while the second waveguide section (outside the electric field application region) has smaller thickness for mode control. This local differentiation resolves the global contradiction.
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 proposed structure achieves low drive voltage and improved modulation characteristics by configuring the optical waveguide to operate in single mode, effectively removing high-order modes and maintaining efficient light confinement.
Implementation Method 1
Optical modulators are one of the typical electro-optic devices, and Mach-Zehnder optical modulators in which an optical waveguide is formed by titanium (Ti) diffusion in the vicinity of a surface of a single-crystal lithium niobate substrate have been put to practical use.
Data Source
AI summary
An electro-optic device is provided with a substrate, an optical waveguide formed of a lithium niobate film with a ridge shape on the substrate, and an electrode that applies an electric field to the optical waveguide. The optical waveguide includes a first waveguide section provided at least in an electric field application region applied with the electric field and having a thickness of 1 μm or larger and a second waveguide section provided in a region other than the electric field application region and having a thickness of 0.3 μm or larger and less than 1 μm.