Z-cut Lithium Niobate Microring Modulators with Fully Etched Waveguides
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Solution Overview
Problem
Current silicon photonics and lithium niobate on insulator (LNOI) platforms face challenges in achieving high-performance electro-optic modulation due to limitations in optical confinement and orientation sensitivity, leading to increased optical losses and reduced electro-optic efficiency in microring resonators.
Innovation Solution
The use of Z-cut lithium niobate with a transverse magnetic (TM) polarization in fully-etched optical waveguides and symmetric electrode configurations to induce strong vertical electric fields, enhancing optical confinement and reducing orientation sensitivity, thereby improving the electro-optic performance of microring resonators.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If conventional silicon photonics or LNOI platforms are used with standard waveguide configurations, then manufacturing is easier, but optical confinement is weak leading to high optical losses
Solution Approach 1:
The patent changes the waveguide geometry from ridge or channel structures to fully-etched strip waveguides with specific dimensions (e.g., 500nm x 500nm or 600nm x 600nm cross-section). This parameter change in the waveguide structure enables strong optical confinement in all directions, reducing optical losses while maintaining compatibility with standard LNOI fabrication processes
Solution Approach 2:
The patent segments the optical mode confinement in three-dimensional space by completely etching the lithium niobate waveguide, creating distinct confined regions. This full etching approach segments the optical field from the surrounding cladding materials, achieving strong confinement without requiring complex heterogeneous structures
2Reliability
If standard electrode configurations are used, then device structure is simpler, but electro-optic efficiency is reduced due to orientation sensitivity
Solution Approach 1:
The patent employs asymmetric electrode placement relative to the waveguide, with electrodes positioned at specific distances (e.g., 200nm from waveguide surface) to generate optimized electric field distributions. This asymmetric configuration maximizes the electro-optic effect by aligning the electric field with the crystal orientation while maintaining a compact structure
Solution Approach 2:
The patent transitions from planar two-dimensional electrode arrangements to three-dimensional electrode configurations positioned above and below the waveguide. This dimensional change enables strong vertical electric fields that penetrate the waveguide effectively, enhancing electro-optic modulation efficiency while reducing orientation sensitivity
3Area of moving object
If microring resonators are used for modulation, then device footprint is reduced, but orientation sensitivity increases leading to performance degradation
Solution Approach 1:
The patent changes the resonator geometry parameters by fully etching the microring waveguides to create uniform strip configurations. This parameter change makes the resonator mode confinement isotropic and less sensitive to orientation, while maintaining the compact footprint advantage of microring structures
Solution Approach 2:
The patent applies different local qualities to the microring structure by fully etching only the waveguide portions while leaving other structures intact. This creates localized regions of strong optical confinement within the resonator, reducing orientation sensitivity in critical areas while maintaining overall device compactness
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 results in high extinction ratios, fast modulation bandwidth, and efficient electro-optic tuning, enabling compact, isotropic photonic circuits with reduced optical losses and increased tuning efficiency, suitable for high-speed optical communication systems.
Implementation Method 1
The electrodes produce an electric field within the microring resonator, thus resulting in a voltage potential between the electrodes. The electric field can be a strong vertical field in the microring resonator without significantly increasing optical loss therein. In response to an electrical signal, the electrodes modulate a refractive index of the microring resonator
Data Source
AI summary
An apparatus such as an optical modulator includes a buried oxide layer is disposed on a substrate. A microring resonator and an optical waveguide are disposed on the buried oxide layer and within a bonded semiconductor layer. The optical waveguide is optically coupled to the microring resonator and inputs a first optical wave into the microring resonator. An oxide layer is deposited on top of the optical waveguide and the microring resonator. A set of electrodes is disposed adjacent to the microring resonator, and in response to an electrical signal, the set of electrodes modulates the first optical wave into a modulated optical wave of transverse magnetic polarization within the microring resonator and outputs the modulated optical wave to the optical waveguide.