Electro-Optic Device Bias Electrode Configuration
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Solution Overview
Problem
Z-cut LiNbO3 electro-optic modulators face issues with charge build-up leading to temperature-induced and DC-induced bias drift, as well as humidity sensitivity, resulting in optical loss and reduced service life due to complex bias electrode structures and potential for corrosion.
Innovation Solution
The RF signal electrode is used as a bias ground electrode, eliminating the need for buried bias electrodes under the RF signal electrode, and a buried bias electrode is placed over the optical waveguide between buffer layers with different conductivity, reducing voltage drops and improving humidity resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If buried bias electrodes are placed under the RF signal electrode to generate biasing electric field, then modulation efficiency is improved, but optical loss and RF wave propagation loss increase, and humidity resistance deteriorates
Solution Approach 1:
The patent extracts the bias electrode from the buried position under the RF signal electrode and relocates it to be disposed on the substrate adjacent to the optical waveguide. This extraction eliminates the overlapping configuration that caused optical absorption and RF interference, thereby reducing both optical loss and RF wave propagation loss while maintaining the biasing function through the side-adjacent configuration.
Solution Approach 2:
The patent transitions the bias electrode from a vertical stacking arrangement (buried under RF electrode) to a lateral arrangement (adjacent to optical waveguide on substrate surface). This dimensional change from vertical to lateral positioning removes the electromagnetic coupling issues and optical absorption problems while preserving the electro-optic modulation function through the side-coupled electric field configuration.
2Reliability
If complex bias electrode structures are used to address charge build-up, then bias drift is reduced, but device complexity increases
Solution Approach 1:
The patent extracts the bias electrode from the complex buried multi-layer structure and simplifies it to a single electrode disposed on the substrate adjacent to the optical waveguide. This extraction eliminates the need for multiple buffer layers and complex stacking arrangements, significantly reducing device complexity while maintaining effective charge management and bias stability.
Solution Approach 2:
Instead of placing the bias electrode under the RF electrode (conventional approach), the patent inverts the configuration by positioning the bias electrode adjacent to the optical waveguide on the substrate surface. This inversion simplifies the overall structure by eliminating the need for buried electrodes and multiple insulating layers, reducing fabrication complexity while maintaining modulation performance.
3Device complexity
If RF signal electrode is used as bias ground electrode, then device structure is simplified, but voltage control precision may be affected
Solution Approach 1:
The patent makes the RF signal electrode serve dual functions: as the RF signal transmission electrode and as the bias ground electrode. This multi-functionality simplifies the device structure by eliminating the need for separate ground electrodes, while the adjacent bias electrode configuration ensures proper voltage control through lateral electric field coupling, maintaining manufacturing precision.
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 configuration reduces optical and RF wave propagation losses, improves humidity resistance, and simplifies the device structure while maintaining modulation efficiency and reducing DC drift, thus enhancing the reliability and longevity of the electro-optic device.
Implementation Method 1
When an electric field is generated in the electro-optic material, the refractive index of the optical waveguide(s) changes, and the optical signal propagating therethrough can be altered
Implementation Method 2
an RF electrode structure for generating an RF electric field in an active section of the optical waveguide
Implementation Method 3
a bias electrode structure for generating a biasing electric field in the active section of the optical waveguide
Data Source
AI summary
An electro-optic device is disclosed, in which an RF signal electrode is used as a bias ground electrode. Thus, for Z-cut lithium niobate electro-optic crystals, there is no need to place a buried bias electrode under the RF signal electrode and over the optical waveguide. As a result, both optical and the RF wave propagation losses are reduced. In another embodiment, a buried bias electrode is placed over the optical waveguide between two buffer layers having a different electrical conductivity. The buffer layer underneath the buried bias electrode has a larger electrical conductivity than the buffer layer above the buried bias electrode. The buffer layer underneath the buried bias electrode reduces the optical loss penalty due to the buried bias electrode located above the optical waveguide, while the buffer layer above the bias electrode reduces leakage currents.