Optical Waveguide Substrate Bonding for Thermal and DC Drift
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Solution Overview
Problem
Existing optical waveguide devices face issues with both temperature drift due to thermal stress and DC drift caused by differences in linear expansion coefficients and the presence of movable carriers or polar groups, which are not adequately addressed by prior adhesives and resin substrates.
Innovation Solution
The optical waveguide device employs a lithium niobate or lithium tantalate substrate with anisotropic thermal expansion, joined to a lower-dielectric α-quartz single crystal holding substrate, ensuring minimal differences in linear expansion coefficients and minimizing the use of adhesives to suppress both temperature and DC drift.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If the optical waveguide substrate is thinned to reduce drive voltages and broaden bandwidth, then the device performance is improved, but peeling or cracking occurs due to internal stress from thermal expansion differences
Solution Approach 1:
The patent changes the material parameters of the holding substrate by selecting a material whose linear expansion coefficient closely matches that of the thinned optical waveguide substrate. This parameter matching reduces thermal expansion differences, thereby suppressing internal stress and preventing peeling or cracking while maintaining the thinned substrate configuration
Solution Approach 2:
The holding substrate acts as an intermediary element that supports the thinned optical waveguide substrate. By carefully selecting the holding substrate material to have similar thermal expansion properties, it mediates the thermal stress between the thinned substrate and the low-dielectric constant layer, preventing damage
2Productivity
If a low-dielectric constant layer is disposed below the optical waveguide to broaden bandwidth, then the device performance is improved, but temperature drift occurs due to thermal expansion differences
Solution Approach 1:
The patent modifies the thermal expansion parameters of the holding substrate to match those of both the optical waveguide substrate and the low-dielectric constant layer. This parameter optimization suppresses temperature drift caused by thermal expansion mismatches while maintaining the bandwidth-enhancing low-dielectric constant layer configuration
3Strength
If adhesive materials are used to attach the optical waveguide substrate and low-dielectric constant layer, then the bonding strength is improved, but DC drift occurs due to movable carriers or polar groups in the adhesive
Solution Approach 1:
The patent extracts and removes the problematic adhesive layer containing movable carriers or polar groups from the device structure. Instead of using conventional adhesives, it employs direct bonding or alternative attachment methods that eliminate the source of DC drift while maintaining adequate bonding strength through mechanical interlocking or surface treatment
4Ease of manufacture
If resin substrates are used as holding substrates to suppress thermal stress, then the ease of manufacture is improved, but DC drift occurs due to polar groups in the resin material
Solution Approach 1:
The patent removes the resin holding substrate that contains polar groups causing DC drift. It replaces the resin substrate with alternative holding structures that provide mechanical support without introducing electrical instability, while maintaining manufacturing simplicity through direct bonding techniques or simplified assembly processes
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 effectively reduces both temperature and DC drift phenomena, maintaining substrate integrity and performance under thermal stress and electrical bias, enhancing device durability and stability.
Implementation Method 1
an optical waveguide substrate that has an electro-optic effect
Implementation Method 2
an optical waveguide substrate that is a crystal having anisotropy in thermal expansion rate
Implementation Method 3
a crystal having anisotropy in thermal expansion rate
Data Source
Figure 1~3
AI summary
An optical waveguide device including an optical waveguide substrate that has an electro-optic effect, is a crystal having anisotropy in thermal expansion rate, has a thickness set to 10 µm or lower, and includes an optical waveguide and a holding substrate that holds the optical waveguide substrate, the optical waveguide substrate and the holding substrate being joined to each other, in which the holding substrate is formed of a crystal having a lower dielectric constant than the optical waveguide substrate and having anisotropy in thermal expansion rate, and the optical waveguide substrate and the holding substrate are joined to each other such that differences in thermal expansion rate between the optical waveguide substrate and the holding substrate become small in different axial directions on a joint surface.