Optical Waveguide Reinforcement Member Layout
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Solution Overview
Problem
In optical waveguide devices, heat shrinkage of objects on substrates with piezoelectric effects leads to refractive index changes and deteriorates transmission characteristics due to stress-induced refractive index distributions, particularly in multilayer structures with different materials, causing unequal branch ratios and loss differences in Mach-Zehnder type waveguides.
Innovation Solution
The optical waveguide device features a substrate with an optical waveguide and an object disposed to cover part or all of the mode conversion/branching portion, ensuring the object does not consecutively cover sections over a predetermined length in the light wave's advancing direction, with a clearance of 20 μm or higher between sections, to minimize refractive index changes and stabilize branch ratios.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If objects (reinforcing members or control electrodes) are disposed on the front surface of the substrate to reinforce or control the optical waveguide, then the structural strength or control function is improved, but stress changes occur due to heat shrinkage differences, causing refractive index distribution and deteriorating transmission characteristics
Solution Approach 1:
The object is disposed to cover only specific portions of the optical waveguide (such as the input/output portions or sections with lower stress sensitivity) while leaving other portions (particularly the mode conversion/branching portion and high stress-sensitive areas) uncovered. This localized disposition allows the object to provide reinforcement or control functions where needed while avoiding the generation of refractive index distribution in critical regions, thus resolving the contradiction between structural strength and transmission characteristics
2Area of stationary object
If the object covers the mode conversion/branching portion of the optical waveguide, then the structural support or control coverage is improved, but stress-induced refractive index changes occur in this critical region, causing unequal branch ratios and loss differences
Solution Approach 1:
The object is strategically disposed to cover areas with lower sensitivity to stress-induced refractive index changes (such as straight waveguide sections) while deliberately leaving the mode conversion/branching portion uncovered. This selective coverage ensures that the critical branching region maintains uniform refractive index and equal branch ratios, while still providing structural support or control in other regions
3Device complexity
If the substrate is made thin to reduce device size and complexity, then the device compactness is improved, but the substrate becomes more susceptible to stress and heat shrinkage effects, exacerbating refractive index distribution
Solution Approach 1:
The object is disposed to provide localized reinforcement or control at specific critical portions of the thin substrate (such as connection portions or high-stress areas) while leaving the optical waveguide propagation regions, particularly the mode conversion/branching portion, uncovered. This localized approach provides stress resistance where most needed without introducing refractive index distribution in the optical paths
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 suppresses deterioration in transmission characteristics by reducing refractive index distributions and branch ratio differences, enhancing the stability of light wave propagation and reducing On/Off extinction ratio losses in Mach-Zehnder type waveguides.
Implementation Method 1
A material such as lithium niobate (LN) used for the substrate 10 has an excellent piezoelectric effect, and, thus, in a case where the substrate 10 receives external force or stress occurs in the substrate 10, a refractive index of the corresponding portion changes
Implementation Method 2
An object (disposed object) such as the reinforcing member 31 or the control electrode 32 disposed on the front surface of the substrate 10 is subjected to heat shrinkage due to a temperature change, but the degree of heat shrinkage differs since linear expansion coefficients or Young's moduli thereof are different from each other. Thus, stress corresponding to a heat shrinkage difference occurs in each object, and, as a result, a refractive index of the substrate 10 changes due to the stress of each object
Implementation Method 3
The optical waveguide 20 has a plurality of Y-branch waveguide sections 21 that distribute a light wave propagating through the optical waveguide into branches an equal power ratio. A mode conversion section 22 that converts a light wave mode before a light wave is branched is disposed on an upstream side of each Y-branch waveguide section 21 in a light wave advancing direction
Data Source
AI summary
An optical waveguide device includes a substrate on which an optical waveguide is formed, and an object that is disposed on the substrate. The optical waveguide includes a mode conversion/branching portion that converts a mode of a light wave propagating through the optical waveguide and branches the light wave, and the object is disposed to cover a part or the whole of the mode conversion/branching portion or not to cover the mode conversion/branching portion when the substrate is viewed in a plan view. In a case where the object is disposed to cover a part of the mode conversion/branching portion, the object is disposed not to consecutively cover a section over a length of a predetermined value or higher in an advancing direction of a light wave.