Optical Modulator Asymmetric Waveguide Layout for Bend Loss Reduction
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Solution Overview
Problem
In optical modulators with multiple Mach-Zehnder type modulation sections arranged in parallel on a single substrate, the challenge is to maintain equal interaction lengths and prevent increased drive voltage and substrate size while ensuring low bend loss and efficient light input, especially when electrode pads are arranged side by side, which typically results in reduced manufacturing efficiency and increased costs.
Innovation Solution
The optical modulator design includes parallel arrangement of Mach-Zehnder type optical waveguides with signal and earth electrodes, where the optical branching sections are displaced in the x-direction and have asymmetric y-direction spacing, allowing for curved waveguides with large radii of curvature to maintain equal interaction lengths and reduce bend loss, facilitating efficient light input and mounting without increasing drive voltage or substrate size.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If multiple optical modulation sections are arranged in parallel on a single substrate with electrode pads arranged side by side, then the device size can be reduced and manufacturing efficiency improved, but the interaction lengths become unequal and drive voltage increases
Solution Approach 1:
The patent applies asymmetry by intentionally designing unequal interaction lengths for different optical modulation sections. Specifically, the first optical modulation section has a longer interaction length than the second optical modulation section. This asymmetric design compensates for the unequal electrode pad arrangements and maintains equal effective interaction lengths after accounting for the different positions and dimensions of the electrode pads, thereby resolving the contradiction between manufacturing efficiency and interaction length equality.
Solution Approach 2:
The patent applies local quality by making the electrode pad configurations different for different optical modulation sections. The first electrode pad has different dimensions and position compared to the second electrode pad, allowing each section to have optimized local characteristics. This enables the system to maintain overall performance while accommodating the specific requirements of each modulation section, thus resolving the contradiction between device compactness and interaction length equality.
2Area of stationary object
If electrode pads are arranged side by side to reduce substrate size, then device miniaturization is achieved, but bend loss increases due to tighter waveguide curvature
Solution Approach 1:
The patent applies curvature by using curved waveguides to connect the electrode pads to the optical modulation sections. The curved waveguides have carefully designed radii of curvature that minimize bend loss while accommodating the compact side-by-side arrangement of electrode pads. This curved geometry allows the waveguides to smoothly transition between straight sections and the electrode pad regions, reducing optical energy loss without requiring larger substrate area.
3Productivity
If interaction length is increased to maintain modulation performance, then modulation efficiency improves, but substrate size and drive voltage increase
Solution Approach 1:
The patent applies dimensionality change by transitioning from a single-dimensional linear arrangement to a two-dimensional planar arrangement of the optical modulation sections. The sections are arranged side by side in the y-direction while maintaining their interaction lengths in the x-direction. This two-dimensional layout allows the substrate to accommodate multiple modulation sections with sufficient interaction lengths without proportionally increasing the overall substrate size, thus maintaining modulation efficiency while controlling substrate dimensions.
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 enables efficient light modulation with minimal bend loss and reduced drive voltage, allowing for cost-effective miniaturization and improved manufacturing efficiency by maintaining equal interaction lengths and preventing substrate enlargement.
Implementation Method 1
an optical waveguide device which uses an electro-optic crystal such as lithium niobate (LiNbO3) or lithium tantalate (LiTaO2)
Implementation Method 2
due to the electric field generated between the signal electrode 131 and the earth electrode 132, the refractive indices of the branching waveguides 123 and 124 respectively change as +na and −nb, so that the phase difference of the light propagated on the branching waveguides 123 and 124 changes
Data Source
AI summary
In an optical modulator, lights that have been branched by an input optical branching section are input via curved waveguides to a plurality of optical modulation sections arranged in parallel on the same substrate. In the optical modulation sections, optical branching sections of an MZ type optical waveguide are arranged shifted to an output side in the longitudinal direction (x direction) of the substrate, corresponding to an arrangement of input ends of signal electrodes. As a result, even if the input ends of the signal electrodes of the respective optical modulation sections are arranged side by side with a predetermined spacing on one side face of the substrate, input light can be applied to the respective optical modulation sections at low loss, without incurring an increase in the drive voltage.