Asymmetrical Ground Patterns for Crosstalk Suppression in Optical Modulators
Solution Overview
Problem
In optical modulators with relay substrates, crosstalk between high-frequency signal lines due to leaked microwaves is a significant issue, particularly at higher transmission rates like 400 Gb/s, which affects modulation characteristics and is challenging to suppress without compromising miniaturization demands.
Innovation Solution
The optical modulator incorporates a relay substrate with asymmetrical ground conductor patterns surrounding signal conductor patterns, and a notched portion on the relay substrate to reduce the intensity of leaked microwaves, thereby minimizing crosstalk between adjacent signal conductor patterns.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If the relay substrate is miniaturized to meet compactness requirements, then the optical modulator size is reduced, but crosstalk between high-frequency signal lines increases due to leaked microwaves
Solution Approach 1:
The patent applies asymmetry by configuring ground conductor patterns with different shapes relative to signal conductor patterns. Specifically, when signal conductor patterns are arranged in a matrix, ground conductor patterns adjacent to signal lines are designed with asymmetric geometries (e.g., different widths, lengths, or positions) rather than uniform symmetric patterns. This asymmetric configuration creates unequal coupling paths for electromagnetic fields, thereby suppressing crosstalk between adjacent high-frequency signal lines while maintaining a compact relay substrate layout.
Solution Approach 2:
The patent implements local quality by varying the characteristics of ground conductor patterns at different locations on the relay substrate. Instead of using uniform ground patterns throughout, the design adjusts the shape, size, and configuration of ground conductors specifically in regions where signal lines are densely packed or where crosstalk is most problematic. This localized optimization suppresses leaked microwaves at critical areas without requiring overall substrate enlargement.
2Productivity
If high-frequency electrical signals are transmitted at higher rates to increase transmission capacity, then transmission capacity is improved, but leaked microwaves and crosstalk between signal lines increase
Solution Approach 1:
The asymmetric ground conductor patterns create unequal electromagnetic coupling environments for adjacent signal lines. When high-frequency signals are transmitted, the asymmetric geometry causes differential reflection and absorption of leaked microwaves, reducing the intensity of radiated emissions and crosstalk. This allows higher transmission rates to be achieved without proportional increases in harmful electromagnetic interference.
3Ease of manufacture
If conventional symmetrical ground conductor patterns are used, then manufacturing is simplified, but crosstalk suppression is insufficient at high transmission rates
Solution Approach 1:
The patent maintains ease of manufacture by using standard PCB fabrication techniques for creating the ground conductor patterns. The asymmetric configurations are implemented through conventional photolithography and copper deposition processes, requiring no special manufacturing equipment or complex assembly steps. The design achieves improved crosstalk suppression through geometric variation rather than manufacturing complexity, preserving reliability at high transmission rates while keeping production straightforward.
Data Source
AI summary
An optical modulator includes a relay substrate having signal conductor patterns that connect input signal terminals and signal electrodes of an optical modulation element and ground conductor patterns, and a housing that accommodates the optical modulation element and the relay substrate. Regarding at least one signal conductor pattern, the two ground conductor patterns sandwiching the signal conductor pattern are formed in an asymmetrical shape in a plan view in a rectangular connection area including a signal connection portion at which the signal conductor pattern and the input signal terminal are connected. The connection area is centered on the at least one signal conductor pattern in a width direction, and has a width equal to a distance to the nearest adjacent signal conductor pattern and a height equal to a distance from an end of the signal connection portion farthest from a signal input side to the signal input side.