Optical Module Feedthrough Cavities for Impedance Matching
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Solution Overview
Problem
In high-speed optical communication systems, achieving impedance matching between transmission lines and signal pads is challenging due to parasitic capacitance issues caused by excess solder and air-filled grooves, which can lead to signal degradation.
Innovation Solution
The optical module incorporates a feedthrough with cavities under the signal pad and between signal and ground pads, filled with air, to reduce parasitic capacitance and prevent excess solder from entering these areas, maintaining designed impedance conditions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a transmission line and signal pad are configured with a micro-strip line accompanying a ground layer to secure designed impedance, then impedance matching is improved, but the transmission line width must be increased which makes the optical module larger
Solution Approach 1:
The patent introduces a vertical cavity dimension beneath the signal pad to control parasitic capacitance, moving the impedance control mechanism from purely horizontal dimensional adjustment to a three-dimensional structure. The cavity depth and configuration provide an additional degree of freedom for impedance management without increasing the transmission line width on the surface.
Solution Approach 2:
The cavity structure creates a localized region with different dielectric properties directly beneath the signal pad. By confining the air-filled cavity to specific areas under the signal pad and ground pad, the patent achieves precise local control of parasitic capacitance while maintaining compact overall dimensions.
2Reliability
If the transmission line width is increased to secure designed impedance, then impedance matching is improved, but the optical module becomes less compact
Solution Approach 1:
The patent utilizes the vertical dimension by introducing cavities beneath the pads to control parasitic capacitance. This allows impedance matching to be achieved through three-dimensional structural design rather than increasing horizontal dimensions, thereby maintaining module compactness while securing designed impedance.
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 design effectively reduces parasitic capacitance and prevents signal degradation, ensuring reliable high-frequency signal transmission without compromising the module's compactness.
Implementation Method 1
parasitic capacitance between the signal pad and the ground pad
Data Source
AI summary
An optical module that provides a feedthrough to carry an electrical signal output from and/or provided to a semiconductor optical device is disclosed. The feedthrough has a signal pad that carries the electrical signal thereon and at least two ground pads sandwiching the signal pad therebetween. The feedthrough further provides a cavity provided under the signal pad and spaces each between the signal pad and the ground pads.