Optical Control Element Module Impedance Matching
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Solution Overview
Problem
The existing optical control element modules face challenges in downsizing due to impedance mismatch between the input signal and the optical control element, which complicates the suppression of microwave reflections and hinders the miniaturization of the module.
Innovation Solution
The optical control element module incorporates an electrical connection part with a lead pin having a varying outer sheath conductor diameter, setting its impedance to be lower than the input signal line, allowing for impedance matching and reducing the housing size by adjusting the characteristic impedance of the electrical connection part.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If the characteristic impedance of the optical control element is reduced to 20-40Ω through substrate thinning, electrode thickening, or gap narrowing, then the bandwidth is widened and drive voltage is reduced, but impedance mismatch occurs with the 50Ω wiring substrate causing microwave reflection
Solution Approach 1:
The patent introduces an intermediary impedance transformation structure between the 50Ω wiring substrate and the 20-40Ω optical control element. This intermediate structure gradually transforms the impedance from 50Ω to 20-40Ω, preventing direct impedance mismatch and reducing microwave reflection while maintaining the high-bandwidth, low-voltage characteristics of the thinned substrate design
Solution Approach 2:
The patent changes the impedance parameter of the electrical connection path by adjusting the outer diameter of the outer sheath conductor in the lead pin. By varying this geometric parameter, the characteristic impedance of the electrical connection part is transformed to match between the 50Ω wiring substrate and the 20-40Ω optical control element, resolving the impedance mismatch problem
2Object-generated harmful factors
If a transmission line for impedance adjustment is formed in the control electrode or relay substrate, then microwave reflection is suppressed, but the device size increases
Solution Approach 1:
The patent extracts the impedance adjustment function from the control electrode or relay substrate and relocates it to the electrical connection part (lead pin). This separation allows the optical control element substrate to maintain its thinned, compact design while the impedance transformation is achieved in the external electrical connection structure, thus suppressing microwave reflection without increasing the device volume
Solution Approach 2:
The patent moves the impedance adjustment mechanism from the planar dimension (control electrode or relay substrate) to the vertical/dimensional space of the electrical connection part. By adjusting the outer diameter of the outer sheath conductor in the lead pin, impedance transformation is achieved in three-dimensional space rather than requiring additional planar space on the substrate, thereby maintaining compact device size
3Length of moving object
If solder connection is performed using an FPC to shorten the RF interface connection, then the connection length is reduced, but impedance mismatch and microwave reflection problems persist
Solution Approach 1:
The patent changes the impedance parameter of the FPC electrical connection part by adjusting the outer diameter of the outer sheath conductor. This allows the FPC to provide both short connection length and proper impedance transformation from 50Ω to 20-40Ω, eliminating microwave reflection while maintaining the compact connection advantages of the FPC approach
Data Source
AI summary
There is provided an optical control element module including: an optical control element having an optical waveguide and a control electrode on a substrate and disposed in a housing; an electrical connection part which is electrically connected to the control electrode, extends along a direction intersecting a plane on which the control electrode of the substrate is disposed, and is disposed in the housing; and a wiring substrate which has an input signal line electrically connected to the electrical connection part, at least a part of which is disposed outside the housing, in which impedance of the electrical connection part is set to be smaller than impedance of the input signal line.