Optical Modulator Ground Electrode Through-Holes Impedance
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Solution Overview
Problem
Optical modulators with ridge optical waveguides and overhang-shaped or mushroom-shaped signal electrodes face challenges in achieving high-speed modulation due to increased capacitance and reduced characteristic impedance, leading to impedance mismatch with external devices and inefficient high-frequency drive.
Innovation Solution
The introduction of through-holes in the ground electrodes, which overlap or face the signal electrode, reduces interelectrode capacitance and increases characteristic impedance, allowing for impedance matching and enabling high-speed modulation while minimizing propagation loss.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If the distance between the signal electrode and the ground electrode is reduced to achieve low drive voltage and velocity matching, then the capacitance between the electrodes increases and the characteristic impedance decreases, making it difficult to attain impedance matching with external devices
Solution Approach 1:
The ground electrode is segmented into multiple separate ground electrodes positioned at different locations. This segmentation reduces the overall capacitance between the signal electrode and ground electrodes while maintaining the low drive voltage benefit of close spacing, thereby resolving the impedance matching issue.
Solution Approach 2:
Different regions of the ground electrode structure are differentiated by positioning multiple discrete ground electrodes at specific locations rather than using a continuous ground plane. This local differentiation allows optimization of both capacitance and impedance characteristics in different regions of the electrode structure.
2Loss of energy
If the signal electrode is designed with an overhang shape to achieve velocity matching and low electrode loss, then the characteristic impedance is reduced, causing divergence from 50Ω and poor reflection characteristics
Solution Approach 1:
The ground electrode is divided into multiple separate electrodes rather than forming a continuous structure. This segmentation compensates for the impedance reduction caused by the overhang-shaped signal electrode, allowing the characteristic impedance to remain closer to 50Ω while maintaining the velocity matching and low loss benefits.
Solution Approach 2:
The geometry and positioning parameters of multiple ground electrodes are optimized to compensate for the impedance effects of the overhang-shaped signal electrode. By adjusting the positions and dimensions of the separate ground electrodes, the characteristic impedance is controlled to maintain good reflection characteristics while preserving the low electrode loss.
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 high-speed modulation and efficient drive with reduced propagation loss, effectively addressing the limitations of characteristic impedance and capacitance in existing optical modulators.
Implementation Method 1
the capacitance between the signal electrode and the ground electrode increased. Due to this, the impedance between the signal electrode and the ground electrode is reduced
Implementation Method 2
an optical modulator based on an electro-optic effect (a phenomenon in which a refractive index changes according to an applied electric field, that is, a Pockels effect and an optical Kerr effect)
Implementation Method 3
a phenomenon in which a refractive index changes according to an applied electric field, that is, a Pockels effect
Data Source
AI summary
An optical modulator has a ridge optical waveguide and a modulation electrode. The modulation electrode is composed of a signal electrode to which a modulation signal is supplied, a first ground electrode, and a second ground electrode, the signal electrode has a wide portion having a width wider than the width of the uppermost portion of the ridge optical waveguide, the first ground electrode has a central portion ground electrode component provided on a first surface so as to extend along a first direction, and the second ground electrode has a central portion ground electrode component provided on a second surface so as to extend along the first direction. The central portion ground electrode components respectively have a first and a second through-holes, and these through-holes overlap the wide portion of the signal electrode as seen in a planar view.