Optical Modulator Layout With Displaced Ground Plane for RF Speed Matching
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Solution Overview
Problem
High-frequency RF signals used in optical communications for high bandwidth modulation pose challenges in efficiently transferring RF modulation onto optical signals, particularly due to the mismatch in the speed of optical and electrical signals, leading to signal distortion and loss.
Innovation Solution
The optical modulator design incorporates a submount with a conducting plane and an optical chip featuring semiconductor optical waveguides with RF electrodes. The optical chip is mounted in an inverted configuration, with the RF electrodes positioned to align with the optical waveguides, and a ground plane is strategically placed to support the RF transmission line, ensuring efficient modulation and minimizing cross-talk.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the RF transmission line is placed close to the optical waveguide to enable efficient RF-to-optical modulation, then the modulation efficiency is improved, but signal distortion and loss increase due to speed mismatch between electrical and optical signals
Solution Approach 1:
The ground plane is moved from the same plane as the RF electrodes to a laterally displaced plane below the optical chip, creating a three-dimensional configuration. This spatial separation allows the RF transmission line to be optimally positioned near the optical waveguide for efficient modulation while the ground plane is positioned to minimize interference and signal distortion, resolving the contradiction between modulation efficiency and signal fidelity
2Device complexity
If a coplanar ground plane is used with the RF electrodes to simplify the structure, then the device complexity is reduced, but cross-talk between adjacent modulators increases
Solution Approach 1:
The ground plane is positioned in a laterally displaced plane below the optical chip rather than in the same plane as the RF electrodes. This vertical separation in the third dimension effectively isolates the electromagnetic fields of adjacent modulators, minimizing cross-talk while maintaining structural simplicity through the use of a single continuous ground plane
3Speed
If the ground plane is placed close to the RF electrodes to reduce the RF wavelength and improve high-frequency performance, then the operating frequency is improved, but the RF signal may couple with the optical waveguide causing interference
Solution Approach 1:
The ground plane is positioned in a laterally displaced plane below the optical chip, creating sufficient vertical spacing that reduces RF wavelength for high-frequency operation while the lateral displacement ensures the ground plane does not directly couple with the optical waveguide, preventing electromagnetic interference
Solution Approach 2:
The configuration creates different spatial zones with different electromagnetic characteristics: the region near the optical waveguide is optimized for optical-RF interaction, while the laterally displaced ground plane region is optimized for RF signal confinement, allowing each zone to perform its specific function without interfering with the other
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-frequency performance up to greater than 40 GHz, maintaining low power consumption and minimizing cross-talk, while effectively matching the RF transmission speed with the optical propagation speed, thus preventing signal distortion and ensuring reliable data transmission.
Implementation Method 1
The RF signal is superimposed onto the optical signal using the RF transmission line through alteration of the index of refraction of the optical waveguide by an electromagnetic RF signal
Data Source
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AI summary
Optical modulators are described having a Mach-Zehnder interferometer and a pair of RF electrodes interfaced with the Mach-Zehnder interferometer in which the Mach-Zehnder interferometer comprises optical waveguides formed from semiconductor material. The optical modulator also comprises a ground plane spaced away in a distinct plane from transmission line electrodes formed from the association of the pair of RF electrodes interfaced with the Mach-Zehnder interferometer. The ground plane can be associated with a submount in which an optical chip comprising the Mach-Zehnder interferometer and the pair of RF electrodes is mounted on the submount with the two semiconductor optical waveguides are oriented toward the submount. Methods for forming the modulators are described.