RF Interconnects for Optical Modulators Using 3D Routing
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Solution Overview
Problem
RF interconnects in optical modulators suffer from increased RF loss and reduced bandwidth due to the need for routing RF signals in multiple directions on the substrate, leading to impedance mismatches and parasitic effects, which complicate the efficient transmission of RF signals to the active region.
Innovation Solution
The implementation of RF interconnects that include interposers, such as multilayer circuit boards or micro-air coaxial stacks, which route RF signals in a three-dimensional manner directly to the active region of the optical modulator, reducing the need for substrate routing and minimizing signal path lengths.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If RF signals are routed on the substrate in a planar manner from RF input bond pads to RF electrodes, then the RF interconnect structure is simple and easy to manufacture, but RF loss increases and bandwidth decreases due to routing path length and direction changes
Solution Approach 1:
The patent transitions from planar 2D routing on the substrate to 3D routing using an interposer with multiple layers. The interposer provides vertical routing paths through vias and three-dimensional signal paths that bypass the substrate plane, reducing the RF signal path length and eliminating the need for 90-degree direction changes that cause RF loss. This dimensional change allows direct routing from RF input bond pads to RF electrodes without compromising manufacturing simplicity.
2Ease of operation
If the coaxial feedthrough is positioned at the side of the substrate and RF input bond pad is positioned parallel to the RF electrode, then the package structure is simplified, but substrate routing is required which increases RF loss and reduces bandwidth
Solution Approach 1:
The interposer serves as an intermediary component between the coaxial feedthrough and the RF electrodes on the substrate. It provides a dedicated routing path that directly connects the RF input bond pads to the RF electrodes through its internal three-dimensional structure, eliminating the need for the RF signal to traverse long paths across the substrate. This intermediary structure minimizes signal path length and reduces RF loss while maintaining the simplified package structure.
3Productivity
If multiple RF signals are planarly routed from an array of RF input bond pads to corresponding RF electrodes, then the interconnect can handle multiple signals, but RF loss is compounded due to multiple direction changes
Solution Approach 1:
The interposer utilizes its three-dimensional structure with multiple layers to route multiple RF signals simultaneously. Each RF signal can be routed through dedicated vertical paths and layers within the interposer, avoiding the need for planar routing that requires multiple 90-degree direction changes. This dimensional approach allows parallel signal routing with minimized path lengths and reduced cumulative RF loss across multiple channels.
Data Source
AI summary
A radio frequency (RF) interconnect for an optical modulator may comprise a circuit board to route a set of RF signals from a corresponding set of RF feeds to a substrate interface on a surface of a substrate of the optical modulator. The circuit board may be positioned along the surface of the substrate of the optical modulator. The circuit board may include a set of traces. A trace, of the set of traces, may be connected to a corresponding RF feed, of the set of RF feeds, at a height different than a height of the surface of the substrate of the optical modulator. The trace may be connected to the substrate interface.