Optical Modulator Recess Design for Resonance Suppression
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Solution Overview
Problem
In optical modulators, the gaps between the flexible printed circuit and the housing, as well as between the circuit board and the housing, lead to the generation of resonance modes and parallel plate modes, which deteriorate broadband characteristics and cause crosstalk, especially in broadband systems.
Innovation Solution
The optical modulator incorporates a recess portion on the housing with varying clearances and dielectric constants, and includes features such as pillars and via holes to prevent resonance modes and parallel plate modes by electrically connecting surfaces and altering the geometry of the recess portion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a recess portion is formed on the housing to mount the flexible printed circuit, then the flexible printed circuit can be connected to the external circuit board, but gaps are generated between the flexible printed circuit and the housing bottom surface, leading to resonance modes and parallel plate modes that deteriorate broadband characteristics
Solution Approach 1:
The patent applies local quality by creating a recess portion with specifically controlled depth and dimensions at the mounting location of the flexible printed circuit. The recess portion is designed with precise local geometric parameters (depth, width, shape) to eliminate gaps between the FPC and housing bottom surface, thereby preventing resonance modes and parallel plate modes only at the critical mounting area without affecting the overall structure.
2Reliability
If the flexible printed circuit is directly connected to the external circuit board through lead pins, then electrical connection is achieved, but the lead pin shape prevents complete tight contact between the flexible printed circuit and the housing bottom surface, generating gaps
Solution Approach 1:
The patent segments the housing structure by introducing a recess portion that separates the mounting area from the rest of the housing bottom surface. This segmentation allows the flexible printed circuit to be mounted in a dedicated recessed area with controlled geometry, enabling tight contact between the FPC and the recess portion bottom surface while maintaining the overall integrity of the housing structure.
3Reliability
If gaps are present between the flexible printed circuit and the housing, then resonance modes and parallel plate modes are generated, but eliminating these gaps requires precise control of the recess portion geometry and FPC mounting position
Solution Approach 1:
The patent applies preliminary action by pre-forming the recess portion with specifically designed geometry (depth, width, shape) during housing manufacturing, before the flexible printed circuit is mounted. This preliminary structural preparation ensures that when the FPC is installed, it naturally achieves tight contact with the recess portion bottom surface, eliminating gaps and preventing resonance modes without requiring complex post-assembly adjustments.
Data Source
AI summary
An optical modulator including an optical modulation element mounted inside a housing, in which at least a portion of an electric line is connected to an external circuit board through a flexible printed circuit, and which is disposed on the external circuit board. A recess portion that mounts the flexible printed circuit is formed on an outer bottom surface of the housing and at a part where the flexible printed circuit is connected, and a device for preventing a resonance mode is provided such that a resonance mode of a microwave and a millimeter wave or a parallel plate mode is prevented from being generated among a surface A of the recess portion facing the flexible printed circuit, an electric wiring part B provided on the flexible printed circuit overlapping the surface A when seen in a plan view, an electric wiring part C provided on the external circuit board overlapping the surface A when seen in a plan view.