Optical Modulation Device With Roughness-Based Light Interference Control
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Solution Overview
Problem
Variation in optical characteristics, particularly modulation extinction ratio, is observed in optical modulation devices using protruding optical waveguides with segmented electrodes due to interference of leaked light beams between segments.
Innovation Solution
The optical modulation device incorporates a substrate with a multilayer structure, where the surface roughness of the back surface and boundary surfaces between support layers is designed to scatter leaked light beams, and the clearance and thickness of the support layers are optimized to suppress interference, ensuring consistent clearance between segments.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a segmented electrode is used as a coplanar modulation electrode, then impedance matching between the modulation electrode and drive circuit is achieved, but interference of leaked light beams between segments causes variation in optical characteristics such as modulation extinction ratio
Solution Approach 1:
A ground electrode is introduced as an intermediary element between the segmented modulation electrode and the substrate. This ground electrode serves as a mediator that provides a reference potential and suppresses the interference of leaked light beams between segments, thereby maintaining both impedance matching and optical characteristics consistency
Solution Approach 2:
The harmful effect of leaked light beam interference is extracted and isolated by introducing the ground electrode structure. The ground electrode specifically targets and suppresses the interference phenomenon without affecting the impedance matching function of the segmented electrode
2Manufacturing precision
If the protruding portion is formed with high accuracy in wafer process, then manufacturing precision is improved, but variation in optical characteristics still occurs due to light beam interference
Solution Approach 1:
The ground electrode acts as an intermediary that suppresses light beam interference between segments. Even when protruding portions are formed with high accuracy, the ground electrode continues to provide protection against interference, ensuring consistent modulation extinction ratio
3Speed
If clearance between gaps of adjacent segments is kept constant, then velocity matching between high-frequency propagation velocity and optical propagation velocity is achieved, but leaked light beams still interfere with each other
Solution Approach 1:
The ground electrode is introduced as a mediator that suppresses the harmful interference of leaked light beams. It provides a reference potential that prevents light beam interference while maintaining the velocity matching achieved through constant clearance design
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 design effectively reduces the intensity of leaked light beams, minimizing their impact on optical characteristics and improving modulation performance.
Implementation Method 1
surface roughness Rab of a back surface of the substrate facing a surface of the optical waveguide layer has a relationship of Rab>λ
Data Source
AI summary
An optical modulation device includes a substrate including a multilayer portion, an optical waveguide configured with a protruding portion extending on an optical waveguide layer in the multilayer portion, and a modulation electrode formed on the optical waveguide layer to control a light wave propagating through the optical waveguide and formed to be divided into a plurality of segments along a propagation direction of light of the optical waveguide, in which in all sections of the electrode or a section excluding a part of the sections of the electrode, a clearance, measured in an extending direction of the optical waveguide, between gaps between adjacent segments is constant, the multilayer portion includes the optical waveguide layer and a plurality of support layers, and surface roughness Rab of a back surface of the substrate has a relationship of Rab>λ with respect to a wavelength λ of the light wave.