Electroabsorption Optical Modulator With Tunable Group Delay

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Solution Overview

Problem

Conventional optical modulators, such as traveling wave optical modulators, do not have a method to adjust the group delay characteristic effectively, which is necessary for electroabsorption optical modulators to suppress the effect of group delay generated when driven by an electrical signal.

Innovation Solution

An optical modulation device comprising an electroabsorption optical modulator, a first signal line, a second signal line, and a resistor, where the resistor is connected in series with the second signal line and has an impedance different from that of the second signal line, allowing for adjustment of the group delay characteristic by varying the reflectivity and length of the second signal line.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Adaptability or versatility

If a termination resistor is provided with impedance matching the signal line (conventional approach), then signal transmission is stable, but group delay characteristic cannot be adjusted

Engineering Contradiction:

Improvegroup delay characteristic adjustmentVSAvoidsignal transmission stability

Core Design Contradiction:

Adaptability or versatilityVSReliability

Solution Approach 1:

The patent changes the impedance parameter of the termination resistor from matching the signal line impedance to being different from it. This parameter change enables group delay characteristic adjustment while maintaining signal transmission stability through controlled reflection.

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The patent converts the harmful effect of signal reflection (which occurs when impedances don't match) into a beneficial effect. The reflected wave is used to adjust the group delay characteristic, transforming what was previously a problem into a useful feature for performance optimization.

Inventive Principle:

Principle #22Blessing in disguise (Convert harm into benefit)

2Adaptability or versatility

If the characteristic impedance of the signal electrode is set different from the termination resistor resistance, then high frequency band characteristics are improved, but group delay characteristic adjustment method is not available for electroabsorption modulators

Engineering Contradiction:

Improvegroup delay characteristic adjustment methodVSAvoidsignal line structure

Core Design Contradiction:

Adaptability or versatilityVSDevice complexity

Solution Approach 1:

The patent divides the second signal line into multiple sections with different impedance values. By segmenting the signal line and assigning different impedances to different sections, the group delay characteristic can be adjusted without requiring complete structural redesign of the entire signal transmission path.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The patent applies different impedance characteristics to different parts of the signal line. The first signal line has one impedance value while the second signal line has a different impedance value, allowing localized optimization of group delay characteristic without affecting the entire system uniformly.

Inventive Principle:

Principle #3Local quality

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

Enables the adjustment of the group delay characteristic to a desired form by setting appropriate values for reflectivity and length, improving the operational performance of the optical modulator across various frequency ranges.

Implementation Method 1

The electroabsorption optical modulator performs optical modulation by applying an electric field and thereby changing an absorption edge of a semiconductor.

Methodology Applied

Scientific EffectElectroabsorption: Absorption (EM radiation)

Implementation Method 2

The resistor is connected in series with a part of the second signal line and has impedance different from impedance of the second signal line... allowing for adjustment of the group delay characteristic by varying the reflectivity

Methodology Applied

Scientific EffectElectrical reflection: Reflection

Data Source

PatentUS7936495B2Optical modulation device

Publication Date: 2011.05.03 MITSUBISHI ELECTRIC CORP

AI summary

A semiconductor optical modulation device includes a semiconductor optical modulator, wires, an output side line, an input side line and a resistor. The semiconductor optical modulator is an electroabsorption optical modulator. One of the wires is connected between an electrode of the semiconductor optical modulator and the input side line. The other of the wires is connected between the electrode of the semiconductor optical modulator and the output side line. The resistor is connected in series with the output side line. Impedance of the output side line and impedance of the resistor are different from each other.