Mach-Zehnder Optical Modulator Pre-Chirp Dispersion Compensation

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Solution Overview

Problem

Existing SFP optical transceivers face challenges in compensating for wavelength dispersion, especially in mobile networks with cost constraints, and in achieving suitable reception sensitivity for long-distance optical communication.

Innovation Solution

A Mach-Zehnder type optical modulator is designed with specific directional couplers and a phase modulation unit to impart a negative α parameter, enabling pre-chirping to compensate for wavelength dispersion and improve transmission characteristics.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Duration of action of moving object

If a Mach-Zehnder type optical modulator is used for long-distance transmission, then transmission distance is improved, but wavelength dispersion causes reception sensitivity to deteriorate

Engineering Contradiction:

Improvetransmission distanceVSAvoidreception sensitivity

Core Design Contradiction:

Duration of action of moving objectVSReliability

Solution Approach 1:

The patent applies pre-chirping technology that imparts a negative α parameter to the optical signal before transmission. This preliminary action compensates for the positive wavelength dispersion that will occur during transmission through standard single-mode fiber, thereby maintaining reception sensitivity over long distances without requiring dispersion compensation fiber or digital coherent processing

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The patent changes the chirp parameter (α parameter) from its conventional positive value to a negative value by modifying the modulation waveform. This parameter change enables the optical signal to have dispersion characteristics that are opposite to those of standard fiber, allowing for dispersion compensation without additional hardware

Inventive Principle:

Principle #35Parameter changes

2Reliability

If dispersion compensation fiber is used to compensate for wavelength dispersion, then reception sensitivity is improved, but device complexity and cost increase

Engineering Contradiction:

Improvereception sensitivityVSAvoidsystem complexity

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The patent extracts the dispersion compensation function from the transmission path and integrates it into the modulation process itself. By implementing pre-chirping in the optical modulator, the need for separate dispersion compensation fiber is eliminated, simplifying the overall system while maintaining reception sensitivity

Inventive Principle:

Principle #2Taking out (Extraction)

Solution Approach 2:

The patent uses a specifically designed modulation waveform as an intermediary that carries pre-chirped characteristics. This intermediary signal compensates for fiber dispersion during transmission, replacing the need for physical dispersion compensation fiber and reducing system complexity

Inventive Principle:

Principle #24Intermediary (Mediator)

3Object-affected harmful factors

If digital coherent technology is applied for waveform compensation, then wavelength dispersion is compensated, but power consumption and cost increase

Engineering Contradiction:

Improvewavelength dispersionVSAvoidpower consumption

Core Design Contradiction:

Object-affected harmful factorsVSUse of energy by moving object

Solution Approach 1:

The patent replaces complex digital signal processing (DSP) with an optical domain solution. By implementing pre-chirping directly in the optical modulator, the need for expensive and power-intensive digital coherent processing is eliminated, achieving dispersion compensation through optical waveform shaping instead of electronic processing

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

Solution Approach 2:

The patent uses a simple pre-chirped modulation waveform that can be generated with basic modulator circuitry, replacing the need for expensive digital coherent receivers and DSP hardware. This approach achieves dispersion compensation with minimal additional cost and power consumption

Inventive Principle:

Principle #27Cheap short-living objects (Disposable)

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

The solution effectively compensates for wavelength dispersion, enhancing the reception sensitivity and enabling long-distance transmission in SFP optical transceivers, while being cost-effective and compatible with silicon photonics technology.

Implementation Method 1

a phase modulation unit configured to provide a phase difference between the light propagating through the first arm and the light propagating through the second arm

Methodology Applied

Scientific EffectElectro-optic effect: Electro-Optic Effects

Data Source

PatentUS12339561B2Mach-Zehnder type optical modulator, optical transceiver, and dispersion compensation method

Publication Date: 2025.06.24 NEC CORP

AI summary

A first directional coupler branching input light into a cross-port path having a branching ratio η and a bar-port path having a branching ratio 1-η. A first arm propagating light from the cross-port path of the first directional coupler; a second arm propagating light from the bar-port path of the first directional coupler. A second directional coupler outputting output light acquired by combining the light being input from the first arm and the light being input from the second arm at the cross-port branching ratio γ and the bar-port branching ratio 1-γ. A phase modulation unit providing a phase difference between the light propagating through the first arm and the light propagating through the second arm. η and 1-η, and γ and 1-γ are determined such that an α parameter being a chirp parameter is a negative value.