Nested Modulator Bias Control for Lower Optical Bit Error Rates

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Solution Overview

Problem

Existing optical communication systems with nested modulators face challenges in minimizing bit error rates due to variations in optimal DC bias voltages over time, and existing methods for asymmetric MZ interferometers do not address the control of nested modulators effectively.

Innovation Solution

A communication device with a nested modulator of Mach-Zehnder configuration, including sub modulators and a phase shifter, is controlled by a controller that adjusts bias voltages based on transmission and reception information to minimize error rates in both intensity and phase modulation, using a nested modulator with first and second sub modulators and a phase shifter to optimize modulation operating points.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If DC bias voltages are fixed for nested modulators, then device complexity is reduced, but modulation operating points drift over time causing increased bit error rates

Engineering Contradiction:

Improvebit error rateVSAvoidbias control mechanism

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The patent implements feedback control by monitoring the output optical intensities of the nested modulators and using this information to adjust the DC bias voltages. The controller receives intensity information, compares it with expected values, and modifies bias voltages accordingly to maintain optimal operating points and minimize bit error rates.

Inventive Principle:

Principle #23Feedback

Solution Approach 2:

The patent dynamically changes the DC bias voltage parameters of the nested modulators based on monitored performance. By adjusting these electrical parameters in real-time, the system adapts to drift and maintains optimal modulation operating points, resolving the contradiction between fixed simplicity and dynamic reliability.

Inventive Principle:

Principle #35Parameter changes

2Manufacturing precision

If output optical intensities are monitored to control DC biases, then modulation accuracy is improved, but measurement and control complexity increases

Engineering Contradiction:

Improvemodulation operating point accuracyVSAvoidintensity monitoring and bias control

Core Design Contradiction:

Manufacturing precisionVSDifficulty of detecting and measuring

Solution Approach 1:

The nested modulator system performs self-diagnosis and self-adjustment by monitoring its own output intensities and automatically correcting its operating points. The controller uses the intensity information from the modulators themselves to adjust their biases, eliminating the need for external complex measurement systems.

Inventive Principle:

Principle #25Self-service

Solution Approach 2:

The patent uses the output optical intensities as an intermediary parameter to indirectly control the DC bias voltages. Instead of directly measuring and controlling electrical parameters, the system uses optical intensity feedback as a mediator to achieve precise electrical parameter adjustment, simplifying the control mechanism.

Inventive Principle:

Principle #24Intermediary (Mediator)

3Reliability

If DC bias voltages are adjusted frequently to maintain optimal points, then communication reliability is improved, but energy consumption increases

Engineering Contradiction:

Improvecommunication reliabilityVSAvoidenergy consumption

Core Design Contradiction:

ReliabilityVSUse of energy by moving object

Solution Approach 1:

The patent implements periodic monitoring and adjustment of DC bias voltages rather than continuous adjustment. The system checks intensity parameters at intervals and adjusts biases when drift is detected, maintaining communication reliability while minimizing energy consumption compared to continuous adjustment mechanisms.

Inventive Principle:

Principle #19Periodic action

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 approach minimizes bit error rates at the receiver side by accurately setting the modulation operating points, ensuring efficient communication performance.

Implementation Method 1

phase modulation is performed on a relative phase between the two consecutive light pulses

Methodology Applied

Scientific EffectPhase modulation: Phase Modulation

Implementation Method 2

intensity modulation is performed on either one of the two consecutive light pulses to turn off it in intensity

Methodology Applied

Scientific EffectIntensity modulation:

Implementation Method 3

a phase shifter that provides a predetermined phase difference between outputs of the first and second sub modulators

Methodology Applied

Scientific EffectPhase shift:

Data Source

PatentUS12549258B2Communication device including nested modulator and bias control method for nested modulator

Publication Date: 2026.02.10 NEC CORP

AI summary

A communication device includes a nested modulator composed of sub modulators and a phase shifter. The nested modulator is controlled by: modulating a double pulse by phase and intensity modulation according to transmission information, wherein the double pulse thus modulated is transmitted to another communication device; controlling bias voltages applied respectively to the sub modulators so that a first error rate on the intensity modulation is minimized; and controlling a bias voltage applied to the phase shifter so that a second error rate on the phase modulation is minimized.