Optical Modulator Phase Error Compensation

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Solution Overview

Problem

Conventional semiconductor Mach-Zehnder modulators experience amplitude changes in output light due to phase modulation based on the quantum-confined Stark effect, leading to intensity variations between codes [0] and [1], which deteriorate transmission performance.

Innovation Solution

An optical modulator configuration with first and second modulation waveguides, phase adjustment waveguides, and controllers to manage voltages and phases, ensuring equal amplitude addition regardless of phase differences, and adjusting phase errors to maintain constant output intensity across codes.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If phase modulation is performed based on the quantum-confined Stark effect in semiconductor Mach-Zehnder modulators, then phase modulation capability is achieved, but amplitude changes occur in output light causing intensity variations between codes

Engineering Contradiction:

Improvetransmission performanceVSAvoidoutput light intensity

Core Design Contradiction:

ReliabilityVSIllumination intensity

Solution Approach 1:

An auxiliary waveguide is introduced as an intermediary element to generate compensation light that counteracts the amplitude variations in the signal light. This compensation light acts as a mediator to cancel out the harmful amplitude changes caused by the quantum-confined Stark effect, thereby maintaining constant output intensity while preserving phase modulation capability

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The invention changes the operating parameters of the modulator by applying reverse-phase modulation signals to the auxiliary waveguide. By controlling the phase and amplitude of the compensation light through parameter adjustment, the system compensates for intensity variations and maintains constant output regardless of the modulation state

Inventive Principle:

Principle #35Parameter changes

2Ease of operation

If the first and second modulation waveguides change refraction factors according to input voltages, then phase modulation is achieved, but absorbed amounts change simultaneously causing amplitude variations

Engineering Contradiction:

Improvephase modulation controlVSAvoidlight absorption

Core Design Contradiction:

Ease of operationVSLoss of energy

Solution Approach 1:

The invention converts the harmful absorption effect into a beneficial compensation mechanism. The auxiliary waveguide is designed to exhibit similar absorption characteristics, but by controlling its modulation signal in reverse phase, the absorption-induced amplitude changes in the compensation light cancel out those in the signal light, transforming a harmful effect into a useful compensation mechanism

Inventive Principle:

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

Solution Approach 2:

The compensation light generated in the auxiliary waveguide acts as a counterweight to the amplitude variations in the signal light. By carefully controlling the phase and amplitude of the compensation signal, the system creates an opposing effect that balances out the harmful absorption variations, resulting in constant total output intensity

Inventive Principle:

Principle #8Anti-weight (Counterweight)

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

Prevents output light intensity variation during phase modulation, thereby maintaining consistent transmission performance despite absorption in the modulator waveguides.

Implementation Method 1

phase modulation is performed based on the quantum-confined Stark effect, the first and second modulation waveguides change in absorbed amounts simultaneously with the changes in refraction factors according to the voltages of the differential modulation signals

Methodology Applied

Scientific Effectquantum-confined Stark effect:

Implementation Method 2

a first phase adjustment waveguide that changes a phase of a light phase-modulated by the first modulation waveguide; a second phase adjustment waveguide that changes a phase of a light phase-modulated by the second modulation waveguide

Methodology Applied

Scientific Effectphase modulation: Phase Modulation

Data Source

PatentUS8638486B2Optical modulator and optical modulation method

Publication Date: 2014.01.28 MITSUBISHI ELECTRIC CORP

AI summary

An optical modulator includes first and second modulation waveguides, a demultiplexer, first and second phase adjustment waveguides that changes phases of a light of the first and second modulation waveguides, a multiplexer that combines light outputs from the first and second phase adjustment waveguides, a gain controller and a modulator bias controller in which voltages of the first and second modulation signals are controlled so that a result of adding light from the first modulation waveguide to light from the second modulation waveguide where light from the first modulation waveguide has a predetermined phase is equal to a result of adding light from the first modulation waveguide to light from the second modulation waveguide where light from the second modulation waveguide has a predetermined phase. A phase-adjustment bias controller that controls phase amounts changed by the first and second phase adjustment waveguides so as to cancel phase errors.