Low-Impedance Optical Modulator With Distributed Amplifier Matching

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Solution Overview

Problem

Standard Mach-Zehnder modulator electrodes require wide electrode gaps to achieve 50-ohm impedance, limiting the figure of merit for optical modulators and necessitating the use of transformers that add insertion loss and limit bandwidth.

Innovation Solution

A distributed amplifier with a 50-ohm input and low impedance output is used to match the impedance of standard components, coupled with an optical modulator having a low impedance coplanar waveguide, eliminating the need for quarter-wave transformers and optimizing system performance for wideband communications.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If wide electrode gaps are used to achieve 50-ohm impedance, then impedance matching with standard components is improved, but the figure of merit for optical modulators deteriorates

Engineering Contradiction:

Improveimpedance matchingVSAvoidfigure of merit

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The patent changes the impedance parameter from the standard 50 ohms to a lower value (e.g., 30 ohms) specifically for the optical modulator electrode. This parameter change allows the electrode gap to be reduced, improving the figure of merit while maintaining acceptable impedance matching through the distributed amplifier interface.

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The distributed amplifier serves as an intermediary component between the standard 50-ohm system and the low-impedance optical modulator. It provides impedance transformation and signal amplification, enabling the optical modulator to operate at lower impedance without directly interfacing with standard 50-ohm components.

Inventive Principle:

Principle #24Intermediary (Mediator)

2Power

If smaller electrode gap width is used to achieve lower half-wave voltage, then voltage requirement is improved, but impedance of transmission line deteriorates (becomes significantly less than 50 ohms)

Engineering Contradiction:

Improvehalf-wave voltageVSAvoidimpedance matching

Core Design Contradiction:

PowerVSReliability

Solution Approach 1:

The patent accepts the impedance deterioration as a necessary consequence of reducing the electrode gap width to achieve lower half-wave voltage. The system parameter for optical modulator impedance is changed from 50 ohms to a lower value, and the distributed amplifier is designed to match this new impedance level.

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

Instead of trying to maintain 50-ohm impedance and accepting high voltage requirements, the patent inverts the approach by deliberately designing for low impedance and low voltage, then using the distributed amplifier to interface with the standard 50-ohm world.

Inventive Principle:

Principle #13The other way round (Inversion)

3Reliability

If quarter-wave transformers are used to match impedance, then impedance matching is improved, but insertion loss and bandwidth limitations worsen

Engineering Contradiction:

Improveimpedance matchingVSAvoidinsertion loss

Core Design Contradiction:

ReliabilityVSLoss of energy

Solution Approach 1:

The patent extracts and eliminates the quarter-wave transformer from the system by directly designing the distributed amplifier to provide the necessary impedance transformation. This removes the source of insertion loss and bandwidth limitation while maintaining impedance matching functionality.

Inventive Principle:

Principle #2Taking out (Extraction)

Solution Approach 2:

The patent replaces the passive mechanical quarter-wave transformer structure with an active distributed amplifier system that provides impedance transformation through its gain stages and output matching network, achieving better performance in terms of loss and bandwidth.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

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 configuration achieves a five-fold improvement in half-wave voltage and 10 dB gain enhancement without sacrificing bandwidth, extending from 10 GHz to 100 GHz, while minimizing return loss and insertion loss.

Implementation Method 1

provide an amplified version of the RF signal with a voltage gain produced through the plurality of gain stages

Methodology Applied

Scientific EffectSignal amplification:

Implementation Method 2

modulate the amplified version of the RF signal to produce an intensity modulated optical signal

Methodology Applied

Scientific EffectElectro-optic modulation: Electro-Optic Effects

Data Source

PatentUS10678113B1Low impedance optical modulator

Publication Date: 2020.06.09 LOCKHEED MARTIN CORP

AI summary

Systems and methods are provided for a low impedance optical modulator in an optical device. The optical device includes a distributed amplifier having a plurality of gain stages and is configured to receive a radio frequency (RF) signal at an input of the distributed amplifier having a first impedance and provide an amplified version of the RF signal with a voltage gain produced through the plurality of gain stages to an output of the distributed amplifier having a second impedance smaller than the first impedance. The optical device includes an optical modulator coupled to the distributed amplifier and is configured to receive the amplified version of the RF signal at an input of the optical modulator having a same impedance as the output of the distributed amplifier and modulate the amplified version of the RF signal to produce an intensity modulated optical signal at an output of the optical modulator.