Optical Modulator DC Voltage Application Without Bias Tees

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Solution Overview

Problem

The existing semiconductor Mach-Zehnder optical modulators face challenges in downsizing due to large inductors in bias tees, leading to difficulties in controlling direct current voltage and increasing power consumption, especially with high resistance bias resistors causing significant voltage drops.

Innovation Solution

The optical modulator design eliminates bias tees by using terminating resistors with values equal to the characteristic impedance of signal electrodes, allowing direct current voltage application without impedance influence on high frequency signals, reducing voltage drops and power consumption.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Use of energy by stationary object

If bias tees with large inductors are used to apply direct current voltage to optical waveguides, then the direct current voltage can be applied, but the device size increases making downsizing difficult

Engineering Contradiction:

Improvedirect current voltage applicationVSAvoiddevice size

Core Design Contradiction:

Use of energy by stationary objectVSArea of stationary object

Solution Approach 1:

The patent extracts and removes the bias tee component (including its large inductor) from the optical modulator structure. Instead of using a bias tee to apply direct current voltage to the optical waveguides, the invention applies the direct current voltage directly to the signal electrodes, thereby eliminating the need for the inductor and achieving device downsizing while maintaining the direct current voltage application function

Inventive Principle:

Principle #2Taking out (Extraction)

Solution Approach 2:

The signal electrodes are given dual functionality: they serve both as high frequency signal input terminals and as direct current voltage application terminals. By removing the separate bias tee structure, the signal electrodes perform multiple functions, which contributes to the overall downsizing of the optical modulator

Inventive Principle:

Principle #6Universality (Multi-functionality)

2Area of stationary object

If high resistance bias resistors are used to apply direct current voltage, then the device can be downsized, but large voltage drops occur and direct current voltage control becomes difficult

Engineering Contradiction:

Improvedevice sizeVSAvoiddirect current voltage control

Core Design Contradiction:

Area of stationary objectVSUse of energy by stationary object

Solution Approach 1:

The patent uses low resistance terminating resistors (with resistance values equal to the characteristic impedance of the signal electrodes, typically 50 ohms) instead of high resistance bias resistors. These terminating resistors are designed to handle the direct current voltage without significant voltage drops, providing stable and controllable direct current voltage to the optical waveguides while maintaining a compact device structure

Inventive Principle:

Principle #27Cheap short-living objects (Disposable)

3Area of stationary object

If high resistance bias resistors are used, then device size is reduced, but power consumption increases due to large voltage drops

Engineering Contradiction:

Improvedevice sizeVSAvoidpower consumption

Core Design Contradiction:

Area of stationary objectVSLoss of energy

Solution Approach 1:

The patent employs low resistance terminating resistors (equal to characteristic impedance, e.g., 50 ohms) in place of high resistance bias resistors. This design minimizes the voltage drops across the resistors when direct current flows, thereby reducing power consumption while maintaining compact device dimensions. The terminating resistors are optimized to provide both impedance matching and low power loss

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

This configuration enables downsizing of the optical modulator, facilitates easier control of direct current voltages, and suppresses power consumption by minimizing voltage drops across terminating resistors.

Implementation Method 1

a first signal electrode that inputs a first high frequency signal into the first optical waveguide

Methodology Applied

Scientific EffectElectromagnetic wave propagation: Electromagnetic Induction

Implementation Method 2

first and second optical waveguides that propagate divided beams of light

Methodology Applied

Scientific EffectTotal internal reflection: Total Internal Reflection

Implementation Method 3

A resistance value of the first terminating resistor is equal to characteristic impedance of the first signal electrode

Methodology Applied

Scientific EffectJoule heating: Joule Heating

Data Source

PatentUS10534239B2Optical modulator

Publication Date: 2020.01.14 MITSUBISHI ELECTRIC CORP

AI summary

An optical modulator having a small-sized circuit and a smaller voltage drop in a terminating resistor is provided. The optical modulator includes first and second optical waveguides, a first electrode inputting a first high frequency signal into the first optical waveguide, a second electrode inputting a second high frequency signal having a reverse phase relative to the first high frequency signal into the second optical waveguide, a first terminating resistor connected to the first electrode, a second terminating resistor connected to the second electrode, a connection point connecting the first and second electrodes via the first and second terminating resistors, and a DC voltage supply connected to the connection point. A resistance value of the first terminating resistor is equal to a characteristic impedance of the first electrode. A resistance value of the second terminating resistor is equal to a characteristic impedance of the second electrode.