Optical Modulator RF Crossing for Low-Frequency Equalization

Resolve Bottlenecks,
Find Innovative SolutionsGenerate Solutions

Solution Overview

Problem

Optical modulators face challenges in achieving equalization across a broad frequency range without increasing optical loss or modulator Vpi, as existing methods like RF bends and ferroelectric domain inversion are complex and inefficient.

Innovation Solution

Incorporating a passive optical equalizer with an RF electrical crossing in the modulator design to achieve destructive interference, particularly at low frequencies, thereby increasing bandwidth without significant optical loss or modulator Vpi.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Speed

If the modulator length is increased to maximize modulation amplitude at low frequencies, then the bandwidth is improved, but the propagation losses increase

Engineering Contradiction:

ImprovebandwidthVSAvoidoptical loss

Core Design Contradiction:

SpeedVSLoss of energy

Solution Approach 1:

The modulator is divided into multiple sections along its length, with RF crossings positioned at specific locations to create frequency-dependent attenuation. This segmentation allows different portions of the bandwidth to be optimized independently, achieving equalization without requiring the entire modulator to be excessively long.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The RF crossing structures are strategically placed at specific locations along the modulator to create localized effects. The crossing introduces destructive interference that preferentially attenuates low-frequency signals, while high-frequency signals remain relatively unaffected. This local quality modification enables bandwidth extension without proportionally increasing overall optical loss.

Inventive Principle:

Principle #3Local quality

2Speed

If driver peaking is applied to equalize the RF response, then the high frequency gain is improved, but the low frequency gain decreases and distortion increases

Engineering Contradiction:

Improvehigh frequency responseVSAvoidsignal distortion

Core Design Contradiction:

SpeedVSReliability

Solution Approach 1:

The patent converts the naturally occurring low-frequency attenuation (which is typically harmful) into a beneficial equalization mechanism. By introducing RF crossings that create additional low-frequency attenuation, the system balances the frequency response without requiring aggressive driver peaking, thereby reducing distortion while maintaining high-frequency performance.

Inventive Principle:

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

Solution Approach 2:

Instead of using driver peaking to boost high frequencies (the conventional approach), the patent inverts the strategy by using the modulator structure itself to attenuate low frequencies through RF crossing-induced destructive interference. This reversal achieves equalization without the harmful side effects of driver peaking.

Inventive Principle:

Principle #13The other way round (Inversion)

3Speed

If existing equalizer schemes are implemented to reduce EO degradation, then the frequency response is improved, but the device complexity and power consumption increase

Engineering Contradiction:

Improvefrequency responseVSAvoidmodulator structure

Core Design Contradiction:

SpeedVSDevice complexity

Solution Approach 1:

The equalization function is merged with the modulator structure itself by integrating RF crossing elements directly into the modulator design. This combination eliminates the need for separate external equalizer components, reducing overall device complexity while achieving the desired frequency response improvement.

Inventive Principle:

Principle #5Merging (Combining)

Solution Approach 2:

The modulator structure provides its own equalization capability through the RF crossing mechanism, eliminating the need for external equalization components. The RF crossings create destructive interference that naturally equalizes the frequency response, allowing the device to serve its own equalization needs without additional complex circuitry.

Inventive Principle:

Principle #25Self-service

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 RF crossing effectively attenuates low frequencies through destructive interference, maximizing modulation amplitude and maintaining Electro-optic response, suitable for various modulator types including Thin-Films Lithium Niobate, Barium titanate, and Mach-Zehnder Modulators, without increasing optical loss or modulator Vpi.

Implementation Method 1

the section after the crossing will add up to the optical wave via destructive interference thereby attenuating the modulation amplitude

Methodology Applied

Scientific EffectDestructive interference: Interference

Implementation Method 2

a plurality of Radio Frequency (RF) electrodes configured to modulate an optical signal in the optical waveguide

Methodology Applied

Scientific EffectElectro-optic effect: Electro-Optic Effects

Data Source

PatentUS12461421B2RF crossing in an optical modulator for equalization

Publication Date: 2025.11.04 CIENA CORP

AI summary

An optical modulator includes an optical waveguide extending a length; and a plurality of Radio Frequency (RF) electrodes configured to modulate an optical signal in the optical waveguide, wherein the RF electrodes include an RF crossing located an end of the length and that is configured to equalize the optical signal. The optical signal is equalized via destructive interference after the RF crossing for attenuating modulation amplitude. At or near the end of the length, high frequencies of the optical signal are already strongly attenuated whereas low frequencies of the optical signal are not such that the low frequencies are equalized after the RF crossing.