Optical Waveguide RF Notch Filter Using Opposite Dispersion Slopes

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Solution Overview

Problem

Existing RF filtering technologies face challenges with narrowband interference, particularly from high-power sources like jammer devices, and are sensitive to environmental polarization changes, with traditional optical notch filters being cumbersome and costly to implement.

Innovation Solution

A tunable RF filter device utilizing a tunable optical source with dual optical waveguide paths having opposite dispersion slopes, an optical splitter and combiner pair, and an optical-to-electrical converter to generate an RF output signal with deep spectral nulls and a broad passband, reducing interference and polarization sensitivity.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If a typical optical notch filter uses a coherent optical source with precise phase control, then filtering performance is improved, but device cost and complexity increase

Engineering Contradiction:

Improvefiltering performanceVSAvoiddevice cost

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The patent replaces the mechanical/electrical phase control system with an all-optical solution using dispersion slopes. The phase difference between optical paths is controlled by the inherent dispersion properties of the waveguides rather than active mechanical or electronic phase shifters, reducing device complexity and cost while maintaining filtering performance

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

Solution Approach 2:

The patent changes the control parameter from active phase modulation to passive dispersion-based phase control. By utilizing waveguides with opposite dispersion slopes, the system achieves wavelength-dependent phase control automatically, eliminating the need for expensive precise phase control mechanisms

Inventive Principle:

Principle #35Parameter changes

2Reliability

If an optical fiber is lengthened to introduce phase delay, then notch filtering is achieved, but implementation becomes cumbersome

Engineering Contradiction:

Improvenotch filtering capabilityVSAvoidimplementation ease

Core Design Contradiction:

ReliabilityVSEase of manufacture

Solution Approach 1:

Instead of changing the physical length of optical fibers to control phase delay, the patent changes the approach by utilizing dispersion slope parameters of the waveguides. The phase delay is controlled by the dispersion characteristics rather than physical dimensions, making the system more compact and easier to manufacture

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The patent inverts the conventional approach: rather than using long fiber lengths to achieve phase delay, it uses short waveguide segments with engineered dispersion slopes. The phase control is achieved through the opposite sign dispersion slopes rather than through length differences

Inventive Principle:

Principle #13The other way round (Inversion)

3Measurement precision

If coherent optical sources are used for notch filtering, then spectral null depth is improved, but polarization sensitivity increases

Engineering Contradiction:

Improvespectral null depthVSAvoidpolarization sensitivity

Core Design Contradiction:

Measurement precisionVSObject-affected harmful factors

Solution Approach 1:

The patent employs a composite waveguide structure with opposite dispersion slopes that creates a polarization-insensitive interference pattern. The combination of two waveguides with opposite dispersion characteristics produces a robust spectral null that is insensitive to polarization changes, maintaining deep nulls while eliminating polarization sensitivity

Inventive Principle:

Principle #40Composite materials

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 tunable RF filter effectively mitigates narrowband interference with deep spectral nulls and broad passband capabilities, providing robustness against high-power sources and environmental changes, while maintaining signal integrity with minimal impact on signals of interest.

Implementation Method 1

The outputs of the optical fibers may be combined to notch filter an input signal via superposition

Methodology Applied

Scientific EffectOptical interference: Interference

Implementation Method 2

first and second optical waveguide paths coupled to the modulator and having first and second dispersion slopes of opposite sign

Methodology Applied

Scientific EffectDispersion: Dispersion (of waves)

Implementation Method 3

an optical-to-electrical converter coupled to the first and second optical waveguide paths and configured to generate an RF output signal with a frequency notch therein

Methodology Applied

Scientific EffectPhotoelectric conversion: Photoelectric Effect

Data Source

PatentUS8971671B2Tunable RF filter device using optical waveguide paths with splitter and combiner pairs and related methods

Publication Date: 2015.03.03 HARRIS CORP

AI summary

A tunable Radio Frequency (RF) filter device includes a tunable optical source generating an optical carrier signal, and a modulator coupled to the tunable optical source and modulating the optical carrier signal with an RF input signal. The tunable RF filter device may include first and second optical waveguide paths coupled to the modulator and having first and second dispersion slopes of opposite sign from each other, one or more of the first and second optical waveguide paths comprising an optical splitter and combiner pair therein, and an optical-to-electrical converter coupled to the first and second optical waveguide paths and generating an RF output signal with a frequency notch therein based upon the tunable optical source.