AM-FM Signal Decoding via Chirp Exploitation

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Solution Overview

Problem

Optical communication systems face limitations due to frequency chirping, which causes chromatic dispersion and requires costly, high-power lasers to suppress chirp, while existing solutions for tolerating frequency chirped modulators are not optimal and increase costs.

Innovation Solution

A communication system that exploits frequency chirping by using combined amplitude and frequency modulation, eliminating the need for phase-locked loops and allowing the use of low-cost lasers with broad line widths, through opto-electrical conversion and rectification, enabling improved receiver sensitivity and transmission performance.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Ease of manufacture

If frequency chirped modulators are used, then cost is reduced, but transmission distance is limited due to chromatic dispersion

Engineering Contradiction:

ImprovecostVSAvoidtransmission distance

Core Design Contradiction:

Ease of manufactureVSLength of moving object

Solution Approach 1:

The patent converts the harmful frequency chirping effect into a beneficial feature by using it for frequency modulation encoding. The chirp-induced frequency broadening is no longer suppressed but rather exploited to carry additional information, transforming a limitation into an advantage for the communication system

Inventive Principle:

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

Solution Approach 2:

The patent changes the operational parameters of the modulator to embrace frequency chirping rather than suppress it. By adjusting the modulation format to combined AM-FM and setting the local oscillator frequency offset to match the chirp bandwidth, the system achieves improved transmission performance and extended reach

Inventive Principle:

Principle #35Parameter changes

2Reliability

If coherent detection is used, then receiver sensitivity is improved, but device complexity increases due to phase-locked loop requirements

Engineering Contradiction:

Improvereceiver sensitivityVSAvoiddevice complexity

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The patent extracts and eliminates the phase-locked loop component from the coherent detection system. By using frequency offset detection instead of phase-locked loop, the system achieves comparable sensitivity without the complex synchronization requirements, removing a major source of device complexity

Inventive Principle:

Principle #2Taking out (Extraction)

Solution Approach 2:

The patent replaces expensive narrow-linewidth lasers with inexpensive broad-linewidth lasers. The frequency chirped modulators and local oscillators no longer require costly stabilization mechanisms, making the system economically viable for metro and access networks while maintaining adequate performance

Inventive Principle:

Principle #27Cheap short-living objects (Disposable)

3Reliability

If frequency chirp is suppressed, then transmission performance is improved, but power consumption and heat increase

Engineering Contradiction:

Improvetransmission performanceVSAvoidpower consumption

Core Design Contradiction:

ReliabilityVSUse of energy by stationary object

Solution Approach 1:

The patent inverts the conventional approach by not suppressing frequency chirp but rather exploiting it. Instead of investing power to reduce chirp through temperature control or specialized laser design, the system uses the chirp effect to enhance frequency modulation, thereby improving transmission performance while reducing power consumption

Inventive Principle:

Principle #13The other way round (Inversion)

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 approach enhances receiver sensitivity and transmission performance while reducing costs by eliminating the need for phase-locked loops and allowing the use of low-cost lasers, effectively tolerating high dynamic frequency chirping and improving chromatic dispersion tolerance.

Implementation Method 1

converting the combined local oscillator and encoded optical signal into one or more electrical signals by means of at least one opto-electrical converter

Methodology Applied

Scientific EffectOpto-electrical conversion: Photoelectric Effect

Implementation Method 2

rectifying the encoded signal current(s), thereby obtaining an encoded power spectrum

Methodology Applied

Scientific EffectRectification: Diode

Data Source

PatentUS10516488B2Decoding a combined amplitude modulated and frequency modulated signal

Publication Date: 2019.12.24 DANMARKS TEKNISKE UNIV

AI summary

The present disclosure relates to a method for decoding a combined AM/FM encoded signal, comprising the steps of: combining said encoded optical signal with light from a local oscillator configured with a local oscillator frequency; converting the combined local oscillator and encoded optical signal into one or more electrical signals by means of at least one opto-electrical converter having a predefined frequency bandwidth, thereby providing an amplified and encoded electrical signal having one or more encoded signal current(s), where one type of states have a higher oscillation frequency than other type of states; rectifying the encoded signal current(s), thereby obtaining an encoded power spectrum, wherein said power spectrum has different states, such as “0”-states and “1”-states, with different power levels such that they can be discriminated, said local oscillator frequency is defined by a positive local oscillator frequency-offset from the frequency of one of the states in said encoded optical signal, and said local oscillator frequency-offset is selected to be dependent on said frequency bandwidth.