Multi-Span DAS Loopback with EDFA Filtering for Long-Range Sensing

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Solution Overview

Problem

Existing distributed acoustic sensing (DAS) systems are limited to a range of <50 km to 150 km and can only sense one fiber span, which is insufficient for long-haul subsea cables that can extend for hundreds or thousands of kilometers.

Innovation Solution

A DAS system with loopback assemblies and Erbium-Doped Fiber Amplifiers (EDFAs) to compensate for Rayleigh scattering loss, combined with filtering to selectively send back the sensing wavelength, allowing for extended sensing over multiple spans.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Length of stationary object

If DAS signal is transmitted over long distances in subsea cables, then sensing range is extended, but signal loss from Rayleigh scattering increases

Engineering Contradiction:

Improvesensing rangeVSAvoidsignal loss

Core Design Contradiction:

Length of stationary objectVSLoss of energy

Solution Approach 1:

The long subsea cable is divided into multiple spans, each with its own loopback assembly containing an EDFA. This segmentation allows the cable to be monitored in sections, with each section having its signal loss compensated independently, enabling extended sensing range while managing signal attenuation.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

Erbium-Doped Fiber Amplifiers (EDFAs) are introduced as intermediary devices at loopback assemblies along the subsea cable. These EDFAs act as mediators that amplify the DAS signal and compensate for Rayleigh scattering losses, enabling the signal to travel longer distances without degradation.

Inventive Principle:

Principle #24Intermediary (Mediator)

2Length of stationary object

If multiple fiber spans are monitored, then sensing coverage is extended, but system complexity increases

Engineering Contradiction:

Improvesensing coverageVSAvoidsystem complexity

Core Design Contradiction:

Length of stationary objectVSDevice complexity

Solution Approach 1:

The loopback assemblies serve multiple functions: they contain EDFAs for signal amplification, filters for wavelength selection, and enable both communication and sensing functions. This multi-functionality reduces the need for separate dedicated components for each function, thereby managing system complexity while extending sensing coverage.

Inventive Principle:

Principle #6Universality (Multi-functionality)

Solution Approach 2:

The patent combines communication infrastructure with sensing functionality by utilizing the same fiber spans for both purposes. The loopback assemblies integrate amplification and filtering functions into unified units, merging multiple operations into single locations along the cable to reduce overall system complexity.

Inventive Principle:

Principle #5Merging (Combining)

3Power

If Rayleigh scattering loss is compensated using EDFAs, then signal strength is maintained, but system cost increases

Engineering Contradiction:

Improvesignal strengthVSAvoidsystem cost

Core Design Contradiction:

PowerVSEase of manufacture

Solution Approach 1:

Instead of using a single centralized amplifier for the entire cable length, the system segments the amplification function across multiple distributed loopback assemblies. Each assembly handles a specific span, which allows for more cost-effective deployment by placing amplifiers only where needed rather than requiring a continuous amplification system along the entire cable.

Inventive Principle:

Principle #1Segmentation

4Measurement precision

If sensing wavelength is selectively filtered, then measurement precision is improved, but signal loss increases

Engineering Contradiction:

Improvewavelength selection precisionVSAvoidsignal loss

Core Design Contradiction:

Measurement precisionVSLoss of energy

Solution Approach 1:

The filtering operation is performed at the loopback assemblies before the signal returns to the DAS station. This preliminary filtering of the sensing wavelength occurs at multiple points along the cable, ensuring that only the desired wavelength is amplified and returned, improving measurement precision while the distributed architecture minimizes overall signal loss.

Inventive Principle:

Principle #10Preliminary action

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 system enables sensing over several thousand kilometers with improved localization capability and reduced system cost by doubling span length and reducing nonlinearity.

Implementation Method 1

compensating for the loss from Rayleigh scattering in the DAS signal

Methodology Applied

Scientific EffectRayleigh scattering: Rayleigh Scattering

Implementation Method 2

an Erbium-Doped Fiber Amplifier (EDFA) that is arranged to compensate a loss from Rayleigh scattering in the DAS signal

Methodology Applied

Scientific EffectErbium-Doped Fiber Amplification:

Implementation Method 3

a filter device having a filtering function that is arranged to selectively send back just the sensing wavelength of the DAS signal

Methodology Applied

Scientific EffectOptical filtering: Filter (optical)

Data Source

PatentUS12571673B2Multi-span optical fiber das system with amplified-filtered loopback (AFLB)

Publication Date: 2026.03.10 SUBCOM LLC

AI summary

A sensing system may include a distributed acoustic sensing (DAS) station to launch a DAS signal as an outbound DAS signal, as well as a plurality of DAS loopback assemblies, arranged along a plurality of spans. The plurality of DAS loopback assemblies may be arranged to separately process the outbound DAS signal, and return to the DAS station, the outbound DAS signal, as a return DAS signal that comprises a backscattered Rayleigh signal. As such, a given DAS loopback assembly of the plurality of DAS loopback assemblies may include an Erbium-Doped Fiber Amplifier (EDFA) that is arranged to compensate the loss from Rayleigh scattering of the DAS signal, and a filter device having an optical filtering function that is arranged to selectively send back just a sensing wavelength of the DAS signal.