RF Phase Optical Time Domain Reflectometer for Subsea Sensing
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Solution Overview
Problem
Current methods for identifying the location of environmental disturbances in subsea optical communication systems are costly, time-consuming, and require additional maintenance, and they struggle to accurately localize seismic events and pressure changes caused by events like earthquakes and tsunamis.
Innovation Solution
The system uses SOP-OTDR and fiber acoustic sensing to measure changes in RF phase by sending an RF modulated optical signal through the in-line nodes of a submarine cable, allowing for the detection and localization of environmental disturbances such as tidal pressure and temperature changes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If prior methods of providing a sensor network along the optical communication system are used, then environmental disturbances can be detected, but the system becomes costly, time-consuming to deploy, and requires additional maintenance
Solution Approach 1:
The patent applies multi-functionality by enabling the existing optical communication fiber to serve dual purposes: data transmission and environmental sensing. The optical signal is modulated with RF signals that interact with acoustic waves in the fiber, allowing the same infrastructure to detect seismic events, temperature changes, and pressure variations without requiring separate sensor networks.
Solution Approach 2:
The system employs self-service by using the optical communication infrastructure itself for sensing purposes. The fiber optic cable, already deployed for communication, becomes the sensing medium through acoustic interactions with the optical signal, eliminating the need for additional dedicated sensor deployment and maintenance.
2Reliability
If SOP-OTDR is used to detect seismic events, then detection capability is improved, but localization accuracy remains difficult due to signal propagation over the entire cable length
Solution Approach 1:
The patent applies segmentation by dividing the continuous optical cable into discrete sensing segments using optical repeaters as reference points. Each repeater creates a localized reflection that serves as a marker, allowing the system to determine which specific segment contains an environmental disturbance by comparing phase changes across multiple segments.
Solution Approach 2:
The system transitions from one-dimensional SOP measurements to two-dimensional localization by incorporating the spatial dimension through optical repeater positions. The phase detector measures RF phase changes at different locations along the fiber, enabling precise localization of events by triangulating between multiple repeater reflections.
3Measurement precision
If fiber acoustic sensing is used, then sensitivity to seismic variations is improved, but the system requires high power and specialized equipment increasing costs
Solution Approach 1:
The patent merges fiber acoustic sensing with existing optical communication infrastructure. The RF-modulated optical signal used for communication also serves as the sensing probe, and the optical repeaters already present in the communication system provide the necessary reflection points, eliminating the need for separate high-power acoustic sensing equipment.
Solution Approach 2:
The system achieves multi-functionality by using the same optical signal for both data communication and acoustic sensing. The RF modulation embedded in the optical signal interacts with acoustic waves in the fiber, allowing the communication infrastructure to simultaneously perform sensing functions without additional specialized equipment.
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 enables real-time detection and localization of environmental disturbances, improving the accuracy and efficiency of seismic and temperature sensing in subsea environments without the need for additional maintenance or costly infrastructure.
Implementation Method 1
measuring changes in RF phase by sending an RF modulated optical signal
Implementation Method 2
fiber acoustic sensing to measure changes in RF phase
Implementation Method 3
receive reflections of the optical signal from optical repeaters
Implementation Method 4
monitoring the State of Polarization in SOP-OTDR can detect and localize earthquakes due to birefringence changes
Data Source
AI summary
A disclosed optical system comprises a repeater disposed between a first span and a second span of an optical cable and a node receiving an optical signal from the first span and transmitting a reflection to the first span. The node comprises a transmitter coupled to the first span to transmit the optical signal, transmit pulses having an RF modulated tone, and provide a local reflection; a receiver to receive the local reflection and the pulse reflection and passing a filtered spectrum; and a DSP to: determine a first RF phase of the local reflection and a second RF phase of the pulse reflection; determine a second RF phase; determine a first span seismic pressure based on the first RF phase and determine a second span seismic pressure based on the second RF phase.