Fiber Optic Sensing (FOS) has transformed the landscape of monitoring and diagnostics. Far beyond its origins in telecommunications, FOS now provides critical data across sectors, from safeguarding infrastructure to advancing environmental conservation. This guide dives into the inner workings of FOS, its capabilities, the revolutionary shift from early generation systems to High-fidelity Distributed Sensing (HDS), and its expansive impact.
We’ll explore the technological evolution that has made FOS a cornerstone of modern industry, opening new avenues for innovation and offering solutions to past challenges.
What is Fiber Optic Sensing?
Fiber optic sensing relies on light rays within optical fibers to detect changes in temperature, strain, and other environmental parameters. Utilizing the fiber as a sensor enables continuous measurement along its full length, sensing every centimeter of the fiber — this is referred to as distributed sensing.
The Basics
FOS is based on the properties of light and how it behaves as it travels through very thin strands of glass, known as fiber. When unperturbed light is sent through a fiber, it travels in a predictable fashion dictated by a phenomenon known as total internal reflection, i.e. bending and reflecting within.
As light moves, any changes in conditions—like temperature or pressure—slightly alter its path. Specialized instruments detect these changes, turning the fiber into a long, continuous sensor, capable of spanning 1000’s of kilometers. This method allows for extensive real-time monitoring without direct access.
The Benefits
FOS offers an array of unique advantages:
- Sensitivity: FOS detects minute changes in environmental parameters like temperature, strain, and acoustics with high precision and fidelity.
- Range: It is capable of continuous monitoring over very long distances (hundreds to thousands of kilometers) making it ideal for monitoring critical infrastructure like pipelines and power cables.
- Inherently Safe: Optical fibers function without electrical conduction, eliminating spark hazards and making them ideal for use in flammable or explosive environments. In addition, the inert nature of the silica (glass) core renders FOS immune to induced currents and electromagnetic interference
- Product Agnostic: FOS technology is effectively product-agnostic, equally capable of monitoring pipelines transporting liquids, gases, and slurry products or even cables conducting electricity. This positions FOS to support the evolving energy mix, including grid-scale electrification as well as transport of hydrogen or super critical CO2.
- Environmental Resilience: FOS operates effectively in harsh conditions, including extreme temperatures and corrosive environments.
- Operational Cost Savings: While FOS offers intuitive financial benefits associated with early detection or avoidance of leaks, it also provides direct operational savings via a host of additional applications including ILI tool (pig) tracking, real-time maintenance and remediation support, and even distributed flow and pressure monitoring.
- Versatility: Adaptable across various industries, including oil and gas, civil engineering, environmental monitoring, and more.
How Light Travels Through Fibers
The journey of light through optical fibers is a fascinating process, fundamentally governed by the physics of light propagation and reflection (also known as optics). This section dives deeper into the mechanics of how light travels within the glass, a process essential to the operation of Fiber Optic Sensing (FOS).
Total Internal Reflection
At the heart of fiber optics is the principle of total internal reflection. Light entering the fiber at a certain angle hits the boundary between the core and the cladding (two types of glass with different refractive indices). Instead of escaping, the light repeatedly reflects back into the core, continuing its journey along the fiber. This phenomenon ensures light can travel long distances through the fiber with minimal loss.
What’s a Refractive Index?
A refractive index is a measure of how much the speed of light slows down when it passes through a material. It determines how much light bends, or refracts, when entering a material from another medium. A higher refractive index means that light slows down more, causing a greater bending effect. This principle is crucial in fiber optic technology since it keeps the light contained within the fibers.
Core and Cladding
The optical fiber comprises two main components: the core and the cladding. The core, a thin glass center, carries the light. Surrounding the core is the cladding, which has a lower refractive index. This difference in refractive index is what facilitates total internal reflection, guiding the light down the fiber and keeping it from being emitted out into the surroundings.
How Sensing Works
Fiber optic sensing harnesses the properties of light within the fiber to detect environmental changes, translating even the smallest of perturbations into measurable data that can be captured, characterized and communicated. This transformation of optical fibers signals into fully distributed sensory input is a major advancement in monitoring technology, allowing for precise, real-time surveillance for a broad range of conditions along every centimetre of the fiber path.
Detecting Environmental Changes
As light propagates through the fiber, any variation in environmental conditions (like temperature, pressure, or strain) affects its behaviour. These changes slightly alter the light’s path or intensity, phenomena that are detectable with specialized equipment. Most FOS systems analyze the minute changes in the timing or intensity of the back reflected light to interpret these alterations and pinpoint exactly when, where and how the environmental conditions are shifting.
The Role of Special Instruments & Software
Instruments connected to the fiber optic network play a central role in sensing. They interpret the subtle changes in light caused by environmental factors, converting them into digital signals that can be readily analyzed by high-performance computers supported by advanced software and customized machine learning algorithms. This capability turns the optical fiber into a distributed sensor, capable of capturing and characterizing the smallest of environmental changes along its entire length.
Importance in Modern Industries
This technology has evolved from basic concepts to various applications, offering solutions for industries ranging from civil engineering to energy.
Applications
- Oil and Gas
- Civil Engineering
- Renewable Energy
- Healthcare
- Environmental Monitoring
- Aerospace and Aviation
- Marine and Subsea Operations
The adaptability of fiber optic sensing to measure a wide range of key parameters makes it invaluable across industrial sectors. Its immunity to electromagnetic interference, capacity to withstand harsh conditions, and high sensitivity enable precise and reliable data collection, crucial for safety and operational efficiency.
The Evolution of Fiber Optic Sensing
The first wave of FOS technologies introduced groundbreaking capabilities to a variety of commercial applications over 30 years ago. These early-generation systems made use of existing telecommunication fibers to ‘piggy-back’ the sensing function. While this allowed for fast and cost-effective introduction of the technology, the inherent limitations of using a fiber designed for telecommunications (referred to as low fidelity or backscatter-based fibers) presented significant challenges to their practical application for sensing.
More recently, next generation FOS technologies have emerged that utilize specialty fibers specifically designed for sensing applications. These custom-engineered sensing fibers overcome signal to noise ratio and noise floor limitations associated with standard telecommunication fiber to dramatically improve system fidelity (fidelity is the optical equivalent of sensitivity).
Next Generation Fiber Optic Sensing with Hifi HDS
Hifi’s High-fidelity Distributed Sensing (HDS) platform represents the cutting edge of FOS evolution, leveraging a patented sensing fiber architecture with unparalleled fidelity to overcome the limitations of early-gen systems while introducing a host of new capabilities and benefits. The HDS architecture relies on wavelength selective reflective elements called Fiber Bragg Gratings to dramatically increase the amount of returned light while preserving fidelity over very long distances. Fiber Bragg Gratings (FBG) are inscribed onto the core of the fiber optic cable, creating variations in the refractive index of light such that the treated fiber segment reflects light of a certain wavelength, while transmitting the other wavelengths unaffected. It’s possible to control the reflectivity of each FBG, making them ideal for high fidelity distributed fiber optic sensing applications, where having sufficient optical reflections is a key component of sensing. Furthermore, using wavelength division multiplexed (WDM) lasers and groups of FBG’s tuned to different wavelengths of light allows the extension of the optical sensing range as the launched optical power for each wavelength can be tuned optimally for the FBG grouping’s distance from the light source.
Compared to legacy systems that rely on backscatter for sensing performance (like telecom fiber-based DAS and DTS) HDS achieves fidelity factors that are orders of magnitude greater, enabling superior integration of advanced Artificial Intelligence (AI) & Machine Learning (ML) tools to deliver real-world benefits like the virtual elimination of false or nuisance alarms.
Implementing AI and ML Algorithms to Identify Event Signatures
The HDS platform pairs highly sensitive, next-generation fiber-optic cables featuring integrated measurement capabilities with advanced machine learning software to rapidly detect and accurately characterize even minor changes in temperature, strain, and acoustics occurring at any point in space or time along the full length of the monitored pipeline. Hifi’s machine learning algorithms leverage both supervised and unsupervised strategies for data clustering and pattern recognition in processing vast amounts of data to focus only on mission-critical, event-related anomalies while minimizing false positives and nuisance alarms.
Minimizing False Positives
A key limitation resulting from the lower fidelity of early-generation FOS systems is their reduced capacity to distinguish mission-critical or event-related anomalies from routine or normal operating signatures. The result is a relatively high frequency of false alarms (where routine data are misdiagnosed as events of concern) or, worse yet, missed true positives (where systems fail to capture and correctly characterize real events of concern). The impacts of these ‘nuisance’ and missed alarms are significant, increasing the demands on operational oversight, maintenance requirements, and financial outlays for asset operators.
Want to Learn More?
Fiber Optic Sensing technologies are reshaping industry standards for monitoring and operational efficiency. Offering real-time insights across various parameters, Hifi’s HDS technology drives operational sustainability, cost efficiency, and enhanced safety. For industries looking to adopt cutting-edge monitoring solutions that contribute to sustainable and efficient operations, adopting next-generation HDS is a step in the right direction.
For more information on implementing fiber optic sensing in your operations and reaping its benefits, contact our team today!