Through distributed fiber optic sensors, one can monitor a range of variables such as strain, temperature, and acoustic perturbations. The sensors have the spatial resolution to make measurements along the fiber’s length. The fiber optic sensor has an optical fiber connected to a source of light to enable detection where a minute profile is beneficial or in tight spaces.
The optical fiber sensors comprise a core and cladding with varying refractive indexes. The incident light beam bounces off the cladding wall and passes through the fiber without losing any light intensity.
The Meaning of Distributed Fiber Optic Sensing
Distributed fiber optic sensing is the latest technology that facilitates numerous concurrent measurements along the fiber optic cable length. Distributed optical fiber sensing utilizes optical fiber to measure physical parameters such as temperature, acoustics, Brillouin scattering, and strain. This is done with a spatial resolution of less than one meter along the optical fiber.
Distributed Acoustic Sensing (DAS) systems provide remote strain monitoring through optical fiber cables. The optical fiber cable in DAS becomes the sensing element. Raman scattering acts as a dispersed temperature sensor while Brillouin scattering is used for both localized temperature and strain sensing.
How Do Distributed Optical Sensors Work?
Optical fiber sensors can detect and quantify light properties such as wavelength, frequency, polarisation, and intensity. The optical sensors depend on light detectors with the capacity to convert incident light into electrical signals. The detectors can sense electromagnetic radiation from infrared to ultraviolet wavelengths. The fiber optic cables act as transmission lines between an external optic sensor and a test station.
When fiber optic sensing is the fiber itself, intrinsic sensing occurs. Since the fiber and external sensors do not need to be interfaced, this fiber-sensing technology reduces complexity and costs. External stimulations have to trigger the light sources inside the optic fiber cable to generate relevant information.
Rayleigh scattering occurs when light protons randomly scatter after contacting particles within the fiber. The principle enables one to determine the magnitude and position of events within an optical fiber sensor. Raman scattering yields temperature-induced alterations in photons backscattered to the source in Stokes bands.
At any point of the fiber, one can determine temperature measurement accuracy by quantifying the difference between backscattered light intensity in the Stokes and anti-Stokes bands.
Brillouin scattering occurs when acoustic sensors and external temperature predictably influence backscattered light wavelengths. The information can help to determine the type of strain the fiber experiences and the affected zones/areas of the cable.
Distributed Fiber Optic Sensing Applications
Applications of distributed optic fiber sensing include:
Optical time domain and network monitoring to characterize, protect, and inspect optical fiber networks.
Infrastructure and structural health monitoring.
Photon counting is used to measure performance beyond traditional techniques in science, quantum physics, oil and gas, life sciences, automotive, security, defense, and aerospace.
How does DAS compare with other Fiber Optic Distributed Sensing Systems?
DAS relies on Rayleigh backscattered light from minute vibrations in the fiber’s refractive index. There are other distributed fiber sensing techniques reliant on varying scattering mechanisms. These include:
Brillouin-based systems measure distributed strain sensor and temperature but are weaker than Rayleigh-based DAS systems.
Ram-based systems measure temperature. Distributed temperature sensing systems rely on Raman technology. A Raman scatter has a lower intensity than a Brillouin scatter and has to release multiple seconds/minute averages to generate valid experimental results during the forecast period. Raman-based systems can accurately measure slowly changing temperatures.
Sensing Technology
The Grand View Research Report valued the world’s distributed fiber optic sensor market at $1,292.7 million in 2021. The report also shows an anticipated cumulative annual growth rate (CAGR) of 7.3% from 2022 to 2030. The growth opportunities for the sensor market stem from enterprises’ and corporations’ need for effective sensing operations in their machines. Industries and business sectors such as automotive, aerospace, and energy utilize optic sensing to enhance their operations.
More enterprises are now investing in sensing technology, courtesy of the high functionality of DFOS. As a result, new products are emerging, enabling companies to own a larger market share.