Glossary
This section contains a list of terms and definitions frequently used in the field of optical fiber sensors technology and their related applications.
Accelerometer: Opto-mechanical device based on FBG technology for measuring acceleration, vibration, mechanical shock and motion.
Accuracy: Random nature quantity representing the closeness of the measured value to the true value of the measurand.
Anti-Stokes scattering: Photons matter interaction in which the material loses energy and emits a photon with higher energy than the absorbed photon.
ATEX: Term identifying EXplosive ATmosphere.
Attenuation: In optical fiber is the reduction in intensity of the light beam propagating through optical fiber medium. In optical fiber the attenuation parameter is typically quantified by the attenuation coefficient expressed in dB/Km.
Backscattering: Diffuse reflection of an electromagnetic wave back to the direction from which it came. In optical fiber is due to point defects along the core induced during the drawing process.
Bandwidth: Width of the optical spectrum of a signal or a light source.
Bend Insensitive Optical Fiber: Thanks to an appropriate doping of the core and cladding, it is possible to realize optical fibers with very low optical losses induced by tight bends of the fiber.
Borehole: It is a narrow vertically or horizontally narrow hole typically constructed to extract petroleum, natural gas or steam from geothermal well.
BOTDA: Brillouin Optical Time Domain Analysis,
BOTDR: Brillouin Optical Time Domain Reflectometry.
Brillouin scattering: Nonlinear effect caused by the nonlinearity of a medium, specifically by that part of the nonlinearity which is related to acoustic phonons.
Cable: Type of cable that has a number of optical fibers bundled together.
Calibration: Process of finding a relationship between two quantities.
Celsius: Scale and unit of measurement for temperature.
Centrifugal compressor: Turbo machine in which energy is transferred from a set of rotating impeller blades to the gas.
CERN: European Organization for Nuclear Research
Cladding: One or more layers of materials of lower refractive index, in intimate contact with a core material of higher refractive index.
Coating: The coating in a fiber optic is a protective layer composed of non-glassy material adhering to the cladding of the optical fiber. The aim of the coating is to provide mechanical protection to the fiber.
Coherence length: Useful to quantify the degree of temporal coherence of an optical signal.
Condition monitoring: Process of monitoring parameters in machinery (vibration, temperature etc.) to identify a significant change which is indicative of a developing fault.
Connector: Optical fiber cable termination in order to provide non-permanent connection between different fibers or fiber-coupled devices.
Core: Optical fiber core is a cylinder of glass that runs along the fiber's length. Which is surrounded by a medium with a lower index of refraction, typically a cladding.
COTDR: Coherent Optical Time Domain Reflectometry.
Dam: Barrier that impounds water or underground streams.
DAS: Distributed Acoustic Sensor exploiting Rayleigh scattering .
DCS: Distributed Control System.
Dead zone: In an OTDR, dead zone result from a temporary blinding of the detector following a reflective event.
Double-end: Fiber optic scheme in which both fiber ends are connected to the DTS control unit so that pump pulses are alternatively sent into the sensing fiber from both fiber end.
Down-hole: It indicates the oil or gas well environment.
Downstream: In the Oil&Gas sector refers to the refining of petroleum crude oil and the processing and purifying of raw natural gas, as well as the marketing and distribution of products derived from crude oil and natural gas.
Drilling: In Oil&Gas sector is the process which allow to build an oil or gas well.
DTS: Distributed Temperature Sensor exploiting Raman scattering.
DTSS: Distributed temperature and strain sensor typically done exploiting Brillouin scattering .
Dyke: A natural or artificial slope or wall to regulate water levels
Dynamic range: It is typically specified in dB scale and is the difference between the initial power level reflected from the fiber under test and the value equal to the noise floor of the detector.
Early warning: Major element of disaster risk reduction.
Embankment: An artificial bank raised above the immediately surrounding land to redirect or prevent flooding by a river, lake or sea.
EMI: Electro-Magnetic Interference.
EN54-22: European Standard for Resettable Line Heat Detectors.
Energy cable: It is an assembly of one or more electrical conductors, usually held together with an overall sheath.
FBG: Fiber Bragg Grating.
FBG Array: A cascade of Fiber Bragg Grating written on the same optical fiber. Thanks to the WDM configuration, FBG arrays are suitable for long distance and multi-point measurement of temperature profile, strain profile or other physical quantities.
Femtosecond laser: A femtosecond laser is a laser which emits optical pulses with a duration in the domain of femtoseconds (1 fs = 10e−15 s).
Fiber optic: An optical fiber is a flexible, transparent fiber made by drawing glass (silica) or plastic. Optical fibers are used most often as a means to transmit light between the two ends of the fiber and find wide usage in fiber-optic communications and sensing.
Floating roof tank: A storage tank commonly used to store large quantities of petroleum products such as crude oil or condensate.
Gas turbine: A type of internal combustion engine with an upstream rotating compressor coupled to a downstream turbine, and a combustion chamber in between.
HRSG: Heat Recovery Steam Generator.
Jacket: An optical cable layer protects optical fibers from external agents and damage.
Leakage detection: used to determine if and in some cases where a leak has occurred in systems which contain liquids and gasses.
LNG: Liquefied Natural Gas.
Laser: Acronym “Light amplification by stimulated emission of radiation” for a device that emits light through a process of optical amplification based on the stimulated emission of electromagnetic radiation.
Index-matching material : A substance, usually an adhesive or gel or liquid, which has an index of refraction close that of an optical fiber or another object. This substance is used in order to mitigate signal reflections.
Multi fiber cable: A fiber-optic cable having two or more fibers independently sheathed and capable of transmitting independent signals. The fibers often surround a central strength member, and can be either loose- or tight-buffered.
Multi-mode fiber: An optical fiber which support multiple transverse guided modes for a given optical frequency and polarization. It is often used as sensing element in Raman based DTS.
OFDR: Optical Frequency Domain Reflectometry.
OSA: Optical Spectrum Analyzer.
OTDR: Optical Time Domain Reflectometry.
Overhead transmission line: A structure used in electric power transmission and distribution to transmit electrical energy over large distances. It consists of one or more conductors suspended by towers.
Photonic sensors: Sensors essentially based on photons - matter interaction.
PEEK: PolyEther Ether Ketone is a high-performance engineering thermoplastic. It is used also to protects optical fibers in the most difficult environments. High strength and abrasion resistance and a maximum continuous operating temperature of 260 °C.
PIC: Photonic Integrated Circuit.
PTFE: Polytetrafluoroethylene.
Power transformer: Electrical device that transfers electrical energy between two or more circuits through electromagnetic induction.
Pressure: Force applied perpendicular to the surface of an object per unit area over which that force is distributed.
Pulsewidth: Temporal duration of an optical pulse
Raman scattering: Inelastic scattering of a photon in which a small fraction of the scattered photons are scattered by an excitation, with the scattered photons having a frequency difference from that of the incident photons. It is the scattering process used to measure the temperature along optical fiber through Raman DTS system.
Rayleigh scattering: Elastic scattering of light or other electromagnetic radiation by particles much smaller than the wavelength of the radiation. It is the scattering process used to measure the vibration along optical fiber through DAS system.
Reciprocating compressor: Positive displacement machines in which the compressing and displacing element is a piston having a reciprocating motion within a cylinder.
Reservoir monitoring: A method for enhancing oil extraction from existing and new ones oil fields. This method involves the use of seismic, pressure and temperature analysis.
RIA: Radiation Induced Attenuation.
Round-trip time: Travel time between launched pulse and returned pulse
RTD: Resistance Temperature Detector.
Sampling resolution: The minimum distance between two consecutive sampling points acquired by an ODTR based instrument.
SCADA: Supervisory control and data acquisition.
SHM: Structural Health Monitoring.
Single mode fiber: An optical fiber which is designed such that they support only a single propagation mode per polarization direction for a given wavelength.
Side Lobe Suppression Ratio (SLSR): In general, the wavelength central peak of a FBG has one or more side lobes with a wavelength slightly greater and lesser than the central one AND These peaks are usually suppressed during the manufacturing of the FBG. The SLSR is calculated as the ratio between the maximum reflected optical power of the most intense lateral lobe on the maximum optical power of the central FBG peak and is expressed in decibel.
Single-end: Fiber optic scheme in which only one fiber end is connected to the DTS control unit.
Spatial resolution: Minimum distance over which a system is able to indicate the value of the measurand within the specified uncertainty.
Splice: Permanent splice between two fibers.
Steam turbine: Device which extracts thermal energy from pressurized steam and uses it to do mechanical work on a rotating output shaft.
Stokes scattering: Photons matter interaction in which the material absorbs energy and emits a photon with lower energy than the absorbed photon.
Strain: A geometrical measure of deformation representing the relative displacement between particles in a material body.
Subsea power cable: Major transmission cable for carrying electric power below the surface of the water.
Thermocouple: A thermocouple is an electrical device for measuring temperature consisting an electrical junction of two dissimilar electrical conductors.
Upstream: In the Oil &Gas sector the upstream includes the searching for potential underground or underwater crude oil and natural gas fields, drilling of exploratory wells, and subsequently drilling and operating the wells that recover and bring the crude oil and/or raw natural gas to the surface.
Vibration: Mechanical phenomenon whereby oscillations occur about an equilibrium point.
Wavelength: The spatial period of a wave or a distance over which the wave's shape repeats.
WDM: Wavelength Division Multiplexing is a technology which multiplexes a series of optical signals onto a single optical fiber distinguishing them by using different wavelengths.
