Fiberpaedia exists as a tool to help explain the terminology that we come across everyday in our working lives. We have found that the definitions, explanations and equations are sought after and appreciated by many currently working in our industry, as well as those studying with the intention of one day becoming part of the industry. We hope you find it useful.
A
Absorption
When a fiber absorbs, less power will be seen at the output than was put into the fiber….
Acceptance Angle
The acceptance angle θa is the maximum deviation from the fiber axis at which light will go into…
Active Medium
Any material that has a dynamic response to light (generally an output gain) can be regarded as an…
Aluminosilicate Glass
Silica (pure SiO2) can be doped with aluminium (Al), mostly as alumina (Al2O3), for several reasons. It increases…
Amplified Spontaneous Emission
Atoms in an excited state will spontaneously emit photons when they fall back to their lower, or ground…
Amplifier
A device which introduces gain into a signal passing through it. In fiber optics amplifiers can be made…
Armored Stainless Steel Tube
For example, if equal lengths of 80um fiber and 125um fiber are coiled to a 15mm diameter, the…
Attenuation
When a fiber attenuates (also known as background loss), less power will be seen at the output than…
B
Beat Length
Light in the fast and slow axes travels at slightly different speeds, and so when a laser source…
Bend Edge
The wavelength region above which, for a certain bend radius, a fiber can no longer effectively guide the…
Bend Induced Loss
Bend induced loss (BIL) is the loss of light due to bending a fiber. When a fiber is…
Bend Insensitive Optical Fiber
Bend insensitivity can be considered in terms of both the mechanical and optical performance of a fiber. In…
Birefringence
Means there are two axes with different refractive indices in the material. When a material is described as…
Birefringent Fiber
When a light wave travels through a birefringent optical fiber, the birefringence of the fiber will lock the…
Borosilicate Glass
Silica (SiO2) can be co-doped with boron (B), which can induce the huge directed stresses associated with bow-tie…
Bow-Tie Fiber
It is a highly birefringent or HiBi SAP fiber where the stress across the core is created by…
Brillouin Scattering
Backscatter of light at a shifted frequency. Interaction of light (photons) with high energy vibrational quanta (phonons) having…
Broadband
In optics the term broadband indicates a system where the wavelength region involved is relatively wide. In a…
Buffered Fiber
In fiber optics, a buffer is a jacket cable that offers additional mechanical protection to the fiber optic….
C
Carbon Coated
Carbon can be applied as a thin primary coating in combination with a secondary coating of high temperature…
Carbon Polyimide
The carbon coating acts as a hermetic seal to stop hydrogen ingress in hydrogen rich environments (up to…
Cardiac Angiography
Cardiac angiography (also known as cardioangiography and coronary angiography) is a type of X-ray examination that creates detailed…
Chromatic Dispersion
The effect where light at different wavelengths spread out (disperse in the material). Chromatic dispersion determines both the…
Cladding
The cladding is the region of the fiber surrounding the core. In order to create guiding conditions for…
Cladding Pump Fiber
A cladding pump fiber has a structure typically formed by a single mode active core, a large area…
Clustering
If too many rare-earth ions are crammed into the glass structure of a fiber, without careful incorporation of…
Co-Operative Up-Conversion
Where two ions work together to absorb energy, which increases the energy level that can be reached. This…
Co-Propagating Pump
Where the pump and signal light are input to a doped fiber in the same direction. Related Products:…
Coating
The coating is a non-glass layer(s) applied to the optical fiber with the objective of offering mechanical protection…
Coating Concentricity
The coating concentricity defines the relative position of the coating with respect to the glass in an optical…
Coherent Light
Light where the wave fronts line up is referred to as spatially coherent and light where the wave…
Color
The color of light is intrinsically related to its wavelength. The ultra-violet (UV) spectrum takes over from x-rays…
Concentricity
The fiber is composed of several layers of coaxial structure; the core, the cladding, the primary coating and…
Confinement Factor
Confinement refers to the amount of the core which is doped. Fibercore fabricate doped fibers with uniform doping…
Connector Types
There are many different types of connectors which have evolved as standard in various applications. The most common…
Core
The core is the central region of the optical fiber where the light is guided. In order to…
Core Concentricity
The core-cladding concentricity defines the relative position of the core with respect to the cladding in an optical…
Core Ellipticity
Generally speaking, core ellipticity (the term ‘core circularity’ usually refers to the inverse concept as core ellipticity) refers…
Core to Cladding Diameter Ratio (CCDR)
This parameter is simply the ratio of core and cladding diameters. In order to minimise the attenuation through…
Counter-Propagating Pump
Where the pump and signal light are input to an amplifier fiber in the opposite direction. Related Products:…
Cross section
A cross section (σ) quantifies the probability of an optical interaction happening. Units are in terms of area…
Cross-Coupling
Cross-coupling is the process by which power is transferred from one mode to another. In the case of…
Cut-Off Wavelength
The second order mode cut-off wavelength (commonly shortened to cut-off) refers to the wavelength above which the fiber…
D
Decibel Scales
Decibels, or dB units, provide a convenient way to express relative levels between powers that differ by many…
Defects
In a perfect germanosilicate glass, the silicon atoms and germanium doping are evenly distributed throughout the glass, and…
Differential Group Delay (DGD)
For a polarization maintaining fiber, this is a measure of the difference in transit time for light launched…
Distributed Temperature Sensing
Distributed Temperature Sensing (DTS). Here, optical fiber is used in situations where it is likely to be exposed…
Doping Density
Doping density (N0) is the amount of deliberately introduced impurities in the glass. Doping density, or concentration, is…
Double-Clad fiber
A typical conventional fiber design has a core of doped silica glass with a cladding of pure silica,…
Downhole Fiber Optic Cable
This is a fiber optic cable that has been specifically designed to withstand the harsh environments of an…
Downhole Fiber Sensor
An optical based sensor that is designed to be used to measure an attribute in an O&G well.
E
Effective Area
Effective area (Aeff) is the intensity in the fiber is commonly related to the power incident over an…
Electromagnetic Spectrum
The electromagnetic spectrum is the range of wavelengths in which electromagnetic waves can exist. It can be thought…
Elliptical Clad Fiber
One design of HiBi fiber. An elliptical cladding of boron doped glass around the core causes an asymmetric…
Elliptical Core Fiber
If the core of a fiber is highly elliptical it can present some birefringence to the light depending…
Emission Cross Section
Emission cross section (σem(λ)) is the probability that there is an excited ion in a given cross sectional…
Emission Measurement
In order to assess the emission spectrum of a fiber, it is excited by pumping into an absorption…
Emission Spectra
When an active fiber, such as an erbium doped fiber (EDF), is pumped at a short wavelength it…
End Face
The section of an optical fiber end which acts as the interface with air or another optical fiber/component….
Energy
Energy is often defined as the capacity of a system to do work. Outside of a physics lesson…
Erbium
Erbium (Er) is a rare-earth metal with particularly useful energy dynamics for making telecoms wavelength optical sources. Erbium…
Erbium Doped Fiber (EDF)
Optical fiber with erbium incorporated (doped) into the core structure. They have particular absorption/emission characteristics which make the…
Erbium Doped Fiber Amplifier (EDFA)
An amplifier is used to boost optical signals to higher power, often used both at launch and within…
Excited State
When an atom or molecule absorbs energy the electrons are excited to move around more dynamically, referred to…
Excited State Absorption (ESA)
Rare earth ions can absorb additional pump or signal photons when it is already in an excited state,…
Extinction Ratio
Cross coupling in regards to a birefringent fiber, quantified by extinction ratio, indicates the amount of light which…
F
Far Infrared
The far infrared (F-IR) consists of the portion of the electromagnetic spectrum with wavelengths in the range ~10-1000µm…
Faraday Effect
The Faraday effect is the rotation of the polarization state of light when it passes through a magnetic…
Fast Axis
The fast axis of a birefringent fiber is the axis in which the index of refraction is lower….
Femtosecond FBG
Unlike standard Fiber Bragg Gratings (FBGs), which are typically inscribed using a ultraviolet (UV) continuous wave laser, it…
Fiber
An optical fiber has a core and cladding layer, where light is guided mainly in the core region….
Fiber Bragg Grating (FBG)
A reflecting filter based on alternating regions of relatively high and low index. FBG’s can be used as…
Fiber In Metal Tube (FIMT)
A construction that has optical fibers encased by a thin walled metal tube that is typically made out…
First Order Susceptibility
First order susceptibility (χ(1)) is the polarization, P, of light in a medium is related to the linear…
Fluorosilicate Glass
Silica (pure SiO2) can be doped with fluorine (F), to reduce index. This is referred to a fluorosilicate…
Form Birefringence
Form birefringence is created as a result of an asymmetric core shape for the two axes. This core…
Frequency
The frequency of an optical wave (and other types of electromagnetic waves) is defined as the number of…
Fresnel Reflection
Any interface where the index of refraction differs will cause light to be reflected, known as Fresnel reflection….
Frit
To incorporate some rare earth ions into the core of a MCVD fiber, a solution doping technique is…
Full-Width at Half Maximum (FWHM)
A source which is said to be one color, or monochromatic, will always contain some spread of wavelengths,…
G
Gain Coefficient
Gain Coefficient (g*(λ)) is equivalent to the emission spectrum per unit length. The gain is offered by a…
Germanosilicate Glass
Silica (pure SiO2) can be doped with germanium (Ge), increasing the index of the doped glass. The resulting…
Giles Parameter
The parameters used to model erbium doped fiber amplifiers. The Giles parameters are α(λ) the absorption spectrum per…
Graded Index MM Fiber
In the case of multimode (MM) fibers, it is common to have a graded refractive index. In the…
Ground State
Electrons in a material are in a ground state when the material is in its lowest energy condition….
Group Delay Dispersion (GDD)
The group delay dispersion is the change in the group delay depending on the frequency of the propagating…
Group Index and Velocity
Light typically has some spread of wavelengths, as it is never truly a single pure colour. The group…
Group Velocity Delay (GVD)
The dispersion resulting from wavelength dependence in the propagation of light, which tends to spread out or delay…
Gyroscope
A gyroscope, also known as a gyro, is a sensor which measures angular acceleration. A fiber gyroscope is…
Gyroscope Fiber
Generally refers to the highly birefringent polarization maintaining fibers used to manufacture fiber optic gyroscope (FOG) coils. These…
H
H-Parameter
H-parameter, or holding parameter, is important because it is another widely-used measure of the polarization-maintaining performance of an…
Haptic Sensing
Haptic sensing recreates the sense of touch when interacting with equipment, such as a medical device, by applying…
Hermetic Sealed Optical Fiber
An optical fiber coated with a non-porous layer of material (often carbon) which seals off the fiber from…
High Temperature Coatings
Fiber optics are provided with various coatings, some of which are optimised for heat protection. The most common…
Highly Birefringent (HiBi)
A highly birefringent optical device has a different index of refraction along each orthogonal axis. In crystals these…
Hydrogen Resistant
Hydrogen resistant fibers can withstand hydrogen-rich environments whilst maintaining a high level of optical performance. There are two…
Hydrogen Scavenging Gel
A filling gel commonly used inside a FIMT (Fiber In Metal Tube) in downhole cables to fill empty…
I
In Vitro
The term in vitro (Latin for ‘within the glass’) refers to a medical study or experiment that is…
In Vivo
The term in vivo (Latin for ‘within the living’) refers to a medical test, experiment or procedure that…
Incoloy®
Incoloy® is the brand name given to a high performance nickel-iron-chromium alloy. There are various grades of Incoloy®…
Infrared (IR)
The longest visible red wavelength is ~750nm, and beyond this is the infrared (IR) spectrum. Near-infrared (N-IR) continues…
Inner Coating
The coating is the non-glass protective material applied to the fiber. It is most commonly a dual layer…
Interferometry
Interferometry is the process of combining two coherent beams of light, in order to measure properties of the…
Irradiance
A measure of light intensity falling on a given area Related Terms: Energy, Light, Photon, Power, Power Density
J
Joule Heating
Absorption of energy by the fiber can lead to heating of the glass lattice, though normally this is…
K
Kerr Coefficient
The intensity of light can modify the propagation in a fiber and the output from it. The non-linear…
L
Large Mode Area (LMA) fiber
Due to the very small core area in optical fibers, as the power contained is increased the power…
Laser
Laser – Light Amplification by Stimulated Emission of Radiation is a very useful optical source, as it can…
Laser Eye Surgery
Laser eye surgery (also known as refractive surgery or vision correction) corrects poor vision, by reshaping the cornea….
LASIK
LASIK (laser-assisted in situ keratomileusis) is the most commonly performed laser eye surgery for treating farsightedness (hyperopia), nearsightedness…
Lifetime Fluorescence
In terms of optics and excited states, the lifetime is the mean time an electron will remain in…
Lifetime Mechanical
In terms of mechanical fatigue, the lifetime is taken to be the most probable duration a fiber will…
Light
Light is optical energy. It is an electromagnetic wave that has an electric field that changes periodically with…
Light Emmitting Diode (LED)
A semiconductor device which emits light. Under an applied current, electrons move between energy states in dissimilar semiconductor…
Linear Susceptibility
Linear Susceptibility (χ(1)) is the susceptibility is associated with bound electrons (dipoles) moving around as the light propagates…
Linewidth
A source which is said to be one color, or monochromatic, will always contain some spread of wavelengths,…
Logging Cable
A type of downhole cable used for well monitoring in the oil and gas sector.
Loss
Losses are essentially the discrepancy between the power launched into a system in comparison to that detected at…
M
Macro-Bending loss
Losses occur at bends as light in the bend tends to want to carry on in a straight…
Material Dispersion
Light of different colors travels at different phase velocity, so it can spread out physically as it moves…
Metal Coated Optical Fiber
Optical fiber that is coated with a metallic protective layer such as Copper, Aluminium or Gold.
Micro-Bending Loss
When the bend diameter is of the order of the fiber diameter, losses can be high. This is…
Mid Infrared
The mid-infrared (M-IR) is typically considered to be in the wavelength range ~2-10µm Related Terms: Electromagnetic Spectrum, Infrared…
Mode
A mode is the energy distribution in which the light travels down the fiber. A multimode fiber can…
Mode Field Diameter (MFD)
Mode field diameter (MFD) is important because, as a measure of the size of the optical field itself,…
Modified Chemical Vapor Deposition (MCVD)
Fibercore manufactures its fibers by MCVD, which involves the deposition of glass particles on the inside wall of…
Monochromator
A monochromator is a filter that removes all but one color, much reducing the linewidth of a wideband…
Multi-Photon and Multi-Phonon Interactions
Multi-photon processes where the ion system can absorb several photons at once – though the more photons that…
Multicore Fiber
Multicore fibers (MCFs) have multiple isolated cores in the same fiber. Each core can have a distinct function…
Multimode
A fiber with a large enough core diameter can support light in many different modes and each mode…
N
Narrow Band
Indicates a limited spread of spectral content is present in the signal, or that a receiver can cope…
Near Infrared
The near infrared (N-IR), typically considered to be the wavelength range ~750-2000nm Related Products: All Silica Double Clad…
Neodymium
A rare earth metal often used in the active medium of lasers. Glass doped with Nd3+ ions exhibits…
Network Modifiers
Co-dopants introduced into the glass to change the molecular structure, or network, may be present in the core…
Non-Radiative Decay
A rare-earth ion in an upper excitation state (reached by absorption of a high energy pump photon) can…
Nonlinear Effects
Many and varied optical interactions between light and material, where the frequency of light that comes out of…
Nonlinear Index
With Nonlinear Index (n2) the intensity of light can modify the propagation in a fiber and the output…
Nonlinear Parameter
The overall nonlinear quality of a fiber is quantified by the nonlinear parameter (γ), which accounts for both…
Nonlinear Scattering
This is usually associated with an interaction of the light with vibrational energy in the molecular lattice, where…
Normalized Frequency
Fibers operating at different wavelengths can be compared by considering the general case where operating wavelength and index…
Numerical Aperture (NA)
The numerical aperture is a measure of the acceptance angle of the fiber. It is very important because…
O
Ocular Surgical Procedures
Ocular (eye) surgery, is surgery on the eye or the area surrounding it and addresses a specific ocular…
Optical Time Domain Reflectometry (OTDR)
A method of investigating losses, splice features and defects along a fiber optical path. The Rayleigh scattering of…
Outer Coating
The coating is the non-glass protective material applied to the fiber. It is most commonly a dual layer…
Outside Vapor Deposition (OVD)
One of many variations of vapour deposition technique for fabricating optical fiber. Here an inert rod is layered…
Overlap Integral Factor
The overlap factor (Γ) describes the amount of mode overlap with the doped core. In a uniformly doped…
P
Pair Induced Quenching (PIQ)
In highly doped rare-earth glasses the ions can end up so close to each other that, rather than…
Phase
The relative orientation in time or space of the maxima in the electric field of a light wave…
Phase Index
The refractive index or phase index is how much slower than the vacuum speed of light, c, the…
Phonons
Energy may be carried through a material as a vibration, and a phonon is essentially the smallest vibration…
Photon
A photon is essentially the smallest piece of light there is, and the energy of a photon is…
Photon Density
In a light beam of a certain power, a corresponding amount of energy will be carried (as photons)…
Photosensitive
Where a fiber changes when light is applied. Often this refers to the change in index that occurs…
Polarization Dependent Loss (PDL)
Any asymmetry in the fiber waveguide will tend to encourage slightly more loss to one polarization mode than…
Polarization Extinction Ratio (PER)
In most applications for PM fiber, only one of the two polarization orientations (states) is used – this…
Polarization Maintaining (PM) Fiber
A PM fiber is a highly birefringent fiber, which maintains the polarization state of light as the large…
Polarization Mode
The orientation of electric and magnetic fields in an electromagnetic wave determines its polarization. In a fiber, the…
Polarization Mode Dispersion (PMD)
The refractive index that light in a fiber experiences will be slightly different depending on the polarization orientation…
Polarizing Fiber
A type of fiber which is designed to support only one polarization mode over a specified wavelength range….
Polyimide
Polyimide is the standard coating for high temperature environments (up to 300°C) in Oil and Gas. This coating…
Population Inversion
Under normal conditions, most of the electron population of a material (such as a rare-earth metal) will exist…
Power
Power is simply the amount of energy flowing in time; typical units are Joules per second [J.s-1]. This…
Power Conversion Efficiency
The ratio of input power, which is converted to useful output power in an active system. For a…
Power Density
The power density describes how much energy is being delivered into the fiber in terms of the area…
Pressure Rating
The amount of pressure that a component can withstand for an extended period of time. Generally used in…
Pressure Sensing
Pressure sensors measure the pressure of the atmosphere, gas or liquid and convert the pressure into an analogue…
Propagation Constant
Propagation constant (β) is a parameter which describes the way light is guided in the fiber. It is…
Pulse Spreading
As a result of material chromatic dispersion, light with a wavelength spread, ∆λ0, will exhibit a temporal spread,…
Pumping
The deliberate introduction of energy into a system is referred to as pumping. This is most relevant to…
Pure Silica Core
In order to create guiding conditions within an optical fiber, the refractive index of the core must be…
Q
Quanta
When considering atomic interactions, it has been shown that energy and light behave as discrete wave packets referred…
Quantum Conversion Efficiency
Quantum conversion efficiency is defined as the ratio of pump photon energy to the signal photon energy. This…
R
Raman Scattering
Backscatter of light at a shifted frequency. Interaction of light (photons) with high energy vibrational quanta (phonons) having…
Rare-Earth Metal
There are two series of rare-earth metals, the Lanthanides and Actinides. The latter contains elements 89-103, many of…
Rayleigh Scattering
This is a linear elastic scattering process caused by the presence of sub-microscopic variations in the density and…
Reduced clad 80 µm fiber
If a fiber is going to be coiled to a small diameter, it is worth considering a reduced…
Refractive Index
The refractive index or phase index of a material defines the ratio of the speed of light in…
Refractive Index Profile (RIP)
The refractive index profile shows how the refractive index changes across the geometry of the fiber. It is…
Risers
A riser is a pipe or cable like structure that runs from a subsea O&G component such as…
S
Scattering Mechanism
There are a number of mechanisms that cause light to be scattered, some of these depend on the…
Second Order Dispersion
The dispersion resulting from wavelength dependence in the propagation of light, which tends to spread out or delay…
Second Order Susceptibility
The second order susceptibility χ(2) is related to nonlinear effects such as linear electro-optic or Pockels effect (where…
Sellmeier Expressions
A Sellmeier expression describes the wavelength dependence of the refractive index, which is related to material dispersion. In…
Sensing
In principle, with the right interrogation technique, the propagation of light can be used to sense anything, from…
Silica
Silica (SiO2) is pure silicon oxide, a refined type of sand or quartz. Silica fiber can be doped…
Silicone Coated Optical Fiber
Optical fiber that is coated with a silicone protective layer.
Single-Mode
A single-mode waveguide propagates only the lowest, or fundamental, mode. This is characterised in a fiber by the…
Slickline Cable/Wireline Cable
A slickline cable used for logging an oil&gas well that has a smooth, round outer surface that allows…
Slow Axis
The slow axis of a birefringent fiber is the axis in which the index of refraction is higher….
Snells Law
The reflection and transmission response of light crossing a boundary depends on both the indices at the boundary…
Solution Doping
Minerals which may not be suitable for introducing in the gas-phase when fabricating fibers with vapor deposition, can…
Splice Loss
Mode field mismatch and alignment mechanisms cause loss when splicing, though it is possible to encourage diffusion across…
Spontaneous Emission
Eventually an excited atom will release the energy that has excited it as a photon, and the electron…
Spot Size
The spot size of a beam is the beam diameter in free space. It varies along the length…
Steam Assisted Gravity Drainage (SAGD)
Method of extracting oil from oil that is trapped in sand, often called tar sands. The method typically…
Step Index Optical Fiber
In the case of single-mode (SM) fibers and a proportion of multimode (MM) fibers, the fiber has a…
Stimulated Emission
A photon incident on an excited atom or molecule can stimulate it to emit another photon and relax…
Stress Applying Parts (SAPs)
The stress applying parts (SAPs) are elements placed in the cladding of a stress based polarization maintaining optical…
Superluminescent Light Emitting Diode (SLED)
A semiconductor device which emits light. Under an applied current, electrons move between energy states in dissimilar semiconductor…
T
Third Order Dispersion (TOD)
Is how the group delay dispersion (how much a delay occurs in a fiber signal between the fastest…
Third Order Susceptibility
The third order susceptibility (χ(3)) is related to nonlinear effects such as the Kerr effect (where index changes…
Through The Coating (TTC)
The ability to transmit laser light through the coating of an optical fiber without the coating absorbing the…
Total Internal Reflection (TIR)
TIR is a term found in Rayoptics which occurs when light hits an index boundary at an angle…
U
Ultra-Violet (UV)
The relatively high energy, short wavelength, photon regime immediately beyond the visible blue/violet end of the spectrum. Beyond…
V
V-Value
V-Value (V) or normalized frequency is the fundamental relationship between numerical aperture, cut-off wavelength and core radius in…
Vapor Axial Deposition
Vapor axial deposition (VAD) is a fiber preform fabrication method where core and cladding layers are simultaneously deposited…
Vascular Surgery
Vascular surgeons deal with all veins and arteries within the body, except for the brain and the heart….
Visible Spectrum (VIS)
The color of light is intrinsically related to its wavelength. The ultra-violet (UV) spectrum takes over from x-rays…
W
Waveguide
A waveguide is simply a structure which guides a wave, keeping the energy confined within its geometry. An…
Waveguide Dispersion
A type of dispersion resulting from the change in index, seen when modes of differing size (due to…
Wavelength
The wavelength of light, λ, in a medium depends upon the refractive index of that medium (see ‘Refractive…
White Light
A light output which contains all the visible colors, but may also contain significant levels of UV, and…
Wideband
Indicates a breadth of spectral content is present in the signal, or that a receiver can cope with…
Wrong Bond
In a perfect germanosilicate glass, the silicon atoms and germanium doping are evenly distributed throughout the glass and…
X
X-Rays
The spectrum below the UV has very short wavelength, and consequently each photon has a very high frequency…
Y
Ytterbium
A rare earth metal with strong absorption at 975nm, within a wide absorption band between ~800nm and 1050nm….
Z
Zing Fiber
ZingTM is a type of fiber which is designed to support only one polarization mode over a specified…
Fibercore