PFO has extensive experience and expertise in the design, manufacture, and support of a wide range of fiber measurement solutions that contain one or more of the measurement types addressed below.
Chromatic Dispersion is caused by the change in the speed of light in the fiber when the wavelength changes. As lasers used in telecom transmitters have finite spectral widths, the spread of wavelengths will travel at varying speeds thus causing the transmitted pulse to spread or ‘disperse’ in time.
There are various technologies available to measure Chromatic Dispersion and each technology lends itself to a particular application for the measurement. What works well on a 5,000km submarine link will not necessarily cope quite so well on a 1km drum of cable and vice-versa.
Contact PFO for guidance in the selection of the appropriate solution for your application.
OTDR is a method of looking at the spatial distribution of the Rayleigh scattering in the fiber. The method is able to acquire information about the attenuation at specific wavelengths and how that varies along the fiber.
The OTDR is used to qualify the linearity of the attenuation slope and to detect any point defects in the core, one such point defect being the end of the fiber; the OTDR reports the time/length to the defect, hence fiber length.
Manufacturing processes change the extrinsic stresses that causes macro bending attenuation so, OTDRs are used at every stage of the cabling process. (Colouring, tubing, stranding, sheathing)
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Polarisation Mode Dispersion(PMD) results from the two polarisation states experiencing different effective refractive indexes (Birefringence) that cause each polarisation state to travel at different speeds that vary randomly along the length of a fiber.
There are various technologies available to measure PMD and each technology lends itself to a particular application for the measurement. What works well on a fiber that has relatively high PMD, will not necessarily cope quite so well when the PMD is relatively low and vice-versa.
Contact PFO for guidance in the selection of the appropriate solution for your application.
The cable is designed to provide mechanical protection for the fiber. Strain in the fiber occurs when the cable is stressed beyond its design limits.
In order to ensure that the cable design and its subsequent manufacture protects the fiber during its installation and operation, it is necessary to expose the cable to stresses that exceed normal installation and operational limits (twist, bend, crush, shear, tensile, temperature, vibration etc..) whilst at the same time monitoring the length and attenuation of the fiber. Limits to these variations in length(strain) and attenuation are well defined in the various standards.
The solution PFO has developed allows the measurement of Fiber Strain whilst monitoring user supplied cable strain and load signals.
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Attenuation in an optical fiber occurs because of the way the light interacts with the structure of the fiber both at a microscopic and a macroscopic level. It is one of the parameters that can significantly be affected by the processes used to manufacture and install the cable.
All the intrinsic and extrinsic mechanisms that create this loss of signal are known to be wavelength dependent and as such are normally measured over the useable spectrum for which the fiber is designed, hence the term ‘Spectral Attenuation’ is used.
There are three main mechanisms to be considered: Scattering, Absorption and Bending.
Whilst it is possible to determine the effects of some of the mechanisms individually, the main purpose of this measurement is to yield a value that describes the sum of all the mechanisms with the fiber in a relaxed and unstressed state.
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The purpose of the waveguide within the fiber is to ensure the optical signal reaches the receiver with as little loss as possible. Absorption and scattering characteristics are frozen into the fiber at the time of manufacturing but, additional loss/attenuation can be introduced through bending as a result of the cabling and installation process.
Fibers are designed to be as in-sensitive as possible to these extrinsic mechanisms and PFO have various solutions to measure this effect.
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It is assumed that the absorption mechanism that causes some of the attenuation is locked into the fiber at the drawing stage. The molecular structure however has voids that are available for occupation by any element. The environment the fiber is exposed to results in hydrogen being the element that is most easily absorbed in the form of hydrogen ions.
This will increase the attenuation at specific wavelengths caused by this effect. Modern manufacturing attempts to replace these hydrogen ions with deuterium thus shifting these absorption peaks to wavelengths outside operating spectrum.
The measurement of attenuation at these specific hydrogen peaks before and after exposure to Hydrogen rich environment (i.e Spilt coffee by average joe) verifies the effectiveness of the deuterium soaking.
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Cut-off wavelength in an optical fiber is defined as the wavelength above which all but the most strongly guided mode is lost from the core. This occurs because of the way the light interacts with the structure of the fiber at a macroscopic level. The main mechanism by which these weakly guided modes are lost from the core is ‘bending’. Even with the fiber in its straightest condition, macro-bending conditions still exist, so the weakly guided modes are subject to bend-induced attenuation.
The bending loss of all guided modes is wavelength dependant, so this loss is tested over a spectral range large enough to capture the point at which only the most strongly guided mode remains with the fiber held in its nominally straight condition.
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The mode field diameter (MFD) is the width of the fundamental (most strongly guided) mode in a single-mode fiber above the cut-off wavelength.
Any significant difference between the MFDs of 2 fibers being spliced will cause unacceptably high splice losses.
Whilst the MFD characteristics are frozen at the time of manufacture and as such are relatively fixed for the life of the fiber, it is a parameter that is influenced by various properties within the fiber that do vary along its length. It is useful and considered good practice to measure the MFD even within a cable manufacturing environment to ensure the consistency of the product.
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A part of the Mode Field Diameter(MFD) measurement, the effective area of the fundamental mode is a measure of the area over which the energy in the electric field is distributed.
Aeff in a single mode optical fiber determines how much energy the core can carry without causing non-linear type signal losses. This parameter is important for DWDM applications.
Whilst the Aeff characteristics are frozen at the time of manufacture and as such are fixed for the life of the fiber, it is a parameter that is influenced by various properties within the fiber that do vary along its length, so it is useful to measure the Aeff even within a cable manufacturing environment to ensure the consistency of the product.
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Geometry is the most fundamental of characteristics of the optical fiber and is indicative of the quality control at the manufacturing stage.
The measurement of the geometry will determine if it is possible to splice two fibers with an acceptably low loss.
Whilst the geometry characteristics are frozen at the time of manufacture and as such are fixed for the life of the fiber, it is a parameter that varies along its length, so it is useful to measure the geometry, even within a cable manufacturing environment to ensure the consistency of the product.
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The Coating Geometry of the optical fiber has a direct influence on its macro bending sensitivity, so it is important to ensure that its geometrical characteristics are within allowable limits.
The coating geometry is frozen at the time of manufacturing. However, most cablers apply a coloured layer to the coating prior to cabling, so it is useful and indeed good practice to measure the total diameter of the coated fiber to ensure the consistency of the product.
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Curl in an optical fiber is a by-product of the stresses that exist at the manufacturing stage and are frozen into the fiber. The curl varies along its length but does not generally change throughout the life of the fiber.
The degree of curl in the fiber is interesting as it has a known influence on the usability of a particular fiber in a ribbon structure. When attempting to splice a ribbon fiber structure, the effect of any curl exhibited by the fiber will be visible in the splicing machines display and will result in one or more of the splices in the ribbon having higher than normal loss.
It is useful and considered good practice to measure the curl even within a cable manufacturing environment to ensure the consistency of the product.
Contact PFO for guidance in the selection of the appropriate solution for your application.
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