top of page
CD/PMD Fibre Testing & Characterisation
FDNS provides full installed singlemode fibre characterisation for dark fibre, DWDM, coherent optics, long-haul transport and data-centre interconnect routes. Characterisation can combine insertion loss, ORL, end-face inspection, bi-directional OTDR, CD, PMD and AP/BBS where required, with methods aligned to ITU-T G.650.3 and applicable IEC/ISO requirements.
Because FDNS owns specialist VIAVI and EXFO test equipment and has engineers with OTT CFCE and VIAVI training experience, clients can obtain a technically controlled characterisation programme with traceable native evidence rather than a limited OTDR-only service.
What is CD/PMD fibre testing and characterisation?
Chromatic dispersion and polarisation mode dispersion are fibre properties that can broaden optical pulses and reduce transmission margin at higher data rates. CD is primarily related to wavelength-dependent propagation, while PMD is associated with changing propagation states within the fibre. Their effect becomes increasingly important on long routes and high-capacity optical systems.
FDNS measures these characteristics to help determine whether an installed route is suitable for the intended transport technology. We consider route length, fibre type, mixed-fibre sections, previous repairs, planned optics and system requirements rather than interpreting the result in isolation.
The resulting characterisation evidence can support dark-fibre acceptance, DWDM engineering, coherent-service planning, capacity upgrades and troubleshooting where conventional loss and OTDR testing alone do not explain transmission performance.
What our CD/PMD fibre testing and optical characterisation service includes
Transmission-system and fibre-route engineering review
FDNS confirms route length, fibre type, transmission rate, modulation format, planned optics, amplifier boundaries and system requirements before testing. This determines whether CD and PMD characterisation is technically relevant to the intended service.
Chromatic dispersion measurement and analysis
Chromatic dispersion is measured across the required wavelength range to show how propagation delay varies with wavelength. Results are interpreted against the intended DWDM, coherent or high-speed transmission system rather than viewed as isolated measurements.
Polarisation mode dispersion measurement
PMD is measured to assess differential group delay caused by birefringence within the fibre. This is particularly relevant on older or longer routes where PMD may affect high-speed coherent or legacy transmission upgrades.
OTDR, loss and supporting fibre characterisation
Where required, FDNS combines CD/PMD with OTDR, optical loss testing and route verification. This helps separate dispersion-related limitations from high loss, reflection, bad splices or other physical fibre issues.
Upgrade suitability and transmission-margin review
Characterisation results are assessed against the intended line system and service rate to help determine whether the existing fibre route is suitable for higher-capacity transmission or needs remediation, compensation or further engineering review.
Characterisation report and engineering evidence
The handover can include fibre IDs, route references, test conditions, measured values, native result files and engineering context. This creates a useful baseline for commissioning, upgrades and future troubleshooting.
Determine when CD and PMD testing is actually required for the fibre route
CD and PMD are not routine tests for every optical link. FDNS reviews fibre type, route length, transmission rate, modulation format, planned optics and system requirements to determine whether characterisation is relevant to the intended DWDM, coherent or high-speed service.
Define test points, route direction and wavelengths before measurement
Accurate characterisation depends on clear test boundaries. FDNS confirms fibre IDs, direction, patching, amplifier or equipment boundaries, route length and required wavelengths so the measured dispersion relates to the correct optical span.
Interpret chromatic dispersion against the intended transmission system
Chromatic dispersion results are assessed in the context of route length, fibre type and planned optics. This helps determine whether an existing fibre can support a higher-capacity service or whether further engineering, compensation or route review may be required.
Assess PMD risk on older, longer and upgraded fibre routes
Polarisation mode dispersion can become relevant on older or longer fibre where high-speed transmission is being introduced. FDNS interprets PMD results alongside the target service requirements rather than treating the measured value as an isolated number.
Combine CD/PMD with OTDR and loss testing for a fuller fibre assessment
Where required, FDNS can combine dispersion characterisation with OTDR, optical loss testing and route verification. This helps distinguish dispersion-related limitations from physical faults such as high-loss splices, reflections or route anomalies.
How FDNS delivers CD/PMD fibre characterisation from route review to engineering report
Our CD/PMD characterisation process is designed around the intended transmission system, not an isolated instrument reading. FDNS confirms fibre route, transmission rate, modulation format, optics, test boundaries and acceptance requirements before measurement, then interprets the results against the high-speed or coherent service being considered.
1
1. Confirm the fibre route, transmission system and upgrade objective
We collect route length, fibre type, existing records, planned optics, transmission rate, modulation format and equipment requirements. This determines whether CD and PMD are relevant to the upgrade or fault-investigation scope.
2
2. Define approved test points, directions and wavelengths
Fibre IDs, route direction, patching, amplifier or equipment boundaries and required wavelengths are agreed before testing so the measured values relate to the intended optical span.
3
3. Prepare the passive route and test configuration
Access, connector condition, launch arrangements, test equipment and safety requirements are checked before measurement. The route is isolated or prepared only within the approved network change process.
4
4. Measure chromatic dispersion and polarisation mode dispersion
CD and PMD are measured across the required fibre section and wavelength range using the appropriate test configuration. Results are checked for consistency and unexpected route behaviour.
5
5
5. Compare characterisation results with the transmission requirement
FDNS interprets the measured dispersion against the intended DWDM, coherent or high-speed transport application to determine whether the fibre route appears suitable or requires further engineering review.
6
6. Produce a traceable fibre-characterisation report
The handover includes fibre IDs, route references, test conditions, wavelengths, native result files, measured values and engineering context so the client has a useful baseline for commissioning, upgrades and future troubleshooting.
CD/PMD measurement standards, interpretation and optical quality assurance
FDNS carries out installed singlemode fibre characterisation in alignment with the applicable IEC/ISO test methods, ITU-T G.650.3 and the engineering requirements of the intended transmission system. A full characterisation programme can include insertion loss, optical return loss, connector end-face inspection, bi-directional OTDR, chromatic dispersion, polarisation mode dispersion and AP/BBS measurements where required. The test plan defines fibre IDs, direction, wavelengths, endpoint condition, instrument configuration, route records and acceptance criteria before measurements begin. Results are reviewed alongside route length, known repairs, attenuation, OTDR events and the planned transmission platform because individual measurements are most useful when correlated with the physical network. Native measurements, route references, engineering observations and exceptions are retained so the system designer or operator receives traceable evidence for commissioning, migration and transmission readiness.
Where CD/PMD characterisation is required
CD/PMD testing is commonly used for dark-fibre acceptance, long-haul and metro routes, DWDM and coherent optical transport, data-centre interconnect, high-capacity upgrades and post-repair route assessment where attenuation and OTDR alone cannot establish transmission suitability. The need depends on fibre type, distance, service rate, modulation format and the requirements of the planned optical platform.
Characterisation risks and how FDNS controls interpretation
Risks include treating a low-loss route as automatically suitable for high-speed transport, testing through unstable or active interfaces, using incomplete route data or applying limits that are not tied to the planned optics. FDNS controls these issues by defining the transmission context, verifying endpoints, recording instrument configuration and correlating CD/PMD results with route information, attenuation and OTDR evidence where available. Final system acceptance remains with the network owner, designer or vendor responsible for the optical platform.
How CD/PMD fits within FDNS optical testing
CD/PMD is an advanced transport-network characterisation service. FDNS can combine it with connector inspection, Tier 1 optical loss testing, Tier 2 OTDR, fibre-route verification and high-speed Ethernet/BERT testing so clients can select the level of evidence appropriate to the network. This provides a fuller engineering picture when planning coherent, DWDM or other high-capacity transmission upgrades.
Planning a CD/PMD fibre characterisation campaign
A CD/PMD test campaign should define the fibre route, fibre family, planned transmission service, endpoints, route length, test direction, wavelength range, access windows and acceptance owner before measurements begin. FDNS uses these inputs to choose the appropriate characterisation method and supporting route evidence for the intended high-capacity optical system.
Route and transmission information to provide
Useful information includes fibre schedules, route length, fibre type, known repairs or mixed sections, endpoint access, intended optics or platform, service rate, wavelength plan, available OTDR or attenuation results and any vendor or client limits that will be used to review the measurements. Where records are incomplete, additional route verification can be included.
What to include in a CD/PMD quotation brief
Define fibre quantities, test directions, wavelength range, supporting measurements, instrument-file requirements, reporting format, access windows and the party responsible for final transmission acceptance. This allows FDNS to price the correct mobilisation, equipment and engineering review rather than assuming every fibre route needs the same characterisation scope.
Why choose FDNS for CD/PMD fibre testing and optical characterisation?
FDNS provides specialist fibre characterisation using an owned in-house fibre test estate and engineers with recognised specialist training. Our capability includes VIAVI long-haul characterisation equipment for CD/PMD and AP/BBS, VIAVI MTS-4000 and ONA-800 platforms with FibreComplete Pro, EXFO OTDR platforms, and professional end-face inspection using VIAVI INX-760, FibreChek and P5000i together with EXFO FIP-430/FIP-435B probes. High-speed Ethernet/BERT/FEC testers are normally hired to suit the required interface, speed and generation because those platforms change rapidly, or where the client requests a specific tester. This lets FDNS keep the transmission-test setup current without outsourcing the core fibre-characterisation capability.
Specialist CD and PMD characterisation for high-capacity optical systems
FDNS measures dispersion where it is technically relevant to the planned service, supporting long-haul, metro, DWDM, coherent and data-centre interconnect applications rather than applying advanced testing indiscriminately.
Results interpreted in the context of the real fibre route
Fibre type, distance, mixed sections, repairs, route history, attenuation and OTDR evidence are considered alongside CD/PMD results so the client receives an engineering view rather than isolated numbers.
Testing aligned to the intended optics and transmission platform
The wavelength range, endpoints and acceptance context are defined around the planned optical system, helping operators evaluate whether an existing route appears suitable for a proposed capacity upgrade.
Advanced characterisation combined with conventional fibre evidence
Where useful, FDNS can combine CD/PMD with OTDR, optical loss testing and route verification to create a more complete picture of physical fibre condition and transmission suitability.
Traceable reports suitable for commissioning and upgrade decisions
Native result files, fibre IDs, route references, test conditions and engineering observations provide a defensible evidence package for network designers, carriers and end clients.
Frequently asked questions about CD/PMD fibre testing and characterisation
1. What are chromatic dispersion and polarisation mode dispersion in optical fibre?
Chromatic dispersion is wavelength-dependent pulse spreading within fibre, while polarisation mode dispersion is differential delay between polarisation modes. Both can reduce transmission margin, particularly on longer or higher-capacity optical systems.
2. When is CD/PMD fibre testing required?
It is commonly used for dark-fibre acceptance, long-haul and metro routes, DWDM and coherent systems, data-centre interconnect, major repairs and upgrades where the optical platform requires measured dispersion evidence.
3. Do 100G, 400G and 800G networks always need CD/PMD testing?
No. Modern coherent optics can tolerate or compensate for significant dispersion, and the need depends on fibre type, route length, modulation, optics, engineering margin and vendor requirements. Testing should be driven by the transmission design.
4. Can a fibre pass OTDR and loss testing but still have a CD/PMD problem?
Yes. OTDR and insertion-loss tests measure different characteristics from dispersion. A fibre can have acceptable attenuation and splice performance while still requiring CD/PMD characterisation before a planned high-speed optical upgrade.
5. What information does FDNS need before CD/PMD testing?
Useful information includes fibre type, route length, endpoints, direction, wavelength plan, intended optics or platform, service rate, known repairs and any available OTDR or attenuation results.
6. Can FDNS combine CD/PMD with OTDR and loss testing?
Yes. Combining characterisation with OTDR, attenuation and route verification can provide a much fuller engineering picture of fibre condition and help distinguish dispersion limitations from physical route faults.
7. What is included in a fibre characterisation report?
The report can include fibre IDs, endpoints, direction, test conditions, wavelengths, CD and PMD values, native files, supporting OTDR or attenuation results where included, and engineering observations.
8. Who decides whether a fibre is suitable for a specific DWDM or coherent platform?
Final transmission acceptance normally sits with the network owner, system designer or equipment vendor. FDNS provides traceable measurements and engineering context so that decision can be made from reliable evidence.
Related optical services for fibre characterisation and high-capacity transport
Planning a DWDM, coherent or high-capacity fibre upgrade? Talk to FDNS
Tell us the fibre type, route length, endpoints, wavelength plan, intended optics or transmission platform, service rate, known repairs and any existing OTDR or attenuation evidence. FDNS can define the CD/PMD characterisation scope, supporting tests and reporting needed to give your network designer or equipment vendor traceable evidence before commissioning or migration.
bottom of page