Choose the test for the question
“Has it been tested?” is only the start. A useful result tells you what was measured, how the test was set up and what the result was compared with.
For a new installation, we agree the required checks before starting. For an existing fault, we first establish what has changed, which services are affected and what records are available. The right test sequence depends on the link and the problem.
End-to-end insertion loss
A light source and optical power meter, or an optical loss test set, measure the light lost through a completed fibre path. The result is normally expressed in decibels (dB) and compared with the agreed loss budget.
That budget accounts for the design’s fibre length, connections and splices. A meaningful assessment also depends on the test wavelength, reference method, compatible reference cords and sound connector condition. A generic pass number is not a substitute for the project’s acceptance requirements.
What an OTDR can show
An optical time-domain reflectometer sends test pulses into the fibre and analyses returning light. Its trace helps estimate distance and identify events along the link. This can support investigation of:
- A fibre break or unexpected end of the route.
- High-loss sections and splices that need closer assessment.
- Reflective events associated with connections or faults.
- Changes in a link when a useful earlier trace is available.
Insertion loss testing assesses the light lost through the end-to-end link. OTDR testing helps locate and characterise events along it. OTDR diagnostics complement the acceptance testing specified for the job.
Interpretation matters
OTDR settings influence what can be resolved and how far the instrument can see. Pulse width, range, averaging and the fibre’s refractive-index setting all affect the trace. Events close together can be hidden within dead zones, and the displayed fibre distance is not always the same as the surface distance along a street.
Launch and receive fibres help separate the end connections from the instrument and the end of the trace. Testing from both ends and averaging event loss can be needed to assess splices properly, particularly where fibres have different backscatter characteristics. The required method should be agreed for the link.
A practical fault investigation
Start with the service history and available drawings, then confirm the fibre identity and assess connections. Connector contamination, a disturbed patch lead, excess bending or physical cable damage may need different remedies.
An OTDR can narrow down where an event occurs; access and physical inspection may still be needed to establish the cause. Testing live fibres requires suitable equipment and a planned method. We confirm whether fibres are in service before connecting test instruments.
Agree the handover
Tell us what the network owner needs. Depending on the scope, the handover may call for fibre and port IDs, measured loss, test wavelengths, relevant OTDR traces and a record of the conditions or remedial work. Agreeing the format early makes the results more useful later.
For installation and connection work, explore fibre installation and splicing and terminations. For technical background, see our reference notes.