Fibre Link Insertion Loss Testing - 1 cord method (AGE)

The INSERTION LOSS OF A FIBRE LINK = Attenuation of Fibre + Attenuation of Connections + Attenuation of Splices

To measure the Insertion Loss, differences between two optical power levels have to be compared:

• First measuring how much light is put into the link at the near end (P1) • Then measuring how much light exits at the far end of the link (P2)

The attenuation value (in dB) is determined by subtraction of the two absolute power levels (in dBm): Insertion Loss or Attenuation (dB) = P1 (dBm) – P2 (dBm)

This “One-Cord” Method procedure has to be used when testing with a basic LSPM - fibres have to be tested one at a time.

Single fibre measurement (Reference Test Method)

The materials you need

To test fibre optic links using LSPM equipment, you will need the following items:

• The field test equipment must be within its annual calibration period. The tester has to be normalised in accordance with the manufacturer’s guidelines (this relates to annual calibration and calibration per test session). Ensure the loss test set is fully functional, the battery is charged, and all the necessary equipment or adapters are available.

• Dual wavelength fibre optic source (EF compliant for Multimode sources) and power meter

Wavelengths: 850 & 1310 nm for Multimode fibres / 1310 & 1550 nm for Singlemode fibres.

• Connectors, Launch and Tail fibre cords

Connectors (SC, LC…) and fibre types (Multimode 50μm, Multimode 62.5μ, Singlemode) shall be compatible with the OF subsystem to be tested

These cords shall be maintained in perfect shape and regularly tested The test cords for LSPM testing shall be between 1 m and 5 m in length Bend insensitive fibre cords can never been used for Launch cord At least one piece of Singlemode connector shall be prepared • Mandrels (Only if the source is not EF complaint)

For LSPM testing NCS advises the use of Mandrels in the cord connected at the side of the light source.

The objective of a mode filter is to remove unwanted transient higher order modes and therefore eliminate measurement inaccuracies.

The mode filter for multimode fibres shall consist of five, close-wound turns on a smooth round mandrel whose diameter is selected to ensure transient modes have been attenuated and steady-state conditions have been achieved. • A fibre scope (VFL) This tool will be useful to inspect the connectors and for trouble-shooting

Fibre Testing Limits

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 Figures for fibre and splices (both ISO 11801 and ISO 14763-3:2006)

Limitation of Attenuation (dB)

Wave Length OM2/OM3/OM4 OS2 850nm 3.5db/km - 1310nm 1.5db/km 0.4dB/km 1550nm -- 0.4dB/km Maximum Splice Loss 0.3dB

 Connection loss limit according ISO 11801

The ISO 11801 connection loss criteria (0.75dB) is valid when the links are tested with Standard grade test cords (random cords). Always set the tester to test against ISO 11801 limits when testing MPO Cassette (MPO connection + LC connection), whatever the type of cords selected to measure.

 Connection loss limits according to ISO 14763-3

The ISO 14763-3 connection loss criteria are valid when the links are tested with reference grade test cords. These cords are supplied by the tester manufacturer. During the initial setup of the tester ISO 14763-3:2006 shall be selected as the Standard to be taken into account to perform the analysis of the test results.

Different insertion loss values have to be used depending on the quality of the two mated connectors.

Mated Insertion Loss Reference plug Random plug

Attenuation criteria for connections Multimode Fibres Singlemode Fibres

Reference plug Random plug Reference plug Random plug

0.1dB 0.3dB 0.2dB 0.5dB 0.3dB 0.75dB 0.5dB 0.75dB

The cord are terminated with 'reference quality' connectors (plugs) whereas connectors (plugs) in the link under test have less tight performance characteristics -> The loss limit is set to 0.3 dB for Multimode connectors and 0.5 dB for Singlemode connectors.

 Loss of MPO Cassettes

A specific rule has to be applied when the testing MPO Cassette: the total loss of one cassette has to be lower than:

0.75 dB for Multimode Fibres 1.05 dB for Singlemode Fibres The limits are valid

For the whole cassette (MPO connection + LC connection)

For testing performed with both Random and Reference test cords

When testing MPO links

Set the number of connections to 2 and the number of splices to 0 for Multimode Fibres Set the number of connections to 2 and the number of splices to 2 for Singlemode Fibres

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Step 1: Reference – P1 measurement

 Clean all fibre connectors

Dirt is harmful to connectors and causes loss, which affect measurements. Always cover the connectors with a dust cap when not in use.

 During the setup of advanced test tools, select the standard to be applied

ISO 11801 / ISO 14763-3:2006 (When the links are tested with Standard grade test cords, or when testing MPO Cassette, test against ISO 11801. When the links are tested with reference grade test cords, test against ISO 14763-3) Set the number of connections and of splices Set the refractive index of the fibre Set the method (One-cord reference)

 Power Meter: Select the dBm range (if needed)

 Source: Select the wavelength (if needed)

850 nm and 1310 nm for multimode loss test set 1310 nm and 1550 nm for singlemode loss test set

 For both wavelengths, measure the power at the power meter

Record these values: P1λ1 & P1λ2

λ1, λ2 means testing at different wave length. These are your two reference power levels for all loss measurements.

Important Information

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• Once the reference is set, do not disconnect the launching cord from the source.

If the connection between the source output and the cord is disrupted, the reference is lost because the P1 value will most probably be different when you will reconnect the cord to the source. If you disconnect it, it is mandatory to repeat the Step 1 and Step 2 (you will see the step 2 later) to have a new reference before continuing the test of the links. • To ensure the stability of the reference, we recommend installing the source at the Building Distributor side (OF backbone testing) to avoid any move of the source to a different location. • Periodically re-establishing (Step 1 and Step 2) the reference in every 2 hours, or if any device is powered off or goes into sleep-mode. • All optical power measurements shall be recorded to one significant digit after the decimal place (For example: - 23.6 dBm)

The power meter connections, the link connectors and the launching cord free-end connectors shall match. If not, it will not be possible to use to this method. If connectors don’t match, the two-cord method has to be used.

Step 2: Control – Test cords verification

Prior to starting link testing the two cords (Launch and Receive) need to be connected together and tested in order to demonstrate the quality of the cords and the correct measurement of the reference.

 A SINGLEMODE ADAPTOR shall be selected to connect the two cords together. This control has to be performed every time the reference is re-established (maybe several times a day).

 Each test cord measurement performed during the testing of the fibre sub-system of the cabling shall be recorded.

 According to the table from ISO 14763-3:2006, the result should be: • ＜0.15 dB when using Multimode Reference grade cords

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• ＜0.3 dB when using Singlemode Reference grade cords

• ＜0.5 dB when using Standard grade cords (Multimode or Singlemode)

 If you don’t reach these values, redo the inspection and cleaning procedure for all the connectors of the two cords and re-establish the reference (Step 1 and Step 2)

 0.0 dB loss is acceptable but Negative loss results (gain) are not acceptable.

 Make sure this step of test cords measurements is recorded (exclude the failed results).

Step 3: Test – P2 measurement

• Move the power meter to the far end of the link • Clean all connectors

• Attach the receiving cord (tail cord) to the power meter

• Connect the free ends of the cords to the terminations of the link on both sides • For both wavelengths, measure the power at the power meter • Record these values: P2λ1 & P2λ2

• Repeat the Step 3 for all the fibres of the link

Lossλ1 = P1λ1 - P2λ1 Lossλ2 = P1λ2 - P2λ2

Test results evaluation

• Loss measurement calculation:

• Compare these results with the acceptable losses calculated in advance (tables mentioned before) • Measured loss values shall be lower than the calculated ones • Record the measurements values 5 / 5