TB002 - Fibre Launch requirements for MMF and SMF Testing-Encircled Flux


Text in blue Italics is reproduced from the standards.

Applicability


The following applies only to telecommunication cabling installations in Australia and New Zealand seeking performance conformance of optical fibre links and channels to AS/NZS 3080.

Summary


It is a normative requirement to meet a specific launch condition at the output of the interface connector of the launch test cord when testing optical fibre cabling systems.

For multimode installations, 62.5 µm and 50 µm cores, the requirement is to meet encircled flux.
Encircled Flux requirements can be met by one or more of the following:-
•    Mode condition cords that produce compliant Encircled Flux conditions at the output of the launch cord
•    A mated light source and mode condition launch cord that produces compliant Encircled Flux conditions at the output of the launch cord.
•    Light source that is Encircled Flux compliant at its output and that is coupled with a specific test cord type that ensures encircled flux compliance at the output of the launch cord.

Note 1:-The validation of compliance should be supported by the manufacturer’s claim of the tester or the mode conditioner cord that encircled flux conditions will be met at the output end of the launch cord.
Note 2:-Encircled Flux launch condition for multimode testing was introduced in 2012.

For singlemode installations the requirement is to meet specific Launched Modal Distribution (LMD) requirements.
LMD requirements for singlemode can be achieved by one or more of the following:-
•    A source that produces LMD at the output (most common)
•    Use of a minimum of two (2) air coils 35 mm to 50 mm diameter in the launch cord
•    A mandrel 35 mm to 50 mm diameter to hold at least 2 coils in the launch cord

This Technical Bulletin states the specific standards requirements for multimode fibre (MMF) and singlemode fibre (SMF) launch cords used in light source and power meter (LSPM) and OTDR testing.

Conformance requirements


The implementation and performance of optical fibre cabling channels shall meet the requirements specified in Clause 8. 1 

Test methods to assess conformance with optical fibre channel and link requirements of AS/NZS 3080 Clause 8 and Annex B, are specified within AS/NZS ISO/IEC 14763.3. 2 
Additional requirements for Australia and New Zealand, information and explanation are available. 3

MMF Launch  -  Encircled Flux


The MMF launch cord for LSPM4 and OTDR5 shall maintain the specified Launched Modal Distribution (LMD).  This is commonly called the Encircled Flux requirement for multimode testing.

The LMD at the point of connection to the cabling under test shall be as defined in Annex A of AS/NZS ISO/IEC 14763.3.  The required LMD shall be achieved by the use of the appropriate light source or by incorporating a mode conditioning device within the launch cord.
6

SMF Launch


The SMF launch cord for LSPM4 and OTDR5 shall maintain the specified LMD.

The provision of a single-mode launch condition requires that launch cords contain a minimum of two single air-coiled turns or mandrel wraps of 35 mm to 50 mm in diameter; however this is usually provided within the test instrument and it is then not necessary to have external coils. 7

Reference Connectors


For LSPM4 and OTDR5 testing, both launch and tail test cords for MMF and SMF shall have Reference Connectors at the interface to the fibre under test. 8

The launch and tail test cords shall be terminated at the other end with one or more reference connectors compatible with the interface to the installed cabling. 4, 5, 8

References

1  AS/NZS 3080  Clause 4 c)     5  AS/NZS ISO/IEC 14763.3  Clause 6.3.3.6
2  AS/NZS 3080  Para 2, pg. 34    6  AS/NZS ISO/IEC 14763.3  Clause 6.4
3  AS/NZS 3080  Appendix ZA     7  AS/NZS ISO/IEC 14763.3  Clause 6.5
4  AS/NZS ISO/IEC 14763.3  Clause 6.3.3.2    8  AS/NZS ISO/IEC 14763.3  Clause 6.3.3

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