MAX-700B/C/D series, OX1 instruments, PON testing
The testing and characterization of Passive Optical Networks (PON) includes some unique challenges; FTTx networks are typically fairly short (compared with transport networks), but the losses introduced by splitting optical signals requires the use of comparatively long pulse widths to test, which can present resolution issues. This has resulted in the development of specialized instruments.
EXFO's FTTH PON Guide provides extensive information and background on PON testing.
When performing testing on networks involving tandem passive optical splitters, you should be careful to ensure that the fiber section following the splitter/s are a suitable length, such that intelligent processing software like EXFO's intelligent Optical Link Mapper (iOLM) are able to accurately perform loss measurements and appropriately characterize network elements.
Instruments and applications specifically designed for 'last mile' PON testing, such as the OX1 and iADV 'Optimode: PON Last-Mile Certification' are not optimized for testing networks with multiple splitters; these require more specialized OTDR instruments.
The non-exhaustive table below provides the minimum fiber lengths required following a single splitter for several different instruments:
In the case of multiple (cascaded) splitters, the span length required following the next splitter (toward the 'far' end of the link) is that of the Group (combined) Ratio.
For example, the network shown below is being tested from the customer premises using a MAX-730C instrument and includes a 1:4 (iOLM 'stage 2 splitter') followed by a 1:8 (iOLM 'stage 1 splitter') optical splitter.
Consulting the table above for the MAX-730C, the minimum fiber length required following the first 1:4 splitter is 100m, whereas the minimum fiber length required following the 1:8 splitter is then instead 1km, since the Group Ratio is now 1:32 (4 * 8 = 32) for the cascade topology.