Triple-Play Service Deployment

Chapter 3: Deploying and Troubleshooting Fiber Networks
Photonic Layer Testing of OLT and ONT Signals
The following discussion assumes that the OLT itself,typically consisting
of a 1490 nm transmitter, a 1590 nm transmitter with amplifier, a 1310
nm photodiode/receiver, WDMs and patch cords, has been fully tested
internally. The ONT, which usually consists of a 1310 nm transmitter,
1490 nm photodiode/receiver, 1550 nm photodiode/receiver, WDMs
and patch cords, is also assumed to be fully tested. In such instances, the
following tests may then be performed.
The first step in characterizing the OLT is to measure the output
level of the OLT with a power meter and to verify the performance
against the manufacturer’s suggested requirement for signal
output level. If 1550 nm video service carried on the line, then a
selective 1490/1550 nm power meter is needed. If a basic power
meter is used, the OLT will activate the 1490 nm and 1550 nm
wavelengths independently. In instances where the video service
uses the 1550 nm transmission with analog signals, the ORL
measurements of the feeder part should be taken from the CO at
the feeder cable location. Then the technician should proceed to
the ONT location. On the ONT side, the following tests are required.
A selective 1310/1490/1550 nm power meter operating in
Through mode is used to measure the output level at the ONT
while the OLT transmits at 1490 and 1310 nm downstream. This
will trigger the ONT to transmit 1310 nm bursts upstream.
Technicians may elect to measure only the 1490 nm and 1550 nm
and not the 1310 nm wavelengths using the selective 1490/1550
nm meter.This test validates overall signal level. If the OLT displays
a warning that there is no 1310 nm signal present, then the ONT
must be replaced.
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