Kingfisher KI23400 Series, Руководство по эксплуатации и техническому обслуживанию

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ACCURACY CONSIDERATIONS
KI23400/KI27400 UM-2 -
62 -
Light Source
Light source power may drift. When you have finished a test, go back
to the start position to check if the light source power is still within
acceptable limits. Note that light source specifications are usually for
typical drift after a warm-up period and assume a stable ambient
temperature and low back reflection. Actual drift will vary between
instruments and test situations.
Optical Return Loss
Optical return loss testing can be limited by the ORL performance of
the instrument output connector or test leads, particularly for PC style
connectors. Connector cleanliness and condition is critically important.
Far-end reflections at the end of a sample must also be controlled, or
they will swamp the intended measurement
The two offset capabilities of the instrument can improve accuracy,
however, note that the Zero function will need to be re-set if the
residual ORL level changes, so car need to be exercised with this
offset.
DWDM Loss & Power Measurements
The DWDM bands are typically within 1525 ~ 1610 nm. For this
application, an InGaAs detector calibrated at 1550 nm gives good
absolute accuracy at all DWDM λ . Testing optical loss at 1610 or 1625
nm is common, since this represents the worst-case attenuation in
most systems.
High power InGaAs detectors may be required to measure the system
power level.
Ge detectors should not be used for accurate testing on WDM systems
beyond 1550 nm, since inaccuracies become large and unpredictable.
CWDM Loss & Power Measurements
The CWDM band is from 1270 ~ 1610 nm at 20 nm spacing, however,
1490 ~ 1610 nm is more common since it avoids the water absorption
peak at 1383 nm.
The most common operating λ for FTTH PON systems are currently
1310 / 1490 / 1550 nm.
As in DWDM application, an InGaAs detector gives good absolute
accuracy.
Because of the broad operating λ encountered, the power meter
calibration λ needs to be matched to the measured λ , or absolute
errors may be excessive.
Many systems are measured at 1390 nm to test for the water peak,
and at 1625 nm to measure the high-end attenuation limit.
At 1625 nm, the fiber attenuation is actually very sensitive to λ , since
the silica infra-red absorption zone is reached. So, the λ tolerance of
this laser is a major issue, especially since many older source
instruments have a tolerance of 30 nm.