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Tutorial 3: Measure Extinction Ratios on Low-Level Signals
Tutorial 3: Measure Extinction Ratios on Low-
Level Signals
Repeatable extinction ratio measurements can be made on low-level signals.
This is accomplished by applying a filter to the signal. This filter improves
measurement sensitivity and is useful for analyzing:
• low-level extinction ratios
• pattern dependent transitions
• intersymbol interference
In this tutorial, the eye-diagram analyzer is placed in eyeline mode so that the
eye filter can be applied to reduce trace noise. To measure the signal, a photo-
diode converter with a responsivity of 30 volts/watt is used.
When making extinction ratio measurements in eyeline mode, the number of
samples should be increased from the default of 1000 to something on the
order of 20000. This insures a number of traces are evaluated to compute the
extinction ratio. The compatible mode is eyeline.
Change to Eyeline Mode
1 Set the instrument to a known state by pressing:
INSTR PRESET, Setup, diagram, EYELINE, Traces
2 Set the number of persistence sweeps by pressing:
persist, VARIABL, PERSIST SWEEPS and enter 5, prev menu
3 Turn on autoscaling by pressing:
Trg,Cal, more 1 of 2, Traces, AUTO-SCALE
The display should look like the following figure.
A low-amplitude response, similar to that shown in this figure, can result when
using non-amplified lightwave converters to measure optical signals.