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2-18
Using the Multi-Wavelength Meter
Defining Laser-Line Peaks
Limiting the input
wavelength range
The Agilent 86120B’s preset condition limits the wavelength measurement
range from 1200 nm to 1650 nm. You can expand the wavelength range to
cover the entire 700 nm to 1650 nm range. Although wavelength range limit-
ing reduces the number of laser lines found, its main purpose is to eliminate
the identification of second harmonic distortion products as described in the
following sidebar. To set the wavelength range, refer to “To use the full wave-
length range” on page 2-8
.
Distortion caused by low-power laser lines
Low-power laser lines (power level near the Agilent 86120B’s specified sensitivity) may
be accompanied by second harmonic (or other) distortion. For example, a low-power
laser line at 1550 nm has a second harmonic line at 775 nm. If this second harmonic is
above the peak threshold level relative to the fundamental line, it is considered a peak.
Its displayed power level may be
greater
than that of the fundamental because the
amplitude correction at 775 nm is much greater (by about 15 dB) than that at 1550 nm
(the interferometer is less sensitive at 775 nm).
To avoid displaying this second harmonic line, limit the input wavelength range from
1200 nm to 1650 nm as described in “To use the full wavelength range” on page 2-8.
Or, reduce the peak threshold below its preset value. Because the peak threshold level is
used to determine which signals are to be displayed
before
amplitude corrections are
applied, the harmonic will be eliminated.