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Using the Instrument
Calibrating Wavelength Measurements
External Multipoint Wavelength Calibration
An external multipoint wavelength calibration can be performed over any specified wavelength
range, up to and including the full wavelength range of the OSA (600 nm to 1700 nm). Narrow
measurement spans can be chosen to provide greater accuracy over a selected range. Calibrat-
ing the wavelength every 10 nm within the desired wavelength range is usually sufficient to
improve wavelength accuracy. After a multipoint wavelength calibration, wavelength accuracy
will be ±10 pm within 10 nm of each calibration wavelength.
on page
N o t e
For a full explanation of external multipoint wavelength calibration, along with a sample program
to perform the calibration, refer to Product Note 86140-2, Wavelength Calibration for the 86140X
Series Optical Spectrum Analyzers (Literature part number 5980-0043E).
The following steps outline one method for an external multipoint wavelength calibration routine.
This assumes a program executed on a external PC controller. The steps outlined are those writ-
ten in the program.
1 A signal is sent from a tunable laser source into a multi-wavelength meter and the OSA
simultaneously.
2 The wavelength of the input signal is measured on both instruments.
3 The two measured values are compared.
4 Taking the multi-wavelength meter readings as actual, the software calculates the error offsets at
each wavelength using the equation:
WL Error = (OSA indicated WL) – (multi-wavelength meter actual WL)
5 The previous steps are repeated over the entire wavelength range.
6 The data is averaged over narrow wavelength spans to provide a suitable correction for each
span. The example below demonstrates this technique.
Once the instrument is calibrated, the new wavelength accuracy can be maintained for many
hours without recalibration, assuming a stable temperature environment.
T i p
If the OSA is turned off, the multipoint data will be retained at the next power-on, but the internal
thermal shift can introduce inaccuracies to the calibration data. To help compensate for this, a
single point calibration using the Offset feature in the Wavelength Calibration Setup panel can be
used to adjust the multipoint data. Access this feature by selecting System > Calibration >
Wavelength Cal Setup and choosing the Offset option before running the single point calibration.
2-16
3-16.
Refer to "Calibrator Multi-Pt Align"
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