Normalization And Measurement; Optical Modulator Bias Adjustment - Agilent Technologies 86038B User Manual

Normalization and Measurement

Optical Modulator Bias Adjustment

74
The measurement results of the 86038B are actually the results
of two measurements, taken with and without the DUT inserted
in the path. A 'normalization' measurement, taken without the
DUT in the path, captures the loss and group delay
characteristics of the measurement system and test path under
the chosen set of measurement parameters. The normalization
measurement establishes a loss and group delay baseline for
later measurements of the DUT itself.
By saving the results after a normalization, the results can be
restored at a later time if they are later replaced by making
measurements with different parameters.
The normalization measurement is accompanied by one or more
additional automatic performance optimizations, all under the
broad heading of 'normalization'. The 86038B contains an
automated modulator bias adjustment function that is
performed during a normalization, or by itself through the menu
item System > Optimize Optical Modulator Bias. Amplitude
modulation in the 86038B is accomplished using a lithium
niobate Mach-Zehnder modulator. In this type of modulator, the
light is split into two paths which experience different phase
shifts in response to a co-propagating RF wave. The two light
paths rejoin at the output, where interference between the
differentially phase-shifted paths determines the instantaneous
optical output level.
The modulator is biased by an adjustable DC voltage in order to
select the optimum operating point. The automatic bias
adjustment routine fixes the wavelength and the modulation
frequency, then measures the variation in modulated optical
output while changing the modulator bias voltage. From the
resulting curve of output level versus bias voltage, the optimum
bias voltage is chosen. For more information refer to
Optical Modulator Bias" on page
Agilent 86038B Photonic Dispersion and Loss Analyzer, Second Edition
"Optimize
102.