The data from the external signal generator is first amplified by four, high-
linearity amplifiers. The bias points for these amplifiers can be monitored
and automatically controlled by the included Tektronix control software. The
user may also take control of the bias points and set the amplifier bias
voltages manually. The high-linearity of these amplifiers makes them ideal
for multi-level signals such as 16QAM. For two-level signals, such as
QPSK, the amplifiers can be can be driven into saturation so that the
modulator drive is less sensitive to input drive level variations due to
external rf cable losses.
The output of either the on-board laser, or a customer-supplied external
laser is passed through a beam splitter and then fed to each of the four
internal Mach-Zehnder modulators. Like the amplifiers, each Mach-Zehnder
modulator has bias controls that can be automatically controlled or
manually set by the user. The amplified signals feed these four modulators
whose outputs are optically combined to create a complex, dual-polarized
optical signal available on the front-panel of the instrument.
Datasheet
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