THORLABS MX10B Series, Руководство пользователя

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MX10B, MX40B Series of Optical Transmitters Chapter 4: Operating Instructions
Rev. D, March 19, 2019 Page 19
The Crossing Point field allows the user to adjust the eye crossing point in the eye diagram as depicted in the diagram below. It
provides an adjustment to optimize the bit-error-rate (BER) performance of a transmission link by adjusting the amplifier’s internal
threshold levels.
Figure 31 Illustration of Different Crossing Point Settings
In the Analog mode, the Max Output Swing is locked at the maximum set point of 7.0 V
pp
, so the amplifier can drive the MZM
linearly with minimal distortion. However, in order to do this, the user must supply a signal with small enough amplitude so the
amplifier does not saturate, or clip. This mode is recommended for analog signals or higher order modulation formats such as
PAM4. The crossing point adjustment can usually be left at 0, but the user may find other values achieve lower distortion.
Maximum linear input is listed in the specifications.
Figure 32 Amplifier Crossing Point Setting
Figure 33 Amplifier Gain Curves Illustrate Difference between Digital and Analog Amplifier Modes
Eye crossings as a function of
the crossing set-point.
Amplifier is in Analog mode,
which sets the output swing to
its maximum value.
Only the crossing point can be
adjusted.
Analog mode sets output swing to
max. Provides largest linear input
region.
Digital mode provides adjustable swing
and adjustable output amplitude.
Output clips at selectable levels.