The control parameters allow the user to optimize the POS-002 control cycle for the
requirements of particular applications. Their effects on the quantities described above
will be explained in the following sections.
Note: The POS-002 does not store user-selected settings in its permanent memory.
After it is powered off, all control parameters will revert to the default settings.
Polarization Tuning Modes
The POS-002 has two polarization tuning modes: variable and fixed step size. The default
mode is variable step size. In this mode, the POS-002 dynamically adjusts the step size
that it uses within a range of one to six times the step size set by the most recent *STS
xx# command. This allows it to react quickly, using a larger step size, when the SOP is
far from the target, and then to use a smaller step size closer to the target to smooth out
the response.
In fixed step size mode, the POS-002 uses a constant step size, set using the *STS xx#
command, for its polarization adjustments.
The *VAR# and *FIX# commands are used to select variable and fixed step size modes,
respectively, and the *FUN? command is used to query the current operation mode.
Control Parameters
The setup commands in the command list are used to set or to request the current values
of the control parameters for the feedback control loop.
-
Command: *STS xx#
The step size defines the control voltage increment applied to the polarization controller
per control loop cycle in response to a change in feedback signal level. The POS-002 uses
a 0V~150V voltage output to control the polarization controller. This control voltage
range is converted to 2
12
= 4096 digital steps for the purposes of the control algorithm. 1
digital step = 150V/4096 = 0.0366V
≈
0.2
°
on the Poincaré sphere. The *STS xx#
command therefore sets the voltage output step size to xx * 0.0366V, and the
corresponding polarization step on the Poincaré sphere to approximately xx * 0.2°.
The default setting is 8, corresponding to a control voltage step of 8 * 0.0366V, which
results in a maximum polarization change of about 1.76° on the Poincaré sphere. In fixed
step size mode, this step size remains constant at the selected value. In variable step size
mode, the set value is used as the base step size when the POS-002 begins polarization
adjustment.
The following figures illustrate the effects of step size selection. For easier illustration,
the measurements were taken with the POS-002 in fixed step size mode.
Document #: GP-UM-POS-002-21
Page 17 of 30
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