-
Command: THH xx#
This command allows the user to control the feedback response threshold.
The response threshold level determines the amount of change in the electrical feedback
signal needed to elicit a polarization change response from the POS-002. When the POS-
002 is enabled, it performs an SOP search for an SOP that maximizes (or minimizes, as
the case may be) the feedback signal. Once this reference level is established, each cycle,
the POS-002 reads the feedback signal level and compares it to the reference level. If the
current feedback signal value differs from the reference level by more than the threshold
setting, the POS-002 will adjust the polarization state. If the difference is less than the
threshold setting, the POS-002 will continue to monitor the AD feedback signal, but will
not change the polarization state. The external feedback POS-002 uses a 0 ~ 5V analog
electrical feedback signal, which is converted to 2
12
= 4096 digital steps for the purposes
of the control algorithm. For the AD feedback, 1 digital step = 5V/4096 = 1.22mV. The
*THH xx# command sets the response threshold (i.e. the minimum amount of change
from the reference level that will result in a polarization state correction from the POS-
002) to xx * 1.22 mV. For example, if for a given laser source, the POS-002 stabilizes the
SOP such that the feedback signal reaches a maximum of 4V, then, with the threshold
level at the default setting, as long as the feedback signal remains higher than 4V-
0.00122V = 3.99878V, the POS-002 will not actively change the polarization.
The threshold control command can be used to reduce the effect of noise. If the SOP
variation is relatively slow and the feedback signal has a known noise level, the threshold
can be set to be larger than the noise so that the POS-002 will react only to perceived
polarization changes above the noise level.
However, a large threshold setting can also result in larger output polarization fluctuation
because the POS-002 will not react to actual polarization drift within the threshold
interval. Figure 15 shows the response of the POS-002, using a relatively large threshold
setting, to the same discontinuous change in the input polarization state used in Figure 7.
The output polarization fluctuation (labeled C in Figure 7) is larger than in Figure 7.
Document #: GP-UM-POS-002-21
Page 21 of 30
苏州波弗光电科技有限公司
苏州波弗光电科技有限公司
苏州波弗光电科技有限公司
苏州波弗光电科技有限公司
苏州波弗光电科技有限公司
苏州波弗光电科技有限公司
苏州波弗光电科技有限公司
苏州波弗光电科技有限公司
苏州波弗光电科技有限公司
苏州波弗光电科技有限公司
苏州波弗光电科技有限公司
苏州波弗光电科技有限公司
苏州波弗光电科技有限公司
苏州波弗光电科技有限公司
苏州波弗光电科技有限公司
苏州波弗光电科技有限公司
苏州波弗光电科技有限公司
苏州波弗光电科技有限公司
苏州波弗光电科技有限公司
苏州波弗光电科技有限公司
苏州波弗光电科技有限公司
苏州波弗光电科技有限公司
苏州波弗光电科技有限公司
苏州波弗光电科技有限公司
苏州波弗光电科技有限公司
苏州波弗光电科技有限公司
苏州波弗光电科技有限公司
网址：www.bonphot.com
电话：0512-62828421
