MOGlabs ARF021, Руководство пользователя

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Chapter 6. PID stabilisation
6.4 Noise-eater implementation
A common application for PID controllers is optical noise eating,
which technical noise arising from power fluctuations in a laser beam.
Figure 6.1 shows a typical configuration, where the intensity of the
undiffracted (zero-order) beam is stabilised as seen in Figure 6.2.
In this configuration, the AOM acts as a high-speed variable optical
attenuator, diffracting some of the light into the unused first-order
output. The transmitted optical power is measured with a photode-
tector, and the ARF/XRF controls the RF power in proportion to the
Photodetector
AOM
Laser
Stabilised
Offset
ARF/XRF
Beamsplitter
+
–
Error
Figure 6.1:
Typical setup for optical power noise eater.
Time Time
Volts
Offset
Photodetector signal
ARF/XRF input error signal
1
2
3
4
5
Figure 6.2:
Photodetector signal (magneta) and conditioned error signal
(blue) before and after activating noise-eater feedback (simulated). Note
that the DC offset must be subtracted during signal conditioning.