4 BASIC CONCEPTS
4.3 Signal flow
The
PICO
SCALE
signals can be divided into three categories: optical
signals, analog electrical
signals and digital signals. The basic and simpli
fi
ed signal
fl
ow is shown in
fi
gure 4.2.
Figure 4.2: Signal
fl
ow in the
PICO
SCALE
.
At the beginning, an optical signal (light) is generated by a wavelength stabilized DFB laser diode.
The infra-red light is phase modulated with a frequency of
ω
=
30 MHz and sent to the three sensor
heads. The interferometric signals generated in the sensor heads are detected by photo detectors
and converted into electronic signals.
The individual photo-electric signals are demodulated by both the modulation frequency and its
second harmonic (60 MHz). The resulting demodulation signals are digitized by analog-to-digital
converters (ADCs).
The digital signals are used to perform the position calculation. After appropriate
fi
ltering, the data
stream is con
fi
gured and the data are transferred to the user PC. You can select the desired data
sources and display them in graphs. Finally, the data can be exported to csv-
fi
les to be available
for data post-processing.
NOTICE
The position values, generated in the FPGA, have a resolution of 1 pm. Thus, all
internal modules, especially the Advanced Trigger System and the Calculation
System, process integer numbers with the unit picometer.
25
PicoScale User Manual
