Rev B Sept 2020
Appendix C Principles of Operation
Page 39
C.1.2 How the NanoTrak Maximizes Optical Power
To understand the principles involved in the alignment, consider the operation in a single axis. When two fibers are aligned,
maximum power is transmitted between them, and if the fiber is moved a few microns to the left (Fig. C.3, position A), the
power is reduced. Furthermore, oscillating the fiber by a few microns causes the detected power signal to assume an AC
component whose amplitude is proportional to the amplitude of the mechanical oscillation (modulating signal).
Fig. C.3 AC component of optical power
The received power signal contains a frequency component at the scanning frequency, and the phase of this (relative to the
circle scan voltages) gives information on which direction to move.
When the circle is centred in the ideal position, the power signal contains no modulation at the scanning frequency. However,
at position A, the signal has a phase difference with respect to the modulating signal. The power signal is Fourier analysed
and the result of the computation is passed to an algorithm which drives the circle to the correct position.'
However, piezo transducers are unipolar and to achieve a positive and negative adjustment either side of center, the piezo
must be at its center of travel when the error signal is zero. This is achieved by adding an offset voltage to the error signal.
Now, the range of the piezo is typically 20 to 30 µm, while the fiber is oscillated by 2 or 3 µm. Therefore, it can be seen, that
by varying this offset voltage we can adjust the position at which the oscillation of the fiber takes place - see Fig. C.4 detail A.
0.0
0.5
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position A
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5 µ
m displacement
0.0
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1.0
0
center
Содержание NanoTrak KNA-IR
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