
616 Selected Applications
apply as correction to some controlling element within the laser. In the case of
a single-mode laser, this will generally be a piezo-element (PZT) controlling the
cavity length.
As we saw in Chapter 5, in the case of the mode-locked laser, both the rep-
etition rate and the carrier frequency have to be stabilized. A single mode can
be stabilized using the same Pound-Drever-Hall [114] technique as for the cw
laser, by selecting a single mode with a grating.
4
The single mode error signal is
obtained by mixing the signal from the detector PD
1
with the phase modulation
(at f
EO
= 10. 7 MHz, for example). Ideally this error signal