MOGlabs DLC202, Manual, Page: 63 / 82

D. External modulators and injection
current modulation
The
MOG
labs
DLC
is designed for
AC
locking a laser to an external
reference such as an atomic resonance or an optical cavity. In many
cases it is convenient to use the internal modulator driver, and Zee-
man modulation of an atomic transition, as described in appendix C.
Zeeman modulation is not always possible (e.g. if the reference is
an optical cavity), or desirable (e.g. due to magnetic interference).
The
MOG
labs
DLC
can dither the laser diode injection current (
DIP
switch
3
), or drive an external modulator, such as an electro-optic
modulator (
EOM
) or acousto-optic modulator (
AOM
).
D.1 Coupling circuit
The
DLC
provides a current-controlled modulation output, with 1 Ω
sense resistor. It can be directly connected to a 50 Ω load, producing
a voltage of
± 5 V with
Iset
adjusted to ± 100 mA.
Impedance-matching and a
DC
level shift may be needed to drive
an external modulator, as in the schematic below, designed for the
D323B
RF
amplifier from
ISOMET
.
Figure D.1: Coupling from MOD OUT to an external modulator.
The
ISOMET D323B
RF
driver has a frequency control input with 4 to
17 V range. We
AC
couple using a simple 10T:10T ferrite bead trans-
53