1.1 Schematics 9
1.1.4 Modulation and scanning
Laser scanning is controlled by either an internal sweep generator
or an external sweep signal. The internal sweep is a sawtooth with
variable period as set by an internal four-position range switch and
a single-turn trimpot marked “RATE” on the front-panel.
The fast and slow servo loops can be individually engaged with
either a TTL input to the rear-panel, or the associated front-panel
switches. Setting either loop to LOCK stops the sweep and activates
stabilisation.
Fast control
MODULATION & SWEEP
MOD IN
+
0v
0v
Bias [3]
FAST OUT
TRIG
HF
FAST
BS
BIAS
RA
RAMP
BIAS
0v
LF sweep
0v
SPAN
0v
0v
Fixed oset [5]
+
OFFSET
SWEEP IN
+
RATE
Ramp
Slope [6]
INT/EXT
LOCK IN (FAST)
LOCK IN (SLOW)
0v
–
Mod [4]
0v
FAST = LOCK
SLOW = LOCK
Figure 1.8: Sweep, external modulation, and feedforward current bias.
The ramp can also be added to the fast output by enabling DIP3 and
adjusting the BIAS trimpot, which may be useful for direct current
modulation of the laser. Note that many laser controllers (such as
the MOGLabs DLC) will generate the necessary bias current using
the slow servo signal and it is unnecessary to also generate it within
the FSC.
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