Last update: 2021/08/26 14:26
d2:quick_start_opls https://www.vescent.com/manuals/doku.php?id=d2:quick_start_opls
https://www.vescent.com/manuals/
Printed on 2021/09/01 05:04
Fig. 4:
Sample
Error
Signal
when
sweepi
ng one
laser.
Reflecti
on
point is
shown
in blue,
two
lock
points are shown in red.
frequency (Error(Δf) = Error(-
Δf)), so there is a reflection
point about Δf=0. The sharp
slope to the left or right of the
Δf=0 point is the lock point
and can be adjusted by
changing the VCO frequency.
Which of the two lock points
the laser will lock to will
depend on the gain sign.
Center the O-scope on one of
the lock points and turn down
the ramp amplitude. Flip the
D2-135 Servo to Lock mode. If
the Servo Output jumps to
+/-10V, repeat with the
opposite gain sign. At this
point, you should have a lock
that is holding the offset
frequency to a specific value.
You may be significantly
broadening the laser because
the servo is oscillating, but
you have a basic lock.
Optimizing the Lock
Fig. 5:
Beat note when locked with coherent peak showing a phase
lock.
The first step is to optimize the gain.
Look at the Error In Monitor and turn
down the gain to minimize the RMS
noise on the Error In Monitor. At this
point you should be able to see the
beat note with the Beat Note (div 2)
monitor on a spectrum analyzer with
a 100 MHz span. You can try to
further optimize the gain by looking
at the beat note monitor and trying
to minimize the width of the beat
note (or if there is a phase lock,
maximize the amplitude of the
coherent peak). The next step is to
optimize the feedback. It is
recommended starting with the ω
HF
in
the off position, ω
I
at 16 kHz, and ω
D
at 64 kHz. Generally, leave ω
HF
off
and adjust ω
D
, ω
I
, diff gain and
overall gain while monitoring the
beat note to see if the lock is getting
better as you make adjustments.
Look for a narrow peak coming out of
