MOGlabs MOA, Manual, Page: 44 / 66

34
Chapter 7. Fibre coupling
4. Make a very small (
1
16
turn or less) adjustment to the
horizontal
axis
of
M3
until the output power is maximised.
5. Again, make very small (
1
16
turn or less) adjustments to the
horizontal
axis of
M4
until the output power is maximised.
6. Repeat above two steps until
P
REF
is optimised.
7. Now for the
vertical
axis of
M3
and
M4
, repeat from step 3 to 6 until
P
REF
is optimised.
8. Compare the
TA
output power with the appropriate value from
Initial
FC target
in the test report. A value within 10 to 15% of the target
is suggested before proceeding.
9. Measure the input power to the fibre coupler, carefully inserting a
mirror to pick off the beam before the coupler if necessary, and cal-
culate the net fibre coupling efficiency. Use the same power sensor
head for the output power measurement where possible and, if used,
make sure to allow for any losses due to the mirror. Do not proceed
unless the total net efficiency is at least 10%. If this is not possible
using the above procedure, review the troubleshooting section 7.4,
implement any changes, and repeat steps 3 to 7. If the net efficiency
is still not sufficient, skip the remaining steps here and proceed to
the advanced fibre alignment procedure in section 7.2.
10. Increase the
TA
current to a value where you expect about 100 mW
of power after the isolator.
11. Repeat steps 3 to 7, being careful to use only the smallest adjust-
ments so that the power does not reduce by more than 50 % for any
given adjustment of a particular mirror axis. Net fibre coupling ef-
ficiency should remain above 10 % at all times when power incident
on the fibre is
>
100 mW.
12. Remeasure the new fibre coupling efficiency. The net efficiency
should be a little higher than the value determined for 10 mW of
input light.