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7.2 Fibre alignment procedure
37
power by less than 25% as the alignment improves, e.g. 10% or
5%.
(e) If the new measured power after step 7c is instead lower than
P
REF
, readjust the horizontal axis of
M3
anti-clockwise to return
to the original angle (as noted at step 7b), then reoptimise the
horizontal axis of
M4
to return to
P
REF
. Now iterate steps 7b
to 7d with an anticlockwise adjustment at step 7b.
(f) Once
P
REF
is maximised, iterate steps 7b through 7e for the
vertical
direction.
(g) Continue to alternately iterate the horizontal and vertical align-
ment procedures until
P
REF
is maximised.
8. If the final net fibre coupling efficiency obtained is within 5 to 7 % of
Output coupling (FC) - Initial FC target
in the test report, skip to
step 10.
9. Taking note of
P
REF
, now make a tiny adjustment to the fibre coupler
lens position with the appropriate fibre coupler focus tool provided
as part of the system toolkit (see fig. 7.3). Make note of the direc-
tion of adjustment. Repeat a single iteration of the horizontal and
vertical walking procedure from step 7 and compare the efficiency to
P
REF
. If the efficiency is greater than the original
P
REF
, make an-
other tiny adjustment to the fibre coupler lens position in the same
direction, otherwise make a tiny adjustment in the opposite direction
and repeat the iteration in either case until
P
REF
has been optimised.
The final efficiency after optimising the fibre coupler lens should be
within 2-3 % of
Output coupling (FC) - Initial FC target
in the test
report, for the same fibre type and test conditions.
10. Return to step 10 of section 7.1 and continue to make adjustments
to the fibre coupler lens after each current increase as per step 9
above. Also note that:
(a) the seed alignment will likely need very small adjustments us-
ing
M2
after each
TA
current increase, as changes to seed align-