MOGlabs MOA, Manual, Page: 41 / 66

7. Fibre coupling
The output beam profile of a
TA
diode can be highly irregular and highly
astigmatic. Nevertheless it is still possible to achieve good coupling into a
singlemode fibre. Some examples of fibre coupling efficiency are provided
in the figure below. Fibre coupling efficiency varies from diode to diode
due to many factors, so as a guide net coupling efficiency from fibre coupler
(FC) input power to FC output power is generally 50% or better, and 60%
is not unusual, despite Fresnel losses at each facet of the fibre (8%).
0
1
2
3
4
5
50% 52% 54% 56% 58% 60% 62% 64% 66% 68%
Nu
m
ber
o
f s
ys
tem
s
Fibre coupling e ffi ciency
Fibre coupling e ffi ciency
Figure 7.1:
Measured fibre coupling efficiency for 20 fibre coupled
TA
systems
ranging from 670nm to 1080nm with input powers from 500mW to 3000mW. The
average result is 57% for this sample set.
The
TA
output beam profile and astigmatism both vary with operating cur-
rent. It is thus advised to correct
TA
beam astigmatism at high current
(or your desired operation current)
before
attempting fibre coupling (see
Chapter 6). Note that
TA
operating powers typically exceed the damage
threshold tolerance at fibre facets and thus it is easy to damage fibre facets
if attempting to correct astigmatism at high currents
during
fibre coupling.
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