Page 159 - High Power Laser Handbook

128 Diode Lasers Semiconductor Laser Diodes 129

140 T = 25°C

120
Power ex-fiber, W: Power efficiency (%) 100 Heatsink

80

60

40

20

0
0 2 4 6 8 10 12 14 16
Current CW (A)
Figure 5.23 Spatial-multiplexed, high-brightness, multimode E-O characteristics.
An output power of 100 W is achieved at 50 percent PCE at 25°C.

forecasting of the failure rate during field deployment. Package reli-
ability is analogous to chip reliability in that a multicell life test should
be used to derive a model with operating parameters, such as optical
power and temperature. As compared with chip multicells, new fail-
ure mechanisms may appear inside the package at relatively lower
temperatures (> 85ºC). High-temperature storage (HTS) may be
extrapolated via activation energy to predict coupling stability versus
time at the use conditions; however, it is insufficient for predicting
the lifetime during operation if optical feedback or contamination
from inside the package degrades the laser facet. Analogous to laser
diode modeling, both random and wear-out failure mechanisms are
presumed to occur that should be independently assessed during the
multicell study. Package life testing is therefore needed to corroborate
the results of the chip multicell model.
Typically, the greatest threat to long-term power stability is related
to lens attachment. Low NA testing should be included to quantify
the true stability, because standard 0.22 NA fiber obscures lens move-
ment up to several micrometers and leads to optimistically forecasted
alignment stability.
For most industrial applications, the failure rate from all package
failure-mode contributions should be small compared with the laser
diode failure modes. However, due to limited acceleration factors
(i.e., maximum temperature) for package multicells, large sample