Page 157 - High Power Laser Handbook

126 Diode Lasers Semiconductor Laser Diodes 127

14 70%
0°C
12 60%

10 PCE 70°C 50%
Ex-fiber power (W) 8 6 Power 70°C 40% PCE
0°C

30%

2 4 20%
10%
0 0%
0 5 10 15
Current (A)

Figure 5.22 Output power and power conversion efficiency (PCE) for a fiber-
coupled, singe-emitter package as a function of drive current at 0°C, 25°C, 35°C,
50°C, and 70°C case temperature (uncoated output).

Best-in-class average fiber-coupling efficiency is approximately
95 percent (AR-coated), and thermal impedance is approximately
7.9 K-mm/W (normalized to cavity length), with ~5.9 K-mm/W allo-
cated to the junction-to-submount bottom interface and 2.0 K-mm/W
18
to the package base. As shown in Fig. 5.22, there is no appreciable
rollover for case temperature less than 50ºC.
For the microfiber laser market, single-emitter-based packages offer
the lowest product price to optical output power ($/W) as compared
with higher-brightness pumps. In high volumes, single-emitter pumps,
such as the one shown in Fig. 5.21, presently cost about $100 per unit, or
about $10/W. Over the past decade, cost per watt has steadily decreased
(nearly 15 percent per year) via a combination of higher-power/diode,
lower-cost packaging and offshore manufacturing.

5.14 Spatially Multiplexed High-Brightness Pumps
2
High-brightness (> 3 MW/cm -Sr) pumping of fiber lasers enables
scaling to multi-kilowatt output power levels. Pumps with higher
brightness offer several advantages for the fiber laser, such as smaller-
diameter glass cladding, shorter fiber, and fewer combiners. As such,
intensive research has been done in the pursuit of combining many
single-emitter diodes into a larger single package with a single fiber
output. Compared with laser bars, the advantages of this architecture
include negligible thermal crosstalk between neighboring emitters,
protection against cascading failed emitters, and, of course, the fact
that their designs and processes are synergistic with fiber-coupled,
single-emitter packages already reviewed.