1. High-brightness fiber coupled pumps
V. Gapontsev, N. Moshegov, P. Trubenko, A. Komissarov, I. Berishev,
O. Raisky, N. Strougov, V. Chuyanov, G. Kuang, O. Maksimov, and A. Ovtchinnikov*
IPG Photonics Corp., 50 Old Webster Rd, Oxford, Ma, USA, 01540
ABSTRACT
Advanced high volume applications require pumps with high power, high brightness, and high power efficiency. New
generation devices meet all of these challenging requirements, while still maintaining the advantages of distributed
pumping architecture including high reliability inherent to single emitter sources. Based on new-generation long-cavity
diode chips, new pumps are capable of more than 60W CW power ex-fiber output (100 μm core diameter) into NA ~
0.12. Peak power efficiency stays over 60%. All of the above is provided at room heatsink temperature, maintained by
basic air- or water-cooling.
Keywords: high-power, high-brightness, high-efficiency, single emitter, pump, diode
1. INTRODUCTION
Recent industry development efforts have been primarily targeted on pump diodes’ power and efficiency. As a result of
these efforts, clear dominance of single emitter over traditional bars has developed in the last few years. For practical
applications, such as industrial, telecom, medical and similar, the single emitter approach means cheaper and brighter
diodes, as well as more reliable overall kilowatt-class pump engines not based on overcomplicated and high-
maintenance micro-channel cooled bar stacks. Single emitters have prevailed not only due to obvious reason of superior
performance, reliability and cost of ownership, but also due to the not so obvious upfront cost advantage traditionally
measured in $/W.
This paper focuses on IPG Photonics most recent developments for high-power high-brightness single emitter
multimode pumps operating in the wavelength range of ~ 8xx nm to ~ 9xx nm. These diodes are best suitable for fiber
laser pumping and other applications, including direct diode systems, graphic arts, medical, dental, and numerous others.
.
2. NEW GENERATION SEMICONDUCTOR CHIP DEVELOPMENT
2.1 Diodes operating in the 9xx nm range
IPG Photonics Chips-On-Submount (COS) and fiber coupled pumps of the previous generation demonstrate state-of-the-
art performance and reliability1. Due to optimized chip design diodes with a cavity length (L) of 3 mm we were able to
achieve industry best performance2,3,4,5 in power, brightness and power efficiency without compromising pump
reliability1. These parameters were achieved for fiber coupled pumps rated to operate up to ~ 20W-25W ex-fiber. Further
increase of rated power in the L=3 mm chip design was impossible without sacrificing reliability of the chip. Scaling of
cavity length is a natural approach to increase the level of reliable output from a single emitter device2,3. Our choice was
a 50% scaling factor resulting in L=4.5 mm. In order to maintain a decent slope efficiency and to keep the threshold
current low, we have performed a layered structure, as well as ridge stripe geometry optimization targeting a
compromise between “high slope and low threshold current”, and the sacrifice in “the far-field divergence and series
resistance”; the latter has a direct impact on power efficiency that is the key parameter for the multi-kilowatt systems.
The far-field divergence greatly determines the coupling efficiency, which in turn affects the rated power level and
power efficiency ex-fiber.
*
aovtchinnikov@ipgphotonics.com; phone 1 508 373 1100; fax 1 508 373 1203; www.ipgphotonics.com
High-Power Diode Laser Technology and Applications VII, edited by Mark S. Zediker,
Proc. of SPIE Vol. 7198, 71980O · © 2009 SPIE · CCC code: 0277-786X/09/$18 · doi: 10.1117/12.809456
Proc. of SPIE Vol. 7198 71980O-1

2. The results presented in Figure 1 summarize the layered structure and the ridge waveguide development effort. As one
can see from the plot, the best COS (W=90 μm wide aperture, L=4.5 mm, 25°C heatsink temperature) launches ~18W
CW free-space at a 25A current not reaching the thermal roll-over. This performance is archived at a very low operating
voltage: CW power efficiency peaks at ~ 72% (WPE > 60% recorded up to 14W CW power) and stays above 50% up to
the ex-facet output of > 17W. To the best of our knowledge, this is the most power-efficient high-power diode reported
so far to operate above cryogenic temperature. In order to reach such efficient operation in manufacturing environment,
we had to take full advantage of AlGaInAs material grown in the most precise and controllable manner by Solid State
Molecular Beam Epitaxy growth method.
Power Efficiency, %
16 1.6
60
12 1.2
L = 4.5 rrrr
W = 90 irn
25CC
> 40
-r....-- 0.8
or
9)
0 WPE > 710
0
WPE 600o up to - 13.5W
4 WPE > 50°o: up to 17.5W
0.4
20
0' 30
0 = 8-9
976 rrr
0
0 5 10 15 20 0 5 10 15 20
Current CW, A
Figure 1 Power and Power Efficiency dependencies on current of the 4.5 mm-long cavity, W=90 μm COS optimized for
efficient performance.
In order to demonstrate ultimate CW power output, we chose a slightly different layered structure and processed it in a
ridge waveguide structure of W, which is slightly wider than 100 μm. The results of CW THS=25°C test are presented in
Figure 2. An output greater than 20W CW was achieved; this power is very close to earlier reported data for diodes
grown by MOCVD2.
peek effioiency 2 650/0
18 60
- 25°C heatsink
2 600/0 WPE op to
15 2 20W CW
13A - 12W CW, 250C
45 2 500/o WPE up to --
12 22A - 19W CW, 250C
U
U
>flWcW__ - 30
0 85CC heatsink
6
15
3
A = 974 nm
0 0 I I
0 5 10 15 20 25 0 5 10 15 20 25
Current CW, A Current CW, A
Figure 2 Power and Power Efficiency dependencies on current of the 4.5 mm-long cavity, W~100 μm COS optimized
for high-power performance.
Proc. of SPIE Vol. 7198 71980O-2

3. Results of the cavity length analysis and the tests of temperature sensitivity of lasing are given in the next two graphs.
While temperature coefficients yielded numbers of T0=167K and T1=358K, the internal quantum efficiency and internal
loss were ηi=99% and αi=0.35 cm-1 respectively. At the time of preparing this paper, the authors were not aware of
previously reported data detailing such low internal loss for semiconductor lasers.
50
- 45
>,
0
=
@9 C)
0
0
0 w
C) 30
0
15
4 8 12 16 20
Current CW A
Figure 3 Set of Power and Power Efficiency dependencies on current of the 4.5 mm-long cavity, W=90 μm COS
recorder at different heatsink temperatures.
700
E
=
a)
500
0
0
-c Q)
U)
a) 1
-c
F-
500
30 60 90 30 60 90
Heatsink temperature, °C
Figure 4 Results of cavity length and power-current characteristics analysis performed on laser diodes of 4.5 mm-long
cavity design, W=90 μm COS at different heatsink temperature.
Proc. of SPIE Vol. 7198 71980O-3

4. 2.2 Diodes operating in the 8xx nm range
The modeling, and layered structure and ridge geometry design rules developed in the course of our investigations,
appear to be rather universal and applicable to devices operating at different wavelengths. The very first attempts to
produce COS with L=4.5 mm operating in the wavelength range of 8xx nm yielded a COS with typical performance
presented in Figure 5; the L=4.5 mm COS performance is plotted against L=3.0 mm COS previously reported in 1. As
one can clearly see from the graph a 50% increase in cavity length (for this particular wavelength) gives the benefit of a
~50% increase in roll-over power and a ~ 50% increase in roll-over current.
Efficiency, 0/0
THIS.k = 25°C
12 50
10
40
8
30
6 fi
20
4
10
---W=9Ogm,L=4.5mm
- W = 90 m, L = 3.0mm
0
10 15 0 5 10 15
Current CW, A
Figure 5 Room temperature Power-Current CW characteristics comparison performed on COS operating in 808 nm
wavelength range of different cavity length (L=4.5 mm and L=3.0 mm); both have similar lateral stripe geometry
W=90 μm.
3. FIBER COUPLED PUMPS BASED ON L=4.5 MM COS
3.1 Low power pumps operating in the 9xx nm range
The pumps reported in this section are based on the same package design, packaging and fiber coupling technology and
previously reported techniques6. The fiber coupled pumps of the early design were based on COS with 2-3 mm cavity
length and the details of their performance were reported elsewhere6,7. Those devices were qualified and proven in
numerous applications, including telecommunications and space operation.
The performance of the L=4.5 mm COS-based pumps is presented in Figure 6. Ex-fiber power (105 μm core diameter)
versus current characteristic is linear, with over 13W CW power launched at a 15A driving current. In the entire driving
current range, the power is confined within a numerical aperture of 0.12 or less. Despite of the long-cavity chips, these
fiber coupled pumps arrear to be very power efficient. As one may see from the efficiency-current dependence, the peak
power efficiency is well above 60%, the efficiency stays above 50% up to the highest driving current of 15A (> 13W
CW ex-fiber output).
Another attractive feature of these devices is low thermal resistance; we recorded thermal resistance as low as 2.5-
2.9°C/W, which corresponds to less than 30°C junction temperature overheat at a 10W CW output. Low chip overheat
favorably contributes to overall pump reliability.
Proc. of SPIE Vol. 7198 71980O-4

5. 12
-Io
E
0
Wlenqth 974uiiii 10
rIiuiI 2.4S - .0 °C/W
U 0
0 q 12 0 3 0 12
Curr.nt CW A
Figure 6 Room temperature Power and Power Efficiency characteristics for “low-power” fiber-coupled pump based on
L=4.5 mm and W=90 μm (λ ~ 975nm) COS
3.2 Mid-power pumps operating in the 9xx nm range
Mid-power pumps are based on the package design and technology previously reported elsewhere1. Replacing L=3mm
COSs with the new-generation chips allowed us to achieve higher power ex-fiber, while keeping the same package.
60
40
55
so
C)
L 30
I 0
20
. 20
'S
10
9 15
5 10 15 20 25 30 35 40
Current CW A
OW Power ex-fiber, W
Figure 7 a. Room temperature Power and Power Efficiency characteristics for “mid-power” fiber-coupled pump based
on L=4.5 mm and W=90 μm (λ ~ 975nm) COS. b. Junction overheat as a function of ex-fiber CW output.
Figure 7 presents the power and efficiency characteristics recorded for one of these packages. Power of slightly less than
40W is reached at a driving current of ~15A. Even at the highest driving currents, the power is still confined within NA
≤ 0.12. Such high efficient operation, stable fiber coupling efficiency and high brightness of radiation were made
possible due to optimized stripe geometry design providing negligible slow-axis far-field blooming with current. Power
efficiency peaks at > 60% and stays over 50% with ex-fiber output up to 35W - 40W CW. Even though this high-
brightness pump has a exceptionally small footprint it demonstrates very stable temperature performance and very little
junction temperature overheat. As one may see from the right-hand plot in Figure 7, the junction temperature overheat
stays below 30°C even at high ex-fiber output, such as 30W CW. Such an efficient and temperature-insensitive
Proc. of SPIE Vol. 7198 71980O-5

6. performance makes these pumps ideal candidates for multi-kWatt system pumping by providing the ideal balance
between performance, reliability, and manufacturing cost.
3.3 High power pumps operating in the 9xx nm range
Although the mid-power pumps reported in the previous section provide power and brightness sufficient to satisfy the
requirements of vast majority of most modern pumping applications by providing almost an ideal balance of
performance, reliability and cost ($/W), some specialty applications or experimental units require even higher pumping
power and brightness. The pump sources reported in this section are designed to address these needs.
60
E
45
60
9)
>
40 0
C)
r
C 0
9) -
C)
uJ
r
U
15
C
n
Wavelength 974 nm
NA 6.12
9) I I I
0
3-
J 6 9 12 15 18 0 20 40 60
Curr6nt CW, A
Power CW ex-fiber, W
Figure 8 a. Room temperature Power and Power Efficiency characteristics for “high” power fiber-coupled pump based
on L=4.5 mm and W=90 μm (λ ~ 975nm) COS. b. Junction overheat as a function of ex-fiber CW output. The insert
photograph shows the mid- and the high-power pumps placed side-by-side.
The graph on the left in Figure 8 depicts the power and power efficiency dependencies of the high-power pumps of the
new design. In the right-hand graph, one will find the dependence of junction temperature overheat with CW ex-fiber
output; the insert photo shows mid- and high-power pumps placed side-by-side to provide the footprint comparison of
the pumps of both designs. As one can see from the graphs, there is almost virtually no penalty in fiber coupling
efficiency, numerical aperture, and power efficiency with power scaling to > 60-70W CW. Stability of these parameters
with power scaling is possible due to proprietary fiber coupling techniques (combined with narrow and stable with
current far-field6). One can see that the junction-temperature-overheat with ex-fiber output is maintained low for this
pump design: the ~30°C-junction-overheat is recorded at a ~ 60W CW output.
3.4 Pumps for specialty application
Few specialty applications require “low-power”, low-cost, ultra-high-brightness pumping. 9xx nm pumps with 50 mm
fiber core diameter may be the perfect solution for these applications. As one can see in Figure 9, the thermal roll-over
power of ~ 10W CW ex-fiber (50 μm fiber core diameter) may be achieved at about 16A at a room temperature heatsink.
These pumps offer brightness of pumping comparable to that of the more expensive higher power devices reported in the
previous sections (100 μm fiber core diameter pumps rated for 20W-30W CW output) due to low NA ~ 0.11 - 0.12 and
high ex-fiber power output. Although these pumps do not provide the lowest $/W pumping solution, they offer the
cheapest solution providing the brightest and the most efficient pumping in the power range up to ~5-7W CW.
Proc. of SPIE Vol. 7198 71980O-6

7. 10
ORO
"5
w
o*r .*-fIb.: S0pr ear., nA
nçntr.$. to 0W 100 on icr.
OQutvJIOrlt o 30W LOC tarn or. 1Dor
0 GS
0 2 4 6 0 10 12 14 16 4 (' 1) 11
Current CW, A
Figure 9 Room temperature Power and Power Efficiency characteristics for 50 μm core diameter fiber-coupled pump
based on L=4.5 mm and W=90 μm (λ ~ 976 nm) COS
The spectral range of 8xx-nm is another wavelength that requires a significant amount of pumping power. Recently
single emitter-based pumps started to provide not only the low-power (2-4W CW), but also higher power pump systems
based on power scaling solutions described elsewhere1. Figure 10 provides an example of the pump based on long-cavity
L=4.5 mm COS. As one may see from the plot ex-fiber (100 μm core fiber diameter), an output of ~ 10W CW with peak
power efficiency of ~ 50% can be achieved from this device. The performance of this device qualifies it as one the
brightest and the most efficient of presently available pumps8 for this wavelength range.
10
>
C
C
4 8 10 1.! I
Ctwre t CW, A
Figure 10 Room temperature Power and Power Efficiency characteristics for “low” power fiber-coupled pump based on
L=4.5 mm and W=90 μm (λ ~ 808nm) COS
Proc. of SPIE Vol. 7198 71980O-7

8. 3.5 Reliability of 9xx nm pumps’ rated for ~20W output for industrial applications
At the time of this publication, we have not accumulated sufficient data to assess reliability of the pumps based on L=4.5
mm chips. The reliability data are available for the previous generation devices: mid-power range pumps rated for ~20W
output that were reported earlier1. These devices are based on a 3 mm-long cavity COS; these pumps are primarily used
in material processing, medical, dentistry, and specialty applications. Typical power current characteristic of these
pumps is presented alongside with power efficiency dependence in the right graph of Figure 11b.
To assess the reliability of these devices we have randomly selected 153 pumps manufactured in different IPG facilities
worldwide. They were put on a multi-cell test that provided stress conditions by operating current overdrive and elevated
heatsink temperature. In the course of this test, over 2,750,000 COS-real-time-hours-on-test (not-accelerated) were
accumulated. Random COS failures were proven to not have any noticeable effect on the reliability of the other single
emitter diodes operating within the same pump enclosure, i.e. COS failures within the same pump can be considered
independent events. The results of COS failure in time distribution analysis yielded the results summarized in the left
graph of Figure 11. As one may can in the graph, MTBF value greater than 100,000 hours at ~20W ex-fiber pump output
was determined for packaged COS of 3 mm cavity length. This MTBF value for packaged chips L=3.0 mm cavity length
ensures less than a 10% drop in output power of a pumping ensemble over a period of time greater than two years of
continuous operation. As of today, numerous devices of this design are deployed in the field serving many diverse
applications. These pumps provide additional proof of the validity of this reliability assessment data, as the actual in-
field reliability exceeds the estimate obtained in this accelerated test.
250220 so
200000
45
l5o00
30
100,000
50,000
C
14 20 21 22 20 24 25 6 12
Power ex-fiber, W Current CW, A
Figure 11 a. Dependence of COS Mean-Time-Between-Failures as a function of ex-fiber output for mid-power pumps
rated for ~20W output1. b. Room temperature Power and Power Efficiency characteristics for the fiber-coupled pump
rated for ~20W output and based on L=3.0 mm and W=90 μm (λ ~ 975nm) COS
4. CONCLUSIONS
Solid Source MBE-grown AlGaInAs lasers performing in the 8xx-9xx nm range demonstrate the highest power
efficiency and lowest internal loss previously reported. These are the key pump laser parameters for high power, high
volume applications. The recent design and manufacturing packaging solutions result in high brightness pumps operating
in the output power range of >60W CW ex 100 μm fiber core diameter. The combination of these parameters makes
these devices the most efficient presently available pumping solutions.
Proc. of SPIE Vol. 7198 71980O-8

9. 5. ACKNOWLEDEGEMENTS
The authors would like to thank their co-workers at IPG Photonics; without their support, contribution, and
encouragement, this work would not be possible.
REFERENCES
1
V. Gapontsev, I. Berishev, V. Chuyanov, G. Ellis, I. Hernandez, A. Komissarov, N. Moshegov, O. Raisky, V.
Rastokine, N. Strougov, P. Trubenko, L. Wright, and A. Ovtchinnikov, “8xx – 10xx nm highly efficient single
emitter pumps”, SPIE Proceedings, V. 6876, paper 6876-17
2
P. Ylamanchili, V. Rossin, J.Skidmore, K. Tai, X. Qui, R. Duesterberg, V. Wong, S. Bajwa, K. Duncan, D. Venables,
R. Verbera, Y. Z. Dai, J. F. Feve, E. Zucker, “High-power, high-efficient fiber-coupled multimode laser diode pump
module (XX nm) with high-reliability”, SPIE Proceedings, V. 6876, paper 6876-37
3
N. Lichtenstein, M. Krejci, Y. Manz, J. Boucart, B. Valk, J. Muller, C. Buttons, S. Weib, S. Pawlik, B. Sverdlov,
“Recent development for BAR and BASE: setting the trends”, SPIE Proceedings, V. 6876, paper 6876-0C
4
R. Martinsen, K. Price, and S. Karlsen, “Next-generation fiber laser pumps”, Applications of High Power
Semiconductor Lasers, San Diego, 06 October 2008
5
E. Wolak, K. Kuppuswamy, B. Fidric, S.-K. Park, D. Liu, S. Cutilas, H. Li, I. Chyr, F. Reinhardt, R. Miller, X. Jin, T.
Nguyen, T. Towe, P. Cross, T. Truchan, R. Bullock, J. Mott, J. Harrison, “Reliability of ensembles multi-stripe laser
diodes”, SPIE Proceedings, V. 6876, paper 6876 0N.
6
V. Gapontsev, I. Berishev, G. Ellis, A. Komissarov, N. Moshegov, A. Ovtchinnikov, O. Raisky, P. Trubenko, V.
Ackermann, E. Shcherbakov, “9xx nm single emitter pumps for multi-kW systems”, SPIE Proceedings V. 6104,
paper 61040K, 2006
7
V. Gapontsev, I. Berishev, G. Ellis, A. Komissarov, N. Moshegov, O. Raisky, P. Trubenko, V. Ackermann, E.
Shcherbakov, J. Steinecke, and A. Ovtchinnikov, “High efficiency 970 nm multimode pumps”, Photonics West, San
Jose, CA, January 24th 2005, SPIE Proceedings 5711-6
8
Schleuning, D.A., Haapamaa, J., Luong, C., Morales, J., Pathak, R., Watson, L., Winhold, H., and Hasenberg, T.,
“Lateral Modes and Slow Axis Divergence in Broad Area Semiconductor Lasers”, Applications of High Power
Semiconductor Lasers, San Diego, 06 October 2008
Proc. of SPIE Vol. 7198 71980O-9