High-Brightness 9XX-nm Pumps with Wavelength Stabilization

High-Brightness 9XX-nm Pumps with Wavelength Stabilization

V. Gapontsev, N. Moshegov, P. Trubenko, A. Komissarov, I. Berishev,

O. Raisky, N. Strougov, V. Chuyanov, O. Maksimov, and A. Ovtchinnikov* IPG Photonics Corp., 50 Old Webster Rd., Oxford, MA 01540, USA

ABSTRACT

Further acceptance and fiber lasers and direct diode systems commercial success greatly depend on diodes’ availability and cost ($/W). These two parameters should not compromise pumps’ performance and reliability. We report on two high-brightness CW devices: high-power module launching over 100W and a pump capable of launching 50W of wavelength-stabilized emission. Devices are based on a single emitter platform and utilize a 105 μm core diameter fiber; radiation is confined within NA<0.13 in both designs. These hermetically sealed modules require passive cooling and are designed to operate with ≤ 30°C diodes’ junction overheat. CW peak power efficiency is higher than 55% for both devices. The 25-30dB isolation option (feedback protection at 10XX-nm) is optional in either package. Modules have the industry’s smallest footprint and are perfectly suited to serve pumping fiber lasers and direct materials processing markets.

Keywords: high-power, high-brightness, wavelength stabilized performance, high-efficiency, single emitter, pump, diode

1. INTRODUCTION During the last 5 years industry development efforts have moved the definition of a high power pump from ~ 3-5W to ~ 50W in 105 μm fiber1,2,3,4. As a result of these efforts, clear dominance of single emitters over traditional monolithic laser arrays has been finalized. For practical applications, such as pumping, 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 in high-power, high-brightness single emitter multimode pumps operating in the wavelength range of 9xx nm. These diodes are best suited for fiber laser pumping and other applications, including direct diode systems, graphic arts, medical, special, and numerous other industries.

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2. WAVELENGTH STABILIZED DEVICES 2.1 Further performance improvement of legacy products

IPG Photonics’ numerous products continue to utilize pumps rated to operate at 30W CW; a photo of such a pump is presented in Figure 1. Previously, peak power efficiency for these pumps was reported at about ≤ 60% ex-fiber. Recent improvements in sub-components quality and design, as well as ongoing chip-on-submount performance improvement, has enabled incremental increases in power efficiency up to value greater than 65% ex-fiber CW (see Figure 2). To the best of our knowledge, 65% electrical to optical power conversion efficiency is the highest ever reported for passively cooled devices operating at room temperature. * [email protected]; phone 1 508 373 1100; fax 1 508 373 1203; www.ipgphotonics.com

High-Power Diode Laser Technology and Applications VIII, edited by Mark S. Zediker, Proc. of SPIE Vol. 7583, 75830A · © 2010 SPIE · CCC code: 0277-786X/10/$18 · doi: 10.1117/12.840940

Proc. of SPIE Vol. 7583 75830A-1

Figure 2

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To improve heat management we have applied the results of thermal modeling to expand the operating range of the 60W pumps reported elsewhere1. Improved thermal performance of a 60W-device is presented in Figure 3. Temperature insensitivity of operating characteristics significantly expands the number of possible applications of these devices beyond conventional pumping. Wavelength insensitive applications such as direct diode, graphics, medical, and special applications would immediately benefit from using these high-brightness (NA < 0.12) small footprint devices.

Figure 3 Set of power and power efficiency dependencies on current of a “60W” pump;

dependence of peak wavelength position on current recorded at heatsink temperature ranging from 10°C to 55°C.

2.2 High-power high-brightness wavelength stabilized pumps

There are several specific applications which would benefit from using wavelength-stabilized pumps operating at the peak of gain media absorption. There have been few demonstrations of wavelength locking of the diode bar-based pumps, but these devices have not materialized into commercial products due to relatively poor and inefficient performance; the bar approach also appears to be a cost prohibitive solution due to poor locking characteristics and a high manufacturing cost. The single emitter solution is a more promising approach to produce wavelength-stabilized devices with high spatial and spectral brightness. In this article we report on wavelength locked devices based on the pumps described above (see Figure 1). These devices are based on MBE-grown epitaxial material as well. This epitaxial technique provides unique control over wavelength uniformity within run, as well as run-to-run reproducibility of deposition process.

Figure 4 depicts the power current characteristic of a wavelength stabilized pump rated to operate at ≥ 25W power. As one can see, this device demonstrates high spectral and spatial brightness; the numerical aperture stays below 0.12 in the entire range of the driving current. Despite of the side-peaks emerging in lasing spectra at current of about 12A, ~ 97% of pumping power is still contained within a 1 nm spectral window, while over 98% of the pump power is contained within a 1.5 nm window. Peak power efficiency of this device is greater than 50%.


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The design of 100W rated pumps is not limited to the solid state pumping application. Direct diode systems would also benefit from utilizing devices of this design, as well as any other non wavelength-specific applications; this applies to the air-cooled devices as well. Demonstration of 100W devices’ ability to operate in the air-cooled applications is demonstrated in Figure 10. In this graph, one can see a series of Power-Current and Efficiency-Current characteristics recorded at several heatsink temperatures. As one can conclude from analyzing these graphs, applications based on limited passive heatsinking solutions, air-cooled devices, or portable designs can clearly benefit from using these high-power, high-brightness sources of light power. All of the above, in combination with low cost ($/W), low weight, low profile, small footprint, and high brightness (ex-fiber NA ≤ 0.13), ensure wide utilization of these devices in various industrial, medical, and special applications.

Figure 10 Set of CW power-current and power efficiency versus current characteristics recorded at several heatsink

temperatures, alongside with peak wavelength versus current dependencies.

4. CONCLUSIONS High-power, high-brightness pumps continue to be a very dynamic and rapidly evolving sector of the laser industry mostly driven by fiber laser requirements and progress. Recent developments in the single emitter pumping platform provide advantages ensuring further domination of fiber lasers over any other alternative solution. Other applications, such as direct diode systems and special applications, can immediately benefit from utilizing these most recent developments.


5. ACKNOWLEDEGEMENTS The authors would like to thank their co-workers at IPG Laser (Germany); without their contribution and on-going support, this work would not be possible.

REFERENCES

[1] Gapontsev V.; Moshegov N.; Trubenko P.; Komissarov A.; Berishev I.; Raisky O.; Strougov N.; Chuyanov V.; Kuang G.; Maksimov O.; Ovtchinnikov A., “High-brightness fiber coupled pumps”, SPIE Proceedings Vol. 7198, (2009) [2] Qiu X. Dai Y.; Au M.; Guo J.; Wong V.; Rossin V.; Venables D.; Skidmore J.; Zucker E., “A high power high-brightness multi-single-emitter laser pump platform”, SPIE Proceedings Vol. 7198, (2009) [3] Pawlik S.; Guarino A.; Matuschek N.; Bättig R.; Arlt S.; Lu D.; Zayer N.; Greatrex J.; Sverdlov B.; Valk B.; Lichtenstein N., “Improved brightness on broad-area single emitter (BASE) modules”, SPIE Proceedings Vol. 7198, (2009) [4] Leisher P.; Price K.; Karlsen S.; Balsley D.; Newman D.; Martinsen R.; Patterson S., “High-performance wavelength-locked diode lasers”, SPIE Proceedings Vol. 7198, (2009)
