High-Brightness 9XX-nm Pumps with Wavelength Stabilization


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High-Power Diode Laser Technology and Applications VIII, edited by Mark S. Zediker, Proc. of SPIE
Vol. 7583, 75830A

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High-Brightness 9XX-nm Pumps with Wavelength Stabilization

  1. 1. 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 ABSTRACTFurther acceptance and fiber lasers and direct diode systems commercial success greatly depend on diodes’ availabilityand cost ($/W). These two parameters should not compromise pumps’ performance and reliability. We report on twohigh-brightness CW devices: high-power module launching over 100W and a pump capable of launching 50W ofwavelength-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 andare designed to operate with ≤ 30°C diodes’ junction overheat. CW peak power efficiency is higher than 55% for bothdevices. The 25-30dB isolation option (feedback protection at 10XX-nm) is optional in either package. Modules havethe industry’s smallest footprint and are perfectly suited to serve pumping fiber lasers and direct materials processingmarkets.Keywords: high-power, high-brightness, wavelength stabilized performance, high-efficiency, single emitter, pump,diode 1. INTRODUCTIONDuring 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 monolithiclaser arrays has been finalized. For practical applications, such as pumping, industrial, telecom, medical, and similar, thesingle emitter approach means cheaper and brighter diodes, as well as more reliable overall kilowatt-class pump enginesnot based on overcomplicated and high-maintenance micro-channel cooled bar stacks. Single emitters have prevailednot only due to obvious reason of superior performance, reliability and cost of ownership, but also due to the not soobvious upfront cost advantage traditionally measured in $/W.This paper focuses on IPG Photonics’ most recent developments in high-power, high-brightness single emittermultimode pumps operating in the wavelength range of 9xx nm. These diodes are best suited for fiber laser pumping andother applications, including direct diode systems, graphic arts, medical, special, and numerous other industries.. 2. WAVELENGTH STABILIZED DEVICES2.1 Further performance improvement of legacy productsIPG Photonics’ numerous products continue to utilize pumps rated to operate at 30W CW; a photo of such a pump ispresented in Figure 1. Previously, peak power efficiency for these pumps was reported at about ≤ 60% ex-fiber. Recentimprovements 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 thebest of our knowledge, 65% electrical to optical power conversion efficiency is the highest ever reported for passivelycooled devices operating at room temperature.* aovtchinnikov@ipgphotonics.com; 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
  2. 2. Figure 1 Photo of the devices rated to operate at p e power of 30W a 50-60W C and CW.Figure 2 Power and pow efficiency of a 97X-nm p wer pump recorded at a heatsink t d temperature of 25°C. Radiation is f i confine within the nu ed umerical apertu of NA < 0.12. ure Proc. of SPIE Vol. 7583 75830A-2
  3. 3. To improve heat management we have applied the results of thermal modeling to expand the operating range of the 60Wpumps reported elsewhere1. Improved thermal performance of a 60W-device is presented in Figure 3. Temperatureinsensitivity of operating characteristics significantly expands the number of possible applications of these devicesbeyond conventional pumping. Wavelength insensitive applications such as direct diode, graphics, medical, and specialapplications 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 pumpsThere are several specific applications which would benefit from using wavelength-stabilized pumps operating at thepeak of gain media absorption. There have been few demonstrations of wavelength locking of the diode bar-basedpumps, but these devices have not materialized into commercial products due to relatively poor and inefficientperformance; the bar approach also appears to be a cost prohibitive solution due to poor locking characteristics and ahigh manufacturing cost. The single emitter solution is a more promising approach to produce wavelength-stabilizeddevices with high spatial and spectral brightness. In this article we report on wavelength locked devices based on thepumps described above (see Figure 1). These devices are based on MBE-grown epitaxial material as well. This epitaxialtechnique provides unique control over wavelength uniformity within run, as well as run-to-run reproducibility ofdeposition process.Figure 4 depicts the power current characteristic of a wavelength stabilized pump rated to operate at ≥ 25W power. Asone can see, this device demonstrates high spectral and spatial brightness; the numerical aperture stays below 0.12 in theentire 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 containedwithin a 1.5 nm window. Peak power efficiency of this device is greater than 50%. Proc. of SPIE Vol. 7583 75830A-3
  4. 4. Figure 4 Room temperaature power-cu urrent and power efficiency C characteristics of a “low-p CW power” wavele ength stabilized pump along w the spectra recorded at 8 10A, and 12A driving cur d with a 8A, rrent.Wavelength stabilized devi ices which are based on 60W pumps (see F e W Figure 1) offer an even brigh pumping s r hter solution.Their rated ppower exceeds 50W while m s maintaining a n numerical aperrture of less th 0.12. Typi han ical power-cur rrent andpower efficiency character ristics are presented in Figu 5 along w ure with ex-fiber spectra recorde at different driving ed tcurrents. As one can see from this gra aph, the wave elength locking technology capability alloows for high spectralbrightness; in the entire ran of driving c n nge currents, over 9 99% of total po ower is contain within a 1.5 nm spectral w ned 5 window.Figure 6 presents the wave elength peak p position depend dence on drivi current for a wavelength ing r h-locked pump rated tooperate at ≥ 50W output. The shift of the wavelength p T e peak position is less than 0.5 nm with the d s driving current increasefrom ~ 1A t ~12A CW. Availability o such pumps adds significa flexibility in design for numerous wav to of ant velengthspecific applications. Proc. of SPIE Vol. 7583 75830A-4
  5. 5. Figure 5 Ro oom temperatu Power and P ure Power Efficien characteris ncy stics for “high-p power” wavele ength-stabilized pump d along with the spectra record 8A, 10A, a 12A drivin current. e ded and ngFigure 6 Ro oom temperatu Power and P ure Power Efficien characteris ncy stics for “high-p power” wavele ength stabilized pump d along with d dependence of p peak waveleng position on current. gth Proc. of SPIE Vol. 7583 75830A-5
  6. 6. 3. ULTRA HI U IGH-POWE HIGH-B ER BRIGHTNE PUMPS ESS SAny type of solid state las would bene from highe ser efit er-power highe er-brightness p pumps. Custom demand co mer onstantlydrives impro ovement in these pumps’ outp Here we r put. report on passi ively cooled p pumps rated to operate at ove 100W erCW. Aside f from being the industry’s mo power effici ost ient solution, t pump has a very small fo this ootprint (see Figure 7),which is an a additional bene for most of the application efit f ns. Fi igure 7 Photog graph of a 100W CW pump h W having a footpri less than 50 area of a bu int 0% usiness card.Room tempe erature perform mance of this pa assively cooled pump (depict in Figure 7) is presented i Figure 8. As one can d ted ) in ssee from pow and efficie wer ency dependen ncies of a 100WW-rated devic (with ~ 12A operating cur ce A rrent), it can b safely beoverdriven u to about 17A (current is lim up A mited by powe supply in tes setup) with r er st roll-over power at around 140 r 0-150W.These values constitute ~50 redundancy in the therma budget of thi device, thus contributing to its high reliab s 0% y al is o bility.Another demmonstration of the 100W pum design’s ro mp obustness is pr resented in Fig raph compares thermal gure 9. This grperformance of 100W-rated device again a legacy pro nst oduct which w rated to op was perate at 30W CCW. There is virtually ssociated with scaling up the power: junction overheat of a 100W devic is only few degrees higher than inno penalty as e f cethe case of t 30W-pump operated at t same drivi current. It is also worth noting that th junction ove the p the ing he erheat in100W pump is not that significantly different from the junction overheat pr ps m n reviously repoorted for a 10 0W-ratedcommodity p pump1. Proc. of SPIE Vol. 7583 75830A-6
  7. 7. Figure 8 Room temp e perature power and power eff ficiency characteristics for a p pump rated to o operate at 100W W.Figure 9 Jun ature overheat a a function of operating cur nction tempera as rrent for passiv cooled pum rated to op vely mps perate at 30W and 100W CW po d ower. Proc. of SPIE Vol. 7583 75830A-7
  8. 8. The design of 100W rated pumps is not limited to the solid state pumping application. Direct diode systems would alsobenefit from utilizing devices of this design, as well as any other non wavelength-specific applications; this applies to theair-cooled devices as well. Demonstration of 100W devices’ ability to operate in the air-cooled applications isdemonstrated in Figure 10. In this graph, one can see a series of Power-Current and Efficiency-Current characteristicsrecorded at several heatsink temperatures. As one can conclude from analyzing these graphs, applications based onlimited 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, lowprofile, small footprint, and high brightness (ex-fiber NA ≤ 0.13), ensure wide utilization of these devices in variousindustrial, 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. CONCLUSIONSHigh-power, high-brightness pumps continue to be a very dynamic and rapidly evolving sector of the laser industrymostly driven by fiber laser requirements and progress. Recent developments in the single emitter pumping platformprovide 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 recentdevelopments. Proc. of SPIE Vol. 7583 75830A-8
  9. 9. 5. ACKNOWLEDEGEMENTSThe authors would like to thank their co-workers at IPG Laser (Germany); without their contribution and on-goingsupport, 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-performancewavelength-locked diode lasers”, SPIE Proceedings Vol. 7198, (2009) Proc. of SPIE Vol. 7583 75830A-9