We report on our recent developments at II-VI Laser Enterprise of laser diode sources for the 79x nm range. High power conversion efficiency in excess of 62% was demonstrated. For high power applications like Thulium fiber laser pumping we have achieved an output power of more than 12.5W in CW operation for 94 μm wide broad-area single-emitters. We added the functionality of wavelength stabilization to the laser diodes by using a distributed feedback grating (DFB). Locking has been obtained over the full current range between 1A and 4A tested so far with some margin for temperature variation. For efficient fiber laser pumping the laser diodes were integrated in a multi-emitter platform, achieving 38 W out of a 105 μm fiber within 0.15 NA.
We report on the development of the latest generation of high power laser diodes at 14xx nm wavelength range suitable for industrial applications such as plastics welding and medical applications including acne treatment, skin rejuvenation and surgery. The paper presents the newest chip generation developed at II-VI Laser Enterprise, increasing the output power and the power conversion efficiency while retaining the reliability of the initial design. At an emission wavelength around 1440 nm we applied the improved design to a variety of assemblies exhibiting maximum power values as high as 7 W for broad-area single emitters. For 1 cm wide bars on conductive coolers and for bars on active micro channel coolers we have obtained 50 W and 72 W in continuous wave (cw) operation respectively. The maximum power measured for a 1 cm bar operated with 50 μs pulse width and 0.01% duty cycle was 184 W, demonstrating the potential of the chip design for optimized cooling. Power conversion efficiency values as high as 50% for a single emitter device and over 40% for mounted bars have been demonstrated, reducing the required power budget to operate the devices. Both active and conductive bar assembly configurations show polarization purity greater than 98%. Life testing has been conducted at 95 A, 50% duty cycle and 0.5 Hz hard pulsed operation for bars which were soldered to conductive copper CS mounts using our hard solder technology. The results after 5500 h, or 10 million “on-off” cycles show stable operation.
We report on the development of high power, 9xx-10xx nm laser diode bars for use in direct diode systems and for solidstate and fibre laser pumping with applications in industrial markets. For 1 cm wide bars on micro channel cooler (MCC) we have achieved a reliable output power of 250 W across the 900 nm – 1060 nm range. At this output power level we have achieved power conversion efficiencies of 65-66 % and 90 % power content slow axis beam divergence of ~6.5°. Results of a 6400 h life test show an average power degradation of 0.6 % per 1000 h at this operating power level. We will also show results of high power bars assembled on the new OCLARO conductive cooler, the BLM. This new cooler has a small footprint of 12.6 mm × 24.8 mm and is designed for lateral or vertical stacking of diodes in multi kilowatt systems but with the benefits associated with a conductive cooler. The thermal properties are shown to be the same as for a standard CS mount. 1 cm wide high fill factor bars and 0.5 cm wide low fill factor half bars assembled on the BLM operate at 63-64 % power conversion efficiency (PCE) with output powers of up to 250 W and 150 W, respectively.
This work presents some aspects of development of ultra-high power single-mode pump modules at λ= 980 nm for erbium-doped fiber amplifiers. We report here on the results of numerical simulations and experimental data of modifications to the laser waveguide structure with a focus on improving the fiber coupling efficiency. The so-called integrated fiber wedge lens was used as a coupling element in the present investigation. Our simulations showed that between the two most widely used laser waveguide types: large optical cavity (LOC) and separate confinement (SCH or GRICC) heterostructures the difference in coupling efficiency can be as high as ten absolute percent We achieved an experimental coupling efficiency of 93 percent for LOC-like lasers structure. The SCH-based lasers showed maximum coupling efficiency of 83 percent. However, in spite of superior coupling efficiency, use of LOC-based lasers in pump modules does not bring any benefits because of subpar electro-optical performance. To improve the situation we had to find a reasonable compromise between LOC and SCH structures. Lasers resulting from this approach gave a coupling efficiency around 90 percent. The laser diodes based on the optimized structure achieve more than 3 W of output power and more than 2 W of kink-free power in CW regime at room temperature. They also demonstrate differential quantum efficiency above 85% and laser power conversion efficiency above 60 percent at use conditions. Thanks to the combination of all these factors pump modules built on these lasers produce 1W of wavelength-stabilized power at an operating current below 1.3 A. Maximum kink-free, wavelength-stabilized output from the pump module reached 1.8 W at room temperature.
We report on high power wavelength stabilized single-mode lasers operating at ~1060 nm. Due to their capability of fast
gain switching (<1 ns) and internal wavelength stabilization, distributed feedback (DFB) lasers are attractive for
utilization as an ultrafast seeder for MOPA fiber laser systems. We successfully developed narrow band single mode
DFB laser emitting at the wavelength of ~1060 nm and providing >1.5W of peak power in pulse mode. Time response of
the DFB lasers was analyzed using both small and large signal modulation techniques. Furthermore, we present the
results of integration of DFB lasers into subnanosecond fiber laser system. We obtained spectrally narrow (~50 pm)
optical pulses as short as 170 ps with peak power of ~7 kW.
The ALPINE project is developing innovative fiber lasers for the scribing of new thin film photovoltaic modules with the
aims to push forward the European research and development of fiber laser systems and solar energy exploitation. The
fiber lasers will be based on photonic crystal fibers, which are characterized by unusual and interesting light guiding
properties exploited to deliver high power with excellent beam quality and high resonator stability and efficiency, and
will be applied to substitute mechanical scribing steps in the photovoltaic module production. In addition, new
photovoltaic thin film technologies is applied, which is based on cadmium telluride and copper indium diselenide
materials. With a potential conversion efficiency just below that of crystalline silicon, these new material approaches are
ready to enter the market with low manufacturing costs for immediate economic or environment impact.
Single-mode-emitting high-power diode laser arrays (SM-HPDLA) are available industrially with more than 50 W
emission power per bar. Based on this platform an expandable prototype solution is realized for fiber coupling of a
stacked array with more than 100 W to an optical fiber with diameter of 200 micron and NA of 0.11. Advanced methods
of controlled assembly of micro-optics by infrared laser-soldering have been developed therefore. We present a compact
and scalable concept with scalability on 2 internal and 2 external factors. Internal factors are the increasing beam quality
and power stability of high-power single-mode-emitting arrays and the improved assembly accuracy for diode bar and
micro-optics. External factors are the interlaced coupling of stacked beam emission from the stacked array and the
further option to use optimized polarisation coupling with several diode laser stacks.
Modules consisting of multiple single emitters pose demanding challenges on assembly, production capabilities and cost.
A fiber coupled module has been produced delivering 100 W optical power from a 105 μm, NA 0.15 fiber. The module
consists of two times six vertically stacked single emitters combined by polarization multiplexing. Special attention was
paid to the development of a very robust low cost pigtail. The developed semiautomatic highly accurate process enables
assembly times way faster than possible in a purely manual procedure. The achievable yield in combination with low
material costs proofs the excellent potential for the manufacturing of cost efficient laser modules.
In this paper we present the 830nm single mode lasers for consumer electronics and computer to plate applications. One
of the key criteria is to develop a robust as well as cost effective design that enables high yield and high reliability
operation. We will present results obtained on single transverse mode, single emitters or arrays of Fabry Perot lasers and
single longitudinal mode lasers emitting in the range of 830nm exhibiting superior reliability performance.
We report on development of novel curved waveguide (CWG) laser devices, where the emission wavelength centered at
~976 nm is stabilized to a 20 dB bandwidth of less than 100 picometer by using fiber Bragg gratings (FBG). Radiation
from the curved waveguide laser is coupled using an anamorphic fiber lens into a single mode polarization maintaining
fiber containing the FBG, the latter acting as a front reflector. The high power gain chip is based on Oclaro's
InGaAs/AlGaAs quantum well laser. Use of the curved waveguide geometry allows to eliminate residual reflections in
the optical path of the cavity, which is formed by the rear chip facet and the FBG. It is well known that additional
reflections lead to significant deterioration of the spectral and power stability. The devices, assembled in telecom type
housings, provide up to 1 W of low-noise and kink-free CW power. In addition pulse operation in nanosecond range is
also investigated. The spectral stabilization time to the wavelength of the FBG is limited by the external cavity roundtrip
of ~2 ns. A side mode suppression ratio of about 40 dB and higher is achieved for pulsed and CW operation. Results are
also presented for a device at 1064 nm. Numerous applications can be envisioned for these devices. For instance devices
with high power and ultranarrow spectral bandwidth allow greater flexibility in the choice of parameters for frequency
conversion applications. In pulsed mode the device can be used in the special sensing applications where spectral
stability is crucial.
A conductively cooled 970nm laser diode bar primarily designed for quasi continuous wave (qcw) pumping of
miniaturized solid state lasers is presented. The robust chip design and the highly efficient two side cooling setup of the
10x12x5mm3 diode assembly allows output peak power levels as high as 600W at 500A drive current and 1% duty cycle.
The high performance laser diode was employed as pump for a miniaturized, conductively cooled, side pumped Er:YAG
laser system. The laser system, with an overall dimensions of 30x25x17mm3, generates 2.8W average power with M2<5.
The demand for high power laser diode modules in the wavelength range between 793 nm and 1060 nm has been
growing continuously over the last several years. Progress in eye-safe fiber lasers requires reliable pump power at 793
nm, modules at 808 nm are used for small size DPSSL applications and fiber-coupled laser sources at 830 nm are used in
printing industry. However, power levels achieved in this wavelength range have remained lower than for the 9xx nm
range. Here we report on approaches to increasing the reliable power in our latest generations of high power pump
modules in the wavelength range between 793 nm and 1060 nm.
We report on laser diode bars with wavelengths ranging from 793 to 1080 nm and optimized for high power and high
temperature operation. For 808 nm bars output power values of 300 W at 300 A drive current and 200 μs pulse length
have been recorded at a cooler temperature of 75°C. Extending our wavelength range to 1080nm we report on bars with
>65% power conversion efficiency in CW operation and more than 500 W output power for a wide range of qCW
modes. Finally, the properties of a 6-bar stack with 3 kW output power at 460 A drive current and 200 μs pulse width
will be discussed.
Xu Jin, Serge Cutillas, Daming Liu, Ed Wolak, Sang-Ki Park, Kelly Johnson, Terry Towe, Dino Lenarduzzi, Touyen Nguyen, Tom Truchan, Jeff Mott, James Harrison, Andrea Guarino, Jürgen Müller, Susanne Pawlik, Boris Sverdlov, Norbert Lichtenstein, Chris Button
In this work we show that mini-bar-based 8xx products show the reliability characteristics of independent emitter
failures and "non-degrading" drift plots similar to those of their 9xx counterparts. This fact is in part an outcome of the
bonding process and heat-sink design. Multi-cell life testing gives projected reliable operation of compact, fiber-coupled
modules (200-μm-diameter, 0.15 NA) at 30 W and 808 nm, with 35 W at 880 nm.
The demand for high power lasers emitting in the 14xx-15xxnm range is growing for applications in fields such as
medical or homeland security. We demonstrate high power laser diodes with emission at 1430, 1470 and 1560 nm.
Single multimode emitters at 1470nm emit about 3.5W in CW operation. Power conversion efficiency can reach values
as high as 38.5%. With this base material, single and multi-emitter fiber coupled modules are built. Additionally, bars on
passive and microchannel coolers are fabricated that deliver 25W and 38W respectively in CW mode, while obtaining
more than 80 W in pulsed mode. All reliability tests show an outstanding stability of the material with no signs of wearout
after 3750 hrs under strong acceleration conditions.
Single-transverse-mode semiconductor laser diodes with broad emission spectrum in pulsed or CW regime are attractive
as seed sources in fiber laser systems. Stimulated Brillouin scattering can be a limiting factor in such systems, causing
damaging high power pulses to reverse propagate in the fibre. The effect can be significantly mitigated by broadening
the linewidth of the seed laser. Here we report on such a seed source capable of operating in either CW or pulsed mode
with a center wavelength at around 1060 nm and spectral full width at half maximum of greater than 10 nm. The new
source is based on well-established ridge waveguide pump laser technology, modified for operation in a
superluminescent regime. A coupling efficiency of ~80 % into a single mode fiber is achieved. Our time resolved
spectral studies show that the device is demonstrating fast modulation rate and very high peak optical power up to 1 W
while maintaining a broad emission spectrum greater than 10 nm.
In this communication we report on the approaches to increase the brightness of Bookham's latest generations of high
power pump modules. Since the single-emitter laser diode is the essential building block in all module designs, the
optimization of the device design towards higher wall-plug efficiency, higher brightness and better reliability is one
focus of the ongoing development efforts at Bookham. By using an analytical simulation tool critical parameters for
efficient emitter-fiber coupling as the beam divergence and coupling scheme could be identified.
The attractiveness of bars for industrial applications depends strongly on the reliable high brightness operation. For 9xx bars we report on high filling factor configurations with 200W reliable output power. Our low filling factor devices with output power between 40W and 90W have proven to operate reliably at output power densities of 85mW per 1µm stripe width, showing power wear-out degradation of less than 0.5% per 1000h operation time. For shorter wavelengths we present solutions for 808-880 nm bars. For our 808nm bars we observe power degradation of less than 4% after 8000h hard-pulse life test at 75W output power.
We report on reliable single-mode laser modules at 1060 nm used in pulsed operation for efficient seeding of fiber amplifiers. The modules incorporate InGaAlAs single quantum well diodes with a design inherited from telecom qualified devices. Pulse parameters can be widely varied with laser intrinsic modulation capability in GHz range. 2.5 W peak power is exhibited in a single-mode fiber at a current of 5 A with 200 ns pulses. Reliability is proven by lifetest in pulsed operation up to 3.5 A. Wavelength stabilization with fiber Bragg gratings is obtained over a wide range of operating conditions.
Coupling to the fiber Bragg grating (FBG) is a well-established technique of emission wavelength stabilization in single mode pump lasers used for instance in Er-doped fiber amplifiers (see e.g. Ref. 1). The output power of these devices usually does not exceed 1 W due to limited heat transfer from narrow active stripe of the single mode laser diode. To satisfy increasing demand for wavelength-stabilized pump lasers with higher output power we attempted to extend FBG stabilization scheme to high power multimode broad area lasers. This scheme brings usual advantages of FBG stabilization such as environmental wavelength stability, compactness and low cost. Development work has been carried out using our reliable high power pump laser with output aperture of ~ 50 - 100 μm. The emission wavelength of the free running laser was around 960 nm at room temperature. The fiber gratings with reflection maximum at about 975 nm were written in a commercially available multimode fiber. In initial experiments the laser was coupled with discrete optics to the multimode fiber containing FBG. Introduction of the spectrally selective optical feedback locked the laser emission to the Bragg wavelength. The laser emission remained locked to this wavelength up to a maximum drive current of 8 A within a heat sink temperature range of 40°C in this experiment. The overall spectral width of stabilized laser emission facilitates effective and stable pumping into absorption lines as narrow as 5 nm FWHM. Similar results were obtained on the Bookham commercial pump modules with FBG in the output fiber. The modules emitted up 4 W of wavelength-stabilized power from the output fiber with 50 μm core diameter.
Bars with high and low filling factors serve the different schemes for beam transformation and fiber coupling. We report on highly efficient 8xx bars for operation in excess of 100 W and reliable broad-area single-emitter lasers (BASE) with 90 um aperture being capable to deliver in excess of 10 W from a 105 um core fiber. For 9xx bars we present solutions with power levels per device ranging from 60 W to 300 W corresponding to linear power levels beyond 8.5 W per 100 um stripe width indicating convergence of BAR and BASE devices. Life test results for these devices will be shown and high brightness fiber coupled solutions will be discussed.
Based on the most recent generation of Bookham's laser diode bars in the 9xx nm wavelength range which are able to deliver in excess of 250 W of output power from 50% filling factor 2.4 mm cavity length design, we have developed low 20% fill-factor bar devices for high brightness applications. Close to 200 W of output power has been achieved in CW mode from actively cooled micro-channel cooler devices without signs of damage. Mounted on conductively cooled copper blocks, still more than 130 W (CW) has been obtained, indicating the high conversion efficiency of >60% reducing the thermal load on the mounting assembly. Based on extensive reliability testing in excess of 5000 h and at power densities ranging up to 36mW/um and beyond, highly reliable operation of 20% fill-factor bars is expected. To facilitate fiber coupling into wide-core multi-mode fibers a further reduction of the emitter aperture has been realized. From a single 3.6 mm cavity length by 800 um wide emitter design ("MaxiChip") about 50 W output power has been obtained in CW mode from devices mounted on standard conductively cooled 1x1 inch copper blocks. While CW operation has been thermally limited, extremely high peak power operation can be expected in qCW operation. Due to the narrow aperture of this MaxiChip efficient and easy coupling into wide aperture multimode fibers can be achieved.
In this communication we present the characteristics of Bookham's MU7-9xx-01 laser module with multimode fiber output. This latest generation of our multimode modules is designed for light output power of up to 7 W in uncooled operation in the wavelength range between 915 nm and 975 nm. The key element of the module is our new SES8-9xx-01 broad area single emitter. These high power lasers in the 9xx nm wavelength range show a high slope efficiency of up to 1.2 W/A in CW room temperature operation. High efficiency combined with low threshold current and low operation voltage result in a maximum wall plug efficiency of above 65%. Almost 4000 h lifetest data at accelerated conditions are available for the laser diodes. The data give estimated reliability values of below 5 kFIT at operating conditions (between 8 A and 8.5 A injection current at up to 35°C heat sink temperature). The robustness of the new lasers is also illustrated by the fact that no catastrophic mirror damage was observed up to 22.5 W of light output power. The low divergence of the laser beam allows coupling into multimode fiber with 0.15 or 0.22 numerical aperture (NA) with a coupling efficiency above 90% at operation condition. Maximum ex-fiber light output powers of 11.5 W are shown. On module level around 2000 h lifetest data are accumulated without any failure or sign of degradation.
KEYWORDS: Semiconductor lasers, High power lasers, Multimode fibers, Resistance, Continuous wave operation, Temperature metrology, Prototyping, Reliability, Broad area laser diodes
In this communication we report on the performance characteristics of Bookham’s latest generation of 915-990 nm broad area single emitter (BASE) laser diodes with around 90 μm wide aperture. Representative high power devices in the wavelength range of 950-960 nm, mounted p-side down onto expansion matched assemblies using our highly reliable AuSn-solder technology, reveal a high slope efficiency of around 1.05 W/A during CW operation at 25°C heat sink temperature. Coupling efficiency into multi-mode fiber with 0.15 or 0.22 numerical aperture exceeds 93% mainly due to the low vertical divergence of the laser beam. In addition, low laser threshold and series resistance enable more than 62% maximum wall plug efficiency of the present generation of the laser diodes. Preliminary tests of new prototypes reveal already excellent performance characteristics of the next generation device with up to 19.9 W light output power in pulsed operation and 16 W for thermally limited CW operation.
In this communication we report on the successful realization of Single-mode Emitter Array Laser (SEAL) bars. Various laser bars with a cavity length of 2.4 mm containing between 25 to 350 narrow stripe lateral single-mode emitters have been realized and mounted epi-side down onto expansion matched heatsinks using a stable AuSn-solder technology. Optical power in excess of 1 W per emitter has been obtained resulting in more than 200 W total output power for the highest emitter density. While these total power levels are comparable to conventional broad-area laser bars (BALB), the brightness of each of the emitters is drastically improved over the BALB approach making theses bars ideal candidates for beam-shaping concepts. Lateral farfield measurements with smooth gaussian patterns, high electro-optical conversion efficiency well above 60% and threshold currents as low as 0.5 A are presented. Similar devices realized from the InGaAsP/InP material system deliver in excess of 20 W from 100 NS emitters at wavelengths around 1480 nm.
Reliable power scaling by stretching the cavity length of the laser bars ranging from 1.2 mm to 3.6 mm at constant filling factor of 50% is demonstrated. While a relatively short cavity length of 1.2 mm allows for thermally limited CW output powers in excess of 180 W, extremely high 325 W at 420 A (CW, 16°C) have been achieved by leveraging the enhanced thermal properties of a 3.6 mm cavity length on standard micro-channel coolers. A high electro-optical conversion efficiency of 62% and 51% respectively is attributed to the low internal losses from an optimized waveguide design and the excellent properties of the AlGaAs-material system accounting for low thermal and electrical resistance. Multi-cell lifetest data at various operation conditions show extremely low wear-out rates even at harsh intermittent operation conditions (1-Hz type, 50% duty-cycle, 100% modulation). At 100 W output power 300 Mshots corresponding to 64000 h mean-time-to-failure (MTTF) have been extrapolated for 20% power drop from initial 2000 h and 4000 h lifetest readouts of a 1.2 mm cavity design. Similar results have been obtained for our next generation of ultra high power laser bars enabling reliable operation at 120 W output power and beyond. From 2.4 mm cavity length bars we have obtained 250 W of CW output power at 25°C while extrapolated reliability data at 120 W and 140 W power levels of up to 2000 h duration indicates that such devices are able to fulfill the requirements for lifetimes in the 20 - 30 kh range.
Diode-pumped solid state laser (DPSSL) and fiber laser (FL) are believed to become the dominant systems of very high power lasers in the industrial environment. Today, ranging from 100 W to 5 - 10 kW in light output power, their field of applications spread from biomedical and sensoring to material processing. Key driver for the wide spread of such systems is a competitive ratio of cost, performance and reliability. Enabling high power, highly reliable broad-area laser diodes and laser diode bars with excellent performance at the relevant wavelengths can further optimize this ratio. In this communication we present, that this can be achieved by leveraging the tremendous improvements in reliability and performance together with the high volume, low cost manufacturing areas established during the "telecom-bubble." From today's generations of 980-nm narrow-stripe laser diodes 1.8 W of maximum CW output power can be obtained fulfilling the stringent telecom reliability at operating conditions. Single-emitter broad-area lasers deliver in excess of 11 W CW while from similar 940-nm laser bars more than 160 W output power (CW) can be obtained at 200 A. In addition, introducing telecom-grade AuSn-solder mounting technology on expansion matched subassemblies enables excellent reliability performance. Degradation rates of less than 1% over 1000 h at 60 A are observed for both 808-nm and 940-nm laser bars even under harsh intermittent operation conditions.
AlGaAs/InGaAs based high power pump laser diodes with wavelength of around 980 nm are key products within erbium doped fiber amplifiers (EDFA) for today's long haul and metro-communication networks, whereas InGaAsP/InP based laser diodes with 14xx nm emission wavelength are relevant for advanced, but not yet widely-used Raman amplifiers. Due to the changing industrial environment cost reduction becomes a crucial factor in the development of new, pump modules. Therefore, pump laser chips were aggressively optimized in terms of power conversion and thermal stability, which allows operation without active cooling at temperatures exceeding 70°C. In addition our submarine-reliable single mode technology was extended to high power multi-mode laser diodes. These light sources can be used in the field of optical amplifiers as well as for medical, printing and industrial applications. Improvements of pump laser diodes in terms of power conversion efficiency, fiber Bragg grating (FBG) locking performance of single mode devices, noise reduction and reliability will be presented.
In this article fabrication techniques and the analysis of AlGaInP semiconductor lasers for single mode emission and high power emission will be reported. Special emphasis will be spent on the appropriate vertical and longitudinal device structures. Furthermore we discuss low damage dry etching and epitaxial regrowth of DFB laser structures. The devices investigated are DBR- DFB- and MOPA-lasers.
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