A multi-mode 9XXnm-wavelength laser diode was developed to optimize the divergence angle and reliable ex-facet power. Lasers diodes were assembled into a multi-emitter pump package that is fiber coupled via spatial and polarization multiplexing. The pump package has a 135μm diameter output fiber that leverages the same optical train and mechanical design qualified previously. Up to ~ 270W CW power at 22A is achieved at a case temperature ~ 30ºC. Power conversion efficiency is 60% (peak) that drops to 53% at 22A with little thermal roll over. Greater than 90% of the light is collected at < 0.12NA at 16A drive current that produces 3.0W/(mm-mr)2 radiance from the output fiber.
The degradation behaviors of 980-nm emitting nominally identical single-spatial mode lasers are studied during continuous wave long-term operation and during single-pulse stress tests. Both tests activate internal catastrophic optical damage as sudden degradation mechanism limiting the device lifetime. In case of high power stress-testing, the mechanism that initializes this effect is a spatial widening of the optical mode, resulting in increased absorption outside the waveguide. A similar disturbance to the optical mode is caused by defects that are generated during long-term operation. Thus two very different aging regimes eventually result in the same degradation scenario. We find that single-pulse stress-testing allows for activation of several degradation mechanisms in a device one after the other. Moreover, it becomes possible to distinguish between effects induced by gradual degradation and such that are independent on operation time. Thus stress-testing is considered a complementary tool, which might pave the way towards more economic device testing.
KEYWORDS: Short wave infrared radiation, Semiconductor lasers, Streak cameras, Pulsed laser operation, High power lasers, Near field, Ions, Continuous wave operation, High power diode lasers, Infrared radiation
Pulsed operation of standard 980-nm emitting single-spatial-mode high power diode lasers at multi-watt power levels is
studied. Primary emission, short wavelength infrared emission, as well as the spatio-temporal evolution of the near field
are recorded. This approach allows for the determination of the operation parameters during which single-mode
operation is maintained. This gives limits of safe operation far beyond the standard specifications as well as information
about the relevant degradation mechanisms in this regime. Reference experiments with a set of long-term operated
devices reveal gradual aging signatures and the starting points of the relevant aging processes become detectable. They
are compared with those obtained from the devices operated under pulsed conditions.
We report modeling and experimental results that demonstrate mechanisms limiting the output power of semiconductor
lasers and a method experimentally yielding a dramatic increase of the maximum continuous wave output power.
Unfolded cavity is used to achieve higher power and efficiency by improving the alignment between the carrier and
photon density profiles in a long cavity device. This method offers reduced longitudinal spatial hole burning (LSHB) and
lower photon density inside the laser cavity; therefore, it decreases possible LSHB and non-linear effects that could limit
the output power of a semiconductor laser. We have demonstrated 29.5W output from 5.7mm long and 100um wide
waveguide at 9xx nm using an unfolded cavity. A semiconductor laser with an unfolded cavity allows scaling of the
output power by increasing the cavity length.
A new 100μm aperture, 920nm laser diode chip was developed to improve fiber coupling efficiency and reliability. These chips have been assembled into single-emitter and multi-emitter packages with 105μm diameter fiber-coupled output. The single-emitter package is rated for 12W operation, while the multi-emitter package is rated at 140W. Power conversion efficiency is 50%. Over one year of accelerated active life testing has been completed along with a suite of passive, environmental qualification tests. These pumps have been integrated into 2kW, 4kW, and 6kW fiber laser engines that demonstrate excellent brightness, efficiency, and sheet metal cutting quality and speed.
Hongbo Yu, Dahv A. Kliner, Kai-Hsiu Liao, Jeff Segall, Martin Muendel, James Morehead, Jane Shen, Matt Kutsuris, Johnny Luu, Justin Franke, Kelvin Nguyen, Dave Woods, Fred Vance, David Vecht, David Meng, Richard Duesterberg, Lei Xu, Jay Skidmore, Matthew Peters, Nicolas Guerin, James Guo, Jane Cheng, Jihua Du, Brad Johnson, Dongliang Yin, Allen Hsieh, Peter Cheng, Abdullah Demir, Jason Cai, Rupa Gurram, Kong-Weng Lee, Reddy Raju, Daniel Zou, Raman Srinivasan, Mandeep Saini, Laura Zavala, Victor Rossin, Erik Zucker, Hiroaki Ishiguro, Hiroshi Sako
We have demonstrated a monolithic (fully fused), 1.2-kW, Yb-doped fiber laser with near-single-mode beam quality.
This laser employs a new generation of high-brightness, fiber-coupled pump sources based on spatially multiplexed
single emitters, with each pump providing 100 W at 915 nm within 0.15 NA from a standard 105/125 μm fiber. The
fiber laser is end pumped through the high-reflector FBG using a 19:1 fused-fiber pump combiner, eliminating the need
for pump/signal combiners. The output wavelength is 1080 nm, with a linewidth of < 0.5 nm FWHM. A peak power of
1.5 kW was reached in modulated operation (1-ms pulse duration) with M2 < 1.2.
We report an 830nm high power single spatial mode DFB laser design in the AlGaAs/GaAs system that offers
performance close to a Fabry-Perot design as well as manufacturing yield compatible with volume production.
Single-mode power in excess of 200mW at case temperature up to 600C is consistently obtained for current below
300mA. This performance level is enabled by use of an efficient, partially-corrugated design and a 2nd order grating
located on the p-side. Through careful design and an optimized epitaxial re-growth on the grating, promising
reliability results compatible with uncooled application are demonstrated.
Richard Duesterberg, Lei Xu, Jay Skidmore, James Guo, Jane Cheng, Jihua Du, Brad Johnson, David Vecht, Nicolas Guerin, Benlih Huang, Dongliang Yin, Peter Cheng, Reddy Raju, Kong Weng Lee, Jason Cai, Victor Rossin, Erik Zucker
We report results of a spatially-multiplexed broad area laser diode platform designed for efficient pumping of fiber lasers
or direct-diode systems. Optical output power in excess of 100W from a 105μm core, 0.15NA fiber is demonstrated with
high coupling efficiency. The compact form factor and low thermal resistance enable tight packing densities needed for
kW-class fiber laser systems. Broad area laser diodes have been optimized to reduce near- and far-field performance and
prevent blooming without sacrificing other electro-optic parameters. With proper lens optimization this produces ~5%
increase in coupling / wall plug efficiency for our design. In addition to performance characteristics, an update on long
term reliability testing of 9XX nm broad area laser diode is provided that continues to show no wear out under high
acceleration. Under nominal operating conditions of 12W ex-facet power at 25C, the diode mean time to failure (MTTF)
is forecast to be ~ 480 kh.
KEYWORDS: Fiber lasers, Reliability, High power lasers, Semiconductor lasers, Prototyping, Laser applications, Multimode fibers, Multiplexing, Diodes, Near field optics
A platform has been developed for high-power, high-brightness, multi-single-emitter laser pumps for fiber lasers, directdiode,
and other applications. Using multi-mode fiber with 105μm core and 0.22 NA, fiber-coupled optical power up to
100 Watts and a brightness as high as 100 kW/mm2/sr can be achieved. Common schemes for increasing brightness include spatial, wavelength, and polarization-beam combination of multiple single-emitters. Spatial multiplexing has been chosen for this platform to leverage JDSU's proven reliability of highpower single-emitter packages and passive optical components. In one configuration, we achieved >60W fiber coupled optical power, 50 kW/mm2/sr, and 45% wall-plug-efficiency using 105 μm core, 0.22 NA fiber from this platform. An optional VBG can also be placed inside the package for achieving spectral locking over a 16 nm wavelength range.
We present performance improvements of fiber-coupled pump modules and broad-area lasers at 8xx nm, 9xx nm and 14xx nm wavelengths. Broad-area lasers with a 200 μm aperture at 808 nm for direct diode applications emit 11W CW and 30W pulsed. Pump modules at 830 nm for printing applications show excellent linearity, power stability of 2% and 95% of the power within 0.12 NA into a 50 μm core fiber at 1W CW. Broad-area lasers at 880 nm for pumping applications emit 18W CW with a peak wallplug efficiency of 64%. An improved design of 9xx pump modules is demonstrated with built-in feedback-protection (>30 dB at 1060 nm) that allows safe operation in multi-kW peak-power fiber lasers. Up to 3W of optical power with slope efficiency and peak wallplug efficiency of 0.64 W/A and 46%, respectively, is presented for 14xx nm broad-area lasers with a 100 μm wide aperture.
Results for a new compact 488 nm solid-state laser for biomedical applications are presented. The architecture is based
on a multi-longitudinal mode external cavity semiconductor laser with frequency doubling in a ridge waveguide fabricated in periodically poled MgO:LiNbO3. The diode and the waveguide packaging have been leveraged from telecom packaging technologies. This design enables built-in control electronics, low power consumption (≤ 2.5 W) and a footprint as small as 12.5 x 7 cm. Due to its fiber-based architecture, the laser has excellent beam quality, M2 <1.1. The laser is designed to enable two light delivery options: free-space and true fiber delivered output. Multi-longitudinal
mode operation and external doubling provide several advantages like low noise, internal modulation over a broad frequency range and variable output power. Current designs provide an output power of 20 mW, but laser has potential for higher power output.
We have developed a single-emitter multi-mode laser-diode-pump platform for high efficiency, brightness and high
reliability in a small form factor. This next-generation package is scalable to higher optical power and offers a low-cost
solution for industrial applications, such as fiber lasers, graphic arts and medical. The pump modules employ high
coupling efficiency, >90%, high power-conversion efficiency, >50%, and low thermal resistance, 2.2°C/W, in an
electrically-isolated package. Output powers as high as 18W have been demonstrated, with reliable operation at 10W
CW into 105μm core fiber. Qualification results are presented for 0.15NA and 0.22NA fiber designs.
Laser diodes and bars with high efficiency, power, and reliability are critical for a wide variety of applications
including direct material processing and pumping high power and efficient fiber lasers and solid state lasers. We
present progress towards the 80% power conversion efficiency goal of the DARPA Super High Efficiency Diode
Sources (SHEDS) program. Currently using JDSU SHEDS technology, laser bars and stacks respectively achieve as
high as 76% and 73% total power conversion efficiency at room temperature. Single-emitter laser diodes
incorporating SHEDS technology achieve up to 19W peak CW power from a 100um wide aperture.
We report results of multi-cell life tests performed on nearly (500) laser diodes representing our new generation of very
efficient high power broad area 9xx nm lasers. The acceleration model showed a steep power dependence of the failure
rate with an exponent of nearly 6. Improvement in the facet passivation process resulted in significantly less power
acceleration of failures. Analysis of the life test on upgraded lasers showed median lifetime of 1,500,000 hours at
operating conditions of 8W and 350°C. Optical powers as high as 17.8W for thermally limited CW operation and 32W
for 20 μs pulsed operation were recorded. The CW life test was complemented by a life test performed at power cycling
conditions (1Hz repetition rate, 50% duty cycle).
Laser diodes and bars with high efficiency, power, and reliability are critical for a wide variety of applications including direct material processing and pumping high power and efficient fiber lasers and solid state lasers. We present progress towards the 80% power conversion efficiency goal of the DARPA Super High Efficiency Diode Sources (SHEDS) program. Currently, laser bars using JDSU SHEDS technology achieve as high as 72.7% total power conversion efficiency at room temperature and 80W operating power.
Developers building high-power fiber lasers and diode pumped solid state lasers can receive significant benefits in thermal management and reliability by using single emitter multi-mode diodes in distributed pump architectures. This proposed distributed architecture relies on independent single emitter pump lasers and a modest level of pump redundancy. Driving the remaining diodes slightly harder componensates individual diode failures. A model of the ensemble lifetime based on module failure rates and power-scaling factors demonstrates that the distributed pump architecture requires random failure rates corresponding to better than 200,000h mean time between failure (MTBF), which meets typical industrial requirements. A high power, pigtailed, multi-mode pump module suitable for commercial applications is created through this model. Critical elements are based on telecom architectures, including the optical train and the fiber alignment. The module has a low thermal resistance of 4°C/W from the chip-on-sub-mount to the external heat sink, coupling efficiency of over 80% into 0.2 NA, and demonstrated reliable output power of over 5W cw with peak wavelengths near 915 nm. Individual pump modules are predicted to produce 5W cw output power with an MTBF of more than 400,000h. The relationship between anticipated MTBF requirements, test duration and test population is shown.
Multi-mode pumps based on single emitter diodes deployed in distributed pump architectures offer significant advantages in thermal management and reliability for pumping high-power fiber lasers and amplifiers. In a distributed architecture, while individual diode failures do not directly generate failures of other diodes in the distributed ensemble, failures do cause the rest of the sources to drive to higher power levels to compensate for the loss of power. A model of the ensemble lifetime based on module failure rates and power-scaling factors demonstrates that the distributed pump architecture requires random failure rates corresponding to better than 200,000 h mean time between failure (MTBF) to meet typical application requirements. A high power multi-mode pump module suitable for commercial aplications is shown. Critical elements are based on telecom architectures, including the optical train and the fiber alignment. The module has a low thermal resistance of 4 C/W from the laser diode junction to the external heat sink, couplng efficiency of over 80% into 0.2 NA, and demonstrated reliable output power of over 5W CW with peak wavelengths near 915 nm. Telecom qualified modules have random failure rates corresponding to better than 1,000,000 h MTBF. Stability of the critical fiber alignment joint for single mode packages has been demonstrated at elevated temperatures (e.g. 85 C) for thousands of hours. The reliability of the commercial multi-mode package can be estimated by similarity to the telecom package, and is verified by testing of conditions considered to be at risk based on the differences between the known telecom, and the new commercial package, designs. Test results are shown for temperature cycling, CW operation, and damp heat. The relationships between anticipated MTBF requirements, test duration and test population are shown.
A new generation of very efficient high power laser diodes has been developed. The design was optimized for efficient operation of a long cavity device necessary to reduce electrical and thermal resistance. CW operation of a 100 μm wide laser at 25C yielded slope efficiency as high as 1.14W/A and 64% electrical-to-optical conversion efficiency. Optical power as high as 13.5 W for thermally limited CW operation and 17.3 W for pulsed operation were also recorded.
The demands of global bandwidth and distribution are rising rapidly as Internet usage grows. This fundamentally means that more photons are flowing within optical cables. While transmitting sources launches some optical power, the majority of the optical power that is present within modem telecommunication systems originates from optical amplifiers. In addition, modem optical amplifiers offer flat optical gain over broad wavelength bands, thus making possible dense wavelength de-multiplexing (DWDM) systems. Optical amplifier performance, and by extension the performance of the laser pumps that drive them, is central to the future growth of both optical transmission and distribution systems.
Exciton-polariton photoluminescence kinetics under short-pulse excitation in pure epitaxial GaAs has been investigated. The observed delayed onset of the polariton luminescence is attributed to the energy relaxation of polaritons and photoexcited electrons. The electron energy relaxation is controlled by inelastic impurity scattering. In an ultrapure sample (ND approximately 1012 cm-3) the maximum of luminescence is reached after a considerable delay of 4 ns. At high repetition rate the next excitation pulse causes a fast quenching of polariton luminescence in the vicinity of exciton resonance due to heating of excitons by photoexcited hot electrons. A model of exciton luminescence kinetics involving exciton-electron interaction has been proposed.
The low temperature photoluminescence of ultra pure GaAs grown by vapour phase
epitaxy was investigated .The free exciton luminescence spectnim of GaAs is described
in the framework of the polari ton theory . An inf luence of the excitation density and
temperature on the polariton luminescence 1 ineshape was studied . Temperature transi
tion from the case of the strong exci ton-photon coupi ing to the case of the weak ex
citon-photon coupl ing was observed . An opportunity of use of the polariton luinines
cence 1 me shape analysis for characterizat ion of pure GaAs crysta 1 s is demoristra
ted.
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