Advances in high performance fiber coupled diode lasers continue to enable new applications as well as strengthen existing uses through progressive improvements in power and brightness . These improvements are most notable in multi-kW direct diode systems and kW fiber laser platforms that effectively transform better beam quality into superior system performance and in DPSS (Diode pumped solid state) application striving to scale TEM00 (fundamental transverse mode) power. We report on our recent single-emitter based fiber-coupled product platform, the elementTM, that addressed these applications at 8xx/9xx nm with optical powers over 200W in a range of fiber core sizes down to 105um and 0.14NA (Numerical Aperture). The product is a culmination of numerous packaging improvements: improving wall plug efficiencies (~50% electrical-to-optical) while improving volume manufacturability, enabling lower costs, improving usable chip brightness by, < 20% over previous generation chips, and increasing the reliable output power to 15W per chip. We additionally report on current developments to extend the power of the product platform to as high as 300W. This will be realized primarily through new chip architectures projected to further increase the useable chip brightness by an additional 20 % and correspondingly scaling reliable output powers. Second order improvements are proposed in packaging enhancements that capitalize on the increased chip power and brightness as well as expand the package’s thermal capabilities. Finally, an extended performance roadmap will translate expected power advances and increasing volumes into a projection of relative $/W decreases over the next several years.
High-power, high-brightness, fiber-coupled pump modules enable high-performance industrial fiber lasers with simple system architectures, multi-kW output powers, excellent beam quality, unsurpassed reliability, and low initial and operating costs. We report commercially available (element™), single-emitter-based, 9xx nm pump sources with powers up to 130 W in a 105 μm fiber and 250 W in a 200 μm fiber. This combination of high power and high brightness translates into improved fiber laser performance, e.g., simultaneously achieving high nonlinear thresholds and excellent beam quality at kW power levels. Wavelength-stabilized, 976 nm versions of these pumps are available for applications requiring minimization of the gain-fiber length (e.g., generation of high-peak-power pulses). Recent prototypes have achieved output powers up to 300 W in a 200 μm fiber. Extensive environmental and life testing at both the chip and module level under accelerated and real-world operating conditions have demonstrated extremely high reliability, with innovative designs having eliminated package-induced-failure mechanisms. Finally, we report integrated Pump Modules that provide < 1.6 kW of fiber-coupled power conveniently formatted for fiber-laser pumping or direct-diode applications; these 19” rack-mountable, 2U units combine the outputs of up to 14 elements™ using fused-fiber combiners, and they include high-efficiency diode drivers and safety sensors.
This paper presents recent progress in the development of high power single emitter laser diodes from 790 nm to 980 nm for reliable use in industrial and pumping applications. High performance has been demonstrated on diode lasers from 790 nm to 980 nm, with corresponding peak efficiency ~65%. Reliability has been fully demonstrated on high power diode lasers of 3.8 mm laser cavity at 3 major wavelengths. We report on the correlation between photon-energy (wavelength) and device failure modes (reliability). A newly released laser design demonstrates diode lasers with 5.0 mm laser cavity at 915-980 nm and 790 nm, with efficiency that matches the values achieved with 3.8 mm cavity length. 915-980 nm single emitters with 5.0 mm laser cavity were especially designed for high power and high brightness applications and can be reliably operated at 12 W to 18 W. These pumps have been incorporated into nLIGHT’s newly developed fiber coupled pump module, element<sup>TM</sup>. Ongoing highly accelerated diode life-tests have accumulated over 200,000 raw device hours, with extremely low failure rate observed to date. High reliability has also been demonstrated from multiple accelerated module-level lifetests.
We report on the continued development of high performance fiber coupled laser diode modules at nLIGHT. We show that by optimizing the laser resonator design single emitter diode lasers can be tailored for high brightness or for reduced $/W applications. For instance, a fiber laser pump module based on 6 single emitter diode lasers couples efficiently into a 105 μm, 0.15 NA fiber with peak operating efficiency <59% and output power < 65W. These results are made possible by optimizing the diode laser slow axis brilliance and by increasing the optical to optical efficiency to 90%. We will also report on the development of tailored laser resonator that meets the power, brightness, and cost targets for industrial applications. For instance, a wider emitter has reliable performance of <18W of output power while maintaining the slow axis divergence required for coupling into a fiber with a 12 mm-mrad beam parameter product. The corresponding 50% increase in output power significantly improves the $/W performance. These results of high brightness and high efficiency demonstrate the pump technology required for next generation solid state, fiber lasers, and materials processing applications.
We report on the performance of a 100 W, 105μm, 0.17 NA (filled) fiber-coupled module operating at 976 nm. Volume
holographic (Bragg) gratings are used to stabilize the emission spectrum to a 0.2 nm linewidth and wavelengthtemperature
coefficient below 0.01nm/°C with virtually no penalty to the operating power or efficiency of the device.
The typical fiber coupling efficiency for this design is >90%, enabling a rated operating efficiency of ~50%, the highest
reported for a 100W/105μm-class diode pump module (wavelength stabilized or otherwise).
This paper presents reliable high power and high brightness 9xx-nm single emitter laser diodes, which have been
designed for various multi-emitter fiber-coupled modules. Diode lasers from legend generation have been life-tested
with currents up to 14A at heat-sink and junction temperatures of 50°C and 80°C respectively, and have accumulated
more than 15,000 hours of life-test duration. In order to further improve reliable operational power and optimize beam
quality, new generation devices have been developed. The new devices demonstrated more than 20W CW rollover
power without catastrophic optical mirror damage (COMD). Near-field/far-field patterns have also been improved
significantly. In addition to step-stress life-tests, a 7-level multi-cell life-test was designed to investigate acceleration
factors relative to the operation conditions. Junction temperatures ranging from 60°C to 110°C and current from 14A
to 18A were used in this multi-cell life-test. The ongoing multi-cell life-test has accumulated 1.3 million raw device
hours and shown very few device failures in up to 7000 hours duration. Such a low failure rate doesn't allow a
meaningful estimation of acceleration factors. When nominal acceleration factors are used, multi-cell life-test data
supports ~500 FIT, with 90% confidence, at 10W, 33°C/50°C heat-sink/junction temperatures.
Direct semiconductor diode laser-based systems have emerged as the preferred tool to address a wide range of material
processing, solid-state and fiber laser pumping, and various military applications. We present an architectural framework
and prototype results for kW-class laser tools based on single emitters that addresses a range of output powers (500W to
multiple kW) and beam parameter products (20 to 100 mm-mrad) in a system with an operating efficiency near 50%.
nLIGHT uses a variety of building blocks for these systems: a 100W, 105um, 0.14 NA pump module at 9xx nm; a
600W, 30 mm-mrad single wavelength, single polarization building block source; and a 140 W 20 mm-mrad low-cost
module. The building block is selected to realize the brightness and cost targets necessary for the application. We also
show how efficiency and reliability can be engineered to minimize operating and service costs while maximizing system
up-time. Additionally we show the flexibility of this system by demonstrating systems at 8xx, 9xx, and 15xx nm. Finally,
we investigate the diode reliability, FIT rate requirements, and package impact on system reliability.
We report on the continued development of high brightness laser diode modules at nLIGHT Photonics. These modules,
based on nLIGHT's Pearl<sup>TM</sup> product platform, demonstrate excellence in output power, brightness, wavelength
stabilization, and long wavelength performance. This system, based on 14 single emitters, is designed to couple diode
laser light into a 105 μm fiber at an excitation NA of under 0.14. We demonstrate over 100W of optical power at 9xx nm
with a diode brightness exceeding 20 MW/cm2-str with an operating efficiency of approximately 50%. Additional results
show over 70W of optical coupled at 8xx nm. Record brilliance at wavelengths 14xx nm and longer will also be
demonstrated, with over 15 W of optical power with a beam quality of 7.5 mm-mrad. These results of high brightness,
high efficiency, and wavelength stabilization demonstrate the pump technology required for next generation solid state
and fiber lasers.
We report on the development of ultra-high brightness laser diode modules at nLIGHT Photonics. This paper
demonstrates a laser diode module capable of coupling over 100W at 976 nm into a 105 μm, 0.15 NA fiber
with fiber coupling efficiency greater than 85%. The high brightness module has an optical excitation under
0.13 NA, is virtually free of cladding modes, and has been wavelength stabilized with the use of volume
holographic gratings for narrow-band operation. Utilizing nLIGHT's Pearl product architecture, these
modules are based on hard soldered single emitters packaged into a compact and passively-cooled package.
These modules are designed to be compatible with high power 7:1 fused fiber combiners, enabling over
500W power coupled into a 220 μm, 0.22 NA fiber. These modules address the need in the market for high
brightness and wavelength stabilized diode lasers for pumping fiber lasers and solid-state laser systems.
We report on the development of a high brightness laser diode module capable of coupling over 100W of optical power
into a 105 μm 0.15 NA fiber at 976 nm. This module, based on nLIGHT's Pearl product architecture, utilizes hard soldered single emitters packaged into a compact and passively-cooled package. In this system each diode is individually collimated in the fast and slow axes and free-space coupled into a single fiber. The high brightness module has an optical excitation under 0.13 NA, is virtually free of cladding modes, and has an electrical to optical efficiency greater than 40%. Additionally, this module is compatible with high power 7:1 fused fiber combiners, and initial experiments demonstrated 500W coupled into a 220 μm, 0.22 NA fiber. These modules address the need in the market for higher brightness diode lasers for pumping fiber lasers and direct material processing.
Rapidly maturing industrial laser applications are placing ever-tighter constraints on spectral width and wavelength
emission stability over varying operating temperatures of high power diode laser pump sources. For example, improved
power scaling and efficiency can be achieved by pumping the narrow upper laser level of Nd:YAG solid state lasers at
885 nm and the 1532-nm absorption band of Er:YAG solid state lasers, though taking full advantage of these
configurations requires wavelength-locked pump sources. nLight offers a wide variety of wavelength-locked diode
products based on external volume grating optics technology. It is often believed that the use of external gratings to
wavelength lock diode lasers leads to an unavoidable loss in power and efficiency. nLight's design methodology is
shown to eliminate the problem in our grating-locked diode laser products. These results are expected to enable
improved performance in diode-pumped solid state and fiber laser systems.
Er:YAG solid state lasers offer an "eye-safe" alternative to traditional Nd:YAG lasers for use in military and industrial
applications such as range-finding, illumination, flash/scanning LADAR, and materials processing. These laser systems
are largely based on diode pumped solid state lasers that are subsequently (and inefficiently) frequency-converted using
optical parametric oscillators. Direct diode pumping of Er:YAG around 1.5 μm offers the potential for greatly increased
system efficiency, reduced system complexity/cost, and further power scalability. Such applications have been driving
the development of high-power diode lasers around these wavelengths. For end-pumped rod and fiber applications
requiring high brightness, nLIGHT has developed a flexible package format, based on scalable arrays of single-emitter
diode lasers and efficiently coupled into a 400 μm core fiber. In this format, a rated power of 25 W is reported for
modules operating at 1.47 μm, with a peak electrical to optical conversion efficiency of 38%. In centimeter-bar on
copper micro-channel cooler format, maximum continuous wave power in excess of 100 W at room temperature and
conversion efficiency of 50% at 6C are reported. Copper heat sink conductively-cooled bars show a peak electrical-to-optical
efficiency of 43% with 40 W of maximum continuous wave output power. Also reviewed are recent reliability
results at 1907-nm.
We report on recent progress in the control of optical modes toward the improvement of commercial high-performance
diode laser modules. Control of the transverse mode has allowed scaling of the optical mode volume, increasing the
peak output power of diode laser emitters by a factor of two. Commercially-available single emitter diodes operating at
885 nm now exhibit >25 W peak (12 W rated) at >60% conversion efficiency. In microchannel-cooled bar format, these
lasers operate >120 W at 62% conversion efficiency. Designs of similar performance operating at 976 nm have shown
>37,000 equivalent device hours with no failures. Advances in the control of lateral modes have enabled unprecedented
brightness scaling in a fiber-coupled package format. Leveraging scalable arrays of single emitters, the conductively-cooled
nLIGHT Pearl<sup>TM</sup> package now delivers >80 W peak (50 W rated) at >53% conversion efficiency measured from
a 200-μm core fiber output and >45 W peak (35 W rated) at >52% conversion efficiency measured from a 100-μm fiber
output. nLIGHT has also expanded its product portfolio to include wavelength locking by means of external volume
Bragg gratings. By controlling the longitudinal modes of the laser, this technique is demonstrated to produce a narrow,
temperature-stabilized spectrum, with minimal performance degradation relative to similar free-running lasers.
Space weather, the study of the Earth's upper atmosphere and forecasting its response due to solar events, depends on knowledge of the state parameters of the neutral and ionized upper atmosphere. In this work, we present a ground-based diode-seeded, high-power, narrow-linewidth Yb-fiber amplifier-based lidar operating at 1083 nm for measuring temperature and density of the neutral atmosphere from 300-1000 km. The current state of the lidar system will be addressed, as well as ongoing work to increase 1) signal to noise ratio through power scaling and 2) spatial resolution and wind measurement capability via pulsed operation.
Narrow-linewidth (<100 kHz) 850 nm distributed Bragg reflector (DBR) three-section tunable laser diodes are reported. An asymmetric cladding ridge-waveguide structure was used for transverse and lateral mode control. Single longitudinal mode performance was achieved via first-order DBR surface-etched gratings fabricated using inductively-coupled plasma reactive ion etching (ICP-RIE). Epitaxial material with spontaneous emission peak values at 835 nm and 850 nm were used for device fabrication. Stable single-mode powers of up to 30-mW were achieved at 100 mA with spectral side-mode suppression ratio (SMSR) values in excess of 35 dB. Laser tuning by DBR current injection in excess of 7 nm was measured. Narrow spectral linewidths were observed on both sets of devices, with linewidths below 40 kHz for devices with the 835 nm spontaneous emission peak. This is due to the reduced spontaneous emission contribution to the device linewidth. These results demonstrate that extremely narrow linewidths can be achieved using onestep epitaxial growth in an unstrained material system with surface etched first-order gratings on asymmetric cladding ridge-waveguide lasers.