This PDF file contains the front matter associated with SPIE Proceedings Volume 10900, including the Title Page, Copyright information, Table of Contents, and Conference Committee listing.

GaAs-based high-power diode lasers are the world’s most efficient light sources and generate the optical energy for the largest and fastest growing laser market: material processing. The performance of these key components is improving dramatically, driven by advances in material quality, process technology and design capability. FBH’s studies to improve the understanding of the physics and material properties that limit performance are an essential part of this development. An overview will be presented, detailing how power, efficiency and beam quality have been improved over the past 20 years, and showing the path to further performance scaling.

Modern vehicle lighting systems are intended to improve safety on the road by providing the adequate visibility to the drivers under different driving conditions from within a compact housing. Using a high-power semipolar GaN-based blue laser diode (>3W) that pumps a yellow phosphor in a remote position, BMW and SLD co-developed a new high-luminance white point-like source having a peak brightness of over 1000 cd/mm², which is 10 times than that of high-power white LEDs. This results in extending the range of the visibility to the maximum regulatory photometric values (~600m) and in enhancing the contrast of different light distributions in the far-field. New lighting functions, devoted to guiding, assistance and communication, for example between self-driving vehicles and pedestrians, require variable, free patterned light distributions that are clearly perceivable by the driver and/or pedestrians. One way to achieve them is through the use of high-luminance, dynamic light sources with a higher luminous flux and a higher “automotive” lifetime. Such sources should enable a relatively high resolution in the far-field. Multiple efficient, high-power semi-polar blue laser emitters have therefore to be integrated in a thermo-optically stable package. Different patterns are generated on an optimized structured phosphor that is excited by a moving blue laser spot. This dynamic is enabled by a robust, compact, fast beam steering MEMS mirror. The pattern is projected in the far-field using a customized secondary optical system. Eye safety measures that ensure a safe usage in the vehicle and in the manufacturing sites, have to be implemented in such sources.

This paper presents a 500 W continuous wave blue laser system for industrial applications, based on high power, high brightness laser diodes at 450 nm. The system builds upon the company’s 150W modules introduced recently. The modular system architecture allows efficient power scaling; a coupling efficiency of 90% into a 400 m 0.22 NA fiber was achieved. This paper will report on the architecture and integration of the laser and describe its key performance parameters. Test results will be presented for welding of copper with power levels and brightness accessible with this system.

The availability of high-power blue diode-lasers established a new class of laser sources for materials processing recently. With the significantly shorter wavelength compared to conventional laser sources for materials processing new applications are moving into the range of the feasible. There is a strong demand for welding applications with copper due to the change from internal combustion engines to electric drives, which even prompts laser manufacturers to find complex solutions to obtain a laser source in the wavelength range where copper shows higher absorption. With the appearance of high-power diode-laser bars in the blue wavelength range, proven optical concepts can be adapted for the setup of straightforward blue high-power diode-laser sources for materials processing. In context of the research project “BlauLas”, which is funded by the German Federal Ministry of Education and Research (BMBF) within the photonic initiative “EFFILAS” [1], Laserline, in cooperation with OSRAM, intends to realize a blue fiber-coupled cw diode-laser with a power exceeding 1 kW. Building on the results of the earlier presented 700 W fiber coupled laser source we present our new blue fiber coupled laser source with output powers surpassing 1 kW. A brief description of the optical concept and setup as well as an outlook on future strategies to increase output power and radiance of blue laser sources based on diode-laser bars are given. Additionally recently carried out application trials with this new powerful laser source are presented.

With the advent of high power blue laser diodes in general and blue laser bars in particular new applications are emerging, utilizing this new technology. Possibly the biggest benefits compared to traditional high power diode laser wavelengths in the infrared spectral range are the improvements seen in copper welding applications, both in weld quality and overall process efficiency. A new generation of high power diode lasers with emission wavelengths near 450 nm is being developed at Coherent DILAS. These modules achieve high brightness levels combined with high power, suitable for materials processing applications. 500 W of optical output power from a 200 μm core fiber and 550 W from a 400 μm core fiber, each with an NA of 0.22, have been demonstrated. Modules are based on existing infrared product platforms already manufactured in high volume, allowing the usage of known-good processes and fully automated manufacturing equipment. At the same time, material costs are kept low, due to the large volume produced at other wavelengths. The main challenge in developing industrial grade laser modules in the blue spectral range is the required life time. While tremendous progress has been made in recent years, the chip material is still more sensitive to environmental factors compared to other high power diode laser bars. The issue is approached by Coherent DILAS in multiple ways with the goal of finding the best possible solution to minimize complexity in module design and operation, while meeting reliability requirements. Latest results, including life-test data under a variety of operating conditions, are presented.

Efficient laser processing of high reflective materials, such as copper and gold, requires shorter wavelengths than those currently used for high power industrial applications, with blue being the optimal choice. However, the limited power of currently available blue laser chips poses important challenges in scaling the power to the required hundreds of watts while preserving the highest possible beam quality. The paper presents a new proprietary patent-pending architecture that allows achieving world record blue laser brilliance using commercially available high power lasers in TO9 package. The developed architecture is based on single emitters for best flexibility and reliability, which are organized in rows staggered along the fast axis; each row can then be placed side by side to other rows in order to spatially multiplex also along the slow axis. The optimized design gave a final architecture based on 3 rows for a total of 36 emitters that could be coupled into a 105 µm / 0.22 NA. Exploiting also polarization multiplexing and using commercially available 3.5 W diodes it is possible to obtain 220 W of coupled power into a 105 µm / 0.22 NA fiber, for a record brilliance of 150 GW/(ster m2). Following an accurate design phase some prototypes have been fabricated and characterized. Detailed results are presented at the Conference.

We present an overview of collaborative research between FBH (diode lasers) and Coherent|Dilas (packaging) to enable applications using red diode lasers. We summarize recent progress, focusing on the development of laser bars for highintensity pulse-pumping of alexandrite lasers. Specifically, high fill factor 1-cm bars packaged and tested (25°C, 10 Hz, 600 μs) on passively cooled mounts confirmed peak power of more than 350 𝑊 (> 0.2 𝐽 per bar), where efficiency was ~35% at 665 nm wavelength. Power was limited by thermal rollover. No evidence was seen for lateral lasing. Passively cooled 8-bar stack performance is presented, confirming a reliable optical power of 250 W/bar in stack format.

BLUE IMPAC^TM, a fiber-coupled high brightness blue laser, has been developed. The blue light is effectively absorbed by copper, thus, BLUE IMPACT is capable of improving manufacturing quality of copper materials, and is expected to be used in the field of electronics and automotive industries. The product has high brightness with a laser output of 100W from a fiber with a core diameter of 100μm, which is shown by BPP value of 10mm x mrad. As a result of the experiment, it was found that the 100W type of BLUE IMPACT can be used for processing of copper foils and melting of copper powder. As one of the application, the 3D printer which can form an object from copper powder was developed with a NEDO project in Japan. Furthermore, we have improved BLUE IMPACT and it has achieved 200W output from the fiber with 100μm core diameter.

We present recent progress of high power 808nm to 1060 nm laser bar operating at both CW and QCW operation. At CW operation, we demonstrate 50FF4.0 mm 940nm to 1060 nm bar can achieve up to 300W output power at 300A with high TE purity on MCCP package. At QCW operation, the 808nm 80FF1.5 mm bar can achieve 600W output power at both 25oC and 75oC on standard CCP; and the 75FF3.0 mm 940nm and 970nm bar can achieve 1KW at 1KA. We will also present results of our 808nm ~ 970nm QCW bar at ns region up to multi KA drive.

Industrial quality high power laser bars operated at 250 W output power are in volume production. Beyond the output power high conversion efficiency, polarization purity and beam quality are key requirements in high power applications. The latter requires controlling the chip beam parameter, especially the slow axis blooming, as well as the flatness or “smile” of the packaged device. The chip and package endurance must be carefully considered in the design. Our new MOCVD-based high power laser platform enables power conversion efficiencies of above 65% over the entire 920 nm to 1080 nm wavelength range at 250 W output power and at drive currents ranging from 250 to 285 A. Endurance test results show the high reliability of the chip and the fully AuSn hard soldered micro channel cooler package. Random emitter failures are the single relevant degradation mechanism present. At normal operating condition a degradation rate as low as 0.2% in 1000 h operation, obtained in 13’000 h test time indicates a MTTF of 100,000 h. Results of the QCW life-tests are in agreement with the CW tests and confirm the robustness of the fully AuSn hard soldered assembly. Also the micro channel cooler shows no sign of degradation from corrosion. The established 250 W MOCVD-epitaxy based platform is now paving the way to 300 W and later 350 W output power. Devices with 420W peak power and rollover currents of 550 A at 1040 nm wavelength were demonstrated.

Multi-kilowatt, continuous-wave fiber lasers continue to drive the need for higher power, higher brightness, and more efficient diode laser pump modules. It is well documented that increases in pump module power either enable higher power CW fiber lasers or minimize complexity of the multi-stage fiber combiners for a given power. Additionally, increasing pump module brightness positively impacts the SRS threshold of a given multi-kilowatt CW fiber lasers architecture. We report on the continued progress by nLIGHT to develop and deliver the highest brightness diode-laser pumps using single-emitter technology at 976 nm for Ytterbium fiber laser pumping. Building upon our prior developments that have enabled higher emitter counts in the element® packages, nLIGHT is releasing two new 976 nm module configurations: a 2×7 module with 155 W into 105 μm – 0.15 beam NA, and a 375 W 2×12 into 200 μm – 0.16 beam NA. Additionally, we have demonstrated high efficiency designs utilizing a new chip on submount (COS) architecture: with a 430 W 2×12 into 200 μm – 0.16 beam NA and 57% electro-optical efficiency, and an alternative 2×15 design resulting in 600 W at 57 % electro-optical efficiency at 23 A when coupled into 200 μm – 0.18 beam NA.

Design optimization of single emitter broad stripe 900-nm laser diodes was experimentally studied to achieve high power conversion efficiency (PCE) for a use in fiber laser systems. We chose two approaches for PCE improvement. The first is an optical confinement factor Γ_well optimization which affects threshold current and internal loss. The second is electric resistance minimization to suppress unwanted power consumption causing heat generation. As a result, the newly designed LD successfully demonstrates the high PCE of 72.5 % at middle power range and 66.7 % at practical high power of 20 W.

We report on new generation high power multimode pumps based on long cavity AlGaInAs/GaAs 9XX-nm chips. These chips are produced in high volume by Solid Source MBE growth on four-inch diameter GaAs wafers. Uniformity of material grown on multi-four-inch wafers is presented. We also demonstrate the uniformity of lasing parameters of ChipOn-Submount (COS) across individual four-inch wafers and across the entire 19”-diameter MBE-platen growth area. We discuss the performance of high power pumps based on simple spatial beam combining. Ultimate ex-fiber (~100 µm core diameter) power launched in CW and QCW modes of operation was recorded in excess of 350 W and 450W, correspondingly. We demonstrate fully wavelength stabilized operation in driving current range in excess of 22A and exfiber power in excess of 135W.

In this paper, we show results of further brightness improvement and power-scaling enabled by both the rise in chip brightness/power and the increase in number of chips coupled into a given numerical aperture. We report a new chip technology using x-REM design providing a record ~340 W output from a 2×12 nLIGHT element® in 105 μm diameter fiber. These diodes will allow next generation of fiber-coupled product capable of >250W output power from 105 μm/0.15 NA beam at 915 nm. There is also an increasing demand for low SWaP fiber-coupled diodes for enabling compact high energy laser systems for defense applications. We have demonstrated 600 watts and 60% efficiency at 15C in 220 μm/0.22 NA fiber resulting in specific mass and volume of 0.44 kg/kW and of 0.5 cm³/W respectively.

This paper reports a DBR High Power Diode Laser (DBR-HPDL) realization, emitting up to 14W CW in the 920nm range. Key feature is the use of a multiple-order Electron Beam Lithography (EBL) optical confining grating, stabilizing on same wafer multiple wavelengths by a manufacturable and reliable technology. In present paper, on the same wafer, three pitches DBR-HPDLs 2.5nm spaced have been demonstrated with excellent characteristics of power, spectral purity and stability. Moreover, excellent uniformity of performances across the wafer with different emitted wavelengths demonstrates the maturity of proposed technology for high yield, high volume laser diode production for wavelength stabilized applications.

Advancements in VCSEL and edge emitter laser diode technology, associated micro-optics and drive electronics has enabled use of direct diode lasers as illumination sources for solid-state lidar. This paper will discuss advancements in integrated, low cost solid-state laser diode based illumination sources that offer pulse widths below 5ns and peak powers over 1kW with very small form factors. Data will be presented on state-of-the-art near-infrared (NIR) and short-wave infrared (SWIR) sources. The impact on beam size and shape upon adding micro-optics to the assembly will also be shown.

Laser diodes emitting at wavelengths around 1060 nm are of great interest as light sources for both medical and industrial applications. For these applications a reliable and efficient operation at high output power is required. In this paper we report on continuous progress in the development of high power laser bars and single emitters emitting at 1060 nm. The development was focused on the epitaxial laser structure design for reliable, long operation at high power levels and various operation modes. As a result we demonstrate 10.000 h life time of laser bars with output power of 200 W in CW hard-pulse mode, as well as 150 Mshots on short cavity laser bars operating at 350 W under pulsed condition. Moreover, initial lifetime tests on single emitters operating at output power of 10 W were performed showing promising reliability.

In this paper, we report the results of our investigation about 940nm AlGaAs/InGaAs single mode laser diodes adopting graded index separate confinement hetero structures (GRIN-SCH) and p, n-clad asymmetric structures with improved temperature and small divergence beams characteristics under the high output power operation for a 3D motion recognition sensors. The GRIN-SCH design provides good carrier confinement and prevents current leakage by adding a grading layer between clad and waveguide layers. In addition, the dopant concentration of the cladding layer is optimized to reduce resistance and internal loss. At the optical power 300mW, measured average values of threshold current (Ith), operating current (Iop), slop efficiency (SE), operating voltage (Vop), peak wavelength (λ) are 80mA, 352mA, 1.12mW/mA, 1.87V, 940nm respectively. Also, we could obtain catastrophic optical damage (COD) of 750mW and excellent long-term reliability characteristic 60°C with TO-56 package. From the experimental measurement results, the developed 940nm high power laser diode is suitable optical source for the sensor applications including 3D motion recognition sensors.

Over the last decades considerable efforts have been undertaken to increase output power, conversion efficiency and beam quality of GaAs based broad-area diode lasers by optimizing the epitaxial layer design as well as the lateral device structure. In this respect the reduction of current spreading is essential to meet future requirements for high power diode lasers. Lateral current spreading enhances the accumulation of carriers at the edges of the active region defined by the contact stripes which results in additional leakage current and lasing of higher-order lateral modes, reducing efficiency and beam quality. We address this issue by implementing a tailored deep implantation scheme as a current block, implanting O and Si, using two-step epitaxy. This work elucidates the effects of buried current apertures, fabricated by Si and O doping at different doses on the optoelectronic properties of broad area lasers. It will be shown how deep O- and Si-implantation significantly suppresses current spreading, leading to lower threshold currents and higher efficiency.

975-nm laser diodes (LDs) are of great demand as pumping sources for Yb-doped fiber lasers. They should provide high output power with high efficiency and good beam quality. In order to satisfy these requirements, the LD structure should be carefully designed. In this paper, we report the results of our investigation in which the influence of the LD emitter width on the maximum output power, power-conversion efficiency (PCE) and beam parameter product (BPP) are analyzed with self-consistent electro-thermal-optical simulation of LDs. In order to establish the accuracy of our simulation, we carefully determine the numerical values of key LD parameters by fitting the simulation results to the measured results for a fabricated 975-nm LD. The device has 15-nm-thick tensile-strained InGaAsP single quantum well with asymmetric AlGaAs separate confinement heterostructure layers, 90-μm wide ridge, and 4-mm long cavity. With the parameter values obtained, LDs having various emitter widths are simulated and their maximum output powers, PCEs, and BPPs are determined as well as the temperature profiles inside the device. The results show that the device with the smaller emitter width has both of thermal roll-over, thermal blooming at the lower output power, mostly due to higher series resistance. However, it provides better BPP. These results are useful for optimizing LD array structures so that the optimal structure for each array element can be determined that can provide the highest possible output power with the best BPP.

High brightness diode laser beam combining techniques are in demand for efficient high power nonlinear conversion. Coherent beam combining (CBC) is the only method that has the potential for brightness scaling by maintaining one single narrow spectral linewidth. CBC in a master oscillator power amplifier (MOPA) configuration using a small number of efficiently cooled tapered amplifiers is a promising approach for efficient brightness scaling in a simple architecture. We present the application of such a source based on CBC of three tapered amplifiers seeded by a DFB laser at λ = 976 nm for second harmonic generation (SHG). A maximum power of 2.1 W at 488 nm was generated by SHG in a MgO:PPLN bulk crystal limited by thermal effects. A clear benefit of the beam clean-up resulting from the CBC setup was documented leading to an improved nonlinear efficiency. As part of our ongoing studies into further brightness scaling in CBC architectures, we present an experimental analysis of the phase dynamics of tapered amplifiers in quasi continuous operation (QCW) at high currents. Furthermore, we are investigating different amplifier designs for improved beam quality at high powers and therefore improved combining efficiency.

High-power laser manufacturers often perform accelerated multi-cell life-tests by applying significant amounts of stresses to lasers to generate failures in relatively short test durations and then use an empirical model to estimate lifetimes of the lasers. A drawback of this approach is overestimation of lifetimes at usage conditions due to the lack of failures generated under intermediate and low stress conditions. Many groups have studied reliability and degradation processes in GaAs-based lasers, but none of these studies have yielded a reliability model based on physics of failure. The lack of such model is a concern for space applications where complete understanding of degradation mechanisms is necessary. Furthermore, our group reported a new failure mode in multi-mode and single-mode InGaAs-AlGaAs strained QW lasers in 2009 and 2016, respectively. Our group also reported in 2017 that bulk failure due to catastrophic optical bulk damage (COBD) is the dominant failure mode of both SM and MM lasers. For the present study, we performed physics of failure (PoF) investigation to develop a PoF-based reliability model. Our physics of failure investigation consisted of (i) a series of long-term and short-term life-tests that exclusively generated COBD failures and (ii) destructive and non-destructive failure analyses using electron beam induced current, time-resolved electroluminescence, time-resolved photoluminescence, focused ion beam, highresolution TEM, and deep level transient spectroscopy.

Strained InGaAs QW lasers present a high power threshold for catastrophic optical damage (COD) as compared to lattice matched AlGaAs QW lasers. The reason for the higher resilience of strained QW lasers is not yet well understood. We analyze the catastrophic optical damage (COD) as a consequence of the dislocations generated by local thermal stresses. The thermomechanical problem is solved for both strained and lattice matched QW lasers. Also, we analyze the role played by point defects in both lasers as root causes of the degradation. The main factors contributing to the robustness of strained QW lasers are discussed.

The self-heating of semiconductor lasers contributes directly to facet heating and consequently to the critical temperature for catastrophic optical mirror damage (COMD) but the existing facet engineering methods do not address this issue. Targeting this problem, we report experimental and modeling results that demonstrate a new method achieving facet temperatures significantly lower than the laser cavity temperature in GaAs-based high-power semiconductor lasers by using electrically isolated and pumped windows. Owing to monolithic integration, the method does not introduce any penalty on the efficiency and output power of the laser. Thermal modeling results show that the laser output facet can be almost totally isolated from heat generated in the laser cavity and near cold-cavity facet temperatures are possible. The method can be applied to single emitters, laser bars, and monolithically integrated lasers in photonic integrated circuits to improve their reliability and operating performance.

We present results of investigations on high-power diode lasers in the spectral range between 780 nm and 1060 nm with different antireflection coatings at the outcoupling facet. Comparative life tests on high-power laser bars and single emitters with and without external optical feedback delivered significantly different results. Depending on the emission wavelength, we found different degradation rates and failure modes such as accelerated gradual degradation and catastrophic optical mirror damage caused by different energy reabsorption scenarios with respect to the energy gap of the device substrate material. We will also show different impacts of general and wavelength selective feedback on the near-field distribution.

High power laser diodes have been widely utilized in many fields, like industry, scientific research, military and medical treatment, etc. However, thermal stress induced by packaging process due to CTE-mismatch between chip and heat-sink is the main source causing near-field non-linearity along laser bar (also known as “SMILE”), decreasing the degree of polarization (DoP), broadening spectrum, and degrading the lifetime of laser diode array (LDA). In this paper, the effect of packaging induced thermal stress on high power laser diode arrays was studied theoretically and experimentally. The FEM simulation and photoluminescence (PL) experimental results showed the difference of packaging induced thermal stress based on different packaging structures. Spectrally resolved spectrum of LDA showed the packaging induced stress is highest in the middle and rapidly drops near both ends of laser bar, in agreement with our theoretical simulation, resulting in spectral broadening due to blue shifting the lasing wavelength of the center emitter more than the edge emitters.

A technique is experimentally demonstrated which allows for the compensation of the smile of a laser diode bar using a beam transformation system and a telescope array. The beam transformation system consists of a fast-axis collimator and an array of biconvex cylindrical lenses, which rotates each collimated beam by 90°. The telescope array is placed immediately behind and allows to address each emitter independently. The telescope array has two effects that reduce the fast-axis divergence: one is the magnification of the beams by effectively filling out the space between the beams, and the other the compensation of the smile-induced beam pointing by decentering the vertices of the concave entrance lens. In theory, this reduces the fast-axis divergence of a laser diode bar with 1 µm smile (peak-to-valley) from 7 mrad to 3.5 mrad, which would significantly increase the efficiency in fiber coupling applications. It is demonstrated in the experiment that it is possible to couple a full 19-emitter bar in a 100 μm core and 0.22 NA fiber with an overall fiber coupling efficiency of more than 75%. The telescope array is designed to be used with different, but similar smile forms. It is shown that slightly different smile forms have a negligible effect on the fiber coupling efficiency. Therefore, it is possible to compensate an arbitrary smile of a random laser diode bar by using a given set of optical modules.

Automated active alignment of optical components during the assembly process of optical systems is state of the art in today’s optics-production. With the increasing demand of optical systems in smart devices and automotive technologies, new methods and strategies have to be developed to guarantee rapid and goal-oriented development of active-alignmentalgorithms. A key approach to this is offline development via simulations. This paper presents and evaluates an efficient approach to generate a continuous data-feedback for the offline development of active-alignment-algorithms by interpolation of a discrete database. Dependent on the system-input the described procedure generates the raw, array-like output data of a CCD-chip from the existing data of the local neighborhood.

Fast axis collimator (FAC) to Chip in the assembly of High Power Diode Lasers (HPDL) systems is state of the art done in active alignment. Micro manipulators and (semi-) automated machines are available for purchase on the market. Neither the precision of the manipulation tools (step resolution < 10 nm) nor the measurement systems utilized in active alignment algorithms (alignment precision of ~50 nm) are the quality limiting factors but the bonding process is. This is due to the volumetric shrinkage of fast curing UV-adhesives in the curing process. The objective of this work is to reduce the absolute volume of adhesives in optical systems by smart design of the glue glap so no significant misalignment while curing is expected. The assertion is that the overall system quality is improved with the implementation of additional adhesive gaps if the amount of adhesive is reduced in this way. In high quality systems as HPDL this approach is state of the art with the implementation of FAC lens on Bottom tab. In other industries as automotive sensors that are drastically reducing component tolerances and improving system quality this approach is rather unknown. Results of glue gap reduction for HPDL assembly is described in this work by combining active alignment of FAC to edge emitter with a tolerance compensated individualized FAC on bottom tab subassembly in a fully automated production process. The approach was described in the papers [SPIE 10086-28] and [SPIE 10514-38]. Furthermore the approach of systemizing the smart glue gap design is done.