This PDF file contains the front matter associated with SPIE Proceedings Volume 11668, including the Title Page, Copyright information, and Table of Contents.

In material processing applications laser diodes are commonly used for pumping of solid-state lasers, providing high efficiencies at demanding optical output powers. Limited by relatively low beam qualities in the high power scheme, their usage in direct material processing applications is still marginal. To achieve power levels in the 30W class, so far the combined radiation of multiple broad area emitters has been necessary. However their output beam quality is far from diffraction limitation and correlated to the aperture width of the emitting laser diode. This work presents a novel miniaturized diode laser module, with an optical output power of more than 30W in continuous wave operation (cw). Simultaneously the output beam is close to the diffraction limit with a beam propagation factor of M² < 3. The laser module layout is based on tapered diode lasers featuring wavelength stabilization by a monolithic distributed Bragg-grating. The tapered diode laser sources achieve an output power in the order of 8W (cw) at a wavelength around 980 nm. To enhance the output power while maintaining the beam quality of the single emitters, six laser beams were combined by the use of polarization and wavelength coupling. The use of custom designed beam couplers is necessary to combine the given radiation intensities. Therefore a thin film polarizer was adapted to the output wavelength and intensity. Wavelength multiplexing is realized by the use of steep edge filters. By changing the angle of incidence the edge position can be tuned which enables multiple combination steps. All optical components were housed inside of a module with a footprint of 58 x 34mm² only. The resulting high power and beam quality delivered by the module enables direct material processing.

This paper reports a multi-emitter laser module realization, based on internally developed InGaAs/GaAs 190 μm ridge High Power Diode Lasers (HPDL), emitting at 976 nm. Single diode lasers shown a highly efficient power conversion and good emitted beam characteristics together with excellent long term reliability. The multi-emitter laser module, using 20 diodes polarization and spatially multiplexed, demonstrated up to 350 W of output power at 976 nm; the absence of fiber coupling degradation at high bias currents, thanks to the limited beam blooming from the laser diodes, ensure a good linearity in the operating conditions. The package has a compact footprint of 54 mm x 140 mm, with an output fiber of 200 um core / 220 um cladding, and 95 % of the emitted power is within 0.16 numerical aperture (N.A.). Present realization of high-power multi-emitter semiconductor laser source is suitable for production of high power single modules fiber laser, moreover contributing to an important reduction of the overall fiber laser cost by effectively reducing the number of the pump modules.

GaAs based high power broad area lasers are the most efficient source of optical energy and are used in many industrial applications. Despite considerable improvement in power and efficiency in recent years, further improvement is needed due to the high demand from industry. We review here progress in vertical epitaxial layer design, showing how higher performance is enabled by migrating from asymmetric large optical cavity (ASLOC) designs to the newly developed extreme-triple-asymmetric (ETAS) vertical structure. Building on earlier studies at 940 nm, we focus on gain-guided lasers that have operating wavelength 970 nm, have 90 μm stripe width and 4 mm resonator length. We can emphasize the positive impact of epitaxial layer design, without need for advanced lateral structures. We show how design improvement increases conversion efficiency ηΕ at 12 W output power from 56% to 66%, whilst peak (saturation) power increases from P_opt = 14 to 19 W in continuous wave (CW) mode for p-down single emitters on CuW carriers (thermal resistance 3 K/W). Progress in epitaxial design also leads to smaller lateral beam parameter product (BP Plat) at higher bias, leading to lateral brightness P_opt/BPP_lat < 3 W/mm × mrad. Specifically, in these most recent ETAS structures, by design BPP_lat increases more slowly with self-heating, and this leads directly to lower BPP_lat at high bias. We will also review options for further increased performance, include efforts to understand and improve BPP_lat, which is also limited by a non-thermal ground level BPP₀ (here ∼ 1 mm × mrad).

Edge emitting laser diodes are well known and used in a vast portfolio of applications. High power pulsed edge-emitting laser diodes in the 905 nm regime have proven to be robust and reliable under operating conditions that require low repetition rates and pulse widths longer than several tens of nanoseconds. Automotive LiDAR requires other typical operating conditions: high repetition rates and short pulse widths at or below 5 ns. Therefore, a suitable reliability model that take into account these unique operating conditions is required. This work will present a universal reliability model focusing on the impact of short pulse widths on the lifetime reliability of GaAs-based high power edge emitting lasers. In order to set an empirical model, a dedicated experimental setup was conducted in-house. Pulse widths as short as 1.5 ns were used in combination with 100 kHz frequency in order to carry out accelerated tests. Proper life tests of more than 1000 hours were conducted in order to gain an insight on the impact of the pulse width on the overall reliability. Influence of the pulse width from 1.5 ns to 200 ns on the mean time to failure of typical lasers will be detailed herein. One of the main validated predictions of the new lifetime model is that use of long pulse widths allows high acceleration factors for a constant duty cycle without damaging the optical cavities for the automotive LiDAR market.

The demand for fiber lasers has increased due to widening of application areas and higher power levels. As fiber lasers have become the main workhorse for high power material processing applications and competition among fiber laser manufacturers have become more evident, the laser manufacturers are in the process to find ways to lower overall cost of ownership to become more competitive. Key areas to look at are the efficiency of the fiber laser, especially the efficiency of the diode pump modules, and the higher reliability of its’ components. There is increasing demand for high power, high brightness, and higher efficiency laser diodes for kW-level fiber laser pumping. We present high-efficiency and high brightness laser diode optimized for lowered operating voltage while maintaining high power conversion efficiency of 60%. The laser diode design is a single quantum-well InGaAs/AlGaAs structure with graded index profile and large optical cavity design. The laser is fabricated into 4 mm long chips with a 94 μm emitter stripe indented for standard 105/125 μm core fiber laser pumping. The chips are mounted on AlN carrier and characterized as chip-on-submount. The laser produces 12.6 W optical power at 13 A and 1.62 V, reaching 60% conversion efficiency at operating point. The beam divergence angles are 8.5° horizontal and 34° vertical enabling high brightness and efficient fiber coupling. Furthermore, the lasers are reliability tested where they show outstanding reliability without sudden failures and ware-out rate less than 1% per 1000 hour over several thousand hours of testing.

High-power InGaAs-AlGaAs strained quantum well (QW) lasers are indispensable components for both terrestrial and space satellite communications systems. However, their degradation mode (catastrophic and sudden degradation) due to catastrophic optical damage is a major concern for space applications. Furthermore, these lasers predominantly degrade by a new failure mode due to catastrophic optical bulk damage (COBD). Also, InAs-GaAs quantum dot (QD) lasers have recently received much attention as an alternative to QW lasers especially for space applications, but their degradation mechanism is not well understood. For the present study, we investigated 9×× nm broad-area strained QW lasers and ~ 1 μm broad-area QD lasers. QW lasers were consisted of an InGaAs QW layer, while QD lasers were consisted of ten stacks of InAs QD layers. As part of our root causes investigation to understand degradation mechanisms in InGaAs-AlGaAs strained QW lasers as well as in InAs-GaAs QD lasers, we performed short-term and long-term life-tests, failure mode analyses, and physics of failure investigations using various techniques. First, we employed electroluminescence techniques to study the formation of dark line defects (DLDs) in degraded lasers. Second, time-resolved electroluminescence (TR-EL) techniques were employed to study the formation and propagation of dark spots and dark lines in window QW lasers in real time during aging. Third, we employed deep level transient spectroscopy (DLTS) and time-resolved photoluminescence (TR-PL) techniques to study a role that electron traps and non-radiative recombination centers (NRCs) play in degradation of these lasers. Finally, we report our understanding on mechanisms responsible for degradation in high-power QW lasers and preliminary results from QD lasers.

The process of catastrophic optical damage (COD) in 9xx-nm laser diodes is typically divided into three phases. In this work we model the first phase of COD by placing a localized additional heat source near the front facet corresponding to accumulated defects or misaligned optical feedback. We then compare two different multiphysical models to investigate thermal runaway, the second phase of COD. The first model considers only the carrier density within the quantum well coupled to a lateral-longitudinal optical model and a 3D thermal model. For this model, the temperature distribution converges within a few iteration steps without indication of thermal runaway and irrespective of the power of the additional heat source. The second model self-consistently computes the electrical and optical properties in the vertical-longitudinal plane and the 3D temperature distribution of the device. A critical power of the additional heat source is found above which the temperature distribution does not converge anymore and the maximum temperature increases to values above 1000 K. This strong temperature increase is accompanied by a thermally induced current crowding near the front facet and excessive carrier leakage from the quantum well. An analysis of the contributions of different heat sources shows that the nonradiative recombination in the waveguide and cladding layers exhibits the strongest changes during thermal runaway. The results of the two models indicate that the frequently proposed explanation of the feedback loop for thermal runaway consisting of a thermally induced bandgap shrinkage and increasing nonradiative recombination needs to be supplemented by thermally induced current crowding.

High brightness, high efficiency laser sources become more and more promising in diode laser applications for fiber laser pumping and materials processing. Dense wavelength beam combining (DWBC) technology has great advantages over other beam combining technologies as the brightness is significantly improved. However, the brightness and efficiency of DWBC technology based on laser diode bars are naturally limited by the laser source due to smile effect and low polarization ratio. By employing single emitter based DWBC technology and optimizing the optical design, a laser diode module capable of delivering above 600 W at 976 nm in a 0.22 NA 100/120 fiber is developed and 48% power conversion efficiency is achieved. The maximal power conversion efficiency, 51%, is reached at 400 W output. The intrinsic wavelength stabilization of DWBC technology allows the use of the module for efficiently pumping.

In this paper, we present the new FACTOR-series of fiber coupled high power diode lasers based on single emitters. While fiber coupled modules at DILAS and COHERENT have mostly been based on high power diode laser bars in the past, increased output power, advances in automated alignment processes and reduction in cost of optical components have tipped the scale towards single emitter-based packages in certain areas. The product portfolio includes emission wavelengths between 790 nm and 1060 nm with output power of up to 600 W. Fiber core sizes of 100 µm and 200 µm are offered. All products are available with optional wavelength stabilization to reduce the spectral line width and minimize the wavelength shift over varying output power and temperature. We present Ytterbium pump modules at 976 nm with up to 600 W output power, modules for Thulium pumping at 793 nm with up to 250 W and modules near 880 nm optimized for different absorption peaks of Vanadate, ranging in output power between 65 W and 150 W. In addition to pump modules, industrial turnkey systems for polymer welding and soldering have been developed based on the same product line. Up to 100 W of output power are offered from a 3 HU - ½ 19” rack mountable chassis including the power supply, diode controller, a pilot beam and safety features complying with performance level ‘e’.

At SPIE 2020 conference, we presented a blue diode laser that provides 200W output from a 200μm core diameter 0.22 NA fiber. Blue laser with high power and high brightness is the best choice for higher efficiency demanded by industrial processing. Based on 7 modules each provides 160W from a 105μm core diameter 0.22 NA fiber (NA 0.15/0.22 power ratio >93%), using fiber beam combining, 1000W output is achieved from a 330μm core diameter 0.22 NA fiber. And the aging test of 160 W unit modules was carried out. 1000W high brightness blue laser source is an ideal choice for processing (welding, 3D printing, etc) of non-ferrous metals, especially copper.

Blue laser diode sources have already proved to be an effective alternative for material processing, especially of high reflective materials, such as copper; now the challenge is to increase their power while improving brightness and reducing the cost-per-watt. The paper presents the development of a family of blue laser modules that, making use of the same platform and assembly lines of similar 9xx nm modules, can achieve an unprecedented combination of power, brightness, compactness and cost reduction. These modules rely on a proprietary architecture to combine a plurality of chips through spatial and polarization multiplexing, obtaining up to 100W of output power in a 100 μm fiber. Preliminary experimental results for module making use of spatial multiplexing report 35W output power in a 50 μm fiber.

Individually addressable laser diode arrays (IABs) are commercially demonstrated in the printing industry. These laser arrays are typically working at 8xx nm and 9xx nm wavelengths. Individually addressable laser diode arrays operating in visible region has been less reported and especially with limited commercial success. Yet, there is increasing interest in different variants of visible laser arrays not only in printing industry, but also in various display applications including head-up-displays and AR/VR products for different fields like automotive, consumer and medical markets. In this work we report the state-of-the-art high brightness individually addressable diode laser arrays operating at visible red wavelengths. The single-mode red IAB design is scalable from a few individually addressable emitters to tens of emitters per array with a highly uniform operation and repeatability and can be applied over the whole visible red spectrum from 630nm to 690nm. The individually addressable arrays at 640-660nm with a dense <100μm device pitch produce a record 3W total output power per array, with 0.85 W/A slope efficiency. The red IABs show excellent uniformity and stable long-term operation and are perfectly suited e.g. for various display applications or wherever there is a need for commercially viable high brightness individually addressable visible laser arrays.

There has been a growing demand of laser welding for copper materials to manufacture industrial products with high electrical and thermal conductivities. The high thermal conductivity characteristic generates rapid thermal diffusion at a welding spot and hence reduces the power efficiency of laser welding. To overcome this issue, we propose to combine a blue laser beam performing a high absorptivity for copper materials, with a 1070-nm high power laser beam, launched from a single mode fiber laser. The blue laser beam can be focused at the welding spot with a sufficiently narrow beam waist, and the absorption of the blue light for copper materials is much higher than that of infrared light. Therefore, the focused blue laser beam causes rapid and highly efficient heat generation at the welding spot, and this localized heat is expected to improve the quality of laser welding. To generate the high-power blue laser beam efficiently, we fabricated a high power blue LD-integrated SLP which achieves an optical output power of 11.7 W at 10.5 A. We also fabricated a blue-DDL module using multiple SLPs and a stepped structure package adopted with a water-cooling system. The blue- DDL module can output a high fiber-coupled optical power exceeding 150 W. Next, we built a blue-NIR hybrid laser equipment which exhibits the excellent quality of laser welding by accurately controlled optical output power and beam spot diameters of both blue and NIR laser beams. In this paper, we describe the design and performance of blue LDintegrated SLP and blue-DDL module. We also report how the blue-NIR hybrid laser equipment contributes to improve the quality of the laser welding.

Aurora’s automotive frequency-modulated continuous-wave (FMCW) lidar technology has been designed and developed to address the needs of level 4/5 autonomous vehicles (AVs). Aurora’s FirstLight provides eye-safe and long-range performance, radial velocity on every point, and high spatial density. These features allow the Aurora Driver to unlock faster perception, tracking, and classification of vehicles and pedestrians. Fiber-based optical technology developed for coherent telecom applications including EDFA’s had been employed for most coherent lidar applications. High power diode lasers and semiconductor optical amplifiers offer an exciting route to reduce the complexity and improve robustness over fiber-based FMCW laser technology. A highly integrated semiconductor FMCW lidar system would greatly aid size, weight, and power considerations while removing dependence on optical fibers which are typically a point of higher manufacturing costs and performance susceptibility

High-power spatially single-mode diode lasers at 15xx nm wavelengths are of interest for Light Detection and Ranging (LIDAR) at eye-safe wavelengths, as pump lasers for Raman and rare-earth doped fiber amplifiers as well as for material processing. A cost-efficient way to realize high-power in combination with high-brightness is the tapered resonator concept. We demonstrate InGaAsP/InP based diode lasers and tapered amplifiers with fast axis far fields of 36° FWHM and wavelengths around 1550 nm which were grown by MOCVD. From processed broad area lasers with 2mm resonator length and 100µm stripe width and 1mm long ridge-waveguide lasers, parameters for the logarithmic gain model are evaluated. With their implementation in 2-dimensional BPM simulations, an optimized resonator geometry has been derived for aiming 1W in cw operation and 2W in pulsed mode. The optimised design consists of a ridge section length of 310µm and a taper section length of 2190μm. Different taper designs have been processed and investigated in detail. In dependence on the taper angle ridge widths are between 4 and 5μm. For narrow-linewidth operation, the tapered devices are provided with anti-reflection coatings of less than 0.01% on the rear facets and spectrally stabilized with an external grating. Beside the electro-optical characterisation, beam quality has been characterized in terms of beam waist analysis and M2.

LiDAR sensors have gathered lot of interest in the field of autonomous driving. Still, the offering of mass-produced, small form-factor all-solid-state LiDAR sensors remain scarce. Furthermore, most of the sensor applications are currently designed for short-range (<50 feet) and medium-range (50-300 feet) applications. There’s a requirement for an efficient solution for long range LiDAR sensor that can be used to monitor the road in front of the vehicle. It must be powerful enough to cover long ranges (300 –800 feet) with high enough refresh rate and minimize detection noise while maintaining eye-safety. For these requirements a flash type LiDAR illuminator would be ideal for fast data collection and minimizing the power density. We propose a novel solution for long-range all-solid-state LiDAR application by using a segmented flash illumination and readout concept utilizing state-of-the-art laser diode technology and CMOS imaging at <1μm wavelength. Employing a stack of individually addressable high-power nanostack arrays as the illumination source allows to produce series of 3D flashes, which significantly improves the transverse resolution of the LiDAR, while at the same time mitigating the requirements for the smallest detector pixel size. The design makes it possible to achieve eye-safety even when targeting long ranges with silicon-based detectors. With this approach, the high illumination intensity requirements for the long range can be fulfilled while at the same time maintaining eye-safe operation. Additionally, the design allows for higher refresh rates while the heat management and the power consumption of the system can be minimized.

Vertical-cavity surface-emitting lasers (VCSELs) have just recently started generating a lot of interest as the illumination source in the multitude of commercial applications. VCSELs capability to provide narrow spectrum emission with low temperature sensitivity and high beam quality, coupled with the possibility of nanosecond pulses generation, makes VCSELs an excellent laser platform for the outdoors, high-precision time-of-flight (ToF) and structured light applications. These advantageous features of VCSELs emission arise from their vertical cavity geometry, which also enables possible VCSELs direct integration onto circuitry and allows power scaling by arranging single-emitting VCSELs into compact high-power 2D arrays. These benefits have made VCSEL the current most popular illumination source for the 3D sensing applications both in the consumer market (e.g. proximity sensors for face and gesture recognition) as well as in the industrial sector (e.g. automotive short- to middle-range LiDAR and in-cabin monitoring). We present development results of both high-efficiency VCSEL single-emitters and multi-Watt VCSEL arrays emitting at the 940 nm purposed for 3D sensing applications. The VCSEL development involved optimization of epitaxial design in terms of DBR doping concentrations and the material content of the bottom DBR and oxide layer. While, on the other hand, optimization of the device parameters and processes targeted oxide aperture and mesa diameters, as well as etching depth. Wet thermal oxidation process has been specifically developed to facilitate precise oxidation depth control, run-torun reproducibility, and uniformity on the wafer scale. Successful VCSEL development is attributed to the Modulight’s full-cycle in-house semiconductor fabrication capabilities.

There are strong demands at the market to increase power and reliability for high power diode laser. In parallel to this the requirements for cooler and package for the high power diode laser increase. Superior heat dissipation capability and low thermal resistance are some of the key attributes for the diode laser package design in the near future. The most common method of removing the large amounts of waste heat in a diode laser is using a micro-channel cooler. However, a microchannel cooler requires water to meet demanding specifications to avoid failures due to corrosion, which increases the overall cost to operate and maintain the laser. We demonstrate advances in a new macro-channel water cooling diode laser which are designed to eliminate the failure mechanisms associated with micro-channel coolers, and enhance the laser heat dissipation and the long-term reliability. For the package adopting the high thermal conductivity material, the maximum output power is 100 W per bar in CW mode. Due to the advantage of compact design, high power, high reliability and fast axis collimation, the new diode laser has the potential to be widely used in many fields, such as pumping solid state laser, hair removal, industry and research.