This PDF file contains the front matter associated with SPIE Proceedings Volume 12403, including the Title Page, Copyright information, Table of Contents, and Conference Committee information.

Diode lasers providing nanosecond long optical pulses are key components for light detection and ranging (LiDAR) systems employed in, e.g., autonomous vehicles. However, achieving high resolution at large distances in real world scenarios remains a challenge due to the high currents required for high pulse powers. To reduce the currents needed, several laser diodes, separated by tunnel junctions, can be epitaxially stacked in series. Here, we present a 4 mm long laser with a stripe width of 50 μm comprising three InGaAs quantum wells and two GaAs tunnel junctions placed in the antinodes and nodes of the 2nd order vertical mode, respectively, to realize a shared optical waveguide. 1 mm long surface Bragg gratings stabilize the emission wavelength. Implemented in a 48-emitter laser bar soldered p-side down on a CuW submount and integrated in an inhouse developed electronic driver providing pulse currents up to 1 kA in a few nanoseconds, pulse powers exceeding 2 kW are achieved in 8 ns long pulses at a 10 kHz rate. Comparison with a similar module using a laser bar with a single active region shows a threefold increase of pulse power. The optical spectrum of the laser bar with a peak wavelength around 910 nm features a spectral bandwidth of only about 0.3 nm (3 dBc) and a wavelength shift with temperature of only 0.07 nm/K which is the same as what was achieved with single active regions. Results of reliability tests show no degradation of performance for more than 6000 h.

Stacking of multiple laser junctions within one device structure enables significantly higher output powers per mm² device size than in conventional diode lasers. This technology makes edge emitting lasers (EEL) and VCSEL favorable for LiDAR applications. In this paper, we show our current performance of multi-junction EEL and VCSEL for industrial and automotive LiDAR applications. We demonstrate output power densities exceeding 1.2 kW/mm² from a VCSEL array as well as output powers of 285 W from an EEL with a footprint of only 400x600 μm². In addition, we propose a solution for the spectral shift in EEL using a wavelength stabilization technology achieving 0.04 nm/K on average in a temperature range of -35°C to 105°C.

Watt-class semiconductor optical amplifiers (SOAs) at 1550 nm are an attractive alternative to replace erbium-doped fiber amplifiers (EDFAs) in various applications including remote sensing, optical communications, and LIDAR, with the potential to be more efficient, compact, and cost-effective. We report a world record of a single mode fiber-coupled packaged semiconductor optical amplifier delivering >30 dBm (1.2 W) of continuous wave ex-fiber power at 1550 nm, enabled by recent advancements in diffraction-limited output from tapered diode laser amplifiers. This result is achieved with an input seed power of 30 mW (~15 dBm), corresponding to an overall gain of ~16 dB, and the noise figure is calculated to be 5.4 dB. We have begun reliability testing of our tapered laser chips, and we are investing in the productization of these packaged watt-class SOAs.

We present an industry-leading semiconductor optical amplifier (SOA) platform that exhibits top performance at both 1550nm and 1310nm used in FMCW (frequency-modulated continuous-wave) LiDAR (Light Detection and Ranging) for autonomous vehicles. The SOA structure is based on a proprietary AlInGaAs material system with multiple quantum wells on InP substrate. The SOAs with curved and tilted straight waveguides were developed and tested. The saturated output power of such SOA at 1550nm and 1310nm can reach higher than 450mW and 600mW. The small signal gain exceeds 40dB for both 1310nm and 1550nm SOA. An array of four SOA waveguides at 127um or 500um pitch can deliver total output power over 2 Watts. SOA arrays can also be processed as individually addressable with electrical and optical isolations. Such high performance offers the design freedom to LiDAR systems with various scanning strategies such that long range detection can be realized. The low anti-reflection (AR) coating can achieve 0.01% reflectivity, and the noise figure and near-field mode fields of various SOA configurations are presented and compared. Gain chip based on the curved waveguide for various laser configurations is tested and discussed. The SOA chips and arrays can be integrated into a Silicon Photonic Integrated Circuit (Si PIC) to minimize the total footprint of a LiDAR system and overall cost. They include self-alignment features for the ease of integration and high coupling efficiency on Si PIC.

Progress in several fields has enabled the use of LiDAR sensing for a multitude of applications like autonomous driving, pre-crash sensors, gesture recognition, and environmental monitoring. All the applications demand challenging specifications of the sensing system components to achieve the required performance parameters detection range, angular resolution, eye-safety, and several others. In this work, we report on recent advances in our pulsed edge-emitting IR laser diodes, which can be used as laser light sources for scanning-beam and flash-mode time-of-flight LiDAR systems. We developed a technique to reduce the temperature-induced emission wavelength shift in our monolithically stacked epitaxial waveguides from 22nm to only 2.8nm over a heatsink temperature range from 25°C to 120°C, which is the crucial temperature range for many systems. Within this 95K range our Fabry-Perot edge-emitters feature a wavelength shift below the 7nm usually achieved in DFB type edge-emitters and VCSELs. There is no power penalty for the wavelength stabilization. We also demonstrate output power scaling by about 60% by increasing the number of waveguide stages in the stacked epitaxy structure from 3 to 5. This results in a short-pulse peak output power of 260W at 50A from a single device with an emission wavelength of 910nm and a near field width of about 220μm. Finally, we discuss the performance improvements of devices with 900μm and 1200μm long resonators compared to standard 600μm resonators. The demonstrated advances of the pulsed edge-emitting laser light sources enable various system improvements and widespread adoption of LiDAR sensing in many applications.

In this study, we present evaluation results of the 905nm pulse laser diode that has power of over 140W adopting 4stack epitaxy structure with 200um×15um emitter size for autonomous vehicle lidar and other lidar applications. The 4stack epitaxy structure was composed of AlGaAs/InGaAs composition and tunnel junction with GaAs and grown by MOCVD. As a results of the characteristic evaluation, 905nm pulse laser diode with 4stack epitaxy obtained an output of about 149.6W under the conditions of 1KHz cycle, 0.01% duty, and 40A input current. Also developed 905nm pulse laser diode achieved an operating voltage of 13V, a horizontal angle of 9.3°, a vertical angle of 29.1°, and peak wavelength of 905.2nm with TO-56 package respectively.

We have developed the world-leading Triple Junction laser diode based on AlInGaAs/InP material systems for LiDAR applications. The monolithic laser structure with tunnel junction layers is designed to reduce the stress and improve the heat dissipation. It has 3x the output power and 2x the wall plug efficiency of a single junction laser due to its low operating voltage and high slope efficiency at 1W/A. A single Triple Junction laser diode at eye-safe 1550nm allows a LiDAR to achieve over 200m detection range in all-weather conditions. It can drastically improve and simplify the LiDAR design compared to other laser choices such as 905nm or fiber lasers. For mass adoption by the automotive industry here we demonstrate the high reliability required for Triple Junction high power laser diodes at 1550nm. The life test was performed on 95um aperture Triple Junction with 2.5mm cavity length in a TO9 package. They were driven at an average power of 700mW with the pulse width of 100 micro-seconds and 10% duty cycle at 90°C. Such stressed electrical and temperature condition is almost 20 times higher than standard operation for automotive LiDAR. We have accumulated for more than 1000 hours of life test on 30 devices. Based on Chi squared distribution analysis and Arrhenius equation the estimated MTTF (mean time to failure) is 248k hours at 20°C and 57k hours at 50°C operating temperature, which is respectively 31x and 7 more than the required 8k hours in automotive applications. We also tested Triple Junction laser diodes up to 100°C without performance degradation and without COD (catastrophic optical damage).

Fiber lasers are becoming an increasingly important option for LIDAR light sources in autonomous driving technology due to their operation in the eye safe 1550 nm spectral region and their intrinsic high beam quality, power and pulse characteristics. As an essential component for the pumping of fiber lasers, semiconductor laser diodes with high temperature stability, power and reliability are necessary. In this report we present the results of a continuous-wave (CW) single edge emitting laser diode designed to operate at 94x nm at 25 °C heat sink temperature and 97x nm at 100 °C. Various epitaxial and laser geometry designs have been implemented to optimize the laser performance over this wide environmental temperature range. The laser epitaxy is based on the AlGaAs/GaAs material system, with an InGaAs strained quantum well (QW). With various designs of laser geometry including emitting area and cavity length, devices are designed, grown, fabricated, and tested with the optimized design improving the temperature stability, power, and efficiency of the laser chip. A peak efficiency of over 54% at heat sink temperature of 105 °C and over 12 W before thermal roll-over occurs has been achieved. In addition to the thermal performance we also report the slow axis beam parameter product of the chip of <5 mm.mrad with polarization purity >98% at operating current and show the preliminary reliability data at the high temperature operation.

The Franco-German »MERLIN Project« was initiated in 2010. The small satellite MERLIN (Methane Remote Sensing LiDAR Mission) will map the methane in the earth’s atmosphere. Fraunhofer ILT has developed the LiDAR laser source and is currently integrating the Engineering Qualification Model. The laser consists of a laser oscillator pumped by fiber coupled diode laser modules, an INNOSLAB amplifier and KTP-based frequency converter. The amplifier pump is based on qcw stacks which are homogenized in the slow axis direction and focused in the fast axis direction. We will present the design of the pump optics and results of reliability tests. In addition, we will give an outlook on the development of a laser source for a future wind LiDAR mission.

In this work, we compare four different design concepts for external-cavity laser diodes (ECDL) with respect to the maximum achievable output power before the onset of catastrophic optical damage (COD). A multiphysics model of the ECDL with a self-consistent description of the electrical, optical and thermal properties of the device is used to evaluate the COD level. The feedback-induced failure is provoked by shifting the fast axis collimation (FAC) lens along the fast axis (smile error) resulting in an absorption of the feedback radiation within the highly p-doped and contact metal layers. The investigated design concepts include three local modifications at the front facet of the laser diode chip itself which are supposed to suppress injected current, optical absorption and leakage current from the quantum well. Within the considered parameter space these approaches lead to an increase of the COD level by 8%, 27% and 27% respectively, however at the cost of drawbacks like slightly reduced efficiency or beam quality along the fast axis. By combining all three approaches the output power can be increased by 37%. The fourth approach uses an additional lens within the external resonator to make it bi-telecentric and allows for a feedback field without image reversal. This approach completely removes the sensitivity of the setup regarding a vertical misalignment of the FAC lens. The drawback in this case is the increase of the resonator size by approximately a factor of 20.

High-power single-mode (SM) and multi-mode (MM) InGaAs-AlGaAs strained QW lasers are critical components for space satellite systems. Both SM and MM QW lasers have shown excellent output power and efficiency characteristics, but these lasers are susceptible to COD. In addition, our group has shown that these lasers predominantly degrade by a new failure mode due to catastrophic optical bulk damage (COBD) leading to catastrophic and sudden degradation, which is a major concern for space applications. In recent years, InAs-GaAs quantum dot (QD) lasers have received much attention as an alternative to QW lasers for Si Photonics because 3-D confinement of carriers in QD lasers reduces the chance of nonradiative recombination of carriers at growth or radiation induced defect sites. This feature also makes the QD lasers attractive for space applications, but their failure modes and mechanisms are still unknown. For the present study, we investigated high-power broad-area lasers with strained InGaAs-AlGaAs QW and InAs-GaAs QD active regions. We performed short-term and long-term accelerated life-tests and failure mode analysis using various destructive and nondestructive techniques. We employed electroluminescence (EL) and time-resolved electroluminescence (TR-EL) techniques to study degradation processes in QW and QD window lasers. This configuration allows for observation of critical events including self-focusing of filaments, formation of dark spot and dark line defects (DLDs), and propagation of DLDs in real time during life-tests. We also employed focused ion beam (FIB) techniques to prepare TEM cross sections and plan-view TEM specimens of degraded QW and QD lasers for structural and defect analysis using a high-resolution TEM. Finally, we report our physics of failure investigation results on failure mechanisms in high-power broad-area lasers.

Catastrophic optical mirror damage (COMD) limits the output power and reliability of laser diodes (LDs). The self-heating of the laser contributes to the facet temperature, but it has not been addressed so far. This study investigates a two-section waveguide method targeting significantly reduced facet temperatures. The LD waveguide is divided into two electrically isolated sections along the cavity: laser and passive waveguide. The laser section is pumped at high current levels to achieve laser output. The passive waveguide is biased at low injection currents to obtain a transparent waveguide with negligible heat generation. This design limits the thermal impact of the laser section on the facet, and a transparent waveguide allows lossless transport of the laser to the output facet. Fabricated GaAs-based LDs have waveguide dimensions of (5-mm) x (100-μm) with passive waveguide section lengths varied from 250 to 1500 μm. The lasers were operated continuous-wave up to the maximum achievable power of around 15 W. We demonstrated that the two-section waveguide method effectively separates the heat load of the laser from the facet and results in much lower facet temperatures (T_f). For instance, at 8 A of laser current, the standard laser has T_f = 90 °C, and a two-section laser with a 1500 μm long passive waveguide section has T_f = 60 °C. While traditional LDs show COMD failures, the multi-section waveguide LDs are COMD-free. Our technique and results provide a pathway for high-reliability LDs, which would find diverse applications in semiconductor lasers.

The optical inspection of the surfaces of diode lasers, especially the p-sides and facets, is an essential part of the quality control in the laser fabrication procedure. With reliable, fast, and flexible optical inspection processes, it is possible to identify and eliminate defects, accelerate device selection, reduce production costs, and shorten the cycle time for product development. Due to a vast range of rapidly changing designs, structures, and coatings, however, it is impossible to realize a practical inspection with conventional software. In this work, we therefore suggest a deep learning based defect detection algorithm that builds on a Faster Regional Convolutional Neural Network (Faster R-CNN) as a core component. While for related, more general object detection problems, the application of such models is straightforward, it turns out that our task exhibits some additional challenges. On the one hand, a sophisticated pre- and postprocessing of the data has to be deployed to make the application of the deep learning model feasible. On the other hand, we find that creating labeled training data is not a trivial task in our scenario, and one has to be extra careful with model evaluation. We can demonstrate in multiple empirical assessments that our algorithm can detect defects in diode lasers accurately and reliably in most cases. We analyze the results of our production-ready pipeline in detail, discuss its limitations and provide some proposals for further improvements.

Recently developed high-power high-efficiency laser bars emitting at 760 nm for aesthetic applications such as hair removal will be introduced. During the development procedure different laser structures utilizing ternary and quaternary active regions, resulting in TE and TM polarized light, embedded in Al_xGa_1-xAs wave-guiding material were grown by means of MOVPE/MOCVD. The limits of the developed structures processed into laser bars with 1.5 mm cavity length and 50% fill-factor were investigated experimentally. The developed laser bars operate at 90 W (CW operation) and 250 W (pulsed operation) with more than 60% electro-optical efficiency, hence comparable to efficiency and output power of our 808 nm laser bars. Moreover, a reliable CW operation at 80 W for more than 9800 h as well as 40 Mshots at 90 A (long pulse operation at 70°C junction temperature) are already verified. The power-current characteristics as well as results of the lifetime tests at different junction temperatures and current density levels will be presented. The failure mechanisms will be discussed shortly.

In recent years, lasers in the wavelength range of 760 nm are getting more and more popular as they are needed in a greater variety of applications like nanometrology, sensors or material analysis. Thus, devices with high optical power and good beam quality are in great demand at these wavelengths. Another need is lasers with very small dimensions. Many of these applications are in “out of the lab” environments with limited space and in hazard conditions; for example, in space and planets exploration. In this context, tapered lasers (TPLs) are very promising candidates to fulfil these needs. TPLs can reach very high optical powers with excellent beam qualities, as individual diode lasers or in laser modules with very small dimensions. In this work, we present our results concerning the development of our new TPLs at 760 nm. We show two different epitaxial laser structures that we used to build these diode lasers. For this purpose, a GaAs_0.75P_0.25 single quantum well was used as active region. The lasers were mounted p-side up onto conductively cooled heat sinks for continuous-wave operation, which allows separate driving currents for the ridge (RW) and tapered (TA) sections. Also, we compare tapered laser diodes with different lengths of the ridge waveguide section and will show the influence of these parameters on the electro-optical performance of the tapered diode lasers. The mounted lasers feature an optical output power of more than 9 W, a conversion efficiency of more than 50 % at a heat-sink temperature of 15 °C and nearly diffraction limited emission.

Improving the power and efficiency of 9xx-nm broad-area laser diodes reduces the cost of laser systems and expands applications. LDs with more than 25 W output power combined with power conversion efficiency (PCE) above 65% can provide a cost-effective high-power laser module. We report a high output power and high conversion efficiency laser diode operating at 915 nm by investigating the influence of the laser internal parameters on its output. The asymmetric epitaxial structure is optimized to achieve low optical loss while considering high internal efficiency, low series resistance, and modest optical confinement factor. Experimental results show an internal optical loss of 0.31 cm^-1 and internal efficiency of 96%, in agreement with our simulation results. Laser diodes with 230 μm emitter width and 5 mm cavity length have T₀ and T₁ characteristic temperatures of 152 and 567 K, respectively. The maximum power conversion efficiency reaches 74.2% at 5 °C and 72.6% at 25 °C, and the maximum output power is 48.5 W at 48 A (at 30 °C), the highest reported for a 9xx-nm single emitter laser diode. At 25 °C, a high PCE of 67.5% is achieved for the operating power of 30 W at 27.5 A, and the lateral far-field angle with 95% power content is around 8°. Life test results show no failure in 1200 hours for 55 laser diodes. In addition, 55.5 W output was achieved at 55 A from a laser diode with 400 μm emitter width and 5.5 mm cavity length. A high PCE of 64.3% is obtained at 50 W with 47 A.

High-power, efficient semiconductor laser bars are demanded in many applications including pumping solid-state lasers and fibers. A narrow beam divergence is essential for increasing coupling efficiency and realizing an overall simple, cost-effective system. In kilowatt-class laser bars with 4 mm resonator length containing multiple broad-area emitters (with stripe width varying within 90–1200 μm) that are fabricated using conventional processing techniques, a strong thermal lens is generated within the individual emitters during laser operation. The lensing effect becomes stronger with increasing operating power. This allows a large number of lateral modes to be guided within the resonator and contribute to the laser emission, consequently deteriorating the beam quality (i.e. leading to larger lateral beam divergence angle). An approach to reduce the lateral divergence of the bar by modifying the in-plane structure of the emitters is presented. Based on simulation results, multiple lateral emitter structures have been developed and measured in quasi-continuous wave mode at low and high heat conditions with thermal resistance of 0.02 K/W and 0.05 K/W, respectively, comparable to continuous-wave testing with advanced coolers. Experimental results show that the improved lateral structures lead to enhanced power-current performance and improved beam divergence. A reduction of around 20% (~2°) in the bar lateral beam divergence angle at 95% power content has been achieved in testing at 800 W, with a simultaneous 5%-points gain in conversion efficiency with the highest performance lateral emitter structure.

Epi-down mounting can degrade performance in broad area lasers when the stress field extends into the active region. Thick p-side epitaxial layers have the potential to isolate the device from external stress, but add electrical resistance and losses from current spreading. Therefore, we use two-step epitaxy to combine highly-doped p-side epitaxial layers (2x thicker than conventional) with a resistive oxygen-implanted layer located close to the active region to block lateral current spreading. The resulting buried-regrown-implant-structure (BRIS) lasers with 100 μm stripes and lasing wavelength of 915 nm show high efficiency (peak of 67%, 55% at 20 W) and high lateral brightness (3.3 W/mm·mrad up to 17.5 W output power), improved over reference devices, in spite of the thick p-side.

The paper reports on the wavelength stabilization of high-power laser diode multi-emitter modules using as the external reflectors fiber Bragg gratings that are directly inscribed into the large mode area module delivery fiber using a femtosecond laser. Experiments have been carried out in a 200 μm fiber at 976 nm, but the approach can be extended at other fiber diameters and wavelengths. The results have demonstrated an effective stabilization over a broad driving current range, with power penalties in line or slightly lower than those of more traditional architectures that make use of discrete components, such as volume Bragg gratings, but with the advantage of not requiring the alignment of additional elements.

Laser generated blue light can be exploited in many fields (welding of metals, entertainment, biomedical…). Several of these applications require an autonomous and compact laser source, with emitted power in the order of tens of watts, keeping low cost-per-watt and enabling high-volume production. Present paper reports a new blue laser multi-emitter source, relying on proprietary low-SWaP (Size Weight and Power consumption) architecture, and integrating on the same package the electronics to control, monitor, perform automatic measurements and satisfying safety requirements. The dedicated electronics is designed to drive the high voltage required by the GaN semiconductor diodes connected in series. This integrated electronic multi-emitter demonstrated emitted power of 100 W on 105 μm core fiber, together with a Numerical Aperture (N.A.) of 0.16.

Innovative technology dispels the myth, that silica/silica, step index, multimode fiber bundles are lossy. This technology provides a number of gains, allowing to push the boundaries in fiber bundling technology: freedom of fiber bundle end shapes and dimensions, wide angle of light acceptance cone, what is described by high numerical aperture (NA) values, packing of fibers in honeycomb-like structures with fill factors close to 1, utility of low refractive index surrounding medium and good heat management of mis-coupled light. The latest technology allows the design of larger NA light coupling systems gaining output power density. Both are studied in this paper – high-OH and low-OH content core - fiber bundles, evaluating performance at high power, large angle of incidence (AOI) light sources. For comparison purposes various fiber bundles were produced differing by utilized bundle end treatment technology. There are compared four different fiber bundle end treatment technologies - glued, fused in silica capillary tube and two latest technology options. There is a proposed transmission measurement setup, that allows a change NA of incident light coupled in the fiber bundle from 0.10 to 0.60. Measurement data at ultraviolet (UV), visible (VIS) and near-infrared (NIR) wavelengths are compiled in graphs for comparison purposes. Results show that the new generation fiber bundles are suitable for low loss applications as the source to fiber bundle coupling is improved when compared with any known fiber bundle end treatment technology. Finally, the new technology allows the implementation of cladding mode stripping – this technology was not possible to utilize with previous generation fiber bundles.

High-power lasers have many applications in diverse fields such as optical communication, material processing (manufacturing), free-space optics, and 3D vision techniques such as LiDAR. These applications require optical components that alter or redirect laser beams to be tolerant to harsh environments, stable to thermal changes, and tolerant of high power levels that might otherwise damage materials or surfaces. It is common to use processes like machining, grinding, or polishing to achieve both form and finish requirements in either refractive or reflective materials. In this paper, we present a new alternative process for reflective freeform optical components suited to high-power assemblies that are made of aluminum for its thermal properties but manufactured by ultra-high precision stamping. The aluminum freeform mirrors can be used in air for free-space applications external to the laser module, or they can be assembled inside a laser diode package to provide beam shaping and redirection of the high-power beams very near the laser diode. This paper presents an exemplary optical design and thermal analyses for two cases: continuous wave (stead-state) lasers and pulsed (transient) lasers. The analyses demonstrate distinct benefits in thermal aberrations and lower operating temperatures for aluminum relative to a similar component made of a common polymer used in molded optics.

Industrial high-power/high-brightness blue diode lasers are quickly becoming a preferred laser source for processing highly reflective materials such as copper, stainless steel, and Aluminum.This paper focuses on the recent advances applying Wavelength Beam Combining (WBC) technology to diode bars emitting in the 445nm region. We will present results from latest developments in power scaling introducing an 800W Blue laser coupled with fiber diameters ≤50um while providing a beam parameter product of < 2.2 mm*mrad. Next, we will share applications results using these blue lasers at various power levels in a variety of processes including micro welding and engraving, conduction mode welding, keyhole welding and cutting of thin metal sheets.Finally, we will discuss the future of this technology regarding power scaling beyond 800W and combining our blue laser sources with multi-kilowatt high brightness diode lasers operating in the 975nm region to achieve improved applications results.

The 1.5kW fiber coupled blue diode laser with a fiber core diameter of 400μm was newly developed and pure copper plates were performed bead on plate welding tests. Laser welding has been usually employed near infrared ray [IR] laser with approximately 1000nm wavelength, such as a fiber laser, a disk laser, and a diode laser. However, it is difficult to weld pure copper with the IR laser due to the low light absorption rate of copper. In the blue region, on the other hand, copper has the high light absorption rate and the fluctuation of this rate with rising temperature is small. Thus, a blue diode laser is suitable for welding copper. Pure copper plates are used in this study. The high speed and high quality copper welding is required for several industries since copper is essential for various products such as fuel cells, automotive motors, and busbars for realization of a carbon-neutral society. Although blue diode lasers have been created worldwide, the keyhole welding was difficult because of the insufficiency of laser power density. Therefore, we developed the 1.5kW high-power blue diode laser and irradiated 10mm^w×30mm^l×2mm^t pure copper plates with sweep speed of 25mm/s and spot diameter of 300μm. The melting and solidification dynamics were observed with high-speed video camera and spectrometer for elucidation of welding mechanism with the blue diode laser. As the results, one of fluctuation factors was found to be presence of neutral Cu and CuO in the laser plume, which may cause instabilities due to interference them with the laser.

We present theoretical and computational investigations of the nonlinear dynamics and heterogeneity-promoted synchronization of diode laser arrays with decayed non-local coupling topology. The diode laser array exhibits a wide variety of dynamical behaviors as laser and coupling parameters vary. Here, we explore the dynamics for the intermediate and large coupling feedback strengths and further analyze the phase diagram and power spectrum as a function of the feedback strength, coupling topology, and misalignment introduced in the array. The dynamics induced by intermediate feedback are complex for small values of external cavity misalignment but display a clustering phenomenon consisting of several separate groups showing incoherent and coherent dynamics for the appropriate value of the cavity misalignment parameter. Furthermore, the dynamics and the power spectrum in the stronger feedback regime show frequency and phase-locking as the amount of misalignment disorder increases.

The line-scanning LiDAR (Light Detection and Ranging) has the advantages of relatively simple structure and longdistance detection, so it is widely adopted by many key players. However, one challenge of this method lies in the realization of the line-beam laser module with high peak power, small divergence angle, high reliability, and low cost. In this work, we introduce our line-beam laser modules based on 905nm triple-junction EEL with unique optical and structure design. The modules have a uniform line beam with a peak power larger than 800W, a pulse width of less than 6ns and repetition rate of 100 kHz. The divergence angle of the line beam is less than 0.15°@ 1/e2. The FOI (field of illumination) is 25° and the intensity uniformity is better than 90%. The Low/High-temperature-operation test data showed that over a wide temperature range from - 40 ℃ to 85 ℃ the power variation of the line beam module is less than 10%, and the variation of the divergence angle is less than 0.02 deg. Other reliability tests including temperature cycling from -40 ℃ to 120 ℃, and lifetime were also introduced.

High power diode lasers are widely used as the pump sources for fiber lasers and solid-state lasers, or the light sources for direct diode laser systems. The lateral brightness of diode lasers is the key parameter for the optical system with fiber coupling. The lateral brightness of a typical broad area diode laser is limited by the far-field booming rather than optical power at high operation current. In this paper, the far-field booming theory will be analyzed based on experimental observation of carrier density distribution and temperature profile along lateral direction. The temperature nonuniformity and the resulting thermal lens effect are supposed to be the dominate factor. We develop a novel high brightness laser diode structure with properly designed contact metal layer to modify the thermal conductivity profile. The thermal simulation indicate that the thermal lens effect is suppressed and the lateral far-field angle is reduced. Laser diodes with 230 μm emitter width and optimized structure are fabricated and the optical properties is investigated. The lateral far-field angle is reduced at current over 40A The optical power with same lateral brightness is increased up to 20%. This structure gives a promising high brightness solution for high power laser diode with power over 35 W. Chips with longer cavity length obtain higher power up to 51W.

A compact high-brightness blue laser is designed and developed. Through BPP theory and ZEMAX simulation, 18pcs TO-packaged 5W blue lasers are coupled into a 113μm core diameter 0.15NA optical fiber using polarization and optical fiber coupling technology. More than 75W output power is obtained, coupling efficiency exceeds 88%. Optical fiber end face spot with uniformity of more than 90% can be achieved by coupling the square optical fiber, which provides an ideal light source for medium power applications with high beam quality requirements such as gold foil welding and cutting, wire stripping, medical, etc.