Download or read book Epitaxial Design Optimizations for Increased Efficiency in GaAs Based High Power Diode Lasers written by Thorben Kaul and published by Cuvillier Verlag. This book was released on 2021-04-09 with total page 136 pages. Available in PDF, EPUB and Kindle. Book excerpt: This work presents progress in the root-cause analysis of power saturation mechanisms in continuous wave (CW) driven GaAs-based high-power broad area diode lasers operated at 935 nm. Target is to increase efficiency at high optical CW powers by epitaxial design. The novel extreme triple asymmetric (ETAS) design was developed and patented within this work to equip diode lasers that use an extremely thin p-waveguide with a high modal gain. An iterative variation of diode lasers employing ETAS designs was used to experimentally clarify the impact of modal gain on the temperature dependence of internal differential quantum efficiency (IDQE) and optical loss. High modal gain leads to increased free carrier absorption from the active region. However, less power saturation is observed, which must then be attributed to an improved temperature sensitivity of the IDQE. The effect of longitudinal spatial hole burning (LSHB) leads to above average non-linear carrier loss at the back facet of the device. At high CW currents the junction temperature rises. Therefore, not only the asymmetry of the carrier profile increases but also the average carrier density in order to compensate for the decreased material gain and increased threshold gain. This carrier non-pinning effect above threshold is found in this work to enhance the impact of LSHB already at low currents, leading to rapid degradation of IDQE with temperature. This finding puts LSHB into a new context for CW-driven devices as it emphasizes the importance of low carrier densities at threshold. The carrier density was effectively reduced by applying the novel ETAS design. This enabled diode lasers to be realized that show minimized degradation of IDQE with temperature and therefore improved performance in CW operation.

Download or read book Optimization of broad area GaAs diode lasers for high powers and high efficiencies in the temperature range 200 220 K written by Carlo Frevert and published by Cuvillier Verlag. This book was released on 2019-07-11 with total page 174 pages. Available in PDF, EPUB and Kindle. Book excerpt: This work focuses on the development of AlGaAs-based diode laser (DL) bars optimized for reaching highest powers and efficiencies at low operation temperatures. Specifically, the quasi continuous wave (QCW) pumping of cryogenically cooled Yb:YAG solid-state lasers is targeted, setting requirements on the wavelength (940 nm), the pulse conditions (pulse length 1.2 ms) and frequency (10 Hz) as well as the lowest DL operating temperature THS ~ 200 K, consistent with economic cooling. High fill-factor bars for QCW operation are to reach high optical performance with optical output powers of P  1.5 kW and power conversion efficiencies of ŋE  60% at these power levels. Understanding the efficiency-limiting factors and the behavior at lower temperatures is necessary to design these devices. Optimizations are performed iteratively in three stages. First, vertical epitaxial designs are studied theoretically, adjusted to the targeted operation temperatures and specific laser parameters are extracted. Secondly, resulting vertical designs are processed into low power single emitters and their electro-optical behavior at low currents is experimentally assessed over a wide range of temperatures. The obtained laser parameters characteristic to the vertical design are then used to extrapolate the laser's performance up to the high targeted currents. Finally, vertical designs promising to reach the targeted values for power and efficiency are processed into high power single emitters and bars which are measured up to the highest currents. Eventually, laser bars are fabricated reaching output powers of 2 kW and efficiencies of 61% at 1.5 kW at an operation temperature of 203 K.

Download or read book Design simulation and analysis of laterally longitudinally non uniform edge emitting GaAs based diode lasers Band 73 written by Jan-Philipp Koester and published by Cuvillier Verlag. This book was released on 2023-09-19 with total page 171 pages. Available in PDF, EPUB and Kindle. Book excerpt: Edge-emitting quantum-well diode lasers based on GaAs combine a high conversion efficiency, a wide range of emission wavelengths covering a span from 630 nm to 1180 nm, and the ability to achieve high output powers. The often used longitudinal-invariant Fabry-Pérot-type resonators are easy to design but often lead to functionality or performance limitations. In this work, the application of laterally-longitudinally non-uniform resonator configurations is explored as a way to reduce unwanted and performance-limiting effects. The investigations are carried out on existing and entirely newly developed laser designs using dedicated simulation tools. These include a sophisticated time-dependent laser simulator based on a traveling-wave model of the optical fields in the lateral-longitudinal plane and a Maxwell solver based on the eigenmode expansion method for the simulation of passive waveguides. Whenever possible, the simulation results are compared with experimental data. Based on this approach, three fundamentally different laser types are investigated: • Dual-wavelength lasers emitting two slightly detuned wavelengths around 784 nm out of a single aperture • Ridge-waveguide lasers with tapered waveguide and contact layouts that emit light of a wavelength of around 970 nm • Broad-area lasers with slightly tapered contact layouts emitting at 910 nm The results of this thesis underline the potential of lateral-longitudinal non-uniform laser designs to increase selected aspects of device performance, including beam quality, spectral stability, and output power.

Download or read book High power GaAs based Diode Lasers with Novel Lateral Designs for Enhanced Brightness Threshold and Efficiency written by Mohamed Elattar and published by . This book was released on 2024 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Optimized Performance GaAs Based Diode Lasers Reliable 800 nm 125W Bars and 83 5 Efficient 975 nm Single Emitters written by and published by . This book was released on 2005 with total page 6 pages. Available in PDF, EPUB and Kindle. Book excerpt: GaAs-based high power diode bars produce wavelengths in the range of 780 to 980 nm and are widely used for pumping a broad range of rare earth doped solid-state lasers. As the markets for these laser systems mature, diode lasers that operate at higher power levels, greater overall efficiency, and higher reliability are in high demand. In this paper we report efficiencies of up to 83.5% in the 9xx-nm band, continuous wave power levels over 360-Watts in the 8xx-nm band, and reliable operation at 125-Watts.

Download or read book A deep ultraviolet laser light source by frequency doubling of GaN based external cavity diode laser radiation written by Norman Ruhnke and published by Cuvillier Verlag. This book was released on 2022-05-13 with total page 130 pages. Available in PDF, EPUB and Kindle. Book excerpt: A compact and portable laser light source emitting in the wavelength range between 210 nm and 230 nm would enable numerous applications outside of laboratory environments, such as sterilization and disinfection of medical equipment, water purification or gas and air analysis using absorption spectroscopy. Such a source is also highly attractive for the identification and quantification of proteins and biomolecules by means of laser-induced fluorescence or Raman spectroscopy. In this thesis, a novel concept to realize such a compact and portable laser light source with low power consumption and an emission around 222 nm is investigated. The developed concept is based on single-pass frequency doubling of a commercially available high-power GaN laser diode emitting in the blue spectral range. Due to the low frequency doubling conversion efficiencies in this wavelength range of about 10-4 W-1, a laser diode with high optical output power above 1 W is required as pump source. Moreover, it has to exhibit narrowband emission in the range of the acceptance bandwidth of the applied nonlinear BBO crystal. Since GaN-based high-power laser diodes typically show broad emission spectra of Δλ = 1…2 nm, stabilizing and narrowing their wavelength by using external wavelength-selective elements is investigated and presented for the first time. With the understanding for the novel concept gained in this work, a compact ultraviolet laser light source was realized. It has a power consumption of less than 10 W and is exceptionally robust due to its immoveable components. The demonstrated output power of 160 μW enables numerous industrial and everyday applications for which previous laser systems have been too complex and overly cost- and energy-intensive.

Download or read book Broad Area Laser Bars for 1 kW Emission written by Matthias M. Karow and published by Cuvillier Verlag. This book was released on 2022-06-27 with total page 143 pages. Available in PDF, EPUB and Kindle. Book excerpt: ndustrial laser systems for material processing applications rely on the availability of highly efficient, high-brightness diode lasers. GaAs-based broad-area laser bars play a vital role in such applications as pump sources for high-beam-quality solid-state lasers and, increasingly, as direct processing tools. This work studies 940 nm-laser bars emitting 1 kW optical power at room temperature, identifying those physical mechanisms that are currently limiting electrical-to-optical conversion efficiency as well as lateral beam quality. In the process, several diagnostic studies on bars with varied lateral-longitudinal design were carried out. The effects of technological measures for performance optimization were analyzed, yielding a new benchmark in efficiency and lateral divergence. The studies into altered resonator lengths of 4 and 6 mm as well as fill factors between 69 and 87 % successfully reduce both the voltage dropping across the device and power saturation at high currents, enabling 66 % efficiency at the operation point. Concrete measures how to reach efficiencies ≥70 % are presented thereafter, showing that doubling the efficiency value of the first 1 kW-demonstration in 2007 – amounting to 35 % – is in near reach. Investigation of the beam quality bases on a herein proposed and realized concept, in which the far field is resolved for each individual bar emitter. In this way, it is possible to determine how far-field profiles vary along the bar width and how much these variations affect the overall bar far-field. Further, such effects specific to bar structures can be separated into non-thermal and thermal influences. The effect of mechanical chip deformation (bar smile) as well as neighboring-emitter interaction has been investigated for the first time in active kW-class devices, yielding a lateral divergence as low as 8.8° at the operation point.

Download or read book Transceiver Technologies for Millimeter Wave Beam Steering Applications Band 71 written by Yi-Fan Tsao and published by Cuvillier Verlag. This book was released on 2022-11-08 with total page 147 pages. Available in PDF, EPUB and Kindle. Book excerpt: During the past years, wireless communication systems have been rapidly advancing to meet the high data-rate requirements of various emerging applications. However, the existing transceivers have typically been demonstrated using CMOS-compatible technologies that deliver a relatively low equivalent isotropic radiated power in a small unit cell. Moreover, the particular device characteristics are limiting the linear region for operation. Therefore, the main focus of this dissertation is to present and discuss new design methods for transceivers to solve these issues. To reduce the complexity of the transceiver module for further phased-array scaling, a low-noise power amplifier design approach is designed using a 0.15-μm GaN-on-SiC high-electron mobility transistor technology (HEMT). Utilizing a traded off interstage matching topology between loss and bandwidth, the conversion loss induced by the matching network could be effectively reduced. A stacked-FET configuration was adopted to enhance the power handling of the RF switch. Further improvement on the isolation bandwidth was investigated using theoretical analysis on the intrinsic effect of the passive HEMTs. With the successful implementation of the RF front-end circuits, transceiver modules were integrated on Rogers RO3010 substrate. The planar dual exponentially tapered slot antenna phased-array system showed a compact size with simple biasing network compared to the conventional transceiver approach. The presented T/R module was characterized with an over-the-air test at a distance of 1 m, overcoming the free space path loss of 64 dB. It also shows a high flexibility for further integration with a larger number of array systems, which is very promising for future 5G communication systems.

Download or read book Realization of High Power Diode Lasers with Extremely Narrow Vertical Divergence written by Agnieszka Pietrzak and published by Cuvillier Verlag. This book was released on 2012-04-18 with total page 144 pages. Available in PDF, EPUB and Kindle. Book excerpt: The doctoral thesis deals with high power InGaAs/GaAsP/AlGaAs quantum well diode lasers grown on a GaAs substrate with emission wavelengths in the range of 1050 nm – 1150 nm. The objective of this thesis is the development of diode lasers with extremely narrow vertical laser beam divergence without any resulting decrease in the optical output power compared to current state of the art devices. The work is focused on the design of the internal laser structure (epitaxial structure), with the goal of optical mode expansion (thus reduction of the beam divergence), and the experimental investigation of the electro-optical properties of the processed laser devices. Diagnosis of the factors limiting the performance is also performed. The optical mode expansion is realized by increasing the thickness of the waveguide layers. Structures with a very thick optical cavity are named in this work as Super Large Optical Cavity structures (SLOC). The vertical optical mode is modeled by solving the one-dimensional waveguide equation, and the far-field profiles are obtained from the Fourier transform of the electrical field at the laser facet (near-field). Calculations are performed by using the software tool QIP. The electro-optical properties (such as vertical electrical carrier transport and power-voltagecurrent characteristics, without self-heating effect) are simulated using the WIAS-TeSCA software. Both software tools are described in this thesis. The lasers chips, grown by means of MOVPE and processed as broad area single emitters, are experimentally tested under three measurement conditions. First, uncoated and unmounted laser chips with various lengths are characterized under pulsed operation (1.5 μs, 5 kHz) in order to obtain the internal parameters of the laser structure. In the second part of the laser characterization, the facet-coated and mounted devices with large (4 - 8 mm long) Fabry-Perot resonators are tested under quasi-continuous wave operation (500 μs, 20 Hz). Finally, these devices are also tested under ‘zero-heat’ conditions (300 ns pulse duration, 1 kHz repetition rate). The ‘zero-heat’ test is performed in order to investigate the factors, other than overheating of the device, that limit the maximum output power. All measurements are performed at a heat-sink temperature of 25°C. The measurement techniques used to characterize the electro-optical properties of the laser and the laser beam properties are also described. More specifically, the influence of the material composition and the thickness of the waveguide layers on the vertical beam divergence angle (perpendicular to the epitaxial structure) and on the electro-optical properties of the laser is discussed. It is shown that, due to the large cross section of the investigated laser chips, catastrophic optical mirror damage (COMD) is strongly reduced and that one of the major factors limiting the maximum optical power of the discussed diode lasers is weak carrier confinement in the active region leading to enhanced carrier and optical losses due to carrier accumulation in the thick waveguide. The reason for the vertical carrier leakage is a low effective barrier between the quantum well and the GaAs waveguide. Moreover, it is shown that the carrier confinement in the active region can be strengthened in three ways. Firstly, the QW depth is increased for lasers emitting at longer wavelength (here ~ 1130 nm). Secondly, utilizing a higher number of QWs lowers the threshold carrier density per QW. In this case, the electron Fermi-level shifts towards lower energies for lower threshold currents and thus the effective barrier heights are increased. Thirdly, in lasers emitting especially at wavelengths shorter than 1130 nm (around 1064 nm, a wavelength commercially interesting) the quantum wells are shallower and thus the effective barrier is lower. It is shown that AlGaAs waveguides are required to improve the carrier confinement. The AlGaAs alloys provide higher conduction and lower valence band edge energies of the bulk material. Consequently, the potential barrier against carrier escape from the QW to the waveguide is increased. Considering the mode expansion in the SLOC structures, it is shown, in simulation and experimentally, that the multi-quantum well active region, due to its high average refractive index, contributes significantly to the guiding of the modes. The optical mode is stronger confined in active regions with a higher number of quantum wells as well as in structures based on AlGaAs waveguides which are characterized by a lower refractive index compared to GaAs material. The increased mode confinement leads to a reduced equivalent vertical spot-size and results in a wider divergence angle of the laser beam. Moreover, by increasing the thickness of the waveguide layers the active region acts more and more as a waveguide itself thus preventing a further narrowing of the vertical far-field. As a new finding, it is presented that the introduction of low-refractive index quantum barriers (LIQB), enclosing the high-refractive index quantum wells, lowers the average refractive index of the multi-quantum well active region and thus reduces the beam divergence (the invention is content of a German Patent Application DEA102009024945). Through systematic model-based experimental investigations of a series of laser diode structures, the vertical beam divergence was reduced from 19° to 8.6° at full width at half maximum (FWHM) and from 30° to 15°, at 95% power content. The achieved vertical farfield angle is smaller, by a factor of ~3, than state-of-the-art laser devices. The 8 mm long and 200 μm wide single emitters based on the investigated SLOC structures deliver more than 30 W peak-power in quasi-continuous wave mode. The large equivalent spot-size together with the facet passivation prevent COMD failure and the maximum measured power is limited due to the overheating of the device. Moreover, a 4 mm long and 200 μm wide single emitter tested under ‘zero-heat’ condition delivers 124 W power. The maximal measured power was limited by the current supply.

Download or read book Two step MOVPE in situ etching and buried implantation applications to the realization of GaAs laser diodes written by Pietro della Casa and published by Cuvillier Verlag. This book was released on 2021-03-25 with total page 250 pages. Available in PDF, EPUB and Kindle. Book excerpt: This work is about two-step epitaxial growth using metalorganic vapor-phase epitaxy (MOVPE) for the realization of edge-emitting near-infrared laser diodes. The fabricated gallium arsenide-based devices fall into two categories: high-power lasers (watt range, multimodal) and tunable lasers (milliwatt range, monomodal). Common to both cases is that surface contamination – particularly that due to oxygen – needs to be removed before regrowth. Thus, in-situ etching with carbon tetrabromide (CBr4) is first studied. The experimental results include kinetic data, the effects of different etching conditions as well as substrate characteristics, and the effectiveness in reducing surface contamination. These investigations pave the way to devices based on 2-step epitaxy combined with in-situ etching. Correspondingly, thermally-tuned SG-DBR lasers operating around 975 nm have been successfully realized, obtaining a tuning range of 21 nm. In addition, the possibility of using electronic tuning in similar devices has been explored. High-power broad-area lasers have also been realized, using two-step epitaxy combined with ex-situ and in-situ etching, to create a buried, shallow “mesa” containing the active zone. This approach allows introducing lateral electrical and optical confinement, and – simultaneously – non-absorbing mirrors at the laser facets. Additionally, a different strategy to create a buried current aperture is presented, which is based on ion implantation followed by epitaxial regrowth. This enables to improve device performance and simultaneously introduce non-absorbing mirrors at the facets with correspondingly increased reliability.

Download or read book AlN base layers for UV LEDs written by Sebastian Walde and published by Cuvillier Verlag. This book was released on 2021-06-22 with total page 156 pages. Available in PDF, EPUB and Kindle. Book excerpt: To enable the fabrication of high performance ultraviolet (UV) light-emitting diodes (LEDs) this work aims at improving the quality of AlN base layers on sapphire substrates. The main issues for UV LEDs are still a limited internal quantum efficiency due to a high amount of threading dislocations along with a limited light extraction efficiency due to total internal reflection at the AlN/sapphire interface. Therefore, high-temperature annealing of AlN/sapphire layers and growth on nanopatterned sapphire substrates were comprehensively investigated. High-temperature annealing was applied to AlN layers of different strain and thickness grown by metalorganic vapour phase epitaxy (MOVPE). The threading dislocation density could be successfully reduced by more than one order of magnitude down to 6 × 108 cm-2. Wave optical simulations of UV LEDs on nanopatterned sapphire substrates (NPSS) were conducted and showed a potential increase in light extraction efficiency compared to a planar substrate. The optimized MOVPE growth process on sapphire nanopillars and sapphire nanoholes resulted in a fully coalesced and atomically smooth AlN surface. The threading dislocation density was reduced to 1 ×109 cm-2 for AlN on both nanopillars and nanoholes. UVC LEDs emitting at 265 nm wavelength were grown on top of the developed templates. Increased internal efficiency was obtained by reduced dislocation density and more efficient light extraction was achieved on NPSS in case of a transparent heterostructure and reflective contacts. Thus, the developed templates yield considerable improvement in light output compared to conventional templates.

Download or read book Efficient Beam Shaping of Linear High Power Diode Lasers by Use of Micro Optics written by and published by . This book was released on with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: We have designed, fabricated, and characterized a micro-optical beam-shaping device that is intended to optimize the coupling of an incoherent, linearly extended high-power diode laser into a multimode fiber. The device uses two aligned diffractive optical elements (DOEs) in combination with conventional optics. With a first prototype, we achieved an overall efficiency of 28%. Straightforward improvements, such as antireflective coatings and the use of gray-tone elements, are expected to lead to an efficiency of approximately 50%. The device is compact, and its fabrication is suited for mass production at low cost. This micro-optical device, used in a range-finder measurement system, will extend the measurement range. In addition to the direct laser writing technique, which was used for fabrication of the DOEs of the prototype, we applied two other technologies for the fabrication of the micro-optical elements and compared their performance. The technologies were multiple-projection photolithography in combination with reactive-ion etching in fused silica and high-energy beam-sensitive glass gray-tone lithography in photoresist. We found that refractive-type elements (gray tone) yield better efficiency for large deflection angles, whereas diffractive elements (multilevel or laser written) give intrinsically accurate deflection angles.

Download or read book Advances In Semiconductor Lasers And Applications To Optoelectronics Ijhses Vol 9 No 4 written by Mitra Dutta and published by World Scientific. This book was released on 2000-06-21 with total page 447 pages. Available in PDF, EPUB and Kindle. Book excerpt: Foreword by Charles H Townes This volume includes highlights of the theories underlying the essential phenomena occurring in novel semiconductor lasers as well as the principles of operation of selected heterostructure lasers. To understand scattering processes in heterostructure lasers and related optoelectronic devices, it is essential to consider the role of dimensional confinement of charge carriers as well as acoustical and optical phonons in quantum structures. Indeed, it is important to consider the confinement of both phonons and carriers in the design and modeling of novel semiconductor lasers such as the tunnel injection laser, quantum well intersubband lasers, and quantum dot lasers. The full exploitation of dimensional confinement leads to the exciting new capability of scattering time engineering in novel semiconductor lasers.As a result of continuing advances in techniques for growing quantum heterostructures, recent developments are likely to be followed in coming years by many more advances in semiconductor lasers and optoelectronics. As our understanding of these devices and the ability to fabricate them grow, so does our need for more sophisticated theories and simulation methods bridging the gap between quantum and classical transport.

Download or read book Diode Lasers and Photonic Integrated Circuits written by Larry A. Coldren and published by John Wiley & Sons. This book was released on 2012-03-02 with total page 752 pages. Available in PDF, EPUB and Kindle. Book excerpt: Diode Lasers and Photonic Integrated Circuits, Second Edition provides a comprehensive treatment of optical communication technology, its principles and theory, treating students as well as experienced engineers to an in-depth exploration of this field. Diode lasers are still of significant importance in the areas of optical communication, storage, and sensing. Using the the same well received theoretical foundations of the first edition, the Second Edition now introduces timely updates in the technology and in focus of the book. After 15 years of development in the field, this book will offer brand new and updated material on GaN-based and quantum-dot lasers, photonic IC technology, detectors, modulators and SOAs, DVDs and storage, eye diagrams and BER concepts, and DFB lasers. Appendices will also be expanded to include quantum-dot issues and more on the relation between spontaneous emission and gain.

Download or read book Novel InP Based High power and High efficiency Single Quantum Well SQW Active Region Diode Laser Emitting at 1 5 mu m written by and published by . This book was released on 2015 with total page 350 pages. Available in PDF, EPUB and Kindle. Book excerpt: This work summarizes the material and iterative device development approach for long-wavelength InP based diode lasers, emitting at 1.53 [mu]m, that have been optimized for maximum continuous-wave (CW) electrical-to-optical power conversion efficiency, so-called wallplug efficiency (WPE). Efficient electron and hole capture into a single-quantum-well (SQW) active region as well as suppression of electron and hole leakage out of the SQW result in high values for the internal differential efficiency: ~ 97% for long-cavity ([greater than or equal to] 2mm) uncoated-facet devices. The characteristic temperature of the slope efficiency, T1, reaches a high value of 323 K. Doping-level optimization over the entire transverse design and the use of the SQW result in low values for the internal loss coefficient: ~ 1.1 cm-1 for long-cavity ([greater than or equal to] 2 mm) uncoated-facet devices and ~ 1.5-2.0 cm-1 for short-cavity (1.5 mm) optimized facet-coated devices. In turn, a maximum CW WPE value of 50% is achieved at room temperature and ~ 1W output power from conductively-cooled 100 [mu]m-wide-aperture devices. The maximum CW power is 2.5 W. One beneficial byproduct of the CW-WPE maximization process is a large transverse spot size which, in turn, provides a very narrow transverse beam-width: 26° full width half maximum (FWHM).

Download or read book High Power Laser Diodes and Applications written by Luis Figueroa and published by . This book was released on 1988 with total page 240 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Selected Papers on Semiconductor Diode Lasers written by James J. Coleman and published by SPIE-International Society for Optical Engineering. This book was released on 1992 with total page 364 pages. Available in PDF, EPUB and Kindle. Book excerpt: