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Author: Publisher: ISBN: Category : Languages : en Pages : 96
Book Description
High-power operation of a simple non-planar index-guided quantum well heterostructure periodic laser array structure is described, in which lateral lasing is prevented in a manner that still allows for uniform and continuous front facet light emission. The compositional disordering and compensation effects of MeV oxygen implantation have been applied to form stripe geometry graded barrier quantum well heterostructure lasers. A new broad area as well as narrow stripe window laser structure is described, in which a nonabsorbing window region is formed in the vicinity of the mirror facets by utilizing a selectively etched substrate and the advantageous properties of uniform MOCVD growth on nonplanar substrates. The growth and characterization of strained layer InGaAs-GaAs heterostructure lasers by MOCVD has been addressed. Ethyldimethylindium has been shown to be suitable as a precursor for the growth of indium compounds. The results of time-zero characterization of strained-layer InxGa(1-x)As-GaAs quantum well heterostructure laser diodes with 70-A-thick wells and indium mole fractions between 0.08 and 0.42 are reported. High power, in-phase locked operation of a wide aperture array is reported in which the lateral lasing and amplified spontaneous emission, characteristic of wide aperture arrays, are suppressed by a nonplanar active region. The antiguiding behavior of InGaAs-GaAs strained layer lasers has been exploited for form multiple-element oxide-defined-stripe phase-locked high power long wavelength (y> 0.95 um) strained layer quantum well heterostructure diode arrays operating in the in-phase fundamental array mode.
Author: Publisher: ISBN: Category : Languages : en Pages : 96
Book Description
High-power operation of a simple non-planar index-guided quantum well heterostructure periodic laser array structure is described, in which lateral lasing is prevented in a manner that still allows for uniform and continuous front facet light emission. The compositional disordering and compensation effects of MeV oxygen implantation have been applied to form stripe geometry graded barrier quantum well heterostructure lasers. A new broad area as well as narrow stripe window laser structure is described, in which a nonabsorbing window region is formed in the vicinity of the mirror facets by utilizing a selectively etched substrate and the advantageous properties of uniform MOCVD growth on nonplanar substrates. The growth and characterization of strained layer InGaAs-GaAs heterostructure lasers by MOCVD has been addressed. Ethyldimethylindium has been shown to be suitable as a precursor for the growth of indium compounds. The results of time-zero characterization of strained-layer InxGa(1-x)As-GaAs quantum well heterostructure laser diodes with 70-A-thick wells and indium mole fractions between 0.08 and 0.42 are reported. High power, in-phase locked operation of a wide aperture array is reported in which the lateral lasing and amplified spontaneous emission, characteristic of wide aperture arrays, are suppressed by a nonplanar active region. The antiguiding behavior of InGaAs-GaAs strained layer lasers has been exploited for form multiple-element oxide-defined-stripe phase-locked high power long wavelength (y> 0.95 um) strained layer quantum well heterostructure diode arrays operating in the in-phase fundamental array mode.
Author: Geert Morthier Publisher: Artech House ISBN: 1608077012 Category : Technology & Engineering Languages : en Pages : 397
Book Description
Since the first edition of this book was published in 1997, the photonics landscape has evolved considerably and so has the role of distributed feedback (DFB) laser diodes. Although tunable laser diodes continue to be introduced in advanced optical communication systems, DFB laser diodes are still widely applied in many deployed systems. This also includes wavelength tunable DFB laser diodes and DFB laser diode arrays, usually integrated with intensity or phase modulators and semiconductor optical amplifiers. This valuable resource gives professionals a comprehensive description of the different effects that determine the behavior of a DFB laser diode. Special attention is given to two new chapters on wavelength tunable DFB laser diodes and bistable and unstable DFB laser diodes. Among many other updates throughout the reference, semi-conductor and electromagnetic professionals are also provided two new appendices. This book fully covers the underlying theory, commercial applications, necessary design criteria, and future direction of this technology.
Author: Thorben Kaul Publisher: Cuvillier Verlag ISBN: 3736963963 Category : Science Languages : en Pages : 136
Book Description
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.
Author: Agnieszka Pietrzak Publisher: Cuvillier Verlag ISBN: 3736940661 Category : Science Languages : en Pages : 144
Book Description
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.
Author: Andreas Jechow Publisher: Universitätsverlag Potsdam ISBN: 3869560312 Category : Science Languages : en Pages : 152
Book Description
A huge number of applications require coherent radiation in the visible spectral range. Since diode lasers are very compact and efficient light sources, there exists a great interest to cover these applications with diode laser emission. Despite modern band gap engineering not all wavelengths can be accessed with diode laser radiation. Especially in the visible spectral range between 480 nm and 630 nm no emission from diode lasers is available, yet. Nonlinear frequency conversion of near-infrared radiation is a common way to generate coherent emission in the visible spectral range. However, radiation with extraordinary spatial temporal and spectral quality is required to pump frequency conversion. Broad area (BA) diode lasers are reliable high power light sources in the near-infrared spectral range. They belong to the most efficient coherent light sources with electro-optical efficiencies of more than 70%. Standard BA lasers are not suitable as pump lasers for frequency conversion because of their poor beam quality and spectral properties. For this purpose, tapered lasers and diode lasers with Bragg gratings are utilized. However, these new diode laser structures demand for additional manufacturing and assembling steps that makes their processing challenging and expensive. An alternative to BA diode lasers is the stripe-array architecture. The emitting area of a stripe-array diode laser is comparable to a BA device and the manufacturing of these arrays requires only one additional process step. Such a stripe-array consists of several narrow striped emitters realized with close proximity. Due to the overlap of the fields of neighboring emitters or the presence of leaky waves, a strong coupling between the emitters exists. As a consequence, the emission of such an array is characterized by a so called supermode. However, for the free running stripe-array mode competition between several supermodes occurs because of the lack of wavelength stabilization. This leads to power fluctuations, spectral instabilities and poor beam quality. Thus, it was necessary to study the emission properties of those stripe-arrays to find new concepts to realize an external synchronization of the emitters. The aim was to achieve stable longitudinal and transversal single mode operation with high output powers giving a brightness sufficient for efficient nonlinear frequency conversion. For this purpose a comprehensive analysis of the stripe-array devices was done here. The physical effects that are the origin of the emission characteristics were investigated theoretically and experimentally. In this context numerical models could be verified and extended. A good agreement between simulation and experiment was observed. One way to stabilize a specific supermode of an array is to operate it in an external cavity. Based on mathematical simulations and experimental work, it was possible to design novel external cavities to select a specific supermode and stabilize all emitters of the array at the same wavelength. This resulted in stable emission with 1 W output power, a narrow bandwidth in the range of 2 MHz and a very good beam quality with M²<1.5. This is a new level of brightness and brilliance compared to other BA and stripe-array diode laser systems. The emission from this external cavity diode laser (ECDL) satisfied the requirements for nonlinear frequency conversion. Furthermore, a huge improvement to existing concepts was made. In the next step newly available periodically poled crystals were used for second harmonic generation (SHG) in single pass setups. With the stripe-array ECDL as pump source, more than 140 mW of coherent radiation at 488 nm could be generated with a very high opto-optical conversion efficiency. The generated blue light had very good transversal and longitudinal properties and could be used to generate biphotons by parametric down-conversion. This was feasible because of the improvement made with the infrared stripe-array diode lasers due to the development of new physical concepts.
Author: University of Illinois at Urbana-Champaign. Office of Engineering Publications Publisher: ISBN: Category : Engineering Languages : en Pages : 380
Author: Nils William Carlson Publisher: Springer ISBN: Category : Semiconductor lasers Languages : en Pages : 424
Book Description
Over the last two decades, the search for a compact, high-power semiconductor source has produced many designs and concepts for monolithic diode-laser arrays and optical amplifiers. However, only a few design approaches have emerged with the potential for producing high-power, high-brightness monolithic sources. Although semiconductor-diode lasers are the most compact, highest gain and most efficient laser sources, challenges remain in developing structures that will produce high-quality, diffraction-limited output beams. This book presents and analyzes the results of work performed over the last twenty years in the development of high-brightness diode-laser arrays.
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Author: Geert Morthier
Author: Thorben Kaul
Author: Agnieszka Pietrzak
Author: Andreas Jechow
Author: University of Illinois at Urbana-Champaign. Office of Engineering Publications
Author: Wei Hsin
Author: Nils William Carlson
Author: J. C. Connolly