T. Kettler

1.24 μm InGaAs/GaAs quantum dot laser grown by metalorganic chemical vapor deposition using tertiarybutylarsine

Metalorganic chemical vapor deposition of GaAs-based laser diodes, using self-organized InGaAs quantum dots (QDs), emitting at >1.24 μm is demonstrated. The environment-friendly alternative precursor tertiarybutylarsine is used as a substitute for arsenic hydride. The active region contains ten closely stacked InGaAs QD layers embedded in a GaAs matrix. Lasing emission at such long wavelengths was achieved by overgrowing the In0.65Ga0.35As QDs with a thin In0.2Ga0.8As film. The application of an in situ annealing step leading to the evaporation of plastically relaxed defect clusters is shown to be decisive for the laser performance. A transparency current density of 7.2 A/cm2 per QD layer and an internal quantum efficiency of 75% were achieved at room temperature.

Ultrahigh-brightness 850 nm GaAs/AlGaAs photonic crystal laser diodes

One-dimensional photonic crystal lasers emitting in the 850 nm range show high internal quantum efficiencies of 93% and very narrow vertical beam divergence of 7.1° (full width at half maximum). 50 μm broad area lasers with unpassivated facets exhibit a high total output power of nearly 20 W in pulsed mode with a divergence of 9.5°×11.3° leading to a record brightness of 3×108 W cm−2 sr−1, being presently the best value ever reported for a single broad area laser diode. 100 μm broad devices with unpassivated facets show continuous wave operation with an output power of 1.9 W.

Single mode cw operation of 658nm AlGaInP lasers based on longitudinal photonic band gap crystal

GaInP–AlGaInP lasers with broad waveguide based on a longitudinal photonic band gap crystal have been studied. Lasers with 10μm stripe width exhibit single transverse mode operation. The vertical beam divergence is about 8° and is insensitive to the drive current. The aspect ratio is ∼2:1. The quality factor for the lateral beam M2 is less than 2 in single mode regime under pulsed excitation. The total maximum continuous wave output power in the single mode regime at 20°C is more than 115mW (for high reflection/antireflection facet coatings), indicating a dramatic reduction in the catastrophic optical mirror damage problem.

High-Power Low-Beam Divergence Edge-Emitting Semiconductor Lasers with 1- and 2-D Photonic Bandgap Crystal Waveguide

We report on edge-emitting lasers based on the 1- and 2-D longitudinal photonic bandgap crystal concept. The longitudinal photonic bandgap crystal (PBC) design allows a robust and controllable extension of the fundamental mode over a thick multilayer waveguide to obtain a very large vertical mode spot size and a narrow vertical beam divergence.

Metamorphic 1.5 µm-range quantum dot lasers on a GaAs substrate

1.5 µm-range laser diodes based on InAs/InGaAs quantum dots (QDs) grown on metamorphic (In, Ga, Al)As layers, which were previously deposited on GaAs substrates using a defect reduction technique (DRT), are studied. More than 7 W total output power operation in the pulsed mode is shown in broad area lasers. It is shown that the narrow stripe lasers operate in the continuous wave (CW) and the single transverse mode at current densities up to 22 kA cm−2 without significant degradation. CW output power in excess of 220 mW at 10 °C heat sink temperature is demonstrated. 800 mW single-mode output power in the pulsed regime is obtained. It is also shown that the lasers demonstrate the absence of beam filamentation up to the highest current densities studied. First studies on the dynamics of the lasers show a modulation bandwidth of ~3 GHz, limited by device heating. Eye diagrams at 2.5 Gbit s−1 and room temperature (RT) have been performed. Aging tests demonstrate >800 h of CW operation at ~50 mW at 10 °C heat sink temperature and >200 h at 20 °C heat sink temperature without decrease in optical output power. The results indicate the high potential of metamorphic growth using the DRT for practical applications, such as 1500 nm GaAs vertical cavity surface emitting lasers (VCSELs).

Degradation-robust single mode continuous wave operation of 1.46μm metamorphic quantum dot lasers on GaAs substrate

Narrow ridge lasers of 1.5μm range based on InAs∕InGaAs quantum dots grown on metamorphic (In,Ga,Al)As layers deposited on GaAs substrates using defect reduction technique are studied. It is shown that the lasers operate continuous wave (cw) in a single transverse mode. Single-mode 800mW output power in the pulsed regime is obtained for a 6μm ridge width. The dynamic studies of the lasers show a modulation bandwidth of ∼3GHz. Aging tests demonstrate >800h of cw operation at ∼50mW at 10°C (60°C) and >200h at 20°C (70°C) heat sink (junction) temperature without noticeable degradation.

High-power high-brightness semiconductor lasers based on novel waveguide concepts

We have designed, fabricated and measured the performance of two types of edge emitting lasers with unconventional waveguides and lateral arrays thereof. Both designs provide high power and low divergence in the fast and the slow axis, and hence an increased brightness. The devices are extremely promising for new laser systems required for many scientific and commercial applications. In the first approach we use a broad photonic crystal waveguide with an embedded higher order mode filter, allowing us to expand the ground mode across the entire waveguide. A very narrow vertical far field of ~ 7° is resulting. 980 nm single mode lasers show in continuous wave operation more than 2 W, ηwp ~ 60%, M2 ~ 1.5, beam parameter product of 0.47 mm×mrad and a brightness ~ 1×108 Wsr-1cm-2 respectively. First results on coherent coupling of several lasers are presented. In the second approach we use leaky designs with feedback. The mode leaks from a conventional waveguide into a transparent substrate and reflects back, such that only one mode at a selected wavelength is enhanced and builds up, others are suppressed by interference. 1060 nm range devices demonstrate an extremely narrow vertical far field divergence of less than 1°.

1.9 W continuous-wave single transverse mode emission from 1060 nm edge-emitting lasers with vertically extended lasing area

High-brightness edge-emitting semiconductor lasers having a vertically extended waveguide structure emitting in the 1060 nm range are investigated. Ridge waveguide (RW) lasers with 9 μm stripe width and 2.64 mm cavity length yield highest to date single transverse mode output power for RW lasers in the 1060 nm range. The lasers provide 1.9 W single transverse mode optical power under continuous-wave (cw) operation with narrow beam divergences of 9° in lateral and 14° (full width at half maximum) in vertical direction. The beam quality factor M2 is less than 1.9 up to 1.9 W optical power. A maximum brightness of 72 MWcm−2sr−1 is obtained. 100 μm wide and 3 mm long unpassivated broad area lasers provide more than 9 W optical power in cw operation.

High Temperature Operation of 1060-nm High-Brightness Photonic Band Crystal Lasers With Very Low Astigmatism

Thermally stable and nearly astigmatism free 1060-nm high-brightness photonic band crystal lasers are presented. A thick asymmetric waveguide with an optimized doping profile is employed. The prominent mode-discrimination property of the structure yields highly stable laser beam characteristics (i.e., beam quality factor M2, astigmatism) regardless of operating current and temperatures up to 80 °C. Ridge waveguide lasers with 6-μm ridge width and 2.64-mm cavity length provide 1.8-W output power and 61-MW · cm-2 · sr-1 brightness in continuous-wave mode at T = 20 °C. Full width at half maximum beam divergence remains below 11° in lateral and 15° in vertical direction up to the highest output power. Output power decreases with increasing heat sink temperature, however, a still large value of 1.3 W is achieved at T = 80 °C. Excellent beam quality with both lateral and vertical M2 <; 1.9 is obtained across the full investigated operating range up to 80 °C heat sink temperature. Astigmatism varies only between 0.4 to 2 μm at all operating conditions.

Simulations of the optical properties of broad-area edge-emitting semiconductor lasers at 1060 nm based on the PBC laser concept

The design principles of multi-stripe edge-emitting lasers based on the photonic band crystal (PBC) laser concept are evaluated numerically. The concept is based on a waveguide with a thick quasi-periodic sequence of alternating high- and low-index layers allowing mode expansion across the whole layer sequence. Effective ways to filter out higher-order modes via control of the confinement and leakage are demonstrated as well as enhanced lateral mode selectivity of multi-stripe lasers by changing their etching profile. Thus, for proper epitaxial and lateral design PBC lasers have an enormous potential to provide high-power/brilliance single-mode radiation with broad-area output spot size and nearly circular narrow far-field pattern.