In the past years vertical-cavity-surface-emitting-lasers (VCSELs) found great interest for many applications in optoelectronic systems. Disadvantages, however, are the frequently reported high series resistances, arising from current injection over the multiple heterointerfaces of the distributed bragg reflectors (DBRs). We circumvent this problem by contacting both cladding layers of the pin-double heterostructure directly. The undoped active region consists of three 80 /spl Aring/ InGaAs strained quantum wells separated by GaAs spacers.< >
Spatial-hole-burning as a limit to the continuous-wave (CW) output power of GaAs-based diode lasers is experimentally studied. For 90 μm stripe lasers with 6 mm resonator length and 0.8% front facet reflectivity, spontaneous emission (SE) intensity data show that the carrier density in the device center rises rapidly at the rear facet with bias and falls at the front, consistent with simulation. At the front, the carrier density at the edge of the laser stripe also rises rapidly with bias (lateral carrier accumulation, LCA), consistent with previous observations of increased local current flow. Devices with 20% front facet reflectivity for a flat longitudinal optical field profile show smaller variation in the local carrier density. Weak variation is seen in the carrier density outside the stripe; hence, current spreading is not a power limit. SE wavelength data show higher temperatures at the front with a twofold higher increase in temperature for 0.8% than for 20% front facet. The increased front temperature likely triggers lateral spatial-hole-burning and LCA in this region, limiting power. Finally, pulsed threshold current is more strongly temperature dependent for devices with 0.8% than 20% front facets, attributed to the higher rear facet carrier density. The temperature dependence of slope in pulsed is comparable for both devices at low bias but is more rapid for 0.8% at 20 A, likely due to non-clamping at the back. The temperature dependence of slope for CW is strong with 0.8% facets, likely due to the high temperature and LCA at the front but reduced for 20% facets.
Tunable diode lasers are essential components in various optical systems. The authors present a concept and simulations of a four-section, widely tunable GaAs-based sampled-grating (SG) distributed-Bragg reflector (DBR) laser emitting at 976 nm. This work includes the design approach of the SG reflectors and the simulation of the behaviour of the modes in the active cavity during the wavelength tuning process. Parameters such as the lasing wavelength, threshold current and the gain of the lasing and of the adjacent side modes during the tuning are presented. The numerical results presented suggest a tunability of at least 17 nm, with a threshold current change of only 2.5 mA and single-mode operation over the entire tuning range, without the need of simultaneous adjustments of the phase section. Finally, the authors present early experimental results of a developed GaAs-based vertical structure, providing a high coupling coefficient of , thus suitable for implementation of an SG-DBR laser design.
670 nm broad area diode lasers with an output power of 5.5 W and a conversion efficiency of 40% will be presented. Reliable operation over 1800 h at more than 1 W will be demonstrated.
Progress in fabrication of packaged discrete L- and X-band power AlGaN/GaN HFETs is presented. By exploiting typical GaN HFET related features such as improved linearity, power density, gain and broad band capability the devices allow for novel architectures for base stations in mobile communications and for space applications. Highlights to be presented are L-band power bar devices designed for continuous wave (cw) operation delivering an cw output power of 30 W and 100 W with 20 dB and 14 dB linear gain respectively. The architecture of these devices is based on novel gate "feed plate" structures. Furthermore discrete, hermetically packaged X-band devices for space based SSPAs in the power range of 10 W (continuous wave) at 8 GHz are presented
We present micro-integrated diode laser modules operating at wavelengths of 767 and 780 nm for cold quantum gas experiments on potassium and rubidium. The master-oscillator-power-amplifier concept provides both narrow linewidth emission and high optical output power. With a linewidth (10 μs) below 1 MHz and an output power of up to 3 W, these modules are specifically suited for quantum optics experiments and feature the robustness required for operation at a drop tower or on-board a sounding rocket. This technology development hence paves the way toward precision quantum optics experiments in space.
Research into power-scaling in GaAs-based broad-area lasers is summarized, focusing on 940nm single emitters, increasing power by combining triply-asymmetric high-gain epitaxial designs with regrown lateral blocking. In parallel, power is increased by transitioning more laser types to highly asymmetric designs, illustrated with 970nm grating-stabilized bars.
The impact of optical feedback on the emission properties of edge-emitting diode lasers is crucial for their use in various applications with unavoidable optical feedback. A hybrid master oscillator power amplifier (MOPA) concept based on a low-power laser (MO) and a tapered amplifier (TPA) is well suited for those applications. The MOPA offers the ability to mechanically separate the MO from the TPA, which allows to shield the MO against possible optical feedback from the TPA by using an optical isolator. However, the feedback emitted from the TPA towards the MO has not been investigated in detail yet. In addition to the feedback from the TPA the MOPA as a whole can be subject to external feedback. Depending on the beam path in the respective application, feedback ratios in the range from 10−4 to 10−2 to the TPA may occur. The optical feedback coupled to the TPA is expected to be also amplified in the TPA which increases the feedback towards the MO dramatically. Therefore, the propagation of feedback light through the TPA and its emission characteristics towards the MO have to be studied in detail. A beam propagation method including a model for the charge carriers and a fast thermal solver utilizing a Green's function approach is used to simulate feedback propagation inside the TPA. A description of the model, with focus on the thermal solver, will be presented as well as a comparison to measurements. The results allow to optimize MOPAs with respect to feedback more accurately.
Laser diode benches (LDBs) with lasing wavelength of 808 nm were developed, manufactured and endurance-tested for utilization as pump lasers for the Nd:YAG oscillator in the climate satellite MERLIN. The LDBs combine customized TE-polarized GaAs-based 5-mm minibars with fast axis collimation lenses to produce a reliable, space qualified component at optical power of 63 W per minibar. Accelerated life tests of 20 LDBs are presented. Except for a small increase in threshold current, no wear out in operating current or sudden failures were observed, and reliable operation over the full mission time of >4 gigashots was confirmed. The electro-optical characteristics remain in the specified ranges after exposure to the total operational load of the mission.
