S. Deubert

InP based lasers and optical amplifiers with wire-/dot-like active regions

Long wavelength lasers and semiconductor optical amplifiers based on InAs quantum wire-/dot-like active regions were developed on InP substrates dedicated to cover the extended telecommunication wavelength range between 1.4 and 1.65 µm. In a brief overview different technological approaches will be discussed, while in the main part the current status and recent results of quantum-dash lasers are reported. This includes topics like dash formation and material growth, device performance of lasers and optical amplifiers, static and dynamic properties and fundamental material and device modelling. (Some figures in this article are in colour only in the electronic version)

Correlation between the gain profile and the temperature-induced shift in wavelength of quantum-dot lasers

The influence of several design parameters on the temperature stability of the emission wavelength of 980 nm GaInAs/(Al)GaAs quantum-dot lasers was studied. The results obtained agree well with a simplified model based on the inhomogeneously broadened transitions of a quantum-dot ensemble. Using this model, the optimum cavity design for a given gain function can be determined. Following this approach, quantum-dot lasers with low wavelength shifts of 0.16 nm/K were realized, which is only half the value of a typical GaInAs/(Al)GaAs quantum well laser.

Improved performance of MBE grown quantum-dot lasers with asymmetric dots in a well design emitting near 1.3 μm

Quantum dots emitting in the 1.3 /spl mu/m wavelength region can be realized following the dots in a well (DWELL) concept. By optimization of growth parameters as e.g. the V/III ratio and the design of the dot layers we could achieve a significant improvement of the dot characteristics as well as of the laser performance.

Time-resolved chirp in an InAs∕InP quantum-dash optical amplifier operating with 10Gbit∕s data

We describe time-resolved chirp measurements in InAs∕InP quantum-dash optical amplifiers operating at 1550 nm. We highlight the roles of gain saturation and of the saturating pulse duration relative to the gain recovery time. Using 10Gbit∕s data, we demonstrate a low transient α parameter of less than one which causes negative chirp at the leading edge and positive chirp during the trailing edge of the input pulse.

Gain, index variation, and linewidth-enhancement factor in 980-nm quantum-well and quantum-dot lasers

An experimental comparative study of the gain, index variation, and linewidth enhancement factor in 980-nm quantum-well (QW) and quantum-dot (QD) lasers structures, designed for high power applications, is presented. The gain spectra of the QW lasers at high injection level revealed three different transition energies, with a low linewidth enhancement factor (/spl sim/1.2) for E2HH2 transitions. Similar values for the linewidth enhancement factor, ranging between 2.5 and 4.5, were found for QW and QD devices, when comparing at similar values of the peak gain. This result is attributed to the contribution of excited state transitions in the measured QD lasers.

High brightness GaInAs/(Al)GaAs quantum-dot tapered lasers at 980 nm with high wavelength stability

High brightness (2 W with M2=3.4) is demonstrated at 980 nm using a gain-guided tapered GaInAs/(Al)GaAs quantum-dot laser. A remarkable low temperature shift (0.09 nm/K) of the emission wavelength is observed. Moreover, at 20 °C, the emission wavelength is quasiconstant as a function of the injected current.

Microthermography of diode lasers: The impact of light propagation on image formation

We analyze the effect of propagating infrared thermal radiation within a diode laser on its thermal image taken by a thermocamera. A ray-tracing analysis shows that this effect substantially influences image formation on a spatial scale of 10 μm, i.e., in the domain of microthermography. The main parameter affecting the thermal radiation spread in the semitransparent semiconductor structure is the free carrier concentration in the substrate, governing its absorption. Two applications are presented: a quantum dot laser and a quantum-well laser, where independent thermal models are developed using the finite element method (FEM). Our ray-tracing analysis verifies the FEM simulated temperature profiles by interlinking them to experimental temperature maps obtained through microthermography. This represents a versatile experimental method for extracting reliable bulk-temperature data from diode lasers on a microscopic scale.

Spectral and spatial single mode emission from a photonic crystal distributed feedback laser

The authors report on the fabrication and characterization of photonic crystal distributed feedback lasers, which are a generalization of distributed feedback and angled distributed feedback lasers. Spectral and spatial mode selection is provided by a two-dimensional, rectangular lattice of etched air holes that is tilted relatively to the cleaved facets. InGaAs∕AlGaAs laser layers emitting around 1μm were used for the fabrication of the devices. The laser emits at a single wavelength with a side mode suppression ratio of 50dB. The emission is concentrated in a narrow far field, indicating that a coherent mode is formed over the entire width of the device.

Photonic crystal waveguides with propagation losses in the 1 dB/mm range

High-quality photonic crystal waveguides have been fabricated in the InGaAsP∕InP and GaAs∕AlGaAs material systems aimed at the communication wavelengths of 1.55 and 1.31 μm. The waveguides consist of omitted rows of holes in a triangular lattice of air holes etched into the semiconductor heterostructures by electron cyclotron resonance reactive ion etching. Efficient waveguiding has been observed in optical transmission measurements, with waveguide losses ranging from 1.5dB∕mm for a waveguide with three missing row of holes (W3) to 0.2dB∕mm for seven missing rows (W7).

Modal Analysis of Large Spot Size, Low Output Beam Divergence Quantum-Dot Lasers

Large spot size ridge waveguide lasers utilizing a low modal gain single quantum dot layer emitting at 925 nm were designed and fabricated. Ridge waveguides with width <3 mum emit in a single transverse mode with a low transverse full-width at half-maximum divergence of 20deg. Wider ridges initially lase in the first-order transverse mode before collapsing to the fundamental mode. This characteristic is explained by a thermally induced increase in the refractive index of the waveguide core. All lasers operate in a single lateral mode