M. van der Poel

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)

Ultrafast gain dynamics in quantum-dot amplifiers: theoretical analysis and experimental investigations

Ultrafast gain dynamics in an optical amplifier with an active layer of self-organized quantum dots (QDs) emitting near 1.3 /spl mu/m is characterized experimentally in a pump-probe experiment and modeled theoretically on the basis of QD Maxwell-Bloch equations. Experiment and theory are in good agreement and show ultrafast subpicoseconds gain recovery followed by a slower 5 ps recovery. This behavior is found to be mainly caused by longitudinal optical phonon scattering and strongly dependents on electronic structure and confinement energy of the dots. A low amplitude-phase coupling (/spl alpha/ factor) is theoretically predicted and demonstrated in the experiments. The fundamental analysis reveals the underlying physical processes and indicates limitations to QD-based devices.

Ultrafast gain and index dynamics of quantum dash structures emitting at 1.55μm

The authors systematically characterize the ultrafast gain and index recovery of a quantum dash semiconductor optical amplifier after it has amplified a strong femtosecond pulse. The results show a recovery dominated by a fast time constant of 1.4ps with an ultimate recovery taking place on a 150ps time scale. The results are distinctly different from the recovery of quantum dot amplifiers and reflect the special density of states of the quantum-wire-like dashes.

Properties of InGaAs quantum dot saturable absorbers in monolithic mode-locked lasers

Saturable absorbers properties are characterised in monolithic mode-locked InGaAs quantum dot lasers. We analyse the impact of weak quantum confined Stark effect, fast absorber recovery time and low absorber saturation power on the mode-locking performance.

Atomic scattering in the diffraction limit: electron transfer in keV Li+–Na(3s, 3p) collisions

We measure angle differential cross sections (DCS) in Li+ + Na → Li + Na+ electron transfer collisions in the 2.7–24 keV energy range. We do this with a newly constructed apparatus which combines the experimental technique of cold target recoil ion momentum spectroscopy with a laser-cooled target. This setup yields a momentum resolution of 0.12 au, an order of magnitude better angular resolution than previous measurements on this system. This enables us to clearly resolve Fraunhofer-type diffraction patterns in the angle DCS. In particular, the angular width of the ring structure is given by the ratio of the de Broglie wavelength λdB = 150 fm at a velocity v = 0.20 au and the effective atomic diameter for electron capture 2R = 20 au. Parallel AO and MO semiclassical coupled-channel calculations of the Na(3s, 3p) → Li(2s, 2p) state-to-state collision amplitudes have been performed, and quantum scattering amplitudes are derived by the eikonal method. The resulting angle-differential electron transfer cross sections and their diffraction patterns agree with the experimental level-to-level results over most scattering angles in the energy range.

Pulse Delay Measurements in Cascaded Quantum-Well Gain and Absorber Media

A tunable delay of ultrashort laser pulses in semiconductor waveguide structures are demonstrated in cascaded amplifying and absorbing semiconductor waveguides and compared with a single sectioned waveguide. The single sectioned waveguide shows a low transmission at the maximum delay. This is effectively avoided with the cascaded waveguide configuration, where it is demonstrated viable achieving a net pulse delay while maintaining a transmission of unity. For both types of devices, a pulse advancement is observed, at large pulse energies, that existing models are unable to account for.

Slow Light in Semiconductor Waveguides

We describe recent experiments demonstrating slow-down of light in a semiconductor waveguide at gigahertz frequencies. The results are explained by a simple model, which is used to analyze the potential and limitations of the technique.

Experimental demonstration and theoretical analysis of slow light in a semiconductor waveguide at GHz frequencies

Experimental demonstration and theoretical analysis of slow light in a semiconductor waveguide at GHz frequencies slow-down of light by a factor of two in a semiconductor waveguide at room temperature with a bandwidth of 16.7 GHz using the effect of coherent pulsations of the carrier density. The achievable delay is shown to be limited by the short lifetime. The maximum time delay observed reflects an approximately two-fold increase of the group refractive index, corresponding to a time delay of approximately 20 % of the carrier (population) lifetime. The experimental observations are well-explained by a model accounting for the absorption saturation in the waveguide, when using a lifetime that depends on the reverse bias.

Carrier dynamics and slow light in semiconductor nanostructures

We give an overview of slow and fast light effects in semiconductor waveguides. Experimental and theoretical results are presented, emphasizing the physics as well as the limitations imposed by the carrier dynamical processes.

Pulse delay and speed-up of ultra fast pulses in an absorbing quantum well medium

Slow down and speed-up of 180 fs pulses in an absorbing semiconductor beyond the existing models is observed. Cascading gain and absorbing sections give us significant temporal pulse shifting at almost constant output pulse energy.