Johann Peter Reithmaier

Er doped nanocrystalline ZnO planar waveguide structures for 1.55 μm amplifier applications

Amplifying planar waveguide structures in Er-doped nanocrystalline II/VI semiconductor layer systems were developed by photolithography and wet chemical etching. 2 μm thick planar waveguides on glass substrates with lateral dimensions down to 5 μm with rectangular cross section were realized. By optical excitation a maximum gain of 82 cm−1 could be determined, which is sufficiently high to allow the design of compact planar amplifiers in this material system. The influence of a thermal sintering step on the gain spectrum and on the fluorescence lifetime has been investigated. By increasing the sintering temperature to 800 °C a consistent increase of gain and fluorescence lifetime was observed.

Transient electromagnetically induced transparency in self-assembled quantum dots

A coherent absorption dip in pump-probe experiment performed on a ten layer optically thin InGaAs/GaAs quantum dot (QD) structure has been observed. Measurements performed for different wavelengths ...

InAs/InP Quantum-Dash Lasers and Amplifiers

InAs quantum-dash structures fabricated by self-assembly growth techniques and based on compound semiconductors lattice matched to InP substrates were used to realize long wavelength lasers and amplifiers for telecom applications. With this new type of laser material special properties of low-dimensional electronic systems can be utilized for device applications, which allow to realize new device features not possible by conventional device designs. In this paper a brief overview is given about application oriented material and device research on this wire/dot-like material system by highlighting laser and high-speed optical amplifiers. Broadband laser material with a gain bandwidth of more than 300 nm could be obtained to cover the extended telecommunication wavelength range between 1.4 and 1.65 . High-speed optical amplifiers could be realized by using this quantum-dash laser material with unique device performance, like multiwavelength amplification without any cross-talk at data rates of 10 Gbit/s and pattern-free and noise reduced signal amplification at saturation condition demonstrated up to 40 Gbit/s.

High gain 1.55 μm diode lasers based on InAs quantum dot like active regions

InP diode lasers with InAs quantum dot (QD) like active regions emitting at 1.55 μm have been fabricated. The QDs were grown in an As2 mode, which reduces the degree of elongation of the nanospecies yielding nearly circular shapes. Lasers with four to six dot layers show low absorption αi<10 cm−1 and high modal gain Γg0 of 10 cm−1 per QD layer (QDL) and above. The high gain values are compatible with an inhomogeneous linewidth that is much narrower than in quantum dash material, which is the common nanoscale gain material in the InP system.

Strong exciton-photon coupling in semiconductor quantum dot systems

An overview is given on strong coupling phenomena in semiconductor quantum dot systems by utilizing cavity-enhanced light–matter interaction. The basic theory on strong coupling, the quantum dot and cavity fabrication technologies are reviewed while mainly three approaches are highlighted, i.e., micropillar, photonic crystal and microdisc cavities. The first and recent strong coupling experiments and the impact for future work are discussed.

Influence of the As2/As4 growth modes on the formation of quantum dot-like InAs islands grown on InAlGaAs/InP (100)

The formation process of InAs quantum dashes and quantum dots (QDs) grown on quaternary InAlGaAs surfaces lattice-matched to n-type InP(100) are investigated. A clear trend of the InAs to form dashes or dots depending on the species of supplied arsenic could be demonstrated. Using As4, elongated quantum dashes can be observed. Changing the growth mode to As2 molecules enables a shape transition from dashes to dome-shaped QDs. The dot ensembles exhibit improved photoluminescence (PL) intensity and linewidth over their elongated counterparts. With this basic concept, low temperature PL linewidths as low as 23 meV have been achieved.

High Speed 1.55 μm InAs/InGaAlAs/InP Quantum Dot Lasers

We report static and dynamic characteristics of InAs/InP quantum dot (QD) lasers emitting near 1.55 μm. The gain section was optimized for a high speed operation using a unique spatially resolved model. The measured modulation capability dependence on structural parameters (barrier width and the number of QD layers) is consistent with the model predictions. Short cavity lasers with a modal gain of more than 10 cm-1 per dot layer exhibit a small signal modulation bandwidth above 9 GHz and large signal modulation at up to 22 Gb/s with an on/off ratio of 3 dB.

Single-mode distributed feedback and microlasers based on quantum-dot gain material

Quantum-dot gain material fabricated by self-organized epitaxial growth on GaAs substrates is used for the realization of 980-nm and 1.3-/spl mu/m single-mode distributed feedback (DFB) lasers and edge-emitting microlasers. Quantum-dot specific properties such as low-threshold current, broad gain spectrum, and low-temperature sensitivity could be demonstrated on ridge waveguide and DFB lasers in comparison to quantum-well-based devices. 980-nm DFB lasers exhibit stable single-mode behavior from 20/spl deg/C up to 214/spl deg/C with threshold currents 1 mW was obtained for 30-/spl mu/m cavity length. Low-threshold currents of 4.4 mA could be obtained for 1.3-/spl mu/m emitting 400-/spl mu/m-long high-reflection coated ridge waveguide lasers. DFB lasers made from this material by laterally complex coupled feedback gratings show stable CW single-mode emission up to 80/spl deg/C with sidemode suppression ratios exceeding 40 dB.

Heterodyne pump probe measurements of nonlinear dynamics in an indium phosphide photonic crystal cavity

Using a sensitive two-color heterodyne pump-probe technique, we investigate the carrier dynamics of an InP photonic crystal nanocavity. The heterodyne technique provides unambiguous results for all wavelength configurations, including the degenerate case, which cannot be investigated with the widely used homodyne technique. A model based on coupled mode theory including two carrier distributions is introduced to account for the relaxation dynamics, which is assumed to be governed by both diffusion and recombination.

High-Speed Low-Noise InAs/InAlGaAs/InP 1.55-

We present the static and dynamic properties of InAs quantum-dot (QD) lasers emitting near 1.55 μm. The used laser material comprises four QD layers and exhibits a high modal gain of about 40 cm-1. The 340-μ.m-long lasers show a room temperature threshold current of 38 mA and a maximum output power of 16 mW. The small signal modulation response is highly damped and carrier transport limited with a moderate 3-dB bandwidth of 5 GHz. This is accompanied by a flat relative intensity noise spectrum at a low level of -150 dBc/Hz. Neverthe- less, the laser exhibits record large signal modulation capabilities for a 1.5-μ.m QD laser: 15 Gb/s with a 4-dB on/off ratio.