The propagation of waves in crystals is known to be strongly affected by the choice and the spatial distribution of inclusions in a matrix. We argue herewith that in-contact, impermeable inclusions lead to extremely wide band gaps for all 2D Bravais lattices. Contact points entail constrictions that efficiently slow wave propagation and lead to strongly flattened bands. A numerical demonstration is provided for a generic Helmholtz equation that is applicable to electromagnetic, acoustic, elastic, or water waves alike. Experiments conducted on square and hexagonal photonic crystals composed of touching copper tubes reveal that waves of certain radio frequencies quite remarkably traverse the minute gaps within the metallic framework, thereby confirming the theoretical predictions, including the presence of deeply subwavelength Bragg band gaps.

In this work, we present an artwork that embodies the by far largest photonic crystal ever published, operating at radio frequencies. We demonstrate both theoretically and experimentally the existence of band gaps. While photonic crystals are typically investigated on the nano and micro scale, our aim is to present not only a remarkable example of art with scientific relevance but also to highlight the potential for large-scale applications that have so far been underrated.

Optical components from nanostructured materials such as photonic crystals have gained special interest for applications in elementary optical and photonic components such as waveguides, scatterers, attenuators and others for optoelectronic systems and components in quantum computation. Robust manufacturing concepts require the handling of systematic and erratic fabrication tolerances. Beyond that, the concept of ‘tailored disorder’ has reached the science and engineering field in which the deviation from order in the nanostructured morphology is intentionally employed for tailoring optical properties. In our work, we propose a theoretical approach based on first principles of electromagnetic wave propagation to study the influence of a tuned disorder of the nanostructured materials on the optical properties of various model components. Our results show that intentional inclusion of disorder can result in a particular spectral tuning of optical reflection and transmission properties, respectively.

Experimental results from literature show equidistant energy levels in thin Bi films on surfaces, suggesting a harmonic oscillator description. Yet this conclusion is by no means imperative, especially considering that any measurement only yields energy levels in a finite range and with a nonzero uncertainty. Within this study we review isospectral potentials from the literature and investigate the applicability of the harmonic oscillator hypothesis to recent measurements. First, we describe experimental results from literature by a harmonic oscillator model, obtaining a realistic size and depth of the resulting quantum well. Second, we use the shift-operator approach to calculate anharmonic non-polynomial potentials producing (partly) equidistant spectra. We discuss different potential types and interpret the possible modeling applications. Finally, by applying nth order perturbation theory we show that exactly equidistant eigenenergies cannot be achieved by polynomial potentials, except by the harmonic oscillator potential. In summary, we aim to give an overview over which conclusions may be drawn from the experimental determination of energy levels and which may not.

We present an advanced model for the simulation of laser dynamics based on the microscopic many-particle equations of motion and going beyond the often used rate equation model. Our model is used to simulate (Al,In)GaN based edge-emitting laser diodes showing longitudinal mode-competition phenomena which are responsible for the effect of mode hopping, i.e. the modes are switched on and off causing mode rolling from higher to lower frequencies. We show that the effect is caused by beating vibrations of the carrier density which result in an asymmetric coupling term between neighboring modes. Here, the results agree with the case where we assume that the coupling of two modes is independent of all the other modes, as long as the mode frequencies are not equidistant. If the mode frequencies are equidistant, the mode dynamics depend strongly on the initial phases and the initial noise.

In this contribution we are analyzing the properties of a gain structure based on seventeen 10 nm wide Al-GalnAs QW designed for operation in the 850 nm range. Optically pumped semiconductor lasers are usually pumped via barrier states from which the generated carriers are relaxing into the quantum well (QW) states. Pumping directly in-well states seems to be an attractive alternative in some situations because it increases the spectrum of pump diodes suitable for a given emission wavelength.

In this presentation, we apply our microscopic approach to the promising GaP-based dilute nitride Ga(NAsP) material system. This new material class may realize a monolithic integration of direct laser material on silicon wafer, thus merging photonic and microelectronic elements.

Optical gain and photoluminescence as well as radiative and Auger losses are calculated for Ga(AsBi)/GaAs quantum wells. The results are obtained using a consistent microscopic theory and an anticrossing model for the band structure. The influence of the band structure parameters on the optical properties is investigated.

Optical gain and photoluminescence as well as radiative and Auger losses are calculated for Ga(AsBi)/GaAs quantum wells. The results are obtained using a consistent microscopic theory and an anticrossing model for the band structure. The influence of the band structure parameters on the optical properties is investigated.

This chapter contains sections titled: Introduction Theory Bandstructure and Wavefunctions Semiconductor Bloch Equations Semiconductor Luminescence Equations Auger Recombination Processes Theory–Experiment Gain Comparison Absorption/Gain General Trends Structural Dependence Spontaneous Emission Auger Recombination Internal Field Effects Summary References

In recent years, vertical cavity surface emitting lasers (VCSEL) have developed into an important semiconductor laser source in multiple applications. However, the limited output power of VCSEL systems restrains industrial applications. The vertical external cavity surface emitting laser (VECSEL) design overcomes this limitation by replacing the upper distributed bragg reflector by an external parabolic mirror. Nevertheless, heating of the active region and related phenomena as e.g. the thermal rollover arise and turn out to be the major problem for further enhancement of VECSEL output power (Zakharian et al., 2003). Those phenomena contain new challenges for the theoretical description. With our model, we have the unique possibility to simulate optical and thermal properties of VECSEL devices. An example shows the laser output spectrum of a VECSEL device experimentally measured with a streak camera setup. The VECSEL is pumped with a strong 500ns pump pulse. One clearly sees the thermal shift of the band gap corresponding to a lattice heating of 4.2K/mus. In comparison, our simulation shows a good agreement with a slope of the thermal heating of 3.6K/ mus for the same structure. Additionally, thermal resistance dependent rollover curves were calculated for the same structure and exhibit the expected behaviour. In the future we expect our simulations to aid in the design and manufacturing process of semiconductor lasers. On the more fundamental level, we are interested in the dynamics of the optical properties in connection to nonequilibrium carrier populations as present e.g. in chirped excitation.

(GaIn)(NAs) lasers of different material compositions are considered with respect to their gain properties and radiative and Auger losses. Scattering and dephasing processes are included on a microscopic basis. The theory shows good agreement to experiment. Optical properties for a 1.55 mum structure are investigated and show no principal degradation as compared to a 1.3 mum structure

We consider two GaAs-based laser materials emitting at telecommunication wavelengths, namely the dilute nitride (GaIn)(NAs) as well as Ga(AsSb), and model their optical properties by including scattering and dephasing on a microscopic basis. The theory shows an excellent agreement with experiment without the inclusion of fit parameters such as phenomenological scattering times. By careful comparison of measurements and computations, one can extract controversial bandstructure parameters such as the band offset.

GaIn)(NAs) lasers ofdifferent material composi- tions areconsidered withrespect totheir gainproperties and radiative andAugerlosses. Scattering anddephasing processes areincluded ona microscopic basis. Thetheory showsgood agreement toexperiment. Optical properties fora 1.55,um structure areinvestigated andshownoprincipal degradation ascompared toa1.3,umstructure. 1 I.INTRODUCTION Inrecent years, the(GaIn)(NAs) material system hasbeen under intense investigation forits laser characteristics attheat- tenuation minimumofoptical fibers. Therelevant wavelengths at1.3,umand1.55,umcanalso bereached intheGaInAsP system, yetthenecessary Braggmirrors forvertical emitters suffer fromthesmall reflective indexachievable intheInP material system andthelowheatcapacity. (GaIn)(NAs) asa GaAs-based material system opensupthepossibility touse theadvanced GaAs/AlGaAs technology forfabrication ofthe Braggreflector. However, asyetthestructures intended forlight emission at1.55,umhavebeenafflicted withlowoptical quality and poorlight output. Various remedies havebeendeveloped, including theaddition ofantimony (1,2).Here,we take another approach andinvestigate whether withtheincrease in wavelength from1.3,umto1.55 ,umanyprincipal degradation oftheoptical properties istobeexpected (3).

A fully microscopic theory is used to perform an analysis of carrier–carrier and carrier-LO phonon scattering in semiconductor quantum wells, focussing on the high-density case relevant for laser structures. A large variance of scattering times is observed depending on the material parameters, apparently contradicting popular belief in some cases. For instance, carrier–carrier scattering may slow down when the carrier density is increased. Electron-hole scattering times are found to be on the same order of magnitude as carrier-phonon scattering, making the introduction of a separate electron and hole temperature necessary. Heating by optical pumping is investigated and plasma cooling is shown to be possible by optical pumping of the laser structure.