Theoretical modelling of single-mode lasing in microcavity lasers via optical interference injection

The effective manipulation of mode oscillation and competition is of fundamental importance for controlling light emission in semiconductor lasers. Here we develop a rate equation model which considers the spatially modulated gain and spontaneous emission, which are inherently governed by the ripple of the vacuum electromagnetic field in a Fabry-Pérot (FP) microcavity. By manipulating the interplay between the spatial oscillation of the vacuum field and external optical injection via dual-beam laser interference, single longitudinal mode operation is observed in a FP-type microcavity with a side mode suppression ratio exceeding 40 dB. An exploration of this extended rate equation model bridges the gap between the classical model of multimode competition in semiconductor lasers and a quantum-optics understanding of radiative processes in microcavities

Emission from quantum-dot high-β microcavities : transition from spontaneous emission to lasing and the effects of superradiant emitter coupling

The research is funded in part by the European Research Council under the Seventh Framework ERC Grant Agreement No. 615613 of the European Union, the German Research Foundation via the projects RE2974/5-1, Ka2318 7-1 and JA 619/10-3, and the U.S. Department of Energy under Contract No. DE-AC04-94AL85000. CG and FJ gratefully acknowledge financial support from the German Science Foundation (DFG). FJ further acknowledges support from the German Federal Ministry of Education and Research (BMBF).Measured and calculated results are presented for the emission properties of a new class of emitters operating in the cavity quantum electrodynamics regime. The structures are based on high-finesse GaAs/AlAs micropillar cavities, each with an active medium consisting of a layer of InGaAs quantum dots and the distinguishing feature of having a substantial fraction of spontaneous emission channeled into one cavity mode (high β-factor). This paper demonstrates that the usual criterion for lasing with a conventional (low β-factor) cavity, that is, a sharp non-linearity in the input-output curve accompanied by noticeable linewidth narrowing, has to be reinforced by the equal-time second-order photon autocorrelation function to confirm lasing. The paper also shows that the equal-time second-order photon autocorrelation function is useful for recognizing superradiance, a manifestation of the correlations possible in high-β microcavities operating with quantum dots. In terms of consolidating the collected data and identifying the physics underlying laser action, both theory and experiment suggest a sole dependence on intracavity photon number. Evidence for this assertion comes from all our measured and calculated data on emission coherence and fluctuation, for devices ranging from light emitting diodes (LEDs) and cavity-enhanced LEDs to lasers, lying on the same two curves: one for linewidth narrowing versus intracavity photon number and the other for g(2)(0) versus intracavity photon number.Publisher PDFPeer reviewe

Metal-cavity surface-emitting nanolasers

Metal-cavity surface-emitting micro/nanolasers are proposed and demonstrated. The design uses metals as both the cavity sidewall and the top/bottom reflectors and maintains the surface-emitting nature. As a result of the large permittivity contrast between the dielectric and metal, the optical energy can be well-confined inside the metal nanocavity. Flip-bonding the device to a silicon substrate with a conductive metal provides efficient heat removal. Several excellent performance characteristics have been observed such as ultra-narrow linewidth, low thermal impedance, and circular beam shapes. The devices proposed and realized are substrate-free with transferability to other platforms. The size of the proposed structure can be further reduced without severe degradation in the performance. This work provides a detailed theoretical model starting from the waveguide analysis to full structure simulations by taking into account both the geometry and the metal dispersion. Several substrate-free metal-cavity surface emitters are demonstrated. Advanced metal-cavity surface-emitting microlasers with submonolayer quantum dots are used as the active medium. Fabrication and experimental data are reported for electrical injection metal-cavity quantum-dot surface-emitting microlasers at room temperature. Detailed studies are conducted of size-dependent cavity modes for future size reduction. This thesis presents the accomplishment of the first room temperature metal-cavity surface-emitting microlaser with the best performance among the existing metal-cavity lasers. A further size reduction strategy for future work will be discussed and analyzed theoretically

Advances in Optofluidics

Optofluidics a niche research field that integrates optics with microfluidics. It started with elegant demonstrations of the passive interaction of light and liquid media such as liquid waveguides and liquid tunable lenses. Recently, the optofluidics continues the advance in liquid-based optical devices/systems. In addition, it has expanded rapidly into many other fields that involve lightwave (or photon) and liquid media. This Special Issue invites review articles (only review articles) that update the latest progress of the optofluidics in various aspects, such as new functional devices, new integrated systems, new fabrication techniques, new applications, etc. It covers, but is not limited to, topics such as micro-optics in liquid media, optofluidic sensors, integrated micro-optical systems, displays, optofluidics-on-fibers, optofluidic manipulation, energy and environmental applciations, and so on

Light control and microcavity lasers based on quantum wires integrated in photonic-crystal cavities

Novel light-emitting devices and micro-optical-circuit elements will rely upon understanding and control of light-matter interaction at the nanoscale. Recent advances in nanofabrication and micro-processing make it possible to develop integrable solid-state structures where the optical- and quantum-confinement effects determine the density and distribution of the energy states, allowing for mastering the output characteristics. In semiconductor nanostructures, such as quantum wires or quantum dots (sometimes referred even to as "artificial atoms") produced by epitaxy, with characteristic dimensions of 10÷20 nm, the quantization determines light absorbtion and emission spectra. Unlike the bulk matter, these important properties depend on the size and shape of the object, which is designed by nanotechnology. In photonic crystals and photonic-crystal micro-resonators, on the other hand, due to pronounced bandgap effects acting on light, unprecedented control over reflectivity, transmission and such a fundamental quantum-mechanical property as the density of electromagnetic vacuum-field fluctuations is achieved, the latter defining the rates of spontaneous emission of an embedded source. Based on these ideas, a number of passive and active optical and optoelectronic devices is anticipated practically, in particular, semiconductor microlasers with extremely low threshold pump-powers and ultimate conversion efficiency. Within the framework of this thesis we successfully integrated site-controlled quantum wires (QWRs) in 2D photonic-crystal (PhC) microcavities, examined the basic spectral and dynamics properties of the system, implemented the QWRs as a testing light source and probed interesting cavity configurations, and finally achieved stimulated emission and lasing. Starting from the previous studies of the QWR nanostructures, we, first, designed the geometry patterns adapted for implementation in the PhC-cavity system. Crystal growth (by metal-organic vapor-phase epitaxy) of InGaAs/GaAs QWRs on such patterns was verified; single and triple vertically stacked identical wires were obtained integrated within a 260-nm thin GaAs membrane. The basic properties of such QWRs were checked by photoluminescence spectroscopy. Spectra, power-dependent blueshift and temperature dependence consistent with previous studies were evidenced. Relatively long radiative lifetimes were found (at low – 20K – temperature) in transient spectroscopy, suggesting exciton localization effects and the effective dimensionality in between 0D and 1D. Identified as the most practically feasible way of exploiting the PhC bandgap effects for achieving high-Q truly single-mode resonators, the membrane approach in 2D photonic crystals was then implemented. In our nanofabrication effort we succeeded in incorporating the QWRs into such PhC cavities with very good site-control. The site control is apparently crucial, as light-matter coupling in an optical cavity and the spontaneous-emission properties are determined by the spatial and spectral matching. Cavity Q-factors of ∼ 5000÷6000 were reached. Our technology can be readily extended to schemes involving multiple site-controlled nanostructures in single or multiple (e.g. coupled) cavities that are currently of interest for various experiments in quantum physics. We then examined several interesting cavity configurations including coupled and 1D-like PhC cavities, exploiting QWRs as an embedded local light source. Such cavity geometries are relevant to on-chip photon-transfer lines, single-photon sources, coupled-cavity lasers and quantum-optics experiments. While with 1D-like cavities we were able to track the 0D-1D transition of the photonic states and observe important implications due to distributed disorder, we also found out experimentally and analyzed numerically that in the formation of the coupled states an important feature of loss splitting appears having implications on the energy transfer. On a more fundamental level, we examined PhC-cavity and bandgap effects on the QWR spontaneous emission. It was found experimentally that, at low temperature, the QWR spontaneous emission resonantly coupled to the cavity mode can be enhanced by factors of ∼ 2 ÷ 2.5. In addition, the off-resonance part is inhibited by a factor of ∼ 3. Such measured factors suggest that the output stems from an ensemble of emitters, which is consistent with a regular QWR inhomogeneous broadening and exciton localization picture. Nevertheless, the enhancement of the spontaneous emission into the cavity mode with respect to any other available modes is then a factor of ∼ 6, which is important for microcavity laser concept based on the spontaneous-emission control. Finally, multi- and single-mode lasing is experimentally demonstrated (for the first time). In order to verify the observation of the stimulated emission and lasing, complex analysis of spectral and photon-dynamics characteristics was undertaken and compared to a rate-equation model. Significantly low threshold values of ≲ 1 μW (incident power) were achieved, with relatively high spontaneous-emission coupling factors of ∼ 0.3