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In this work, monolithic mode-locked GaSb-based lasers at 1.7 µm emission wavelength with heterodyne measurement of the frequency comb are presented. Mode-locking operation was confirmed by measuring the optical beatnote at the round-trip frequency of 9.56 GHz and analysing the frequency comb. Mode-locking operation occurred from 0.1 to 3.3 V reverse bias voltages at the absorber section and driving currents from 160 to 400 mA at the laser section with a minimum beatnote width of 6.6 kHz. The frequency comb spans over 13 nm with a mode spacing of 0.10 nm, measured by heterodyne-detection with a distributed feedback laser.

In this letter, we present evanescently coupled semiconductor laser arrays designed with a distributed Bragg reflector section for spectrally narrow emission and a combined waveguide section for high optical output powers. These devices were designed and fabricated in the AlGaAs material system with an InGaAsP quantum well providing emission in the 760–770 nm wavelength range. Measurements of the light-current characteristics reveal high optical output powers of 600 mW at 20 °C and 700 mW at 5 °C limited by thermal rollover without any signs of a catastrophic optical mirror damage or rapid power degradation. Spectrally narrow emission of 0.2 nm at −3 dB and a high wavelength stability with a small current tuning coefficient of 0.7 pm/mA were found. Far-field investigations reveal pre-dominant coupling of lowest order in-phase supermode emission without any sections for adjusting the phase of the electrical field vector for adjacent elements. Postprint

Following the ultrafast optical excitation of an inhomogeneously broadened ensemble, the macroscopic optical polarization decays rapidly due to dephasing. This destructive interference is, however, reversible in photon echo experiments. Here, we propose a concept in which a control pulse slows down either the dephasing or the rephasing of the exciton ensemble during its presence. We analyze and visualize this optical freezing process by showing and discussing results for different single and multiple sequences of control pulses using a simple model of inhomogeneously broadened two-level systems. This idea has been realized in experiments performed on self-assembled (In,Ga)As quantum dots where it was possible to retard or advance the photon echo emission time by several picoseconds. The measurements are in very good agreement with numerical simulations for a more realistic model which, in particular, takes the spatial shape of the laser pulses into account.

━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━ DATA DESCRIPTION FOR "Difference-frequency generation in an AlGaAs Bragg-reflection waveguide using an on-chip electrically-pumped quantum dot laser" Alexander Schlager ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━ also available as readme.txt 2021-06-16 Table of Contents ───────────────── 1) Figure 2 - Lasing Threshold 2) Figure 3 - Difference Frequency Generation 3) Table 1 - Conversion Efficiency 4) Figure A3 - Temperature Dependency 5) Table A3 - Further Conversion Efficiencies Each filename pre-pended with the figure/table number of the main and supplementary text that it contributes to. All files relevant to each figure/table are included. All numeric data is presented in tab separated variable (in a '*.txt' file) which can be opened with standard spreadsheet or text editing programs. Aside from the JSI ('FIG3c-JSI.txt') and the temperature dependency of the internal laser spectrum ('FIGA3a-laser-temp.txt') all the plots are directly generated with a Latex package called `pgfplots'. For the two exceptions a high resolution image ('*.png') has been generated with Wolfram Mathematica and imported via 'pgfplots'. The code used to process this data and calculate e.g. the conversion efficiencies is not contained in this repository, but can be requested from the authors if required. 1) Figure 2 - Lasing Threshold ══════════════════════════════ 'FIG2-threshold-data.txt' contains the raw data of the lasing threshold measurement. Column 1 and 2 contain the current and its standard deviation in Ampere and column 3 and 4 the optical power and its standard deviation in micro Watt after a measurement time of 30 seconds. 'FIG2-inset-540mA.txt' and 'FIG2-inset-700mA.txt' contain the data representing the spectra of the internal laser below and above lasing threshold. Column 1 is the wavelength in nanometers and column 2 the signal strength in kCounts/s and MCounts/s for a current of 540mA and 700mA, respectively. 2) Figure 3 - Difference Frequency Generation ═════════════════════════════════════════════ 'FIG3b-example-data.txt' contains a background subtracted dataset utilizing the internal laser and a seed wavelength of 1614nm. Column 1 is the wavelength in nanometers and column 2 the signal strength in Counts per second (Hz). This data has been averaged for an acquisition time of 300 seconds. 'FIG3c-JSI.txt' contains processed data for the joint spectral intensity. The DFG peaks collected in the measurements (such as in 'FIG3b-example-data.txt') have been fitted with a Gaussian function and these functions have been utilized to generate the data in this file. This allows us to properly show the Full-Width-Half-Maximum of the measured spectrum and get rid of residual background light from e.g. the telecom seed laser near the degeneracy. This data has been corrected for the bandpass filters utilized in the experiment and the detection efficiency of our detector at different wavelengths. It has then be renormalized to ease the creation of the plot. The raw data for the individual wavelength settings are not included in this repository, but can be requested from the authors if required. The data for Fig. 3d) is included 3) Table 1 - Conversion Efficiency (next section). 3) Table 1 - Conversion Efficiency ══════════════════════════════════ 'TAB1-DFG-power-int-1626nm.txt', 'TAB1-DFG-power-ext-1619nm.txt' and 'TAB1-DFG-power-pas-1510nm.txt' include the data to get the slope for the conversion efficiency for the internal laser, the external laser and the passive sample, respectively. Column 1 and 2 describe the optical power and its standard deviation of the seed laser within the waveguide in milli Watt (for correction, see supplementary materials) for a measurement time of 30 seconds. Column 3 and 4 contain the signal strength of the DFG light in counts/s (Hz) and its poissonian standard error of mean for an acquisition time of 300 seconds (internal), 10 seconds (external) and 2 seconds (passive). To extract the signal strength, we simple take sum of the maximum of the corresponding peak in the raw data (such as in 'FIG3b-example-data.txt') and its nearest neighbors, as this corresponds to the peak width of about 1-2 nm. The raw data are not included in this repository, but can be requested from the authors if required. 4) Figure A3 - Temperature Dependency ═════════════════════════════════════ 'FIGA3a-laser-temp.txt' contains the spectra of the internal laser for different temperature settings as shown in the supplementary materials. Column 1 is the temperature in °C, column 2 the wavelength in nanometers and column 3 the normalized signal strength. Note, that the picture used in Fig. A3a) is only a small cutout of the spectra, but contains all the important information, as there is only background below 788nm and above 794nm. 'FIGA3b-shg-type0.txt', 'FIGA3b-shg-type1.txt' and 'FIGA3b-shg-type2.txt' contain the spectral information of the type-0, type-1 and type-2 second harmonic generation process, respectively. This data has been processed already, as it contains the peak maximum position (column 3) and half-width-half-maximum (column 4) in nanometers extracted from Gaussian fits for the individual SHG spectra at different temperatures in °C (column 1) with an accuracy of 0.05°C (column 2). The maximum peak position is used to create the thick line and the half-width-half-maximum is used to create the slightly transparent bands in Fig. A3b). The raw data are not included in this repository, but can be requested from the authors if required. 'FIGA3c-spectrum-693mA.txt' and 'FIGA3c-spectrum-700mA.txt' include the raw internal laser spectrum at a temperature of 3.5°C and 693mA and 700mA of current, respectively. Column 1 is the wavelength in nanometers and column 2 the normalized laser power. 'FIGA3d-shg-spectrum.txt' shows the second harmonic generation spectrum of the type-2 process in our waveguide at a temperature of 3.5°C. Column 1 is the wavelength in nanometers and column 2 the normalized SHG power. This data has been generated by measuring the maximum of the SHG spectrum for different pump laser wavelengths. This way, we can extract the SHG spectrum at a much higher resolution by slowly varying the laser wavelength in steps of 0.01nm. The raw data are not included in this repository, but can be requested from the authors if required. 5) Table A3 - Further Conversion Efficiencies ══════════════════════════════════════════════ All files starting with 'TABA3-DFG-power-*.txt' include the data to get the slope for the conversion efficiency for the internal laser, the external laser and the passive sample shown in the supplementary materials, respectively. Aside from additional wavelength settings for the telecom seed laser, the description is exactly the same as in 3) Table 1 - Conversion efficiency.

There is a great desire to extend ultrasonic techniques to the imaging and characterization of nanoobjects. This can be achieved by picosecond ultrasonics, where by using ultrafast lasers it is possible to generate and detect acoustic waves with frequencies up to terahertz and wavelengths down to nanometers. In our work we present a picosecond ultrasonics setup based on miniaturized mode-locked semiconductor lasers, whose performance allows us to obtain the necessary power, pulse duration and repetition rate. Using such a laser, we measure the ultrasonic echo signal with picosecond resolution in a Al film deposited on a semiconductor substrate. We show that the obtained signal is as good as the signal obtained with a standard bulky mode-locked Ti-Sa laser. The experiments pave the way for designing integrated portable picosecond ultrasonic setups on the basis of miniaturized semiconductor lasers., 9 pages, 4 figures

Photon echo from trions and excitons in (In,Ga)As/GaAs quantum dots was studied theoretically and experimentally. Theoretical analysis allowed us to distinguish between photon echo signals from excitons and trions measured in the same range of wavelength using different polarization configurations of laser excitation. The theoretical predictions are in good agreement with the experimental data.

We describe the wet-chemical synthesis of high-aspect-ratio single-crystalline gold platelets with thicknesses down to 20 nm and edge lengths up to 0.2 mm. By employing statistical analysis of a large number of platelets, we investigate the effect of temperature on the growth velocities of the top and side facets for constant concentrations of the three common ingredients: ethylene glycol, chloroauric acid, and water. We further show that by varying the chemical environment during growth, the ratio between the growth velocities can be adjusted, and thus thickness and lateral size can be tuned independently. Very large but ultrathin single-crystalline gold platelets represent an important starting material for top-down nanofabrication and may also find applications as transparent conducting substrates as well as substrates for high-end scanning probe and electron microscopy.

The recent progress in integrated quantum optics has set the stage for the development of an integrated platform for quantum information processing with photons, with potential applications in quantum simulation. Among the different material platforms being investigated, direct-bandgap semiconductors and particularly gallium arsenide (GaAs) offer the widest range of functionalities, including single- and entangled-photon generation by radiative recombination, low-loss routing, electro-optic modulation and single-photon detection. This paper reviews the recent progress in the development of the key building blocks for GaAs quantum photonics and the perspectives for their full integration in a fully-functional and densely integrated quantum photonic circuit.

We present passive mode locking of a GaSb-based monolithic diode laser emitting at 2.2 μm with a fundamental repetition rate around 9.57 GHz. A pulse width of ∼2.4 ps is reconstructed by shifted wave intermode beat Fourier transform spectroscopy-measurements, yielding a time-bandwidth product of 1.8. Mode-locking is observed for a range of reverse bias voltages from 1.3 to 3.3 V and driving currents from 110 to 300 mA. The continuous wave output power is ∼17.5 mW with the absorber segment left floating and ∼4.5 mW at a reverse bias of 3.1 V in the mode-locked regime. The full-width-half-maximum of the radio frequency signal is measured for all operation conditions, with a minimum of 8.4 kHz.

Molecule and gas sensing is a key technology that is applied in multiple environmental, industrial and medical fields. In particular optical detection technologies enable contactless, nondestructive, highly sensitive and fast detection of even smallest concentrations of trace gases and molecules. During the past years, an increasing demand for mid-infrared (MIR) light sources suitable for, e.g. molecule or gas sensing applications, has driven the development and optimization of novel MIR lasers and light sources, such as quantum cascade lasers (QCL) or interband cascade lasers (ICL). Despite the progress on MIR light sources, there is still a lack in appropriate MIR detectors. Here, we present and discuss two promising and novel GaSb/InAs-based detector concepts. First, resonant tunneling diode (RTD) photodetectors as an alternative to avalanche photodetectors. In RTDs, amplification of photogenerated minority charge carriers is based on modulation of a majority charge carrier resonant tunneling current. Second, interband cascade photodetectors (ICD), in which a cascading scheme allows for fast carrier extraction and a compensation of the diffusion length limitation.

Funding: European Research Council under the European Union’s Seventh Framework Program (ERC Grant Agreement No. 615613); German Research Foundation (CRC 787, GRK1558); project EMPIR 14IND05 MIQC2 co-financed by the Participating States and from the European Union’s Horizon 2020 research and innovation program. Microlasers are ideal candidates to bring the fascinating variety of nonlinear complex dynamics found in delay-coupled systems to the realm of quantum optics. Particularly attractive is the possibility of tailoring the devices’ emission properties via non-invasive delayed optical coupling. However, until now scarce research has been done in this direction. Here, we experimentally and theoretically investigate the effects of delayed optical feedback on the mode-switching dynamics of an electrically driven bimodal quantum-dot micropillar laser, characterizing its impact on the micropillar’s output power, optical spectrum and photon statistics. Feedback is found to influence the switching dynamics and its characteristics time scales. In addition, stochastic switching is reduced with the subsequent impact on the microlaser photon statistics. Our results contribute to the comprehension of feedback-induced phenomena in micropillar lasers and pave the way towards the external control and tailoring of the properties of these key systems for the nanophotonics community. Publisher PDF

The research leading to these results has received funding from the European Research Council under the European Union's Seventh Framework ERC Grant Agreement No. 615613, within the EURAMET joint research project MIQC2 from the European Union's Horizon 2020 Research and Innovation Programme and the EMPIR Participating States and from the German Research Foundation within the project RE2974/10-1. The authors thank the State of Bavaria for financial support. A photon-number resolving transition edge sensor (TES) is used to measure the photon-number distribution of two microcavity lasers. The investigated devices are bimodal microlasers with similar emission intensity and photon statistics with respect to the photon auto-correlation. Both high-β microlasers show partly thermal and partly coherent emission around the lasing threshold. For higher pump powers, the strong mode of microlaser { A } emits Poissonian distributed photons while the emission of the weak mode is thermal. In contrast, laser { B } shows a bistability resulting in overlayed thermal and Poissonian distributions. While a standard Hanbury Brown and Twiss experiment cannot distinguish between simple thermal emission of laser { A } and the temporal mode switching of the bistable laser { B }, TESs allow us to measure the photon-number distribution which provides important insight into the underlying emission processes. Indeed, our experimental data and its theoretical description by a master equation approach show that TESs are capable of revealing subtle effects like mode switching of bimodal microlasers. As such our studies clearly demonstrate the benefit and importance of investigating nanophotonic devices via photon-number resolving transition edge sensors. Postprint

The dynamics of spatial coherence and momentum distribution of polaritons in the regime of Bose-Einstein condensation are investigated in a GaAs microcavity with embedded quantum wells under nonresonant excitation with picosecond laser pulses. It is shown that the onset of the condensate first order sparial coherence is accompanied by narrowing of the polariton momentum distribution. At the same time, at sufficiently high excitation densities, there is significant qualitative discrepancy between the dynamic behavior of the width of the polariton momentum distribution determined from direct measurements and that calculated from the coherence spatial distribution. This discrepancy is observed at the fast initial stage of the polariton system kinetics and, apparently, results from the strong spatial nonuniformity of the phase of the condensate wave function, which equilibrates on a much longer time scale., Comment: 5 pages, 4 figures

We report on nonlinear transport phenomena in an asymmetric Y-transistor. The left branch acting as gate for the channel formed between the stem and the right branch of the Y-transistor is isolated from the branching section via a narrow constriction. The transfer characteristics of the Y-transistor is studied at low temperature in two configurations for which the stem is used either as drain contact or source contact. In the latter configuration, internal feedback coupling allows us to demonstrate subthreshold slopes 30% below the thermodynamic kT-limit for conventional field effect transistors.

This project has received funding from the European Commission's Horizon 2020 Research and Innovation Programme iCspec under grant agreement No. 636930 and has also been supported by the National Science Centre of Poland within Grant No. 2014/15/B/ST7/04663. Two designs of active region for an interband cascade laser, based on double or triple GaInSb/InAs type II quantum wells (QWs), were compared with respect to passive mode-locked operation in the mid-infrared range around 4 µm. The layer structure and electron and hole wavefunctions under external electric field were engineered to allow controlling the optical transition oscillator strength and the resulting lifetimes. As a result, the investigated structures can mimic absorber-like and gain-like sections of a mode-locked device when properly polarized with opposite bias. A significantly larger oscillator strength tuning range for triple QWs was experimentally verified by Fourier-transform photoreflectance. Publisher PDF

Super-resolution techniques such as direct Stochastic Optical Reconstruction Microscopy (dSTORM) have become versatile and well-established tools for biological imaging over the last century. Here, we theoretically and experimentally show that clever combination of different fluorescence modalities allows further improvements. We found that the interaction of fluorophores with plasmonic surfaces boost super-resolution performance in dSTORM approaches as it allows for tailoring the excitation and emission properties. The strength of the approach is that no further specialized microscope setup is required as the described enhancement solely rely on metal-dielectric coated glass coverslips that are straightforward to fabricate. Such biocompatible plasmonic nanolayers enhance the signal-to-noise ratio of dSTORM, and thus sharpens the localization precision by a factor of two.

The authors are grateful for financial support by the European Union (FPVII (2007-2013) under grant agreement no. 318287 LANDAUER), and the Brazilian Agencies FAPESP (grants 2012/13052 - 6, and 2012/51415 - 3), CNPq and CAPES. V. L.-R. acknowledges the support of FAPESP (grant: 2014/02112-3). Y.V.P. was supported by National Science Foundation grant ECCS-1202383. Electronic circuits composed of one or more elements with inherent memory - memristors, memcapacitors and meminductors - offer lower circuit complexity and enhanced functionality for certain computational tasks. Networks of these elements are proposed for novel computational paradigms that rely on information processing and storage on the same physical platform. We show a nanoscaled memdevice able to act as an electronic analogue of tipping buckets that allows reducing the dimensionality and complexity of a sensing problem by transforming it into a counting problem. The device offers a well adjustable, tunable and reliable periodic reset that is controlled by theamounts of transferred quantum dot charges per gate voltage sweep. When subjected to periodic voltage sweeps the quantum dot (bucket) may require up to several sweeps before a rapid full discharge occurs thus displaying period doubling, period tripling and so on between self-governing reset operations. Postprint Postprint

Financial support by the German Federal Ministry of Education and Research in terms of the APOSEMA project (contract no: 13N13083) within the funding program Photonics Research Germany is gratefully acknowledged. In this work, single-mode distributed feedback interband cascade lasers with tapered ridges are presented. The lasers consists of a 500 μm long and 5.7 μm wide ridge wave guide section followed by a 1400 μm long tapered section with an output facet width of 35 μm. The device is operational in continuous wave mode and well above room temperature. At 25°C, the threshold current and threshold current density were 81 mA and 324 A/cm², respectively. We demonstrate a tuning range of over 14 nm with side mode suppression ratios larger than 25 dB. The device showed temperature and injection power tuning coefficients of 0,35 nm/K and 4.09 nm/W, respectively. Output powers of 18 mW single mode and 35 mW multimode were achieved. Postprint

The research leading to these results has received funding from the European Research Council under the European Union's Seventh Framework ERC Grant Agreement No. 615613, from the German Research Foundation via the projects RE2974/9-1, SCHN1376/1-1, and the collaborative research center CRC787. Implementing time-delayed feedback in optoelectronic circuits allows one to uncover the rich physics and application potential of nonlinear dynamics. Important feedback effects are, for instance, the generation of broadband chaos, or laser self-pulsing. We explore the effect of optoelectronic feedback in an ultracompact microlaser–microdetector assembly operating in the regime of cavity quantum electrodynamics (cQED). This system is used to generate self-pulsing at MHz frequencies in the emission of a microlaser, which is qualitatively explained by a rate equation model taking cQED effects into account. The results show promise for exploring chaos in ultracompact nanophotonic systems and for technological approaches toward chaos-based secure communication, random number generation, and self-pulsed single photon sources on a highly integrated semiconductor platform. Postprint

This project has received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement No 636930 (iCspec). The work proposes possible designs of active regions for a mode-locked interband cascade laser emitting in the mid infrared. For that purpose we investigated the electronic structure properties of respectively modified GaSb-based type II W-shaped quantum wells, including the effect of external bias in order to simultaneously fulfil the requirements for both the absorber as well as the gain sections of a device. The results show that introducing multiple InAs layers in type II InAs/GaInSb quantum wells or introducing a tensely-strained GaAsSb layer into “W-shaped” type II QWs offers significant difference in optical transitions’ oscillator strengths (characteristic lifetimes) of the two oppositely polarized parts of such a laser, being promising for utilization in mode-locked devices. Publisher PDF

Using semiconductor quantum dots in a cavity-quantum electrodynamics laser we show a direct connection between superradiant pulse emission and the photon correlations. This demonstrates the importance of quantum correlations in novel optoelectronic devices.

We introduce an analytical theory for mode switching in a microcavity, which shows excellent agreement with experiment and numerics. This switching process is triggered by the intermode kinetics and resembles the physics of Bose condensation.

We investigate the switching of the coherent emission mode of a bimodal microcavity device, occurring when the pump power is varied. We compare experimental data to theoretical results and identify the underlying mechanism to be based on the competition between the effective gain on the one hand and the intermode kinetics on the other. When the pumping is ramped up, above a threshold the mode with the largest effective gain starts to emit coherent light, corresponding to lasing. In contrast, in the limit of strong pumping it is the intermode kinetics that determines which mode acquires a large occupation and shows coherent emission. We point out that this latter mechanism is akin to the equilibrium Bose-Einstein condensation of massive bosons. Thus, the mode switching in our microcavity device can be viewed as a minimal instance of Bose-Einstein condensation of photons. We, moreover, show that the switching from one cavity mode to the other occurs always via an intermediate phase where both modes are emitting coherent light and that it is associated with both superthermal intensity fluctuations and strong anticorrelations between both modes., minor changes, typos corrected, acknowledgments supplemented, references added

We are grateful for receiving financial support within the BMBF Project “LASELO” (FKZ: 13N13773). Interband cascade lasers (ICLs) with dual wavelength emission have been realized by utilizing two spatially separated active regions in the same device. The two wavelengths (3.1 and 3.7 µm) were chosen in order to demonstrate that the usual spectral gain bandwidth of an ICL can be overcome. At 20°C, threshold current densities as low as 215 A/cm² (short wavelength) and 158 A/cm² (long wavelength) could be achieved in pulsed mode. It was possible for an epi-up mounted device to maintain dual-wavelength continuous-wave emission up to 0°C. Despite the longer wavelength emission being suppressed at higher temperatures, the shorter wavelength maintained an output power of more than 10 mW at 15°C. Postprint

We report on the modeling and optical characterization of AlGaAs/InAs quantum-dot microring diode lasers designed for terahertz (THz) difference frequency generation (DFG) between two whispering gallery modes (WGMs) around 1.3 μm. In order to investigate the spectral features of this active device in the two frequency ranges, we performed different measurements on ad hoc passive samples. For the study in the telecom range, we used transmission measurements on microcylinders with integrated coupling waveguides. For the analysis in the THz range, we used reflectivity spectra on 2D arrays of identical double-metal microcylinders. The good agreement that we demonstrate between experimental results and design parameters is crucial towards the achievement of active phase-matched THz emitters.

Conventional semiconductor laser emission relies on stimulated emission of photons1, 2, which sets stringent requirements on the minimum amount of energy necessary for its operation3, 4. In comparison, exciton–polaritons in strongly coupled quantum well microcavities5 can undergo stimulated scattering that promises more energy-efficient generation of coherent light by ‘polariton lasers’3, 6. Polariton laser operation has been demonstrated in optically pumped semiconductor microcavities at temperatures up to room temperature7, 8, 9, 10, 11, 12, and such lasers can outperform their weak-coupling counterparts in that they have a lower threshold density12, 13. Even though polariton diodes have been realized14, 15, 16, electrically pumped polariton laser operation, which is essential for practical applications, has not been achieved until now. Here we present an electrically pumped polariton laser based on a microcavity containing multiple quantum wells. To prove polariton laser emission unambiguously, we apply a magnetic field and probe the hybrid light–matter nature of the polaritons. Our results represent an important step towards the practical implementation of polaritonic light sources and electrically injected condensates, and can be extended to room-temperature operation using wide-bandgap materials.

The Wurzburg group acknowledges the financial support by the state of Bavaria and the DFG within the project Schn1376-3.1. We study the nonequilibrium exciton-polariton condensation in 1D to 0D and 1D to quasi-2D junctions by means of non-resonant spectroscopy. The shape of our potential landscape allows to probe the resonant transmission of a propagating condensate between a quasi-1D waveguide and cylindrically symmetric states. We observe a distinct mode selection by varying the position of the non-resonant pump laser. Moreover, we study the the case of propagation from a localized trapped condensate state into a waveguide channel. Here, the choice of the position of the injection laser allows us to tune the output in the waveguide. Our measurements are supported by an accurate Ginzburg-Landau modeling of the system shining light on the underlying mechanisms. Postprint

Financial support by the European Union in terms of the WideLase project (grant agreement no: 318798) within the Seventh Framework Programme is gratefully acknowledged. Monolithic two-section interband cascade lasers offering a wide wavelength tunability in the wavelength range around 3.7 μm are presented. Stable single mode emission in several wavelength channels was realized using the concept of binary superimposed gratings and two-segment Vernier-tuning. The wavelength selective elements in the two segments were based on specially designed lateral metal grating structures defined by electron beam lithography. A dual-step dry etch process provided electrical separation between the segments. Individual current control of the segments allowed wavelength channel selection as well as continuous wavelength tuning within channels. A discontinuous tuning range extending over 158 nm in up to six discrete wavelength channels was achieved. Mode hop free wavelength tuning up to 14 nm was observed within one channel. The devices can be operated in continuous wave mode up to 30 °C with output powers of 3.5 mW around room temperature. Postprint

Interband cascade lasers with low power consumption emitting in the mid infrared spectral region between 2.8 μm and 5.7 μm are presented.

Gas sensing is a key technology with applications in various industrial, medical and environmental areas. Optical detection mechanisms allow for a highly selective, contactless and fast detection. For this purpose, rotational-vibrational absorption bands within the mid infrared (MIR) spectral region are exploited and probed with appropriate light sources. During the past years, the development of novel laser concepts such as interband cascade lasers (ICLs) and quantum cascade lasers (QCLs) has driven a continuous optimization of MIR laser sources. On the other hand side, there has been relatively little progress on detectors in this wavelength range. Here, we study two novel and promising GaSb-based detector concepts: Interband cascade detectors (ICD) and resonant tunneling diode (RTD) photodetectors. ICDs are a promising approach towards highly sensitive room temperature detection of MIR radiation. They make use of the cascading scheme that is enabled by the broken gap alignment of the two binaries GaSb and InAs. The interband transition in GaSb/InAs-superlattices (SL) allows for normal incidence detection. The cut-off wavelength, which determines the low energy detection limit, can be engineered via the SL period. RTD photodetectors act as low noise and high speed amplifiers of small optically generated electrical signals. In contrast to avalanche photodiodes, where the gain originates from multiplication due to impact ionization, in RTD photodetectors a large tunneling current is modulated via Coulomb interaction by the presence of photogenerated minority charge carriers. For both detector concepts, first devices operational at room temperature have been realized. Publisher PDF

Within this work we propose and demonstrate a technological approach to efficiently suppress excitation laser stray-light in resonance fluorescence experiments on quantum dot-micropillars. To ensure efficient stray-light suppression, their fabrication process includes a planarization step and the subsequent covering with a titanium mask to fabricate self-aligned apertures at the micropillar positions. These apertures aim at limiting laser straylight in side-excitation vertical-detection configuration, while enabling detection of the optical signal through the top facet of the micropillars. Beneficial effects of these apertures are proven and quantitatively evaluated within a statistical study in which we determine and compare the stray-light suppression of 48 micropillars with and without metal apertures. Actual resonance fluorescence experiments on single quantum dots coupled to the cavity mode prove the relevance of the proposed approach and demonstrate that it will foster further studies on cavity quantum electrodynamics phenomena under coherent optical excitation. Postprint

The Interband Cascade Laser (ICL) [1, 2] combines the interband transition as in a conventional diode laser with the cascading scheme of a Quantum Cascade Laser. ICLs allow for an external quantum efficiency greater than which is enabled because of the special band alignment of GaInSb/AlAs/InAs-interfaces that separates hole and electron injector and internally feed each cascade with carriers. This makes ICLs a unique with great design flexibility. By changing the InAs layer thickness of the typically used W-shaped quantum well (W-QW) the emission wavelength can be tuned within the entire mid infrared region which is known as the fingerprint region of a variety of industrially relevant molecules. Absorption spectra of two prominent ones (acetone and nitric oxide) are shown in Figure 1 together with room temperature spectra of broad area ICLs driven under pulsed condition. Meanwhile GaSb-based ICLs that are operational in continuous wave mode at room temperature have been realized from 2.8 µm [3] to 5.6 µm [4].

Tunable Laser Absorption Spectroscopy (TLAS) in the mid-infrared (MIR) wavelength region from 3 to 6 µm has proven to be a versatile tool for a variety of challenging gas sensing applications, especially for many technologically or environmentally relevant gases like e.g., methane or sulfur dioxide.

The authors gratefully acknowledge financial support from the European Union (FPVII (2007-2013) under Grant Agreement No. 318287 Landauer) as well as the State of Bavaria. The Brazilian authors acknowledge the support from CNPq. V.L.-R. acknowledges the support from FAPESP (Grant Nos. 2014/02112-3 and 2015/10765-0). We report the optical control of localized charge on positioned quantum dots in an electro-photo-sensitive memristor. Interband absorption processes in the quantum dot barrier matrix lead to photo-generated electron-hole-pairs that, depending on the applied bias voltage, charge or discharge the quantum dots and hence decrease or increase the conductance. Wavelength-dependent conductance control is observed by illumination with red and infrared light, which leads to charging via interband and discharging via intraband absorption. The presented memristor enables optical conductance control and may thus be considered for sensory applications in artificial neural networks as light-sensitive synapses or optically tunable memories. Postprint

The authors gratefully acknowledge financial support from the European Union [FPVII (2007-2013) under Grant Agreement No. 318287 Landauer], as well as the state of Bavaria. We present optically and electrically tunable conductance modifications of a site-controlled quantum-dot memristor. The conductance of the device is tuned by electron localization on a quantum dot. The control of the conductance with voltage and low-power light pulses enables applications in neuromorphic and arithmetic computing. As in neural networks, applying pre- and postsynaptic voltage pulses to the memristor allows us to increase (potentiation) or decrease (depression) the conductance by tuning the time difference between the electrical pulses. Exploiting state-dependent thresholds for potentiation and depression, we are able to demonstrate a memory-dependent induction of learning. The discharging of the quantum dot can further be induced by low-power light pulses in the nanowatt range. In combination with the state-dependent threshold voltage for discharging, this enables applications as generic building blocks to perform arithmetic operations in bases ranging from binary to decimal with low-power optical excitation. Our findings allow the realization of optoelectronic memristor-based synapses in artificial neural networks with a memory-dependent induction of learning and enhanced functionality by performing arithmetic operations. Postprint

The semiconductor polariton laser promises a new source of coherent light, which, compared to conventional semiconductor photon lasers, has input-energy threshold orders of magnitude lower. However, intensity stability, a defining feature of a coherent state, has remained poor. Intensity noise at many times of the shot-noise of a coherent state has persisted, which has been attributed to multiple mechanisms that are difficult to separate in conventional polariton systems. The large intensity noise in turn limited the phase coherence. These limit the capability of the polariton laser as a source of coherence light. Here, we demonstrate a polariton laser with shot-noise limited intensity stability, as expected of a fully coherent state. This is achieved by using an optical cavity with high mode selectivity to enforce single-mode lasing, suppress condensate depletion, and establish gain saturation. The absence of spurious intensity fluctuations moreover enabled measurement of a transition from exponential to Gaussian decay of the phase coherence of the polariton laser. It suggests large self-interaction energies in the polariton condensate, exceeding the laser bandwidth. Such strong interactions are unique to matter-wave laser and important for nonlinear polariton devices. The results will guide future development of polariton lasers and nonlinear polariton devices., 23 pages, 6 figures

This article may be downloaded for personal use only. Any other use requires prior permission of the author and AIP Publishing. This article appeared in Appl. Phys. Lett. 108, 081110 (2016) and may be found at https://doi.org/10.1063/1.4942650., We demonstrate the on-chip detection of light using photosensitive detectors based on quantum dot micropillar cavities. These microscale detectors are applied exemplarily to probe the emission of a monolithically integrated, electrically pumped whispering gallery mode microlaser. Light is detected via the photocurrent induced in the electrically contacted micropillar detectors under reverse-bias. In order to demonstrate the high potential and applicability of the microdetector presented, we determine the threshold current of an integrated microlaser to be (54 ± 4) μA, in very good agreement with the value of (53 ± 4) μA inferred from the optical data. Within this work, we realize the monolithic integration of a laser and a detector in a single device operating in the regime of cavity-quantum electrodynamics. Our results thus advance the research on microscale sensor technology towards the few-photon quantum limit and pave the way for on-chip opto-electronic feedback experiments.

The authors acknowledge support the European Cooperation in Science and Technology (COST) Action BM1205. This research was supported under Australian Research Council’s Discovery Projects funding scheme (DP 120 103703) and the State of Bavaria. Y.L.L. acknowledges support under the Queensland Government’s Smart Futures Fellowships programme. P.D. acknowledges support from the EPSRC (UK). S. H. gratefully acknowledges support by the Royal Society and the Wolfson Foundation. In this work, we demonstrate a simple square-wave electrical modulation scheme for imaging with laser feedback interferometry (LFI). Distinct advantages of this scheme include (a) the straightforward creation of the modulating signal, even for high-current lasers, and (b) its natural suitability for lock-in detection. We compare this simple scheme against two established imaging modalities for LFI: mechanical modulation using an optical chopper and the swept-frequency feedback interferometry approach. The proposed scheme lends itself to high frequency modulation which paves the way for high frame-rate LFI imaging with no motion artefacts using off-the-shelf equipment. Publisher PDF

O.A.E. acknowledges financial support by the Deutsche Forschungsgemeinschaft (DFG project EG344/2-1) and by the EU project (FP7, PIRSES-GA-2013-612600) LIMACONA. I.G.S. acknowledges support from the Academy of Finland through its Centre of Excellence Programs (Projects No. 250280 and No. 251748); Government of Russian Federation (project MK-5903.2016.2); and Dynasty Foundation. E.E., T.G., I.G.S., and E.A.O. acknowledge support by the Australian Research Council. We study the loading of a nonequilibrium, dissipative system of composite bosons - exciton polaritons - into a one dimensional periodic lattice potential. Utilizing momentum resolved photoluminescence spectroscopy, we observe a transition between an incoherent Bose gas and a polariton condensate, which undergoes further transitions between different energy states in the band-gap spectrum of the periodic potential with increasing pumping power. We demonstrate controlled loading into distinct energy bands by modifying the size and shape of the excitation beam. The observed effects are comprehensively described in the framework of a nonequilibrium model of polariton condensation. In particular, we implement a stochastic treatment of quantum and thermal fluctuations in the system and confirm that polariton-phonon scattering is a key energy relaxation mechanism enabling transitions from the highly nonequilibrium polariton condensate in the gap to the ground band condensation for large pump powers. Postprint Postprint

This project has received funding from the European Union's Horizon 2020 research and innovation programme under grant agreement No 636930. We would also like to acknowledge the National Science Centre of Poland for support within Grant No. 2014/15/B/ST7/04663. Optical properties of modified type II W-shaped quantum wells have been investigated with the aim to be utilized in interband cascade lasers. The results show that introducing a tensely strained GaAsSb layer, instead of a commonly used compressively strained GaInSb, allows employing the active transition involving valence band states with a significant admixture of the light holes. Theoretical predictions of multiband k·p theory have been experimentally verified by using photoluminescence and polarization dependent photoreflectance measurements. These results open a pathway for practical realization of mid-infrared lasing devices with uncommon polarization properties including, for instance, polarization-independent midinfrared light emitters. Publisher PDF

Using a designable cavity to control the polariton modes, we demonstrate a single-mode polariton laser with Poisson intensity noise and intrinsic phase coherence. Strong interactions within the polariton condensate manifest in Gaussian dephasing at high condensate densities.

The regime of strong light-matter coupling is typically associated with weak excitation. With current realizations of cavity-QED systems, strong coupling may persevere even at elevated excitation levels sufficient to cross the threshold to lasing. In the presence of stimulated emission, the vacuum-Rabi doublet in the emission spectrum is modified and the established criterion for strong coupling no longer applies. We provide a generalized criterion for strong coupling and the corresponding emission spectrum, which includes the influence of higher Jaynes-Cummings states. The applicability is demonstrated in a theory-experiment comparison of a few-emitter quantum-dot--micropillar laser as a particular realization of the driven dissipative Jaynes-Cummings model. Furthermore, we address the question if and for which parameters true single-emitter lasing can be achieved, and provide evidence for the coexistence of strong coupling and lasing in our system in the presence of background emitter contributions., Comment: 12 pages, 9 figures

This talk gives an insight into the development and the device performance of various ICL based sources in the mid infrared (MIR) wavelength region for application in high accuracy sensing. As an example, DFB type ICL devices based on a lateral metal grating structure were fabricated using an overgrowth free processing route. These devices have been realized in the entire spectral range from 2.8 to 5.2 μm in the MIR. Total tuning ranges of around 20 nm can be covered by these DFB devices providing typically 5 mW of optical output power with low power consumption based on a low operating current and voltage. Device concepts for extended wavelength coverage in the MIR will also be presented. All fabricated MIR sources are targeting high performance sensor applications in fields like industrial process control or environmental monitoring and various application examples will be highlighted in the talk.

Electrically connected resonant optical antennas hold promise for the realization of highly efficient nanoscale electro-plasmonic devices that rely on a combination of electric fields and local near-field intensity enhancement. Here we demonstrate the feasibility of such a concept by attaching leads to the arms of a two-wire antenna at positions of minimal near-field intensity with negligible influence on the antenna resonance. White-light scattering experiments in accordance with simulations show that the optical tunability of connected antennas is fully retained. Analysis of the electric properties demonstrates that in the antenna gaps direct current (DC) electric fields of 10(8) V/m can consistently be achieved and maintained over extended periods of time without noticeable damage.

The work has been supported by Project Widelase (no. 318798) of the Seventh Framework Programme of the European Commission. The effect of interface intermixing in W-design GaSb/AlSb/InAs/Ga0.665 In0.335 AsxSb1 − x/InAs/AlSb/GaSb quantum wells (QWs) has been investigated by means of optical spectroscopy supported by structural data and by band structure calculations. The fundamental optical transition has been detected at room temperature through photoluminescence and photoreflectance measurements and appeared to be blueshifted with increasing As content of the GaInAsSb layer, in contrast to the energy-gap-driven shifts calculated for an ideally rectangular QW profile. The arsenic incorporation into the hole-confining layer affects the material and optical structure also altering the InAs/GaInAsSb interfaces and their degree of intermixing. Based on the analysis of cross-sectional transmission electron microscopy images and energy-dispersive X-ray spectroscopy, we could deduce the composition distribution across the QW layers and hence simulate more realistic confinement potential profiles. For such smoothed interfaces that indicate As-enhanced intermixing, the energy level calculations have been able to reproduce the experimentally obtained trend. Publisher PDF

Electron spin in quantum dots are extensively studied as a qubit for quantum information processing. However, the coherence of electron spin is deleteriously influenced by nuclear spin. Quantum-dot holes are a potential alternative. Full control over hole-spin qubits is now achieved using picosecond lasers.

Fluorescence microscopy allows specific and selective imaging of biological samples. Unfortunately, unspecific background due to auto-fluorescence, scattering, and non-ideal labeling efficiency often adversely affect imaging. Surface plasmon-coupled emission (SPCE) is known to selectively mediate fluorescence that spatially originates from regions close to the metal interface. However, SPCE combined with fluorescence imaging has not been widely successful so far, most likely due to its limited photon yield, which makes it tedious to identify the exact window of the application. As the strength of SPCE based imaging is its unique sectioning capabilities. We decided to identify its clear beneficial operational regime for biological settings by interrogating samples in the presence of ascending background levels. For fluorescent beads as well as live-cell imaging as examples, we show how to extend the imaging performance in extremely high photon background environments. In a common setup using plasmonic gold-coated coverslips using an objective-based total internal reflection fluorescence microscope (TIRF-M), we theoretically and experimentally characterize our fluoplasmonics (f-Pics) approach by providing general user guidance in choosing f-Pics over TIRF-M or classical wide-field (WF).

Wavelength control of tapered quantum dot (QD) lasers was achieved by adding a distributed Bragg reflector as wavelength-selective element to the devices. The Bragg wavelength of around 920 nm is matched to the gain of the single layer of InGaAs QDs that is used as active material. Devices with 1.4-mm-long tapers have reached output powers of over 1 W, and over 2 W were obtained from lasers with 3-mm-long tapers. The emission of the devices is restricted to a very narrow spectral range, with side-mode suppression ratios of over 40 dB.

GaInNAs-based high-power laser diodes with emission in the 1220-1240 nm wavelength range are presented. Broad-area (BA) devices show very low internal losses of only 0.5 cm-1, allowing high continuous-wave room-temperature output powers of almost 9 W and emission at a wavelength of 1220 nm. Based on the needs for applications like, e.g., pumping of Raman amplifiers, wavelength-stabilized tapered laser diodes are shown with maximum output powers of 1 W together with a high beam quality. Beam propagation factors M 2 down to 1.4, high brightness of up to 23 MW/cm2middotsr, and nearly spatial single-mode emission have been obtained.

Reducing the threshold power and the active material are key issues in the development of semi-conductor lasers. Considerable advances have been achieved in this field by combining high quality microre-sonators with self assembled quantum dots as the active material. While QDs exhibit superb gain characteristics due to their three dimensional carrier confinement and low non-radiative decay rates, high quality microresonator laser structures provide high spontaneous emission (SE) cou-pling β-factors. Low-threshold lasing from a small number of QDs has been reported in various microcavity systems such as microdisks, photonic crystal (PC) nanocavities and micropillar cavities [1–4]. Here, we report on recent ad-vances in lasing of InGaAs QDs embedded in high-Q AlAs/GaAs micropillar cavities with a special focus on single QD gain modulation. The strong interest in lasing action of QDs in high-Q microcavities is explained by the efficient coupling of spontaneous emission into the lasing mode. In contrast to usual quantum well laser diodes with β ≈ 10