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Providing a spin-free host material in the development of quantum information technology has made silicon a very interesting and desirable material for qubit design. Much of the work and experimental progress has focused on isolated phosphorous atoms. In this article, we report on the exploration of Ni–Si clusters that are atomically manufactured via self-assembly from the bottom-up and behave as isolated quantum dots. These small quantum dot structures are probed at the atomic-scale with scanning tunneling microscopy and spectroscopy, revealing robust resonance through discrete quantized energy levels within the Ni–Si clusters. The resonance energy is reproducible and the peak spacing of the quantum dot structures increases as the number of atoms in the cluster decrease. Probing these quantum dot structures on degenerately doped silicon results in the observation of negative differential resistance in both I–V and dI/dV spectra. At higher surface coverage of nickel, a well-known √19 surface modification is observed and is essentially a tightly packed array of the clusters. Spatial conductance maps reveal variations in the local density of states that suggest the clusters are influencing the electronic properties of their neighbors. All of these results are extremely encouraging towards the utilization of metal modified silicon surfaces to advance or complement existing quantum information technology. Silicon-based quantum dots are artificial two-level systems, whose long coherence times make them ideal candidates as qubits for quantum information technology. Researchers from the University of Illinois at Chicago and Argonne National Laboratory present an approach to fabricate via self-assembly randomly distributed clusters, by manipulating the density of nickel on a silicon substrate. Deposition of nickel below a critical density leads to the formation of two types of clusters, both of which behave as isolated quantum dots: confinement gives rise to well-spaced quantized levels similar to the structure of atoms, while measurements under positive and negative bias reveal two symmetric resonances, signatures of tunneling through the highest occupied and lowest unoccupied energy levels, respectively. Such a scalable fabrication method, based on self-assembly, may be further exploited for the design of silicon-based qubits

A portable system for fluorescence measurement has been developed for cyanobacteria detection. Exploiting commercially available low-cost photodiodes and a single 9 V supply, the system was able to measure two fluorescence emissions simultaneously. Output voltages resulting from the fluorescence intensity were measured by utilizing two quantum dots of QD565 and QD655. These quantum dots were employed into a NanoGene assay for mcyD gene (synthetase of toxic microcystin) detection of Microcystis aeruginosa. We investigated various operational parameters (e.g., distance, angle between laser emission and sample, and so on) for the proposed system. Measurements indicated the highest output voltage signal was obtained at a distance of 0.5 cm with the right angle (90°) between the laser source and a sample vial. Also, the mcyD gene hybridized with QD565 and QD655 was quantitatively detected by the proposed detection system, i.e., the normalized output voltage (QD655/QD565) was linearly proportional to the mcyD gene copy numbers (y = 0.41 log $x +6.6$ , $\text{r}^{2} =0.92$ ). Finally, the quantitative data were transferred wirelessly to the readout via Bluetooth.

A self-aligned, highly tolerant “open top” cavity design is proposed and shown to enhance the spontaneous emission of InGaN quantum dots. Compared to the “closed top” counterpart, removing the metal cap, creating an “open top” cavity, enhances both the emission intensity and recombination rate. The localized surface plasmon resonance of the Ag “open top” cavity was matched to the InGaN quantum dots’ emission wavelength, resulting in an observed final emitter lifetime of 132 ps. The proposed cavity structure exhibits high cavity antenna quantum efficiency, can be self-aligned to the quantum dot, and has good tolerance to quantum dot emission wavelength, polarization, and processing variations.

In this work, we modeled and simulated aZnxCd1-xTe/ZnTe based single quantum well structure. We have taken into account the effect of carrier density, alloy composition, temperature and wells width on the optical gain as well as threshold current density. The use of ZnTe as a barrier leads to the improvement of the carrier confinement such as Qc (83%)/Qv (17%). Then, we have optimized the quantum well structure that allows obtaining a threshold current density Jth = 500 A/cm2. This study allowed us to achieve laser diodes VCSEL quantum well reliable and emitting around 0.740 μm.

The manipulation of bistable curve in the infrared (IR) region has been investigated theoretically in a unidirectional ring cavity doped by a four-level InGaN/GaN quantum dot nanostructure. The four-level quantum dot nanostructure is designed numerically by using the Schrodinger and Poisson equations. By controlling the size of the quantum dot and external voltage, one can design a four-level quantum dot with appropriate energy levels which can be suitable for interaction with IR signals. It is realized that the incoherent pumping fields play an essential role in controlling the intensity threshold of optical bistability. Decoherence effects such as the dephasing rate and electron density of the quantum dot are also analyzed at the threshold of optical bistability. Our proposed model due to its important application in all-optical systems may be favorable for real experimental evolution in infrared regions.

We present experimental investigations of a novel mid-infrared gas sensor relying on a laser system consisting of two quantum cascade sources mutually coupled with each other. The free-space path between the two lasers contains the sensing cell which is filled with the gas of interest. This laser system proves to be a very interesting dynamical system which can offer enhanced detectivity when compared to a conventional direct absorption spectrometer utilizing a laser, the gas cell, and a detector. We present comprehensive investigations of the operation regimes under which the laser system behaves as an efficient sensor and demonstrate its dependence on critical parameters such as the coupling strength between the two lasers and their bias currents. The experimental study is supported by numerical simulations, which provide a theoretical understanding of the underlying mechanisms. A six fold improvement of the sensitivity in a N2O absorption spectroscopy experiment is demonstrated in comparison to a conventional direct absorption spectrometer. This sensitivity improvement is exhibited for a wide range of N2O concentrations.

In this paper, a G a A s / A l x G a 1 − x A s quantum dot laser with a semi-parabolic spherical well potential is assumed. By using Runge-Kutta method the eigenenergies and the eigenstates of valence and conduct bands are obtained. The effects of geometrical sizes, external electric fields and hydrogen impurity on the different electronic transitions of the optical gain are studied. The results show that the optical gain peak increases and red-shifts, by increasing the width of well or barrier, while more increasing of the width causes blue-shift and decreases it. The hydrogen impurity decreases the optical gain peak and blue-shifts it. Also, the increasing of the external electric fields cause to increase the peak of the optical gain, and (blue) red shift it. Finally, the optical gain for 1s–1s and 2s–1s transitions is prominent, while it is so weak for other transitions.

We consider high harmonic generation from a quantum dot (QD) in the presence of chirped laser pulse. The system dynamics is described by coupled equations which are solved numerically for various material parameters of QD and external laser field. Results show the effective controlling effect on the generation of High Harmonic Generation by changing the Chirping parameter of the laser pulse and the size of the QD which otherwise is not possible in other systems.

Experimentally, mutually coupled quantum dot lasers demonstrate a greatly reduced modal linewidth when mutually phase-locked. The authors investigate this phenomenon theoretically. Specifically, they examine a delay differential equation coupled phase model and use it to find the laser linewidth in several configurations. The numerical results are in excellent agreement with previously reported experimental findings. They show that while the model predicts a restoring force on the phase difference of the coupled lasers, this translates to an effective restoring force on the individual laser phases. The phenomenon should be robust to changes in device type and in particular for modern, integrated coupled lasers.

Energetic disorder in quantum dot solids adversely impacts charge carrier transport in quantum dot solar cells and electronic devices. Here, we use ultrafast transient absorption spectroscopy to show that homogeneously broadened PbS quantum dot arrays (σhom2:σinh2 > 19:1, σinh/kBT < 0.4) can be realized if quantum dot batches are sufficiently monodisperse (δ ≲ 3.3%). The homogeneous line width is found to be an inverse function of quantum dot size, monotonically increasing from ∼25 meV for the largest quantum dots (5.8 nm diameter/0.92 eV energy) to ∼55 meV for the smallest (4.1 nm/1.3 eV energy). Furthermore, we show that intrinsic charge carrier hopping rates are faster for smaller quantum dots. This finding is the opposite of the mobility trend commonly observed in device measurements but is consistent with theoretical predictions. Fitting our data to a kinetic Monte Carlo model, we extract charge carrier hopping times ranging from 80 ps for the smallest quantum dots to over 1 ns for the largest, with ...

Monolithic integration of high-performance semiconductor lasers on silicon enables wafer-scale optical interconnects within photonic integrated circuits on a silicon manufacturing platform. III–V quantum dot (QD) lasers on silicon stand out for their better device performances and reliability. QD lasers grown on III–V substrates have been integrated by wafer-bonding techniques with high quality. Direct growth of QD lasers on silicon offers an alluring alternative, using widely available large-area silicon substrates. However, to date, notable achievements have been reported only in InAs/GaAs lasers emitting at 1.3 μm, while 1.55 μm InAs/InP QD lasers on silicon remain in uncharted territory. Here we demonstrate the first 1.55 μm band InAs/InAlGaAs quantum dot microdisk lasers epitaxially grown on (001) silicon substrates. The lasing threshold for the seven-layer quantum dot microdisk laser at liquid-helium temperature is 1.6 mW under continuous optical pumping. The observed lasing is attributed to a uniqu...

Structural and optical properties of hybrid structures with multiple layers of semiconductor InAs/AlGaAs quantum dots and indium clusters on the surface are investigated. Before we have shown that in such hybrid structures strong exciton-plasmon interaction takes place. It results in non-radiative energy transfer to a large quantum dot that acts as an acceptor and the consequent enhancement of the long-wavelength photoluminescence that was obtained in our experiments. Here, we demonstrate vertical alignment of indium clusters over quantum dots with direct method of scanning transmission electron microscopy. Analysis of photoluminescence spectra reveals that the main contribution to exciton-plasmon interaction is provided by the upper layer of quantum dots located near metal particles.

An optically pumped GaN-based laser structure with 10th-order laterally coupled surface grating is demonstrated. The fabrication involved i-line photolithography and dry etching, avoiding more complex technologies such as multiple epitaxy steps. The lasing threshold of the laterally coupled distributed-feedback (LC-DFB) laser was similar to that of a ridge waveguide Fabry–Perot (RW-FP) laser. Single-peak emission with a full width at half maximum of 0.06 nm at 404.2 nm was achieved for LC-DFB lasers. In contrast to the RW-FP lasers, the LC-DFB laser is shown to exhibit a smaller shift of the emission wavelength with temperature.

A system of quantum dots on the basis of AlxIn1-xAs/AlyGa1-y As solid solutions has been studied. The usage of broadband AlxIn1-x solid solutions as the basis of quantum dots makes it possible to expand considerably the spectral emission range into the short-wave region, including the wavelength region near 770 nm being of interest for the design of aerospace systems of quantum cryptography. The optical characteristics of single AlxIn1-xAs quantum dots grown according to the Stranski–Krastanov mechanism are studied by the cryogenic microphotoluminescence method. The fine structure of exciton states of quantum dots is studied in the wavelength region near 770 nm. It is shown that the splitting of exciton states is comparable with the natural width of exciton lines, which is of great interest for the design of emitters of pairs of entangled photons on the basis of AlxAs1-x quantum dots.

The intraband optical absorption have been investigated in the presence of hydrogenic donor impurity in GaAs/GaAlAs quantum dot and quantum ring in the intense laser field. The single electron energy spectrum and wave functions have been found using the effective mass approximation and exact diagonalization technique. Different selection rules are obtained for intraband transitions depending on the direction of incident light polarization. Due to the accidental degeneracy of the laser dressed impurity states the crossings of the curves of the threshold energies and the dipole matrix elements on laser field parameter have been observed. The intraband absorption coefficient is calculated for different locations of hydrogenic donor impurity and different values of intense laser field parameter. The obtained results show that the absorption spectrum can exhibit either a blue- or redshift depending on the impurity location, values of the laser field parameter and direction of incident light polarization. The obtained theoretical results indicate a novel opportunity to tune the performance of new devices, based on the quantum dots and quantum rings and to control their specific properties by means of intense laser and hydrogenic donor impurity.

This paper presents a detailed experimental wavelength modulation spectroscopy approach and demonstrates its applicability to various types of semiconductor lasers in the near infrared and mid-infrared. A 5250 nm continuous-wave distributed feedback quantum cascade laser, a 2004 nm vertical cavity surface emitting laser, and a 1650 nm distributed feedback edge-emitting laser are used to extract the concentration and pressure values of nitric oxide, carbon dioxide, and methane, respectively, using the $2f$ wavelength modulation spectroscopy (WMS) technique under controlled conditions. The generality of the technique is demonstrated by extending it to $3f$ WMS for the three different kinds of lasers used in this study. The methodology required to provide in-situ real-time measurements of both gas parameters and operating characteristics of the laser are described in detail. Finally, the advantages and limitations of the technique are discussed in view of the fact that the characteristic behavior of the laser sources is significantly different. We specifically discuss the issue of targeting non-absorbing wavelength regions and the choice of modulation frequency and modulation amplitude of the laser, as well as the choice of the detection harmonic.

We demonstrate theoretically that a topological insulator quantum dot can be formed via double topological insulator constrictions (TICs). The TICs are created by appropriate split-gate electrode patterns on the top of a HgTe/CdTe quantum well (QW) with inverted band structures. In sharp contrast to conventional semiconductor quantum dots, the presence or absence of topological insulator edge states in the proposed quantum Hall bar system leads to distinct propagating behaviors. This topological insulator quantum dot can be used as a charge and/or spin carrier trap memory element with near perfect program/erase efficiency by properly adjusting the voltages applied to the split-gates. For completeness, we also demonstrate that a small perturbation of the Rashba spin orbit interaction (RSOI) or a magnetic field in the quantum dot does not destroy the topological edge states and has negligible impact on the on-(edge)-state transport behaviors of the quantum Hall bar.

A new method for the high-order harmonic generation on the quantum dots is proposed. Interaction of the kicking laser field with a single-electron cylindrical quantum dot without and in the presence of an external magnetic field is considered. The finite hard wall model and heterostructured semiconductor quantum dot are assumed in order to provide relation to real system which could be studied in an experiment. In particular, GaAs/AlxGa1-xAs quantum dot is examined throughout the paper. Harmonics to a very high-order are obtained which is significant for the attosecond pulse generation. This result can be explained on the basis of the quantum-confined Stark effect. During the kick, the electron energy is increased and it is associated with the pronounced quantum-confined Stark effect in the energy spectrum. The electron transitions to the inner shells give such harmonic emission as a result. It is shown that the range of the harmonic spectrum is strongly dependent on the pulse duration. The influence of a realistic form of kick present in experiments, as the Gaussian approximation for delta function, to the harmonic emission is examined.

The energy levels and binding energies of hydrogenic impurity associated with the ground state and some low-lying states in GaAs/AlGaAs core/shell quantum dots are theoretically studied by using the finite difference method. It is shown that energy levels and binding energies are depended dramatically on the size of the quantum dot due to quantum size effect. The change of the level ordering for hydrogenic impurity can be found and then to cause the corresponding changes in the binding energies, which can be adjusted by the radius of the quantum dot. Based on the analysis of these energy levels, the third-harmonic generation susceptibility in this quantum dot with (or without) impurity is investigated by using the compact-density-matrix approach. The results show that the third harmonic generation susceptibility obtained in the two cases can reach the magnitude of ∼10 −7 m 2 V −2 by choosing a large radius of quantum dot. For the large quantum dot with impurity, it is found that the third-harmonic generation susceptibility can be effectively enhanced about 1.3 ∼ 1.5 times than the case regardless of the impurity. Finally, the resonant peak and its corresponding to resonant energy are also taken into account.

This paper reports results on investigations of the dynamical behavior of a semiconductor laser with quantum dots active medium under the influence of a feedback from double external cavity. This configuration is treated in the framework of Lang-Kobayashi equations. The locus of external cavity modes is found to be elliptic, as in case of conventional optical feedback, but also represents different shapes, even with possible satellite bubbles. A bifurcation analysis is carried out revealing the points of saddle-node and Hopf bifurcations. Finally, the nature of bifurcations and the stability of steady state solutions are analyzed in dependence on different parameters.

InP/GaInP quantum dot laser structures exhibiting broad optical gain spectra suitable for mode-locking have been demonstrated. Two-section narrow ridge passive mode-locked lasers were fabricated from this material. Mode-locking conditions have been investigated for devices with different cavity lengths, with maximum frequency of 15.21 GHz.

A white light source composed with the blue laser diode (LD) and green and red quantum dots is investigated for joint lighting and visible light communications. Some issues about the properties of the proposed white light source are experimentally analyzed in details. They are very suitable to be applied in the long distant high speed visible light communication.

Funding: European Research Council (ERC) under the European Union’s Seventh Framework ERC Grant Agreement No.615613 and from the German Science Foundation (DFG) via the collaborative research center CRC787, CRC910 and GRK1558. BL acknowledges funding by the Deutsche Forschungsgemeinschaft (DFG, German Research Foundation) – 404943123. Mutual coupling and injection locking of semiconductor lasers is of great interest in non-linear dynamics and its applications for instance in secure data communication and photonic reservoir computing. Despite its importance, it has hardly been studied in microlasers operating at μW light levels. In this context, vertically emitting quantum dot micropillar lasers are of high interest. Usually, their light emission is bimodal, and the gain competition of the associated linearly polarized fundamental emission modes results in complex switching dynamics. We report on selective optical injection into either one of the two fundamental mode components of a bimodal micropillar laser. Both modes can lock to the master laser and influence the non-injected mode by reducing the available gain. We demonstrate that the switching dynamics can be tailored externally via optical injection in very good agreement with our theory based on semi-classical rate equations. Publisher PDF

Optically injected quantum dot lasers display many unique nonlinear phenomena and are in particular, excellent testbeds for different forms of excitability. We analyse the recent discovery of Type II excitability in such devices. An optothermal instability leads to the phenomenon and while an underlying Hopf bifurcation is ultimately responsible for the observation, intriguingly there are two potential routes: One via a subcritical bifurcation and an associated bistable region and the other via a supercritical bifurcation and an associated canard explosion.

We present preliminary characterization results of the first InAs/InAlGaAs/InP 1.3μm quantum dots (QDs) laser directly grown on (001) silicon. A threshold current density of 1.05 kA/cm2 under pulsed current injection has been obtained. A 50 ns width optical pulse was observed under gain-switching measurement.

Using correlated electron microscopy techniques, we characterize optoelectronic and structural properties of dislocation in InAs quantum dots (QD) structures. Results indicate that although dislocations significantly affect QD luminescence, the rate of recombination enhanced dislocation climb slows noticeably during the aging process from quantum well structures.

This paper focuses on the effect of threshold current density on different characteristics of quantum dot based laser. To investigate the effect, different characteristics have been analyzed using quantum dot as the active layer material of the laser structure. Performance improvement of quantum dot laser using InN has been achieved in terms of minimization of the threshold current dependence such as mirror loss, modal gain, turn-on delay and so forth. Numerical results have been analyzed considering the values of threshold current densities of GaN, AlN and InN based quantum dot lasers. Analytical results show that internal loss increases linearly with the increase of the threshold current density. However, other characteristics like mirror loss, modal gain, turn-on delay have nonlinear dependence on the threshold current density for any material used in the active layer. The threshold current density of InN quantum dot based laser is lower than that of other existing quantum dot based lasers. Analytical results ascertained that mirror loss has been increased a little bit. Conversely, internal loss and modal gain have been minimized considerably using InN based quantum dot in the active layer of the laser structure. In addition, turn-on delay time has been also minimized significantly.

The T-band (1000-1260 nm), which offers more than 60 THz worth of bandwidth and wider than C- and L-band combined. The large scale photonic router using 3-stage arrayed-waveguide grating for T-band and O-band is configured.

A submonolayer quantum dot infrared photodetector (SML-QDIP) was grown on a GaAs(001) substrate by molecular beam epitaxy and processed using conventional optical lithography, wet etching and electronbeam metallization. Additionally, a side of the device was polished at 45 degrees in order to allow optical measurements with s- and p-polarized light. The electro-optical properties of the device were investigated both in normal incidence and at 45 degrees in order to study the quantum confinement of the SMLQD along the lateral and vertical directions. The s-to-p photocurrent ratio was found to be between 0.10 and 0.43, showing that, in this new type of quantum dot, the lateral confinement is still weaker than along the vertical direction, but is better than the one of conventional QDs fabricated in the Stranski-Krastanov growth mode. The maximum specific detectivity in normal incidence was $1.3 \times 10^{11}$ cm Hz1/2/W at 30 K and 0.9V.

We demonstrate a III-V avalanche photodiode (APD) grown by heteroepitaxy on silicon. This InGaAs/InAlAs APD exhibits low dark current, gain >20, external quantum efficiency >40%, and similar low excess noise, k∼0.2, as InAlAs APDs on InP.

InAs/GaAs quantum dot lasers epitaxially grown on silicon substrates are promising candidates as light sources for silicon photonic integrated circuits. We discuss their dynamic properties via small-signal and pulsed simulation and experiment, with a special focus on their potential for data transmission applications.

In this work, the feasibility of a monolithically integrated laser and electroabsorption modulator based on the same active quantum dot epistructure is studied. The net modal gain and the absorption in the modulator were measured using the segmented contact method from 25 °C to 125 °C. The maximum of the net modal gain active region of the laser decreases from 10 cm -1 at 25 °C to 3.9 cm -1 at 125 °C. The non-optimized maximum extinction ratio of the modulator, 4.1 dB·mm -1 , is almost constant until 25 °C. The wavelengths at which the net modal gain and the change in absorption are maximum shifts with temperature by 0.04 eV.

Recently, the theoretical model of the quantum dot (QD) semiconductor lasers has been developed where the excited state (ES) lasing has been taking into account. It has been shown that the ES QD semiconductor laser demonstrates a larger modulation bandwidth, lower frequency chirp and a smaller line enhancement factor (LEF) as compared to the ground state (GS) QD semiconductor lasers. The applications of high-speed directly modulated ES lasers in future optical communications is possible. In this paper, we investigated theoretically the 4 level pulse amplitude modulation (4-PAM) and 8 level PAM (8-PAM) formats of the ES QDWELL laser. We solved numerically the modified rate equation system and have shown that is such cases the QDWELL laser modulation bandwidth is substantially increased.

A theory is presented for mode-locked quantum-dot lasers used in time- and wavelength-division multiplexing in telecommunications. Multimode semiclassical laser theory is used to treat active-medium nonlinearities resulting in mode competition, gain saturation, carrier-induced refractive index, and combination tones leading to spontaneous mode-locking and frequency-comb creation.

Funding: Austrian Science Fund (F4909-N23, P28914-N27,W1243); Österreichische Forschungsförderungsgesellschaft (ATMO-SENSE, ERANet Photonic Sensing program, COMTERA-FFG849614); European Science Foundation (ESF) (CZ.02.2.69/0.0/0.0/16_027/0008371); Air Force Office of Scientific Research(AFOSR FA9550-17-1-0340). The generation of mid-infrared pulses in monolithic and electrically pumped devices is of great interest for mobile spectroscopic instruments. The gain dynamics of interband cascade lasers (ICL) are promising for mode-locked operation at low threshold currents. Here, we present conclusive evidence for the generation of picosecond pulses in ICLs via active mode-locking. At small modulation power, the ICL operates in a linearly chirped frequency comb regime characterized by strong frequency modulation. Upon increasing the modulation amplitude, the chirp decreases until broad pulses are formed. Careful tuning of the modulation frequency minimizes the remaining chirp and leads to the generation of 3.2 ps pulses. Publisher PDF

Optically injected semiconductor lasers generate limit-cycle dynamics of period-one and period-two oscillations at microwave frequencies. At specific operating points, the periodic oscillations can be rendered insensitive to small-signal fluctuation in the operating conditions of the master and slave lasers. Periodic oscillations with low-sensitivity to fluctuation in the slave laser bias current, injection strength, or detuning frequency can be enhanced through tailoring the intrinsic laser parameters. Here, through numerical calculations, the effects of each intrinsic parameter on the various low-sensitivity operating points are demonstrated through detailed maps as functions of the operating parameters. For enhanced low sensitivity to bias-current and injection-strength fluctuations, a laser with a small linewidth enhancement factor is favored. Conversely, a large linewidth enhancement factor enhances low sensitivity to detuning-frequency fluctuations. Lasers with a more negative value of the gain saturation factor confine the regions of low sensitivity to fluctuations in the bias current and detuning frequency to the extrema of the periodic oscillation frequency. The laser relaxation rates that enhance the periodic-oscillation dynamic regions of an optically injected semiconductor laser, in turn, increases the regions of the various types of low-sensitivity operating points.