Kathy Lüdge - Academia.edu (original) (raw)
Papers by Kathy Lüdge
Chaos: An Interdisciplinary Journal of Nonlinear Science, 2021
Bovine viral diarrhea (BVD) is a disease in cattle with complex transmission dynamics that causes... more Bovine viral diarrhea (BVD) is a disease in cattle with complex transmission dynamics that causes substantial economic losses and affects animal welfare. The infection can be transient or persistent. The mostly asymptomatic persistently infected hosts are the main source for transmission of the virus. This characteristic makes it difficult to control the spreading of BVD. We develop a deterministic compartmental model for the spreading dynamics of BVD within a herd and derive the basic reproduction number. This epidemiological quantity indicates that identification and removal of persistently infected animals is a successful control strategy if the transmission rate of transiently infected animals is small. Removing persistently infected animals from the herd at birth results in recurrent outbreaks with decreasing peak prevalence. We propose a stochastic version of the compartmental model that includes stochasticity in the transmission parameters. This stochasticity leads to sustained oscillations in cases where the deterministic model predicts oscillations with decreasing amplitude. The results provide useful information for the design of control strategies.
Chaos: An Interdisciplinary Journal of Nonlinear Science, 2020
The Deep Time-Delay Reservoir Computing concept utilizes unidirectionally connected systems with ... more The Deep Time-Delay Reservoir Computing concept utilizes unidirectionally connected systems with timedelays for supervised learning. We present how the dynamical properties of a deep Ikeda-based reservoir are related to its memory capacity (MC) and how that can be used for optimization. In particular, we analyze bifurcations of the corresponding autonomous system and compute conditional Lyapunov exponents, which measure the generalized synchronization between the input and the layer dynamics. We show how the MC is related to the systems distance to bifurcations or magnitude of the conditional Lyapunov exponent. The interplay of different dynamical regimes leads to an adjustable distribution between linear and nonlinear MC. Furthermore, numerical simulations show resonances between clock cycle and delays of the layers in all degrees of the MC. Contrary to MC losses in single-layer reservoirs, these resonances can boost separate degrees of the MC and can be used, e.g. to design a system with maximum linear MC. Accordingly, we present two configurations that empower either high nonlinear MC or long time linear MC.
New Journal of Physics, 2020
In this paper we theoretically investigate the statistical light-emission properties of an optica... more In this paper we theoretically investigate the statistical light-emission properties of an optically injected bimodal quantum-dot micropillar laser with high spontaneous emission rates. The nanostructured device is described in terms of a stochastic, semiclassically derived rate equation model. We focus on the stochastic switching dynamics between the two fundamental modes and correlate the results with an in-depth bifurcation analysis of the underlying deterministic dynamics. By analyzing different statistical measures, e.g. average intensity, auto- and cross-correlation functions, as well as dwell-time distributions, we give a road map on how to unravel the different dynamic regimes in the presence of large noise from experimentally accessible quantities.
Neural Networks, 2020
The time-delay-based reservoir computing setup has seen tremendous success in both experiment and... more The time-delay-based reservoir computing setup has seen tremendous success in both experiment and simulation. It allows for the construction of large neuromorphic computing systems with only few components. However, until now the interplay of the different timescales has not been investigated thoroughly. In this manuscript, we investigate the effects of a mismatch between the time-delay and the clock cycle for a general model. Typically, these two time scales are considered to be equal. Here we show that the case of equal or resonant time-delay and clock cycle could be actively detrimental and leads to an increase of the approximation error of the reservoir. In particular, we can show that non-resonant ratios of these time scales have maximal memory capacities. We achieve this by translating the periodically driven delay-dynamical system into an equivalent network. Networks that originate from a system with resonant delay-times and clock cycles fail to utilize all of their degrees of freedom, which causes the degradation of their performance.
Chaos: An Interdisciplinary Journal of Nonlinear Science, 2017
Passively mode-locked semiconductor lasers are compact, inexpensive sources of short light pulses... more Passively mode-locked semiconductor lasers are compact, inexpensive sources of short light pulses of high repetition rates. In this work, we investigate the dynamics and bifurcations arising in such a device under the influence of time delayed optical feedback. This laser system is modelled by a system of delay differential equations, which includes delay terms associated with the laser cavity and feedback loop. We make use of specialised path continuation software for delay differential equations to analyse the regime of short feedback delays. Specifically, we consider how the dynamics and bifurcations depend on the pump current of the laser, the feedback strength, and the feedback delay time. We show that an important role is played by resonances between the mode-locking frequencies and the feedback delay time. We find feedback-induced harmonic mode locking and show that a mismatch between the fundamental frequency of the laser and that of the feedback cavity can lead to multi-pulse or quasiperiodic dynamics. The quasiperiodic dynamics exhibit a slow modulation, on the time scale of the gain recovery rate, which results from a beating with the frequency introduced in the associated torus bifurcations and leads to gain competition between multiple pulse trains within the laser cavity. Our results also have implications for the case of large feedback delay times, where a complete bifurcation analysis is not practical. Namely, for increasing delay, there is an everincreasing degree of multistability between mode-locked solutions due to the frequency pulling effect.
Optical and Quantum Electronics, 2018
We investigate the nonlinear light propagation in InAs/InGaAs quantum-dot-ina-well semiconductor ... more We investigate the nonlinear light propagation in InAs/InGaAs quantum-dot-ina-well semiconductor optical amplifiers in the limit of strong optical excitation where Rabi oscillations are excited in the active medium. The amplifier is analyzed in a degenerate four-wave-mixing setup and characterized by its frequency conversion and creation performance. Our simulations show that the interplay between the nonlinear four-wavemixing process and the coherent Rabi oscillations greatly influences the frequency conversion process. Rabi oscillations can be resonantly excited by the correct choice of the frequency detuning between pump and probe signals, which greatly enhances the nonlinear frequency conversion efficiency at frequencies up to several THz. We furthermore show that the coherent pulse shaping of ultrashort optical pulses in the quantum-dot medium can greatly enhance their spectral bandwidth, potentially allowing for ultra-broad-band frequency comb generation.
Scientific Reports, 2019
We experimentally and theoretically investigate the pulsed emission dynamics of a three section t... more We experimentally and theoretically investigate the pulsed emission dynamics of a three section tapered semiconductor quantum dot laser. The laser output is characterized in terms of peak power, pulse width, timing jitter and amplitude stability and a range of outstanding pulse performance is found. A cascade of dynamic operating regimes is identified and comprehensively investigated. We propose a microscopically motivated traveling-wave model, which optimizes the computation time and naturally allows insights into the internal carrier dynamics. The model excellently reproduces the measured results and is further used to study the pulse-generation mechanism as well as the influence of the geometric design on the pulsed emission. We identify a pulse shortening mechanism responsible for the device performance, that is unique to the device geometry and configuration. The results may serve as future guidelines for the design of monolithic high-power passively mode-locked quantum dot sem...
Optics express, Jan 20, 2018
Microlasers are ideal candidates to bring the fascinating variety of nonlinear complex dynamics f... more 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 contr...
Optica, 2017
An integrated optoelectronic feedback system based on semiconductor quantum dot-micropillars is p... more An integrated optoelectronic feedback system based on semiconductor quantum dot-micropillars is presented. The device consists of an electrically driven microlaser optically coupled to monolithically integrated photodetectors. Via the external amplification and reinjection of the detector photocurrent into the microlaser, self-pulsing in the optoelectronic signal is observed. The feedback-induced self-pulsing is explained qualitatively by a rate equation model, which considers the thermally induced shift in the gain of the laser during pulsing and a Gaussian white-noise term for spontaneous emission. The results show promise for exploring chaos in ultra-compact nanophotonic systems and for technological approaches towards chaos-based secure communication, random number generation, and selfpulsing single photon sources on a highly integrated semiconductor platform.
2016 18th International Conference on Transparent Optical Networks (ICTON), 2016
Optical feedback stabilization is a powerful concept to improve the timing stability of passively... more Optical feedback stabilization is a powerful concept to improve the timing stability of passively mode-locked lasers. We first study experimentally the repetition rate and timing jitter behavior of a single-cavity optical feedback as a function of the microscopic delay length. By a dual-cavity optical feedback configuration, we then present experimental and numerical results on the repetition rate and timing jitter dependence on dual-cavity fine-delay. Simulations are performed by a delay differential equation model. We obtain an improvement in timing jitter and an increase in pulse repetition rate tuning range as compared to the laser without optical feedback.
New Journal of Physics, 2016
The super-thermal photon bunching in quantum-dot (QD) micropillar lasers is investigated both exp... more The super-thermal photon bunching in quantum-dot (QD) micropillar lasers is investigated both experimentally and theoretically via simulations driven by dynamic considerations. Using stochastic multi-mode rate equations we obtain very good agreement between experiment and theory in terms of intensity profiles and intensity-correlation properties of the examined QD micro-laser's emission. Further investigations of the time-dependent emission show that super-thermal photon bunching occurs due to irregular mode-switching events in the bimodal lasers. Our bifurcation analysis reveals that these switchings find their origin in an underlying bistability, such that spontaneous emission noise is able to effectively perturb the two competing modes in a small parameter region. We thus ascribe the observed high photon correlation to dynamical multistabilities rather than quantum mechanical correlations.
![Research paper thumbnail of Publisher's Note: Amplitude-phase coupling drives chimera states in globally coupled laser networks [Phys. Rev. E91, 040901(R) (2015)]](https://attachments.academia-assets.com/102581563/thumbnails/1.jpg)
](Physical Review E, 2015
with an error in Eq. (1). Equation (1) should read as dE n dt = (1 + iα)E n N n + e −iC p κ Z j e... more with an error in Eq. (1). Equation (1) should read as dE n dt = (1 + iα)E n N n + e −iC p κ Z j e −iC p E j (t − τ) (1) The equation has been corrected as of 9 December 2015. The equation is incorrect in the printed version of the journal.
2013 Conference on Lasers & Electro-Optics Europe & International Quantum Electronics Conference CLEO EUROPE/IQEC, 2013
ABSTRACT We study experimentally and numerically the changes in pulse shape a Gaussian laser puls... more ABSTRACT We study experimentally and numerically the changes in pulse shape a Gaussian laser pulse undergoes when propagating through an electrically pumped quantum dot semiconductor optical amplifier (QD-SOA). The pulse energy is set to be resonant to the quantum dot ground state transition, and the pulse shape is analyzed in phase and amplitude in a heterodyne cross-correlation experiment. For the case of an inverted system, we observe the appearance of a periodic modulation of the temporal pulse profile above a critical pulse power. Similar signatures of pulse break-up have been observed at low temperature in quantum dot ensembles without electrical pumping and were linked to optically induced Rabi oscillations imprinting the coherent switching between absorption and stimulated emission of photons by the material system.
Physik in unserer Zeit, 2014
ABSTRACT Halbleiter-Laserdioden werden ständig weiterentwickelt. Neben den weit verbreiteten Quan... more ABSTRACT Halbleiter-Laserdioden werden ständig weiterentwickelt. Neben den weit verbreiteten Quantentroglasern führte das zu den Quantenpunktlasern. Halbleiter-Quantenpunkte sind winzige Kristallpyramiden, die für die Wellenpakete der Elektronen nulldimensionale Objekte darstellen. Sie wirken als künstliche Atome im Halbleitermaterial, die zum Lasern angeregt werden. Die Anregung geschieht über Elektronenstreuung. Quantenpunktlaser sind in ihrem dynamischen Verhalten viel stabiler als Quantentroglaser, was von Vorteil für die optische Datenübertragung ist. Die Quantenpunkte variieren in ihrer Größe und können so in verschiedenen Wellenlängen lasern, was kurze Pulse erlaubt. Mit einem Laserstrahl von außen kann man sie wie künstliche Neuronen oder optische Schalter mit zwei Schaltzuständen steuern. Dies und ihr geringer Energieverbrauch machen sie für technische Anwendungen interessant, darunter auch völlig neue.
2008 IEEE 21st International Semiconductor Laser Conference, 2008
ABSTRACT The complex turn-on behavior of semiconductor quantum-dot lasers is determined by the no... more ABSTRACT The complex turn-on behavior of semiconductor quantum-dot lasers is determined by the nonlinearity of the carrier-carrier scattering rates. Hole- and electron dynamics in the dots decouple leading to small cutoff frequencies of these lasers.
2013 13th International Conference on Numerical Simulation of Optoelectronic Devices (NUSOD), 2013
We investigate the nonlinear dynamics of a quantum-dot laser coupled to an electro-optic modulato... more We investigate the nonlinear dynamics of a quantum-dot laser coupled to an electro-optic modulator using the Lang-Kobayashi model. We determine the effect of the detuning between the EOM and the QD laser and the influence of the static phase shift on the QD laser dynamics. The electrooptical modulator's model is based on semiconductor Maxwell-Bloch equations with voltage dependent loss rates.
Nonlinear Optics, 2013
ABSTRACT Rabi oscillations imprint an intensity modulation on the electric field of the laser pul... more ABSTRACT Rabi oscillations imprint an intensity modulation on the electric field of the laser pulse creating them. We experimentally observe this signature in a quantum dot ensemble at room temperature for arbitrary degrees of inversion.
Optics express, Jan 2, 2014
Excitability and coherence resonance are studied in a semiconductor quantum dot laser under short... more Excitability and coherence resonance are studied in a semiconductor quantum dot laser under short optical self-feedback. For low pump levels, these are observed close to a homoclinic bifurcation, which is in correspondence with earlier observations in quantum well lasers. However, for high pump levels, we find excitability close to a boundary crisis of a chaotic attractor. We demonstrate that in contrast to the homoclinic bifurcation the crisis and thus the excitable regime is highly sensitive to the pump current. The excitability threshold increases with the pump current, which permits to adjust the sensitivity of the excitable unit to noise as well as to shift the optimal noise strength, at which maximum coherence is observed. The shift adds up to more than one order of magnitude, which strongly facilitates experimental realizations.
Nonlinear Laser Dynamics, 2012
CLEO: 2014, 2014
ABSTRACT Excited-state lasing in quantum dot lasers is theoretically demonstrated to exhibit a br... more ABSTRACT Excited-state lasing in quantum dot lasers is theoretically demonstrated to exhibit a broader modulation response, lower chirp-to-power ratio, and smaller linewidth enhancement factor in comparison with the conventional lasing in the ground state.
Chaos: An Interdisciplinary Journal of Nonlinear Science, 2021
Bovine viral diarrhea (BVD) is a disease in cattle with complex transmission dynamics that causes... more Bovine viral diarrhea (BVD) is a disease in cattle with complex transmission dynamics that causes substantial economic losses and affects animal welfare. The infection can be transient or persistent. The mostly asymptomatic persistently infected hosts are the main source for transmission of the virus. This characteristic makes it difficult to control the spreading of BVD. We develop a deterministic compartmental model for the spreading dynamics of BVD within a herd and derive the basic reproduction number. This epidemiological quantity indicates that identification and removal of persistently infected animals is a successful control strategy if the transmission rate of transiently infected animals is small. Removing persistently infected animals from the herd at birth results in recurrent outbreaks with decreasing peak prevalence. We propose a stochastic version of the compartmental model that includes stochasticity in the transmission parameters. This stochasticity leads to sustained oscillations in cases where the deterministic model predicts oscillations with decreasing amplitude. The results provide useful information for the design of control strategies.
Chaos: An Interdisciplinary Journal of Nonlinear Science, 2020
The Deep Time-Delay Reservoir Computing concept utilizes unidirectionally connected systems with ... more The Deep Time-Delay Reservoir Computing concept utilizes unidirectionally connected systems with timedelays for supervised learning. We present how the dynamical properties of a deep Ikeda-based reservoir are related to its memory capacity (MC) and how that can be used for optimization. In particular, we analyze bifurcations of the corresponding autonomous system and compute conditional Lyapunov exponents, which measure the generalized synchronization between the input and the layer dynamics. We show how the MC is related to the systems distance to bifurcations or magnitude of the conditional Lyapunov exponent. The interplay of different dynamical regimes leads to an adjustable distribution between linear and nonlinear MC. Furthermore, numerical simulations show resonances between clock cycle and delays of the layers in all degrees of the MC. Contrary to MC losses in single-layer reservoirs, these resonances can boost separate degrees of the MC and can be used, e.g. to design a system with maximum linear MC. Accordingly, we present two configurations that empower either high nonlinear MC or long time linear MC.
New Journal of Physics, 2020
In this paper we theoretically investigate the statistical light-emission properties of an optica... more In this paper we theoretically investigate the statistical light-emission properties of an optically injected bimodal quantum-dot micropillar laser with high spontaneous emission rates. The nanostructured device is described in terms of a stochastic, semiclassically derived rate equation model. We focus on the stochastic switching dynamics between the two fundamental modes and correlate the results with an in-depth bifurcation analysis of the underlying deterministic dynamics. By analyzing different statistical measures, e.g. average intensity, auto- and cross-correlation functions, as well as dwell-time distributions, we give a road map on how to unravel the different dynamic regimes in the presence of large noise from experimentally accessible quantities.
Neural Networks, 2020
The time-delay-based reservoir computing setup has seen tremendous success in both experiment and... more The time-delay-based reservoir computing setup has seen tremendous success in both experiment and simulation. It allows for the construction of large neuromorphic computing systems with only few components. However, until now the interplay of the different timescales has not been investigated thoroughly. In this manuscript, we investigate the effects of a mismatch between the time-delay and the clock cycle for a general model. Typically, these two time scales are considered to be equal. Here we show that the case of equal or resonant time-delay and clock cycle could be actively detrimental and leads to an increase of the approximation error of the reservoir. In particular, we can show that non-resonant ratios of these time scales have maximal memory capacities. We achieve this by translating the periodically driven delay-dynamical system into an equivalent network. Networks that originate from a system with resonant delay-times and clock cycles fail to utilize all of their degrees of freedom, which causes the degradation of their performance.
Chaos: An Interdisciplinary Journal of Nonlinear Science, 2017
Passively mode-locked semiconductor lasers are compact, inexpensive sources of short light pulses... more Passively mode-locked semiconductor lasers are compact, inexpensive sources of short light pulses of high repetition rates. In this work, we investigate the dynamics and bifurcations arising in such a device under the influence of time delayed optical feedback. This laser system is modelled by a system of delay differential equations, which includes delay terms associated with the laser cavity and feedback loop. We make use of specialised path continuation software for delay differential equations to analyse the regime of short feedback delays. Specifically, we consider how the dynamics and bifurcations depend on the pump current of the laser, the feedback strength, and the feedback delay time. We show that an important role is played by resonances between the mode-locking frequencies and the feedback delay time. We find feedback-induced harmonic mode locking and show that a mismatch between the fundamental frequency of the laser and that of the feedback cavity can lead to multi-pulse or quasiperiodic dynamics. The quasiperiodic dynamics exhibit a slow modulation, on the time scale of the gain recovery rate, which results from a beating with the frequency introduced in the associated torus bifurcations and leads to gain competition between multiple pulse trains within the laser cavity. Our results also have implications for the case of large feedback delay times, where a complete bifurcation analysis is not practical. Namely, for increasing delay, there is an everincreasing degree of multistability between mode-locked solutions due to the frequency pulling effect.
Optical and Quantum Electronics, 2018
We investigate the nonlinear light propagation in InAs/InGaAs quantum-dot-ina-well semiconductor ... more We investigate the nonlinear light propagation in InAs/InGaAs quantum-dot-ina-well semiconductor optical amplifiers in the limit of strong optical excitation where Rabi oscillations are excited in the active medium. The amplifier is analyzed in a degenerate four-wave-mixing setup and characterized by its frequency conversion and creation performance. Our simulations show that the interplay between the nonlinear four-wavemixing process and the coherent Rabi oscillations greatly influences the frequency conversion process. Rabi oscillations can be resonantly excited by the correct choice of the frequency detuning between pump and probe signals, which greatly enhances the nonlinear frequency conversion efficiency at frequencies up to several THz. We furthermore show that the coherent pulse shaping of ultrashort optical pulses in the quantum-dot medium can greatly enhance their spectral bandwidth, potentially allowing for ultra-broad-band frequency comb generation.
Scientific Reports, 2019
We experimentally and theoretically investigate the pulsed emission dynamics of a three section t... more We experimentally and theoretically investigate the pulsed emission dynamics of a three section tapered semiconductor quantum dot laser. The laser output is characterized in terms of peak power, pulse width, timing jitter and amplitude stability and a range of outstanding pulse performance is found. A cascade of dynamic operating regimes is identified and comprehensively investigated. We propose a microscopically motivated traveling-wave model, which optimizes the computation time and naturally allows insights into the internal carrier dynamics. The model excellently reproduces the measured results and is further used to study the pulse-generation mechanism as well as the influence of the geometric design on the pulsed emission. We identify a pulse shortening mechanism responsible for the device performance, that is unique to the device geometry and configuration. The results may serve as future guidelines for the design of monolithic high-power passively mode-locked quantum dot sem...
Optics express, Jan 20, 2018
Microlasers are ideal candidates to bring the fascinating variety of nonlinear complex dynamics f... more 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 contr...
Optica, 2017
An integrated optoelectronic feedback system based on semiconductor quantum dot-micropillars is p... more An integrated optoelectronic feedback system based on semiconductor quantum dot-micropillars is presented. The device consists of an electrically driven microlaser optically coupled to monolithically integrated photodetectors. Via the external amplification and reinjection of the detector photocurrent into the microlaser, self-pulsing in the optoelectronic signal is observed. The feedback-induced self-pulsing is explained qualitatively by a rate equation model, which considers the thermally induced shift in the gain of the laser during pulsing and a Gaussian white-noise term for spontaneous emission. The results show promise for exploring chaos in ultra-compact nanophotonic systems and for technological approaches towards chaos-based secure communication, random number generation, and selfpulsing single photon sources on a highly integrated semiconductor platform.
2016 18th International Conference on Transparent Optical Networks (ICTON), 2016
Optical feedback stabilization is a powerful concept to improve the timing stability of passively... more Optical feedback stabilization is a powerful concept to improve the timing stability of passively mode-locked lasers. We first study experimentally the repetition rate and timing jitter behavior of a single-cavity optical feedback as a function of the microscopic delay length. By a dual-cavity optical feedback configuration, we then present experimental and numerical results on the repetition rate and timing jitter dependence on dual-cavity fine-delay. Simulations are performed by a delay differential equation model. We obtain an improvement in timing jitter and an increase in pulse repetition rate tuning range as compared to the laser without optical feedback.
New Journal of Physics, 2016
The super-thermal photon bunching in quantum-dot (QD) micropillar lasers is investigated both exp... more The super-thermal photon bunching in quantum-dot (QD) micropillar lasers is investigated both experimentally and theoretically via simulations driven by dynamic considerations. Using stochastic multi-mode rate equations we obtain very good agreement between experiment and theory in terms of intensity profiles and intensity-correlation properties of the examined QD micro-laser's emission. Further investigations of the time-dependent emission show that super-thermal photon bunching occurs due to irregular mode-switching events in the bimodal lasers. Our bifurcation analysis reveals that these switchings find their origin in an underlying bistability, such that spontaneous emission noise is able to effectively perturb the two competing modes in a small parameter region. We thus ascribe the observed high photon correlation to dynamical multistabilities rather than quantum mechanical correlations.
Physical Review E, 2015
with an error in Eq. (1). Equation (1) should read as dE n dt = (1 + iα)E n N n + e −iC p κ Z j e... more with an error in Eq. (1). Equation (1) should read as dE n dt = (1 + iα)E n N n + e −iC p κ Z j e −iC p E j (t − τ) (1) The equation has been corrected as of 9 December 2015. The equation is incorrect in the printed version of the journal.
2013 Conference on Lasers & Electro-Optics Europe & International Quantum Electronics Conference CLEO EUROPE/IQEC, 2013
ABSTRACT We study experimentally and numerically the changes in pulse shape a Gaussian laser puls... more ABSTRACT We study experimentally and numerically the changes in pulse shape a Gaussian laser pulse undergoes when propagating through an electrically pumped quantum dot semiconductor optical amplifier (QD-SOA). The pulse energy is set to be resonant to the quantum dot ground state transition, and the pulse shape is analyzed in phase and amplitude in a heterodyne cross-correlation experiment. For the case of an inverted system, we observe the appearance of a periodic modulation of the temporal pulse profile above a critical pulse power. Similar signatures of pulse break-up have been observed at low temperature in quantum dot ensembles without electrical pumping and were linked to optically induced Rabi oscillations imprinting the coherent switching between absorption and stimulated emission of photons by the material system.
Physik in unserer Zeit, 2014
ABSTRACT Halbleiter-Laserdioden werden ständig weiterentwickelt. Neben den weit verbreiteten Quan... more ABSTRACT Halbleiter-Laserdioden werden ständig weiterentwickelt. Neben den weit verbreiteten Quantentroglasern führte das zu den Quantenpunktlasern. Halbleiter-Quantenpunkte sind winzige Kristallpyramiden, die für die Wellenpakete der Elektronen nulldimensionale Objekte darstellen. Sie wirken als künstliche Atome im Halbleitermaterial, die zum Lasern angeregt werden. Die Anregung geschieht über Elektronenstreuung. Quantenpunktlaser sind in ihrem dynamischen Verhalten viel stabiler als Quantentroglaser, was von Vorteil für die optische Datenübertragung ist. Die Quantenpunkte variieren in ihrer Größe und können so in verschiedenen Wellenlängen lasern, was kurze Pulse erlaubt. Mit einem Laserstrahl von außen kann man sie wie künstliche Neuronen oder optische Schalter mit zwei Schaltzuständen steuern. Dies und ihr geringer Energieverbrauch machen sie für technische Anwendungen interessant, darunter auch völlig neue.
2008 IEEE 21st International Semiconductor Laser Conference, 2008
ABSTRACT The complex turn-on behavior of semiconductor quantum-dot lasers is determined by the no... more ABSTRACT The complex turn-on behavior of semiconductor quantum-dot lasers is determined by the nonlinearity of the carrier-carrier scattering rates. Hole- and electron dynamics in the dots decouple leading to small cutoff frequencies of these lasers.
2013 13th International Conference on Numerical Simulation of Optoelectronic Devices (NUSOD), 2013
We investigate the nonlinear dynamics of a quantum-dot laser coupled to an electro-optic modulato... more We investigate the nonlinear dynamics of a quantum-dot laser coupled to an electro-optic modulator using the Lang-Kobayashi model. We determine the effect of the detuning between the EOM and the QD laser and the influence of the static phase shift on the QD laser dynamics. The electrooptical modulator's model is based on semiconductor Maxwell-Bloch equations with voltage dependent loss rates.
Nonlinear Optics, 2013
ABSTRACT Rabi oscillations imprint an intensity modulation on the electric field of the laser pul... more ABSTRACT Rabi oscillations imprint an intensity modulation on the electric field of the laser pulse creating them. We experimentally observe this signature in a quantum dot ensemble at room temperature for arbitrary degrees of inversion.
Optics express, Jan 2, 2014
Excitability and coherence resonance are studied in a semiconductor quantum dot laser under short... more Excitability and coherence resonance are studied in a semiconductor quantum dot laser under short optical self-feedback. For low pump levels, these are observed close to a homoclinic bifurcation, which is in correspondence with earlier observations in quantum well lasers. However, for high pump levels, we find excitability close to a boundary crisis of a chaotic attractor. We demonstrate that in contrast to the homoclinic bifurcation the crisis and thus the excitable regime is highly sensitive to the pump current. The excitability threshold increases with the pump current, which permits to adjust the sensitivity of the excitable unit to noise as well as to shift the optimal noise strength, at which maximum coherence is observed. The shift adds up to more than one order of magnitude, which strongly facilitates experimental realizations.
Nonlinear Laser Dynamics, 2012
CLEO: 2014, 2014
ABSTRACT Excited-state lasing in quantum dot lasers is theoretically demonstrated to exhibit a br... more ABSTRACT Excited-state lasing in quantum dot lasers is theoretically demonstrated to exhibit a broader modulation response, lower chirp-to-power ratio, and smaller linewidth enhancement factor in comparison with the conventional lasing in the ground state.