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III-nitride quantum dot (QD) lasers have potential applications in visible light regime, yet one of its most important dynamic parameters, the linewidth enhancement factor (LEF), has been rarely studied. We studied the LEF of InGaN QD lasers with a comprehensive theory model and found that the LEF values of InGaN QD lasers can be smaller and more robust against inhomogeneous broadening than those of InGaAs QD lasers. In addition, the LEF improvement from quantum well to QD in III-nitride semiconductors is much larger than that in III-arsenide. It is believed that the large confinement energy in III-nitrides and atomic-like density of states of QDs contribute to these advantages of III-nitride QD lasers. Our results not only reveal the advantages of using III-nitride QD for high spectral purity, low-chirp laser applications, but also provide a general guideline for designing QD lasers with lower LEF values in various semiconductor materials.

We directly compare the performance of 1.55 $\mu \text{m}$ Fabry-Perot lasers using quantum well (QW) and quantum dash gain regions. Other than the gain medium the designs were identical, grown in the same growth system, and processed at the same time. The static laser performance (light-current and spectral) were similar for both gain materials but the intensity and phase noise characteristics of the dash based lasers were significantly better. This was attributed to the self mode-locking of the dash lasers that was not observed for the QW lasers. This reduction in noise allowed individual lasing lines from the Fabry-Perot dash lasers to be used for data transmission using high order modulation schemes, with quadrature phase-shift keying (QPSK) demonstrated at a symbol rate of 32GBaud. This performance could not be achieved using the equivalent QW based laser.

Semiconductor nanocrystals represent a promising class of solution-processable optical-gain media that can be manipulated via inexpensive, easily scalable colloidal techniques. Due to their extremely small sizes (typically

In this letter, we report the dynamics and performance of a 1.3- $\mu \text{m}$ InAs/GaAs directly modulated quantum-dot laser (QDL) under strong feedback. At a direct modulation speed of 10 Gbps, error-free back-to-back operation of the QDL under a feedback level of −12 dB was realized. Feedback-resistant fiber transmission over 20 km under a maximum optical feedback level of −9 dB was also demonstrated with a power penalty of less than 1 dB at a bit error ratio (BER) of 10−3. The performance of the QDL was compared with directly modulated quantum-well laser (QWL) with similar parameters, showing a clear advantage in feedback resistance of QDL.

A low phase noise millimeter-wave (MMW) signal generator is proposed and experimentally demonstrated with a C-band passively Fabry-Perot (F-P) quantum dot mode-locked laser. A novel method is proposed to generate low phase noise MMW signal, which is simply based on a commercial off-the-shelf dual-driven LiNbO3 Mach-Zehnder modulator and a passively F-P quantum dot mode-locked laser. MMW signal with the frequency of 30 GHz, 45 GHz and 90 GHz respectively is obtained experimentally. Single-sideband phase noise of the 30 GHz and 45 GHz MMW signal is −112 dBc/Hz and −106 dBc/Hz at an offset of 1 kHz, respectively. The linewidth of the 30 GHz and 45 GHz MMW signal is about from 225 Hz and 239 Hz. This is considered a very simple MMW generator with a quasi-tunable broadband and ultra-low phase noise.

In this work we provide numerical results concerning an all-optical inhibitory integrate and fire neuron based on a single section quantum-dot InAs/GaAs laser. The numerical model employs a detailed multi-population approach that accommodates electron-hole dynamics and can efficiently describe waveband transitions from both the ground and excited energy state. The underlying physical mechanism of waveband switching in an inhibitory neuron is unveiled and is attributed to hole-electron's transport time asymmetries. A detailed dynamical analysis allowed the identification of suitable optical injection regimes so as to trigger highly sought neuro-computational behaviors such as rate encoding and neural spikes with picosecond temporal resolution.

In this work, we present an approach to modelling III-V lasers on silicon based on a travelling-wave rate equation model with sub-micrometer resolution. By allowing spatially resolved inclusion of individual dislocations along the laser cavity, our simulation results offer new insights into the physical mechanisms behind the characteristics of 980 nm In(Ga)As/GaAs quantum well (QW) and 1.3 mu quantum dot (QD) lasers grown on silicon. We identify two effects with particular importance for practical applications from studying the reduction of the local gain in carrier-depleted regions around dislocation locations and the resulting impact on threshold current increase and slope efficiency at high dislocation densities. First, a large minority carrier diffusion length is a key parameter inhibiting laser operation by enabling carrier migration into dislocations over larger areas, and secondly, increased gain in dislocation-free regions compensating for gain dips around dislocations may contribute to gain compression effects observed in directly modulated silicon-based QD lasers. We believe that this work is an important contribution in creating a better understanding of the processes limiting the capabilities of III-V lasers on silicon in order to explore suitable materials and designs for monolithic light sources for silicon photonics.

In this article, we report the demonstration of directly modulated grating-assisted microcylinder surface-emitting lasers (GAMSELs) with low threshold. Two second-order gratings are added onto the side and top of the microcylinder cavity to select a single mode with a radially polarized emission pattern and efficiently emit the mode vertically, respectively. Laser with cavity radius of 6.05 μm is demonstrated with continuous-wave lasing ranging from 1 °C to 50 °C. This radius is approaching the theoretically smallest radius for the microcylinder laser to work at O band. A low threshold of 3.6 mA at 15 °C is obtained for the GAMSEL laser. Single-mode lasing with side-mode suppression-ratio (SMSR) larger than 40 dB is also shown here. GAMSELs with different cavity radii are demonstrated as laser arrays. 3 dB direct modulation bandwidth of 12 and 14 GHz of GAMSELs with radius of about 8 and 10 μm are obtained, respectively. Besides, effects of the duty cycle of the top and side gratings, scattering losses of the cavity, gain peak of the epitaxial wafer and ion implantation are experimentally investigated.

In this study, the research on the nonlinear dynamics of semiconductor quantum dot laser with two time-delayed optical feedbacks is numerically investigated. Results show that the nonlinear dynamics behaviors of the laser are very sensitive to the rich system parameters in which both feedback strength and bias current are easily controlled to significantly influence the nonlinear dynamics including the periodic state and chaotic state. By judiciously adjusting the bias current of the laser or the feedback strength in the external cavity, period one, period doubling, quasi-period, and chaos are achieved. The feedback level-related bifurcation diagrams are analyzed in detail while fixing another feedback level at a constant or varying the bias current. In addition, the translation variables of the 0–1 test method that are clearly bounded for regular behavior and exhibit the Brownian motion for irregular phenomenon are adopted to further evaluate the periodic state and the chaotic state. These results can give insight into the quantum dot laser–based applications in various optical technologies.

We measure the FM noise power spectral density of quantum-dot mode-locked lasers (QD-MLLs) and compare this to their measured linewidths as predictors of performance in a digital coherent system. We explain our observations in terms of the non-Lorentzian line shape of the source wherein linewidth is determined by the low frequency part of its FM noise. Investigation of system performance with simulations based on the measured phase sequences and back-to-back coherent transmission experiments show that QD-MLLs with linewidths of several megahertz can have comparable performance to that of a laser with only a few hundreds of kilohertz of Lorentzian linewidth, due to the non-white part of their FM noise. We show that spectral linewidths of lasers with similar spectral properties can underestimate their performance in coherent systems, regardless of the linewidth measurement technique used. We propose a “ Lorentzian-equivalent linewidth ” measure to characterize lasers with non-white FM noise and to estimate their impact in digital coherent optical systems. This measure is obtained from phase variations at frequencies higher than typical frequencies often used to characterize lasers with white FM noise and comparable to the system baud. The proposed measure is shown to be a better predictor of system performance than the measured linewidth, for lasers with non-white FM noise. The impact of non-white FM noise on the optimization of carrier phase recovery and system performance is also discussed.

This work investigates the degradation processes affecting the long-term reliability of 1.3 μm InAs quantum-dot lasers epitaxially grown on silicon. By submitting laser samples to constant-current stress, we were able to identify the physical mechanisms responsible for the optical degradation. More specifically, the samples (i) exhibited a gradual increase in threshold current, well correlated with (ii) a decrease in sub-threshold emission, and (iii) a decrease in slope efficiency. These variations were found to be compatible with a diffusion process involving the propagation of defects toward the active region of the device and the subsequent decrease in injection efficiency. This hypothesis was also supported by the increase in the defect-related current conduction components exhibited by the electrical characteristics, and highlights the role of defects in the gradual degradation of InAs quantum dot laser diodes. Electroluminescence measurements were used to provide further insight in the degradation process.

Dynamics of a multimode quantum dot laser with polarization-rotated optical feedback is investigated in a wide range of bias current. The results reveal that the laser is more sensitive to optical feedback when the polarization of feedback beam is rotated a large angle from the original polarization, which is different from the results in DFB lasers. Anticorrelated fluctuations between orthogonal polarizations are observed in a certain range of selected polarizations. Accordingly, dynamics in the total power can be weaker than that in a selected polarization. The anticorrelated polarization dynamics may be related to different polarizations of longitudinal modes.

We report high-performance broad-area eight-layer InAs/GaAs quantum-dot lasers (QDLs) emitting at 1.3 μm in the pulse and continuous-wave (CW) operations. Operational characteristics of the fabricated QDLs, including the emission wavelength, output power, threshold-current density, differential quantum efficiency, and characteristic temperature, are investigated at different temperatures. For as-cleaved facets of 100 μm wide and 1 mm cavity-length device, an output power of 100 mW is achieved at 1 kHz with 5% duty cycle and 49 mW in the CW operation. The device exhibits a threshold-current density of 56 A/cm2 at room temperature in both the operating modes and increases to 71 and 80 A/cm2 the in the pulse and CW modes, respectively, at 343 K. Over a temperature range of 298K to 343 K, we calculate the threshold characteristic temperature of 166K and 119K and slope-efficiency characteristic temperature of 2061K and 408K in the pulse and CW modes, respectively. The laser exhibits differential quantum efficiency of 41% and 32% in the pulse and CW mode, respectively. We observed that the device exhibited negligible dependence over a temperature range of 298K to 343 K.

Quantum dot (QD) laser as a light source for silicon optical integration has attracted great research attention because of the strategic vision of optical interconnection. In this paper, the communication band InAs QD ridge waveguide lasers were fabricated on GaAs-on-insulator (GaAsOI) substrate by combining ion-slicing technique and molecular beam epitaxy (MBE) growth. On the foundation of optimizing surface treatment processes, the InAs/In0.13Ga0.87As/GaAs dot-in-well (DWELL) lasers monolithically grown on a GaAsOI substrate were realized under pulsed operation at 20 °C. The static device measurements reveal comparable performance in terms of threshold current density, slope efficiency and output power between the QD lasers on GaAsOI and GaAs substrates. This work shows great potential to fabricate highly integrated light source on Si for photonic integrated circuits.

A semi-empirical model is compared with measurements to establish limiting factors in the performance of p-modulation doped InAs quantum dot (QD) lasers. Fitted absorption spectra allow identification of supposed factors and comparison of multiple samples isolates their origin, providing insights for future laser design.

III-V semiconductor lasers integrated on Si-based photonic platforms are eagerly awaited by the industry for mass-scale applications, from interconnect to on-chip sensing. The current understanding is that only quantum dot lasers can reasonably operate at the high dislocation densities generated by the III-V-on-Si heteroepitaxy, which induces high non-radiative carrier recombination rates. Here we propose a strategy based on a type-II band alignment to fabricate quantum well lasers highly tolerant to dislocations. A mid-IR GaInSb/InAs interband cascade laser grown on Si exhibits performances similar to those of its counterpart grown on the native GaSb substrate, in spite of a dislocation density in the 10 8 c m − 2 range. Over 3800 h of continuous-wave operation data have been collected, giving an extrapolated mean time to failure exceeding 312,000 h. This validates the proposed strategy and opens the way to new integrated laser development.

The realization of monolithic integration of a stable III–V laser on a standard silicon-on-insulator (SOI) substrate has been regarded as a challenging technology for silicon-based photonic integration circuits (PICs). Here, we successfully demonstrated the electrically pumped P-doped 1300 nm InAs/GaAs quantum dot (QD) laser epitaxially grown on {111}-faceted SOI hollow substrates. These III–V QD lasers, which are epitaxially grown on an SOI substrate, generally exhibit strong thermal accumulation due to the oxide layer underneath. By applying a double-side heat dissipation design, the maximum operation temperature of the SOI-based InAs/GaAs QD laser under a continuous-wave (CW) operation mode is ramped up to 35°C from 20°C. Moreover, the thermal profile simulation of three different structures has also been carried out to show the effectiveness of the top heat sink design in order to improve laser performance. An integrated thermal shunt design is proposed to improve heat dissipation without using the external top heat sink. The successful realization of room-temperature SOI-based InAs/GaAs QD lasers pave a viable way for integrating light sources in PICs.

We review results on the optical injection of dual state InAs quantum dot-based semiconductor lasers. The two states in question are the so-called ground state and first excited state of the laser. This ability to lase from two different energy states is unique amongst semiconductor lasers and in combination with the high, intrinsic relaxation oscillation damping of the material and the novel, inherent cascade like carrier relaxation process, endows optically injected dual state quantum dot lasers with many unique dynamical properties. Particular attention is paid to fast state switching, antiphase excitability, novel information processing techniques and optothermally induced neuronal phenomena. We compare and contrast some of the physical properties of the system with other optically injected two state devices such as vertical cavity surface emitting lasers and ring lasers. Finally, we offer an outlook on the use of quantum dot material in photonic integrated circuits.

We propose a multilayer silicon nitride (SiN) -on-silicon photonic integrated circuit (PIC) platform with a monolithic laser at the C-band. A tapered edge coupler and a meta-structure-based interlayer directional coupler in the platform were designed to realize low-loss broadband laser-to-chip 3D coupling with small footprint. The coupling length of the interlayer directional coupler and the gap between different SiN layers were optimized as 12.7 µm and 1.4 µm. We measured the 1-dB-drop optical operation bandwidth of greater than 76 nm and the coupling loss of 6.1 ± 0.1 dB at 1550 nm for the interlayer directional coupler. The hybrid integration was demonstrated as a proof of concept for monolithic integration of light sources. The butt-coupling loss of 3.7 ± 0.1 dB between an on-chip DFB laser and a SiN edge coupler at 1549.48 nm was achieved. This approach opens the possibility of employing monolithic laser in the silicon photonics platform.

With exponential growth in data traffic and limitations of Moore’s Law, electronic integrated circuits have reached a bottleneck period. Photonic Integrated Circuits (PICs) are seemed as candidate for solving the problem of data transmission. Moreover, robust laser sources are significant building block for PICs design. Here, we demonstrate several InAs/GaAs quantum dot microcavity lasers monolithically grown on planar on-axis Si (001) substrates, including microdisk cavity [1], 2D Photonic Crystal with L3 defects cavity [2], 1D Photonic Crystal nanobeam cavity, bandedge Photonic Crystal cavity, bound states in the continuum (BIC) cavity, etc.

Regrown quantum-dot distributed feedback lasers on Si demonstrate record performance, with a threshold current of 10 mA, an intrinsic linewidth of 41.2 kHz, a side-mode suppression ratio of 57.5 dB, and a maximum power of 11.7 mW.

For the first time, with an optical beam illumination, gain-switched short pulses with a width of 25–40 ps with a high peak power are generated owing to excited state transitions, and the change in the laser parameters does not affect the output pulses strongly.

We demonstrate the superior emission properties of a red-emitting self-assembled quantum dot microsphere laser made from a blend of green and red bandgap CdS x Se 1-x / ZnS quantum dots. The addition of the higher bandgap material reduces self-absorption and improves the Q-factor.

International audience; How far can we go in shaping the luminescence of quantum emitters? It is well known that by using cavities or nano-antennas, one can beam their luminescence into well-controlled directions of space. Here, we push this control to a level of complexity usually achieved with laser radiation: we make an assembly of colloidal quantum dots spontaneously emit vector vortex beams, which are swirls of light combining a non-zero angular momentum and an inhomogeneous field structure. The key ingredient to obtain this result is to increase the spatial coherence of the emitted photons. To fulfill this condition, we design and use plasmonic holograms that also impart a non-zero orbital angular momentum and a radial polarization state to the beam.

Direct epitaxy of InP quantum dot (QD) lasers on silicon (Si) provides an on-chip red laser source for integrated Si photonics with different applications. Here, we demonstrate the first, to the best of our knowledge, InP QD lasers directly grown on (001) Si. Combining highly emissive InP QDs and a GaAs/Si template with low defect density, continuous-wave (CW) lasing of micro-disk lasers (MDLs) on Si is achieved at room temperature. The lowest threshold of MDLs on Si is ∼ 500 n W , without considering the micro-disk surface absorption efficiency of the pump power. The MDLs grown on the native GaAs substrate with the same growth and fabrication process are compared using statistical data analysis. Similar material characterization results and device performances on these two substrates further confirm the performance of QD lasers on Si. This demonstration paves the way for future realization of integrated photonic circuits with red and near-infrared (NIR) lasers on Si.

For the first time gain-switched short pulse generation with a width of 25-40 ps from excited state is demonstrated applying an external optical Gaussian beam to the excited state of InAs-InP-(113)B quantum dot laser.

We discuss the integration of quantum dashes (QDashes) into laser simulations using Crosslight Pics3D, outlining the approach for developing a model featuring asymmetrical active regions. The importance of including wetting layers to accurately represent carrier transport is investigated using results obtained for an InAs/InP QDash laser. While leakage current across the active region is unaffected by the absence of wetting layers, their presence enhances Auger recombination losses in the active region, leading to lower overall device efficiencies.

Quantum cascade lasers (QCLs) facilitate compact optical frequency comb sources that operate in the mid-infrared and terahertz spectral regions, where many molecules have their fundamental absorption lines. Enhancing the optical bandwidth of these chip-sized lasers is of paramount importance to address their application in broadband high-precision spectroscopy. In this work, we provide a numerical and experimental investigation of the comb spectral width and show how it can be optimized to obtain its maximum value defined by the laser gain bandwidth. The interplay of nonoptimal values of the resonant Kerr nonlinearity and cavity dispersion can lead to significant narrowing of the comb spectrum and reveals the best approach for dispersion compensation. The implementation of high mirror losses is shown to be favorable and results in proliferation of the comb sidemodes. Ultimately, injection locking of QCLs by modulating the laser bias around the round trip frequency provides a stable external knob to control the frequency-modulated comb state and recover the maximum spectral width of the unlocked laser state.

Inversion boundaries (IBs) are charged planer defects that arise from the growth of polar III-V materials on non-polar Si (001) substrate. This paper demonstrates a novel technique to achieve all-MBE grown, IB-free GaAs on on-axis Si (001) substrates by employing periodic Si single-atomic-height steps to re-distribute the nucleation of IBs and promote IB self-annihilation in the subsequent GaAs growth. Furthermore, an electronically pumped quantum-dot (QD) laser has been demonstrated on this IB-free GaAs/Si platform with a maximum operating temperature of 120 °C. These results could be a significant step towards the monolithic integration of III-V materials and devices with mature CMOS technology.

We propose and numerically demonstrate a photonic microwave generation scheme based on the dynamic period-one oscillation of a solitary spin-polarized vertical-cavity surface-emitting laser (spin-VCSEL). The evolution of the oscillation amplitude, frequency, power, and linewidth of the generated microwave is systematically investigated by using two-dimensional maps. The results show that the generated microwave signals with a dominant linewidth of about 3 MHz have a broad tunable frequency (from several gigahertz to hundreds of gigahertz), which benefits from the birefringence-induced oscillation in spin-VCSELs. Moreover, with the help of optical feedback, the microwave linewidth can be effectively minimized ( ∼ 51 k H z ) by increasing the feedback strength and feedback delay time. Importantly, this Letter offers prospects for applications requiring a feasible and resource-efficient microwave source in microwave photonic fields.

We semianalytically and numerically investigate the static and dynamical characteristics of quantum-dot (QD) lasers directly grown on silicon by considering the Shockley-Read-Hall (SRH) recombination. The static characteristics are studied through small-signal analysis, including the ${\ensuremath{\alpha}}_{H}$ factor, damping factor, and modulation dynamics. In addition, the feedback dynamics are analyzed through improved corpuscular rate equations based on the classical Lang-Kobayashi (LK) model with time series, bifurcation diagrams, and phase portraits. We find that a smaller ${\ensuremath{\alpha}}_{H}$ factor but larger damping factor are obtained by decreasing the nonradiative recombination lifetime. On top of that, in both the short- and long-external-cavity regimes, any decrease of the SRH recombination lifetime obliterates significantly chaotic regions and shifts the first Hopf bifurcation point to higher feedback values. Overall, this work provides insights into the understanding of QD laser physics, hence highlighting the influence of the SRH lifetime on the reflection sensitivity of epitaxial QD lasers on silicon. These results are qualitatively consistent with recent experiments and are therefore helpful for designing feedback-resistant lasers for future photonic integrated circuits operating without optical isolation.

We experimentally investigate the complex dynamics of a multi-mode quantum-dot semiconductor laser with time-delayed optical feedback. We examine a two-dimensional bifurcation diagram of the quantum-dot laser as a comprehensive dynamical map by changing the injection current and feedback strength. We found that the bifurcation diagram contains two different parameter regions of low-frequency fluctuations. The power-dropout dynamics of the low-frequency fluctuations are observed in the sub-GHz region, which is considerably faster than the conventional low-frequency fluctuations in the MHz region. Comparing the dynamics of quantum-dot laser with those of single- and multi-mode quantum-well semiconductor lasers reveals that the fast low-frequency fluctuation dynamics are unique characteristics of quantum-dot lasers with time-delayed optical feedback.

Similar to vertical-external-cavity surface-emitting lasers (VECSELs) [1] , MECSELs [2] are high beam quality light sources with typical M 2 values close to an ideal Gaussian beam. The difference is the absence of the mono-lithically integrated distributed Bragg reflector. Because of this, MECSELs have a better wavelength flexibility and the potential to provide a wide spectral coverage, achievable by the existing semiconductor material systems. An additional feature of the MECSEL is the double-side cooling [3] , which allows a more efficient thermal management of the laser active structure by the implementation of two transparent heat spreaders. Since the MECSEL is fully operating in transmission, it is possible to pump the laser active structure optically from both sides. This double-side pump approach as present in solid-state lasers, has been applied to 780 nm emitting MECSELs [4] . Also, lateral power scaling by increasing the pump and cavity mode size has been presented in 825 nm emitting MECSELs [5] . So far, MECSELs have been demonstrated and fully characterized with quantum wells in their active regions [6] - [8] .

Silicon-based epitaxial quantum dot (QD) lasers with strong tolerance for back-reflections have paved the way for developing isolator-free photonics integrated circuits (PICs). This remarkable feature is attributed to the peculiar benefits of QDs, including a large material gain, a strong damping, and a small linewidth enhancement factor [1] . The laser performance can also be optimized by applying p-modulation doping in the active region [1] . In a previous study, the sensitivity of epitaxial QD lasers on silicon subject to short- and long-delay optical feedback were performed [2] . On the top of that, a further investigation of the feedback dynamics on the intra- and inter-chip scale is of significant importance for photonic integration applications.

Monolithic semiconductor quantum dot lasers [1] , [2] are millimeter-sized compact high-precision optical frequency comb sources emitting a spectrum of phase coherent equidistant lines in the near-infrared spectral region. While amplitude-modulated (AM) frequency comb lasers generate a train of optical pulses, frequency-modulated (FM) optical frequency comb lasers emit a quasi continuous-wave output, ideal for on-chip spectroscopy and optical communications. The FM comb state corresponds to splay-phase synchronization, where the inter-modal phases are splayed uniformly around the unit circle, spanning across 2 π [3] , [4] .

In the last decades, significant efforts have been devoted to developing semiconductors III-V lasers on silicon substrates, due to the prospects for the implementation of the high-speed lasers for optical communication systems integrated with silicon electronics and transistor logic. Low-threshold ridge-waveguide and microdisk/microring lasers based on AlGaAs heterostructures with self-organizing quantum dots In(Ga)As grown on Si substrates were demonstrated [1] , [2] . However, lasers synthesized on silicon are still inferior to analogs grown on native substrates (GaAs) [3] , due to higher defect densities caused by differences in polarity, lattice constants and coefficients thermal expansion of III-V materials and silicon. The epitaxial growth of laser heterostructures on native substrates (e.g. GaAs) and subsequent transfer of ready-made microlasers to silicon can help to avoid problems associated with monolithic integration of III-V and Si. Ring and disk microlasers have attracted more and more attention and are considered as promising sources of emission for inter-chip data transmission. The advantages of such microcavities are the high Q-factor of the whispering gallery (WG) modes, small size and, accordingly, low threshold currents and power consumption. In this work we study integration of InAs/GaAs quantum dot microdisk lasers on silicon either retaining the native substrate or separating from the substrate using a sacrificial layer.

A feedback insensitive laser is a prerequisite for a desirable laser source for silicon photonic integration, as it is not possible to include an on-chip optical isolator. This work investigates the feedback insensitivity of an InAs/GaAs quantum dot laser epitaxially grown on an Si (001) substrate by operating in a sole excited state. The experimental results show that the sole excited-state lasing InAs quantum dot lasers on Si are less sensitive to external optical feedback than both Fabry-Perot and distributed-feedback quantum-well lasers. By comparing the laser behavior under different feedback levels, sole excited-state InAs quantum dot lasers on Si exhibit at least a 28 dB stronger feedback tolerance than quantum-well lasers. This result proposes a possible route for a high feedback insensitive laser as an on-chip light source towards Si waveguide integration with the absence of an optical isolator.

Free-running quantum cascade lasers (QCLs) show a natural tendency to operate in the multimode regime as a result of both spatial and spectral hole burning. While multimode operation by itself is far from unusual, what distinguishes QCLs from other lasers is that the phases of the individual modes in them can be locked in the absence of any additional intracavity elements, thus forming frequency combs (FCs) that have many practical applications. Unlike typical FCs produced in mode-locked lasers or microcavities, the temporal shape of a QCL FC is not a short pulse but rather a combination of frequency and (to a lesser extent) amplitude modulated signals, the origin of which is not obvious. In this paper, we develop a theory aimed at explicating the most recent experimental measurements of temporal characteristics of QCL FCs. We identify spatial hole burning as the root cause of frequency modulation and show that, in addition to previously analyzed rapid, pseudo-random frequency modulation, the experimentally observed long linearly chirped signal can also alleviate spatial hole burning efficiently. We find that in the absence of spectral hole burning, a linearly chirped regime has the lowest threshold. Furthermore, we show that for relatively weak frequency modulation, amplitude modulation should also arise as confirmed experimentally. The result of this paper is a first step toward reliably engineering FCs with specified characteristics in mid IR and THz regions.

This paper investigates the intensity noise and pulse oscillation characteristics of an InAs/GaAs quantum dot laser epitaxially grown on germanium. We show that the relative intensity noise of the free-running laser generally decreases with increasing pump current, and the minimum value reaches down to about $-$ 126 dB/Hz. The intensity noise is hardly affected by the optical feedback, unless there is a resonance or pulse oscillation in the noise spectrum. The laser pumped at a high current is more sensitive to the optical feedback. Interestingly, it is found that the free-running Ge-based quantum dot laser generates self-sustained pulse oscillations with one period or two periods upon the pump current, without incorporating saturable absorbers. This behavior is valuable for both self-generation of photonic microwaves and for understanding nonlinear dynamics of semiconductor lasers.

Initial age-related degradation mechanisms for InAs quantum dot lasers grown on silicon substrates emitting at 1.3 μ m are investigated. The rate of degradation is observed to increase for devices operated at higher carrier densities and is therefore dependent on gain requirement or cavity length. While carrier localization in quantum dots minimizes degradation, an increase in the number of defects in the early stages of aging can increase the internal optical-loss that can initiate rapid degradation of laser performance due to the rise in threshold carrier density. Population of the two-dimensional states is considered the major factor for determining the rate of degradation, which can be significant for lasers requiring high threshold carrier densities. This is demonstrated by operating lasers of different cavity lengths with a constant current and measuring the change in threshold current at regular intervals. A segmented-contact device, which can be used to measure the modal absorption and also operate as a laser, is used to determine how the internal optical-loss changes in the early stages of degradation. Structures grown on silicon show an increase in internal optical loss, whereas the same structure grown on GaAs shows no signs of increase in internal optical loss when operated under the same conditions.

An InP based tunnel injection quantum dot (QD) laser and a reference quantum dot laser designed to emit at 1.55 μ m were grown by molecular beam epitaxy. The lattice matched tunnel injection (TI) structures consist of an InGaAs quantum well (QW), an InAlGaAs barrier and multiple InAs quantum dot layers. Quantum well and quantum dot test structures as well as the actual laser structures were treated with rapid thermal annealing (RTA) at varying temperatures (680–780 °C). Photoluminescence measurements were performed at 10 K on all samples and a strong effect of this annealing process on the emission properties is observed. The laser structures were processed into broad area lasers. Power-current characteristics were measured and evaluated. A strong improvement in device performance is observed after annealing for QD lasers while for TI-QD lasers no significant improvement was obtained, which might be caused by detuning of band energy alignment and different impact of the RTA process on the material quality of QW and QD layers.

In the goal to improve the self-assembled quantum-dot lasers (SAQDL) performance and properties, we propose in this paper a structure based on a material that gained a great attention in the recent years, the ZnO and their alloys. In this study, a theoretical model is used. The rate equations for CdZnO/ZnO/MgZnO were numerically solved using the fourth-order Runge–Kutta method. Several results have been found such as the carrier and photon density, laser turn-on behavior, light–current, output power, and gain characteristics. In each time, the injected current and the homogeneous broadening (HB) (the effects of temperature) have been varied to highlight their impacts on these characteristics. The results have shown that good performances of SAQDL have been achieved with optimal values of current injection and HB. In addition, the peak of optical gain has not changed with the variations of these factors. Based on the results obtained, ZnO and their alloys are found emerging materials to improve the laser performances.

Laser gain regions using quantum dots have numerous improvements over quantum wells for photonic integration. Their atom-like density of states gives them unique gain properties that can be finely tuned by changing growth conditions. The gain bandwidth can be engineered to be broad or narrow and to emit at a wide range of wavelengths throughout the near infrared. The large energy level separation of the dot states from the surrounding material results in excellent high-temperature performance and gain recovery at sub-picosecond timescales. The fact that the quantum dots are isolated from each other and act independently at inhomogeneously broadened wavelengths results in ultralow linewidth enhancement factors, highly stable broadband mode-locked lasers, single-section mode locking, and the possibility of reduced crosstalk between amplified signals at low signal injection and enhanced four-wave mixing at high signal injection. The high carrier confinement and areal dot density provide reduced sensitivity to crystalline defects allowing for long device lifetimes even when epitaxially grown on silicon at high dislocation densities.

We investigated the optical gain properties and lasing characteristics of a pulsed electrically pumped laser structure, which consists of a single layer of self-assembled InP quantum dots (QDs) assembled in (Al 0.10 Ga 0.90 ) 0.52 In 0.48 P barriers. The optical gain and absorption spectra were obtained by analyzing the amplified spontaneous emission as a function of the excitation length. At a current density of 1.2 kA/cm 2 , an internal optical loss value of 5 ± 2 cm -1 and a peak modal gain of 39.3 cm -1 corresponding to a material gain of approximately 2675 cm -1 per QD layer were determined at room temperature. For a 2.24-mm-long laser with uncoated facets emitting at 660 nm, a low threshold current density of 281 A/cm 2 and an external differential quantum efficiency of 34.2% were determined. The internal quantum efficiency of 66% and the transparent current density of 65.8 A/cm 2 for a single layer of QDs were also demonstrated.

Opportunities for the monolithic integration of a novel common quantum dot (QD)-active electroabsorption modulated laser are explored. An electric-field and temperature-dependent spectroscopic study of optical absorption and gain are presented in the state-of-the-art 1.3- $\mu \text{m}$ In(Ga)As/GaAs QD active material. The unique gain/absorption spectral shape, attributed to the QD’s density of states, allows for a number of possible modulation schemes dependent upon the selected laser wavelength detuning from the gain peak. Intensity modulation and change in absorption, leading to negative chirp operation, are demonstrated via absorption spectroscopy and gain measurement of eight-layer-stack QD-active material. Such a device would be able to provide positive or negative chirp dependent upon modulation scheme and gain/Bragg wavelength detuning.

The effect of out-tunneling leakage of carriers from quantum dots (QDs) on modulation bandwidth of semiconductor double tunneling-injection (DTI) QD lasers is studied. In this type of laser, as an alternative to conventional pumping, electrons and holes are injected into QDs by tunneling from two separate quantum wells (QWs) located on the opposite sides of the QD layer and separated from the latter by thin barrier layers. Fast tunneling-injection into QDs should be maintained to ensure the high modulation bandwidth. It may also seem that out-tunneling leakage from QDs (tunneling of electrons to the hole-injecting QW and holes to the electron-injecting QW), which is an undesirable process, should be kept as slow as possible (or even totally suppressed) to maximize the modulation bandwidth. However, it is shown in this paper that, due to zero-dimensional nature of QDs, the modulation bandwidth is practically unaffected by out-tunneling leakage from them—it depends only slightly on the out-tunneling time. Hence, concerning out-tunneling leakage, DTI QD lasers are robust—provided that tunneling-injection is fast, no significant effort should be necessary to suppress out-tunneling leakage in practical devices.

In this paper, we present measurements and simulations of the small-signal modulation response of monolithic continuous-wave 1.3 μ m InAs/GaAs quantum dot (QD) narrow ridge-waveguide lasers on a silicon substrate. The 2.5 mm-long lasers investigated demonstrate 3 dB modulation bandwidths of 1.6 GHz, D -factors of 0.3 GHz/mA1/2, modulation current efficiencies of 0.4 GHz/mA1/2, and K -factors of 2.4 ns and 3.7 ns. Since the devices under test are not designed for high-speed operation due to their long length and hence long photon lifetime, the modulation response curves are used as a fitting template for numerical simulations with spatiotemporal resolution to gain insight into the underlying laser physics. The obtained parameter set is used to unveil the true potential of the laser material in an optimized device geometry by modeling the small-signal response at different cavity lengths, mirror reflectivities, and for different numbers of QD layers. The simulations predict a maximum 3 dB modulation bandwidth of 5 GHz to 7 GHz for a 0.75 mm-long cavity with 99% and 60% high-reflection coatings and ten QD layers. Modeling the impact of dislocations on the dynamic performance qualitatively reveals that enhanced non-radiative recombination in the wetting layer leaves the modulation bandwidth of QD lasers on silicon almost unaffected, while dislocation-induced optical loss does not pose a problem, as long as sufficient gain is provided by the QD active region.

In this work, the impact of fine-delay tunable dual-cavity optical self-feedback (DC-OFB) on the pulse timing stability and pulse repetition rate (RR) frequency of a 1 mm long single-section self-mode-locked quantum-dot (QD) laser emitting at 1255 nm is studied experimentally and by simulation. By tuning both microscopic dual-cavity delay lengths, we find a maximum RR tuning range of 70 MHz. A two-fold periodic structure is apparent every 25 ps which corresponds to the internal round trip time of the laser. A timing jitter (TJ) reduction by a factor of 16 down to 3.5 fs is obtained. Simulation results reproduce the experimentally observed RR trends with a good qualitative and quantitative agreement

In this paper, a theoretical model is used to study the optical gain characteristics of quantum dot lasers. The model is based on the density matrix theory of semiconductor lasers with relaxation broadening. The effect of doping with varying the side lengths of the box in the structure is taken into account. A comparative study of the gain spectra of p-doped, undoped and n-doped structures of cubic quantum-dot (QD) laser respectively, is presented for various side lengths. The variation of peak gain on carrier density is also presented. The effect of side length on the variation in modal gain versus current density is plotted too. The results indicate that the p type doping is efficient to reach a better optical gain value, and to achieve low threshold current densities compared with undoped and n-doped structures, and the optimum value for quantum dot width to achieve the lower threshold current density for the three cases is L=100A .

In order to achieve ultrahigh data capacity and to overcome the wireless spectrum crunch, 5G is going to adopt millimeter-wave (mmW) frequencies (30 GHz - 300 GHz). To generate high-quality mm W signals by lasers, it requires optical sources with ultra-narrow optical linewidth and low relative intensity noise (RIN). In this paper, we have developed InAs/InP quantum dot (QD) multi-wavelength lasers (MWLs) around 1550 nm with the frequency spacing from 10 GHz to 1000 GHz. Those QD MWLs have very low RIN, ultra-narrow optical linewidth, small timing jitters, compact size, low power consumption and the ability for hybrid integration with silicon substrates. As an example, we present a buried heterostructure (BH) QD dual-wavelength (DW) DFB laser as an optical beat source for mmW generation. The BH QD DW-DFB laser with the optical linewidth of 16 KHz and the RIN of -158 dB/Hz is capable of generating spectrally pure mm W signals between 46 GHz and 48 GHz. By using it, we have demonstrated a real time 24-Gbit/s (64QAM x 4Gbaud) data bandwidth wireless transmission operating at 47.2-GHz carrier over 25-km SSMF., 2021 Photonics North (PN), May 31 - June 2, 2021, Toronto, ON, Canada