Quantum Dot Lasers Research Articles

Reduction of GaAs Buffer Thickness and Its Impact on Epitaxially Integrated III-V Quantum Dot Lasers on a Si Substrate.

Monolithic integration of III-V quantum dot (QD) lasers onto a Si substrate is a scalable and reliable approach for obtaining highly efficient light sources for Si photonics. Recently, a combination of optimized GaAs buffers and QD gain materials resulted in monolithically integrated butt-coupled lasers on Si. However, the use of thick GaAs buffers up to 3 μm not only hinders accurate vertical alignment to the Si optical waveguide but also imposes considerable growth costs and time constraints. Here, for the first time, we demonstrate InAs QD lasers epitaxially grown on a 700 nm thick GaAs/Si template, which is approximately four times thinner than the conventional III-V buffers on Si. The optimized 700 nm GaAs buffer yields a remarkably smooth surface and low threading dislocation density of 4 × 108 cm-2, which is sufficient for QD laser growth. The InAs QD lasers fabricated on these ultrathin templates still lase at room temperature with a threshold current density of 661 A/cm2 and a characteristic temperature of 50 K. We believe that these results are important for the monolithically integrated III-V QD lasers for Si photonics applications.

Turnkey locking of quantum-dot lasers directly grown on Si

Ultralow-noise laser sources are crucial for a variety of applications, including microwave synthesizers, optical gyroscopes and the manipulation of quantum systems. Silicon photonics has emerged as a promising solution for high-coherence applications due to its ability to reduce the system size, weight, power consumption and cost. Semiconductor lasers based on self-injection locking have achieved fibre laser coherence, but typically require a high-quality-factor external cavity to suppress coherence collapse through frequency-selective feedback. Lasers based on external-cavity locking are a low-cost and turnkey operation option, but their coherence is generally inferior to self-injection locking lasers. In this work, we demonstrate quantum-dot lasers grown directly on Si that achieve self-injection-locking laser coherence under turnkey external-cavity locking. The high-performance quantum-dot laser offers a scalable and low-cost heteroepitaxial integration platform. Moreover, the chaos-free nature of the quantum-dot laser enables a 16 Hz Lorentzian linewidth under external-cavity locking using a low-quality-factor external cavity, and improves the frequency noise by an additional order of magnitude compared with conventional quantum-well lasers.

E-Band InAs Quantum Dot Micro-Disk Laser with Metamorphic InGaAs Layers Grown on GaAs/Si (001) Substrate.

The direct growth of III-V quantum dot (QD) lasers on silicon substrate has been rapidly developing over the past decade and has been recognized as a promising method for achieving on-chip light sources in photonic integrated circuits (PICs). Up to date, O- and C/L-bands InAs QD lasers on Si have been extensively investigated, but as an extended telecommunication wavelength, the E-band QD lasers directly grown on Si substrates are not available yet. Here, we demonstrate the first E-band (1365 nm) InAs QD micro-disk lasers epitaxially grown on Si (001) substrates by using a III-V/IV hybrid dual-chamber molecular beam epitaxy (MBE) system. The micro-disk laser device on Si was characterized with an optical threshold power of 0.424 mW and quality factor (Q) of 1727.2 at 200 K. The results presented here indicate a path to on-chip silicon photonic telecom-transmitters.

Effect of non-uniform carrier injection on two-state lasing in quantum dot microdisks with split electrical contact

In this papaer, the emission characteristics of InAs/InGaAs quantum dot (QD) microdisk lasers, of different cavity diameters, with a top split electrical contact formed using the focused ion beam technique are investigated. The dependences of the threshold currents of two-state lasing (i.e. currents corresponding to the start of the ground- and excited-state lasing) for microdisks of 24 and 28 μm diameters on the electrical contact area are presented. The contact area was found to influence the threshold currents of two-state lasing in microdisks. It is shown that a decrease in the area of the injected electrical contact leads to a decrease in the current corresponding to the start of the excited-state lasing, while the ground-state (GS) lasing threshold remains virtually unchanged. The temperature evolution of the threshold currents for two-state lasing was also studied in microdisks with different electrical contact areas. We demonstrate that the use of contacts of different areas is a method of controlling the threshold currents of two-state lasing and can be used in engineering of QD lasers intended, for example, for multi-level signal transmission with wavelength multiplexing by switching from the GS to excited-state lasing.

Observation of amplitude squeezing in a constant-current-driven distributed feedback quantum dot laser with optical feedback

We illustrate the generation of single-mode amplitude squeezing in a distributed feedback quantum dot laser driven by a constant-current pump. Achieving broadband amplitude squeezing of 1.7 dB over a 10 GHz range at room temperature is realized by suppressing carrier noise and implementing optical feedback. The noise-corrected squeezing level reached 5.1 dB. Furthermore, the examination of the zero-delay second-order correlation function demonstrates the robust feedback stability of the amplitude-squeezed state in the quantum dot laser compared to a reference quantum well laser. This investigation lays the groundwork for future advancements in integrated optical quantum chips.

1.3 μm InAs/GaAs quantum-dot lasers grown on planar on-axis Si (001) substrates with high slope-efficiency and low differential resistance

We report electrically pumped continuous-wave (CW) InAs/GaAs quantum dot lasers monolithically grown on planar on-axis Si (001) substrates. Combining an asymmetric waveguide epitaxy structure with aluminium-free upper cladding layers and a symmetrical cathode chip structure, 1.3 μm band lasers with low differential resistance and high slope-efficiency have been achieved. Moreover, the optimized symmetrical cathode structure of the laser chips is used to improve the slope-efficiency by reducing the differential resistance and waste heat. The Fabry–Perot broad-stripe edge-emitting lasers with 2000 μm cavity length and 15 μm stripe width achieve a single-facet output power of 73 mW, a single-facet slope efficiency of 0.165 W A−1, and a differential resistance of 1.31 Ω at ∼1.31 μm wavelength under CW conditions at room temperature (25 °C). Importantly, these results provide an effective strategy to achieve 1.3 μm wavelength band single-mode distributed feedback lasers directly on planar on-axis Si (001) substrates with high efficiency.

High-power, electrically-driven continuous-wave 1.55-μm Si-based multi-quantum well lasers with a wide operating temperature range grown on wafer-scale InP-on-Si (100) heterogeneous substrate

A reliable, efficient and electrically-pumped Si-based laser is considered as the main challenge to achieve the integration of all key building blocks with silicon photonics. Despite the impressive advances that have been made in developing 1.3-μm Si-based quantum dot (QD) lasers, extending the wavelength window to the widely used 1.55-μm telecommunication region remains difficult. In this study, we develop a novel photonic integration method of epitaxial growth of III-V on a wafer-scale InP-on-Si (100) (InPOS) heterogeneous substrate fabricated by the ion-cutting technique to realize integrated lasers on Si substrate. This ion-cutting plus epitaxial growth approach decouples the correlated root causes of many detrimental dislocations during heteroepitaxial growth, namely lattice and domain mismatches. Using this approach, we achieved state-of-the-art performance of the electrically-pumped, continuous-wave (CW) 1.55-µm Si-based laser with a room-temperature threshold current density of 0.65 kA/cm−2, and output power exceeding 155 mW per facet without facet coating in CW mode. CW lasing at 120 °C and pulsed lasing at over 130 °C were achieved. This generic approach is also applied to other material systems to provide better performance and more functionalities for photonics and microelectronics.

Quantum dot laser dynamics and external filtered modes under the influence of double-filtered optical feedback

We study the dynamics and solution structure of a semiconductor quantum dot (QD) laser system that gets delayed FOF from two filter loops: the double-filtered optical feedback (DFOF) laser. Two filters are utilized in optical communication applications to regulate and stabilize the laser output, which served as the inspiration for this study. The entire mathematical model of the DFOF laser consists of delay differential equations for the inversion of the QD laser with the two filters. We focus on continuous-wave DFOF QD laser systems because reliable laser source operation is essential for optical communication applications. These basic responses are called external filtered modes (EFMs), and they significantly affect the stability and structure of the EFMs as well as the laser’s performance in comparison to the single FOF QD laser. The parameter C eff is a measure of the interference between the two filter fields, and it is identified as a key to the EFM structure. To analyse how the structure and stability of the EFMs depend on all the filter and feedback loop parameters, we make extensive use of the EFM surface in the (Ω(ω s), C eff , Y s )-space of frequency s, filter phase difference C eff , and population inversion Y s of the QD laser. In general, the EFM surface is the natural object that should be taken into account to comprehend the dynamical characteristics of the DFOF laser. In general, our study involved searching for regions in the QD laser output with stable amplitude and frequency. The time delay suppression is dependent on the spectral width Λ of the filter and how far it is from the solitary laser frequency, according to numerical calculations. In addition to studying the dynamic behavior using a bifurcation diagram at the filter working areas, the results showed two stages of operation due to the occurrence of phase entanglement stochastic.

Optically injected quantum dot lasers and its complex dynamics

Abstract Lasers are paradigmatic examples of nonlinear systems and have played a crucial role in developing nonlinear dynamics into an interdisciplinary topic. Indeed, a freely operating laser represents a nontrivial system, but the phenomena that occur are much more interesting when the laser is exposed to external factors such as optical feedback (OFB) and optical injection (OI). This paper deals with the analysis of the dynamic behavior of a quantum dot semiconductor laser (QDSL) model under the influence of optical injection from another laser. The proposed model was studied numerically with the help of MATLAB. A QDSL system with optical injection was proposed and studied numerically. The quantum dot (QD) laser was used, which is a quantum semiconductor laser and has strong stability without external perturbation. When it is subjected to feedback, it has a critical effect on the follower laser and changes its stable behavior before injection to a set of nonlinear dynamics. The effect of both optical feedback strength and the delay time on the performance and behavior of the bifurcation patterns in the follower laser output was studied, taking into account changing the bifurcation parameters, the injection force k, the slave laser frequency, and the slave laser delay time. The behavior of the slave was studied each time and compared with the behavior of the master. We observed the chaotic paths (essentially stable and continuous pulsating oscillations evolving into periodic and semi-periodic oscillations and then chaotic ones). The time series corresponding to the bifurcation diagrams and the probability of the time interval between spikes and attractors were studied.

Solution‐Processed Perovskite Quantum Dot Quasi‐BIC Laser from Miniaturized Low‐Lateral‐Loss Cavity

AbstractLaser devices produced via solution‐processed perovskite quantum dots (QDs) offer broad spectral tunability as well as ease of fabrication. Utilizing quasi‐bound states in the continuum (quasi‐BIC) modes, solution‐processed QD laser devices have been demonstrated with a nanostructure coated in a thin‐film gain media configuration. However, light leakage through thin‐film guiding from the cavity side edges becomes more pronounced when shrinking the cavity size, posing challenges for the miniaturization of quasi‐BIC‐based lasers. Here, the fabrication of well‐defined patterns of QDs via a solution process allows them to take advantage of the pattern edges to reduce losses through the cavity edges. A single‐mode BIC laser is reported by using CsPbBr3 QDs with a narrow linewidth of ≈0.1 nm. Importantly, a miniaturized quasi‐BIC laser is realized with a device size as small as 10 × 10 µm2, making it the smallest among existing solution‐processed BIC lasers. This work provides a strategy for developing ultra‐compact BIC lasers via solution‐processed gain media.

Efficient, high-power, narrow-linewidth, continuous-wave quantum-dot semiconductor comb laser

We report a continuous-wave, O-band quantum-dot semiconductor comb laser for WDM optical interconnects exhibiting a 2.2 THz optical bandwidth with up to 89 comb wavelengths spaced at 25 GHz, over 30% peak ex-facet electrical-to-optical power conversion efficiency, up to 270 mW of usable laser power, relative intensity noise below − 135 dB/Hz per individual mode, individual laser mode linewidth of 140 kHz, mode beating linewidths of 50 kHz across all modes, and stable far-field output with 75% coupling efficiency to PM fiber in a butterfly package.

Modelling the effects of p-modulation doping in InAs/InGaAs quantum dot devices

A modelling routine has been developed to quantify effects present in p-modulation doped 1.3 μm InAs/InGaAs quantum dot laser and modulator devices. Utilising experimentally verified parameters, calculated modal absorption is compared to measurements, prior to simulation of structures under reverse and forward bias. Observed broadening and a reduction of absorption in p-doped structures is attributed primarily to increased carrier scattering rates and can bring benefit when structures are configured as optical modulators with enhancements in the figure of merit. However, increased carrier scattering limits the maximum modal gain that can be achieved for lasers. The state filling caused by p-doping only marginally reduces absorption but assists laser operation with increased differential gain and gain magnitude at lower current densities.

High-temperature and continuous wave-operation of all-MOCVD grown InAs/GaAs quantum dot laser diodes with highly strained layer and low temperature p-AlGaAs cladding layer

InAs/GaAs quantum dot laser diodes (QDLDs) on a GaAs substrate grown by utilizing all-metalorganic chemical vapor deposition (MOCVD) technology with a p-AlGaAs cladding layer are systematically investigated to produce 75 °C continuous-wave (CW) operation for the first time. First, the InAs quantum dots (QDs) in a dot-in-a-well (DWELL) structure formed by engineering the strained bottom InGaAs layer are successfully grown without detectable clusters, making it possible to increase the number of DWELL stacks effectively. To avoid degradation of the DWELL active layer during the high-temperature growth of the upper p-AlGaAs cladding layer, a detailed analysis of the p-AlGaAs cladding layer grown at low temperature is then carried out. The results of electron-channeling contrast imaging reveal that dislocations in the p-cladding layer are generated due to the accumulative strain of the DWELL and low-temperature growth. The fabricated InAs/GaAs QDLDs show good electrical and optical characteristics with O-band emission wavelength without high-reflection coating, indicating that the suggested growth technologies and the fabricated devices are promising options for future Si-photonic light source components.

Effect of junction temperature on 1.3 µm InAs/GaAs quantum dot lasers directly grown on silicon

Laser junction temperature (Tj) is an essential parameter that directly affects the light power and lifetime of semiconductor lasers. Here, we investigate the effect of Tj on an InAs/GaAs quantum dot (QD) laser grown on a Si(001) substrate. Under 1% low pulsed current (1 µs pulse width and 100 µs period), the pure temperature-induced mode shift rate is 0.084 nm/°C. By increasing the duty cycle and measuring the corresponding mode wavelength shift, the laser’s Tj under the continuous-wave (Tj-CW) mode is predicted to be from 31.1 to 81.6 °C when the injection current increases from 100 to 550 mA. Next, the average thermal resistance is 36.2 °C/W. Moreover, the non-negligible increase in Tj-CW is analyzed to significantly reduce the mean-time-to-failure of Si-based QD laser, especially for cases under high CW injection currents. These results provide an accurate reference for the thermal analysis of silicon-based QD lasers and point the way to high performance on-chip light sources by improving the laser heat accumulation.

Steady-State Semi-Analytical Modeling of p-Doped Quantum Dot Lasers Thermal Characteristics and Extrapolation to Membrane Lasers

Steady-State Semi-Analytical Modeling of p-Doped Quantum Dot Lasers Thermal Characteristics and Extrapolation to Membrane Lasers

General and Complete Synchronization of Mutual Coupling System of Quantum Dot Semiconductor Lasers With Optical Feedback

Abstract The study examines an extensive and complete synchronization of optimal feedback with quantum dot semiconductor laser mutual coupling system. This has been achieved by resolving the transmitter and receiver equations of the quantum dot lasers. Numerous crisis areas have been observed at the time of investigating the relationship between photon density and time. The authors have selected an optimal time delay for the optical feedback so as to render an appropriate situation for intermittent dynamics. The study analyses the impact created by a long external cavity of QDSL upon the synchronization process in this mutual coupling system, in the presence of the enhancement factor of (α =3).

Gradual degradation in InAs quantum dot lasers on Si and GaAs.

Reliable quantum dot lasers on silicon are a key remaining challenge to successful integrated silicon photonics. In this work, quantum dot (QD) lasers on silicon with and without misfit dislocation trapping layers are aged for 12 000 hours and are compared to QD lasers on native GaAs aged for 8400 hours. The non-trapping-layer (TL) laser on silicon degrades heavily during this time, but much more modest gradual degradation is observed for the other two devices. Electroluminescence imaging reveals relatively uniform gradual dimming for the aged TL laser on silicon. At the same time, we find nanoscale dislocation loop defects throughout the quantum dot-based active region of all three aged lasers via electron microscopy. The Burgers vector of these loops is consistent with . We suggest that the primary source of degradation, however, is the generation and migration of point defects that substantially enhance non-radiative recombination in the active region, the visible symptom of which is the formation of dislocation loops. To prevent this, we propose that laser fabrication should be switched from deeply etched to shallow etch ridges where the active region remains intact near the mesa. Additionally, post-growth annealing and altered growth conditions in the active region should be explored to minimize the grown-in point defect density.

Advances in silicon photonics with quantum dot lasers

More than forty years ago, in 1982, we proposed the concept of quantum dot lasers and at the same time theoretically predicted the temperature insensitivity of the threshold current. With advances in growth technology, the predicted characteristics were demonstrated in 2004, and high-temperature operation up to 220°C became possible in 2011. Currently, quantum dot lasers are positioned as a promising light source for silicon photonics, especially in terms of their ability to operate at high temperatures in co-packaged optical technology. In this talk, I will describe the historical development of quantum dot lasers and their integration into 5 mm square silicon-based transceiver chips, as well as the direct epitaxial growth of quantum lasers on silicon. The talk will also demonstrate the integration of quantum dot-based light sources, including single-photon sources, on silicon integrated circuits using transfer printing methods.

Near-infrared self-assembled laser based on Ag<sub>2</sub>Se quantum dots

The development of colloidal near-infrared quantum dots (QD) lasers has been hindered by the high state degeneracy of lead salt QDs and the difficulty in coupling colloidal quantum dots to the resonant cavity. In this study, we show that above challenges can be addressed by the self-assembly laser based on Ag<sub>2</sub>Se QDs. Ag<sub>2</sub>Se QDs with the lowest quantized states 2-fold degeneracy are used to replace lead salt quantum dots to achieve low threshold near-infrared optical gain. We employ the finite element method to deeply analyze the mode field distribution and oscillation mechanism of the coffee-ring microcavity. Our results reveal that the light field oscillates in a zig-zag path along the cross-sectional area, indicating strong coupling between the QDs and the cavity mode. Furthermore, we investigate the relationship between cavity length and free spectrum range and laser emission wavelength. Leveraging this relationship and the gain spectrum characteristics of Ag<sub>2</sub>Se QDs, we design a single-mode near-infrared laser and conduct a comprehensive analysis. Using simulation results to fabricate a single-mode near-infrared Ag<sub>2</sub>Se QD coffee-ring microlaser, which exhibits a linewidth of 0.3 nm and a threshold of 158 μJ cm<sup>-2</sup>. Currently, it holds the record for the lowest laser threshold among near-infrared colloidal QD lasers. Increasing the laser cavity length, resulting in an increase in the emission wavelength from 1300 nm to 1323 nm. In addition, the toxicity of Ag<sub>2</sub>Se QDs is remarkably negligible. Our work promotes the development of environment-friendly near-infrared lasers to practical lasers.

Effects of gamma radiation on the electrical properties of InAs/InGaAs quantum dot-based laser structures grown on GaAs and Si substrates by molecular beam epitaxy.

This study investigates the impact of gamma radiation on the electrical properties of InAs/InGaAs quantum dot-based laser structures grown on both GaAs (Sample A) and Si (Sample B) substrates using molecular beam epitaxy. The research explores the electrical characteristics of the lasers before and after being exposed to gamma radiation employing current-voltage (I-V), capacitance-voltage (C-V), deep level transient spectroscopy (DLTS) and Laplace DLTS techniques. The results show that the electrical properties of the lasers change due to gamma radiation exposure, and the extent of the change depends on the substrate used for growth. The I-V results revealed that the ideality factor (n) and built-in voltage were increased in Sample A and Sample B after radiation. Nonetheless, the series resistance (Rs) at room temperature decreased in both samples after radiation. Overall, this study provides valuable insights into the effects of gamma radiation on the electrical properties of InAs/InGaAs quantum dot lasers and highlights the importance of considering substrate materials in the design of radiation-hardened electronic devices.